PRACTICAL GUIDE ON THE SELECTION OF PROCESS TECHNOLOGY FOR THE TREATMENT OF AQUEOUS ORGANIC EFFLUENT STREAMS

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PRACTICAL GUIDE ON THE SELECTION
OF PROCESS TECHNOLOGY FOR THE
TREATMENT OF AQUEOUS ORGANIC
EFFLUENT STREAMS
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PRACTICAL GUIDE ON THE SELECTION OF PROCESS TECHNOLOGY FOR
THE TREATMENT OF AQUEOUS ORGANIC EFFLUENT STREAMS
CONTENTS
0 INTRODUCTION/PURPOSE
1 SCOPE
2 FIELD OF APPLICATION
3 DEFINITIONS
3.1 IPU
3.2 AOS
3.3 BODs
3.4 COD
3.5 TOC
3.6 Toxicity
3.7 Refractory Organics/Hard COD
3.8 Heavy Metals
3.9 EA
3.10 Biological Treatment Terms
3.11 BATNEEC
3.12 BPEO
3.13 EQS/LV
3.14 IPC
3.15 VOC
3.16 F/M Ratio
3.17 MLSS
3.18 MLVSS
4 DESIGN/ECONOMIC GUIDELINES

5 EUROPEAN LEGISLATION
5.1 General
5.2 Integrated Pollution Control (IPC)
5.3 Best Available Techniques Not Entailing Excessive Costs (BATNEEC)
5.4 Best Practicable Environmental Option (BPEO)
5.5 Environmental Quality Standards(EQS)
6 IPU EXIT CONCENTRATION
7 SITE/LOCAL REQUIREMENTS
8 PROCESS SELECTION PROCEDURE
8.1 Waste Minimization Techniques (WMT)
8.2 AOS Stream Definition
8.3 Technical Check List
8.4 Preliminary Selection of Suitable Technologies
8.5 Process Sequences
8.6 Economic Evaluation
8.7 Process Selection
APPENDICES
A DIRECTIVE 76/464/EEC - LIST 1
B DIRECTIVE 76/464/EEC - LIST 2
C THE EUROPEAN COMMISSION PRIORITY CANDIDATE LIST
D THE UK RED LIST
E CURRENT VALUES FOR EUROPEAN COMMUNITY ENVIRONMENTAL
QUALITY STANDARDS AND CORRESPONDING LIMIT VALUES
F ESTABLISHED TECHNOLOGIES
G EMERGING TECHNOLOGY
H PROPRIETARY/LESS COMMON TECHNOLOGIES
J COMPARATIVE COST DATA

FIGURES
1 INTERMEDIATE PROCESS UNIT SYSTEM
2 AOS TREATMENT - SELECTION PROCEDURE (INLET
CONCENTRATION)
3 AOS TREATMENT - SELECTION PROCEDURE (OUTLET
CONCENTRATION)
4 LIQUID WASTE TREATMENT PROCESSES

0 INTRODUCTION/PURPOSE
This Guide is one in the series of GBHE's Environmental Technical Practice Guides. Its
purpose is to provide the practicing Process Engineer with:
(a) A brief, simple environmental framework within which initial process design work
handling aqueous organic streams (AOS) can proceed efficiently.
(b) A structured selection procedure which will facilitate the generation of a small
number of competing flowsheet schemes. These options will then be further
refined prior to selection of the preferred process.
(c) A summary of the commercially proven and emerging technologies for the
treatment of Aqueous Organic Streams.
1 SCOPE
This Guide presents in outline those key factors which need to be
addressed by the chemical engineer when faced with the task of
generating preliminary flowsheet schemes for the treatment of AOS. The
guide does not present technical data to be used for design purposes, nor
does it attempt to replicate detailed descriptions of alternate technologies.
This information should be sought in Research reports, from in-house
specialists, in the literature and from contractors.
2 FIELD OF APPLICATION
This Guide is available to Process Engineers in GBH Enterprises
Worldwide.
3 DEFINITIONS
3.1 IPU
An Intermediate Process Unit utilizes any suitable technology to treat plant
Aqueous Organic Streams in such a way that all water, surplus to
production requirements, is exported from the plant as Product streams.
Such streams may require further treatment prior to discharge to receiving
waters. Further treatment may be on site or off site (e.g. a biological
treatment unit), (see Figure1).

The IPU system will be designed to achieve the best overall economics
while meeting environmental constraints focusing on:
(a) Recycle of material back into the process either for reuse or
destruction.
(b) Technical and economic integration with any downstream biological
unit, e.g. selective removal of those chemicals which are not to
enter receiving waters but are impractical or more expensive to
remove either by biological treatment or subsequent tertiary
treatment.
(c) Achievement of adequate quality control of the exported aqueous
product stream.
All AOS should be listed as candidates for treatment by an IPU system.
3.2 AOS
Aqueous Organic Streams are single phase, contain dissolved organics,
and are surplus to process requirements, (see 8.3).
3.3 BODs
The chemical oxygen demand is determined by a batch reactor test in
which microbes are allowed to degrade organic matter in the presence of
oxygen over a period of 5 days at 20°C.
3.4 COD
The chemical oxygen demand is determined by a procedure in which a
chemical oxidizing agent is added to the sample and refluxed for 2 hours.
The amount of oxidizing agent destroyed in the test is proportional to the
COD of the sample. The COD value will normally be higher than the
BODs.

3.5 TOC
Total organic carbon is measured by converting all of the carbon present
in the sample into carbon dioxide by combusting the sample in a high
temperature furnace and measuring the carbon dioxide formed by infrared
spectroscopy.
3.6 Toxicity
The definition of toxicity raises complex issues beyond the scope of this
Guide.
The considerable concern that waste waters can convey hazardous
materials into the environment has led to legislation in virtually every
country. In the EC and U.K., lists of dangerous substances (see 5.1) have
been issued under legislation with selection based on considerations of
toxicity, persistence and bio-accumulation. In the U.S.A. the situation is
similar, but greater emphasis is placed on acute toxicity tests.
The key test for acute toxicity is LC50 which means that approximately
50% of the aquatic species (usually fish) used in the test will die under the
conditions of concentration and time given. The term TLm (Median
Tolerance Limit) means that approximately 50% of the fish will show
abnormal behavior (including death) under the conditions given.
Legislation, which may be different from one country to another, is moving
toward "toxicity based consent" based on identified species. In cases of
discharges to municipal treatment plants, the toxicity of the discharged
effluent to the microbes in the treatment process has to be determined.
3.7 Refractory Organics/Hard COD
These are organic chemicals which resist biodegradation. Examples
include some halogenated hydrocarbons and chlorinated pesticides.
3.8 Heavy Metals
Any cation having an atomic weight greater than 23 should be considered
to be a heavy metal. These are persistent and can be toxic/carcinogenic.

3.9 EA
Environment Agency
3.10 Biological Treatment Terms
"Equalization" is the provision of storage capacity for effluent in order to
reduce the variability of waste water flow rates and composition to
acceptable levels which protect the treatment plant from shock pollutants
and hydraulic loadings. These variations may occur, for example, due to
cyclical process operations, unsteady state process operation,
spillage, plant maintenance operations, fire-water and storm-water.
"Primary Treatment" means the first major operation in a waste water
treatment works in which a substantial proportion of the suspended solids
contained within the incoming waste water are removed, usually by
sedimentation.
"Secondary Treatment" means treatment by biological methods and is
usually preceded by primary treatment.
"Tertiary or Advanced Treatment" processes control specific organic and
inorganic pollutants. The more common processes are used for the
removal of nitrogen and phosphorus nutrients. Other more special-
purpose processes include carbon adsorption, ion exchange and reverse
osmosis.
3.11 BATNEEC
Best Available Techniques Not Entailing Excessive Costs.
3.12 BPEO
Best Practicable Environmental Option.
3.13 EQS/LV
Environmental Quality Standards, this is usually expressed as an annual
average. Limit Value.

3.14 IPC
Integrated Pollution Control.
3.15 VOC
Volatile Organic Compounds.
3.16 F/M Ratio
Feed to biomass ratio usually expressed in (g/day)/g.
3.17 MLSS
"Mixed-Liquor Suspended Solids"; the concentration of suspended solids
in the "mixed-liquor", measured by filtration and drying. Beware: dissolved
salts can lead to misleading results. The value includes active biosolids,
inactive biosolids and inert non-biosolids.
3.18 MLVSS
"Mixed-Liquor Volatile Suspended Solids"; the concentration of suspended
solids in the "mixed-liquor" which are capable of being vaporized in at
500°C. Measured by filtration on ashless paper and incineration in a
muffle-furnace. Commonly used to estimate (MLSS - inorganic inerts); not
equal to active biomass.
4 DESIGN/ECONOMIC GUIDELINES
During the design of any plant the following recommendations should be
considered by the process engineer:
(a) Check out the Project philosophy regarding "Cleaner Technology"
and contribute to its formulation as appropriate.
(b) Rigorously apply waste minimization techniques by avoiding the
production of waste or reducing its rate of production

Note: AOS may contain material that could be profitably upgraded and
sold as a byproduct.
(c) Assess the selection of process technology/operating conditions and
methods of process control with a view to eliminating/reducing AOS.
(d) Assess the design of equipment with a view to minimizing AOS produced
during start-up, shutdowns, product changes, plant maintenance and
equipment cleaning operations.
(e) The AOS produced in the process should not be flow sheeted to enter the
site drainage system except where specific approval is given by Site
Environmental Group.
(f) AOS produced in a plant should not be mixed with each other unless there
is a clear economic case for treating several AOS in a single IPU. In most
cases, it is more economic to treat a concentrated stream at source.
(g) All on-plot plant AOS, including intermittent discharges, should be piped
above ground to an IPU, except where this can be shown to be
unnecessary.
(h) Special consideration should be given to the case for removing any
volatile compounds contained in AOS in an IPU.
(j) Each on-plot effluent stream leaving an IPU should have Product Status
and therefore a specification to show that it meets the requirements of the
Site Drainage system and the input conditions of any downstream
biological treatment that may be required.

The specification should include definition of:
(1) Flow Rate
(2) Composition
(3) Temperature
(4) BOD/COD/TOC
(5) pH
(6) Volatiles
(7) Color
(8) Suspended/dissolved solids/salts
(9) Toxicity
(10) Metals
(11) Stream availability/variability
(k) Any project economic evaluation should include the cost involved in
treatment of AOS to meet the Site and legal requirements.
(l) Work on preliminary flowsheet schemes should assume that EA
authorization will take into account the effect of any downstream treatment
stages through which the plant effluent would pass. In consequence, the
process engineer should make an early check on existing/planned on-site
or off-site facilities and establish through the Project Team the technical
basis on which these facilities could be utilized.
5 EUROPEAN LEGISLATION
5.1 General
Most EC Directives relating to the discharge of "dangerous substances" to
water are based on the framework Directive 76/464/EEC. The aim of this
Directive is to cause a reduction in the level of pollution of Community
water by defined "dangerous substances". The most harmful of these
substances were selected on the basis of their toxicity, persistence in the
environment and bio-accumulation and are included in List 1 of the
Directive (Appendix A), known as the "Black List". The less harmful
substances were selected because they have a deleterious effect on the
aquatic environment and are included in List 2, the " Grey List"
(Appendix B).

It should be understood that List 1 and List 2 contain both individual
substances and families and groups of substances from which specific
substances will be identified and characterized in subsequent daughter
Directives but this is proving to be a slow process. Daughter Directives
have been issued for mercury, cadmium plus some pesticides and
chlorinated organic compounds. The European Commission has
established a priority list of 132 substances (Appendix C) which are
candidates for inclusion under the Directive.
"The Red List" was defined in the United Kingdom North Sea Action Plan
1985-1995. The Trade Effluent Regulations 1989 and 1992 require special
control of the discharge of Red List substances (plus carbon tetrachloride
and trichloroethylene) to sewer. The Red List was used as a basis for
defining prescribed substances to water under the Environmental
Protection Act 1990. Appendix D is the original Red List.
5.2 Integrated Pollution Control (IPC)
Release of prescribed substances is subject to integrated pollution control
(IPC) measures as required by the Environmental Protection Act 1990 and
in line with the EC Directive's requirement that any discharge of List 1 or
List 2 substances into the aquatic environment should be subject to
prior authorization.
In practice, IPC covers the whole of the chemical industry. For the
purposes of this guide its most important requirements are covered by 5.3
to 5.5.
5.3 Best Available Techniques Not Entailing Excessive Costs
(BATNEEC)
Ensure that best available techniques not entailing excessive costs
(BATNEEC) will be utilized to:
(a) Prevent the release of prescribed substances or, where that is not
practicable, reduce the release of such substances to a minimum
and sufficiently low level which is judged to be harmless.
(b) Similarly render harmless any other substances which might cause
harm if released.

5.4 Best Practicable Environmental Option (BPEO)
Ensure that BATNEEC will be used for minimizing the pollution which may
be caused by releases to the environment taken as a whole having regard
to the best practicable environmental option (BPEO) available.
5.5 Environmental Quality Standards(EQS)
Compliance with any Environmental Quality Standards(EQS) prescribed
by the Secretary of State.
Whereas the EQS (or quality objective in EC terminology) approach
applies to List 2 substances throughout the European Community,
Member States have a choice of two methods of control for discharges of
List 1 substances. The U.K. favors the use of EQS which specify
concentration limits in the receiving water. Therefore, the chemical
engineer should seek guidance from the Site Environmental Adviser
regarding the degree of dilution between the discharge point and the
receiving water before using EQS. The alternative Limit Value (LV)
approach utilizes fixed maximum emission quantities/concentrations which
are specific to a given sector of industry. In consequence, these LVs can
be used directly to arrive at an exit stream design specification.
Unfortunately, from the viewpoint of the chemical engineer, the number of
substances for which LVs have been issued is limited (see Appendix E).
6 IPU EXIT CONCENTRATION
Determining for design purposes the quantity and composition of Product leaving each
IPU is a complex exercise. The following factors should be taken into account:
(a) Project Team directed discussion with GBHE has the expertise to advise on
environmental matters.
(b) Process definition and performance of BATNEEC.
(c) Assessment of BPEO options.
(d) Receiving waters - more than one option?
(e) Downstream treatment options:
(1) plant Works or Site bio unit;
(2) municipal sewerage undertaker;
(3) direct discharge to receiving waters;
(4) tertiary treatment.

(f) Relevant Environmental Quality Standards and Limit Values (see!5.5).
(g) Toxicological test results.
(h) Existing and projected EA authorization and NRA/RPB consent requirements
and conditions.
7 SITE/LOCAL REQUIREMENTS
It is recommended that all project flowsheet proposals should be
discussed at an early stage with:
(a) Site Environmental Group.
(b) GBH Enterprises
In consequence, the Project Team may then decide to obtain further
information from external sources as appropriate.
In the case of projects not preceded by a research stage, these
discussions should be part of the work undertaken to generate basic
flowsheet options.
All ongoing research projects should review their future work program
periodically in this way as part of an environmental impact assessment.
This may require some experimental evaluation of the specific toxicity of
the individual components of the effluent stream which, together with the
discharge rates, may be an important factor in the selection of treatment
processes.
8 PROCESS SELECTION PROCEDURE
The recommended procedure for selection of candidate processes for use
by an IPU includes seven stages. See 8.1 to 8.7.
8.1 Waste Minimization Techniques (WMT)
Apply WMT to achieve waste elimination, recovery and recycle within the
process to minimize the size of an AOS. [See Ref 1].

8.2 AOS Stream Definition
Define each AOS in terms of:
(a) Chemical analysis/VOC
(b) Toxicological tests
(c) Temperature/pressure
(d) pH, BOD, COD, TOC
(e) Flow rate/availability pattern
(f) Variability
Once the composition and key toxic components are known, it is
necessary to form an initial view of the allowable final emission levels from
the IPU for each of the parameters listed above (see Clause 6).
8.3 Technical Check List
8.3.1 Parameters
Apply the following technical check list. These parameters, if present in
the AOS, can influence substantially the choice of treatment technology.
(a) Foams
(b) Emulsions
(c) Suspended solids
(d) Immiscible liquids
(e) Azeotropes
(f) Color
(g) Volatile organics
(h) Salts/Complexes

8.3.2 Other Factors
In multi-step treatment processes the progressive change in AOS
composition may cause problems to occur in subsequent stages e.g.:
(a) A stream suitable for Bio-treatment may become unsuitable
following extraction with a solvent which is toxic to the bio-
organism.
(b) A change in pH may precipitate some soluble organics or metals.
(c) Acids may form during an oxidation step and cause corrosion.
(d) The properties of a non-foaming liquid may be changed in such a
way that it will generate frothing.
8.4 Preliminary Selection of Suitable Technologies
8.4.1 General
Review the Established Technologies and Emerging Technologies listed
in 8.4.2 and 8.4.3 and expanded in Appendices F and G respectively, then
select a short list of technology options. This activity may be assisted by
utilizing Figures 2 and 3 which differentiate treatment technologies by
applying two criteria:
(a) Initial concentration of dissolved Organics in the water (Figure 2).
(b) The final concentration required (Figure 3).
In addition, reference should be made to Appendix H and Figure 4 which
categorize liquid waste treatment processes by application.

8.4.2 Established Technologies
The technologies listed below are described in outline in Appendix F.
(a) Bio Treatment: Aerobic: - Activated Sludge
- VITOX
- Deep Shaft
- Bio Towers
Anaerobic
(b) Physical Separation
(1) Coagulation/Flocculation
(2) Distillation
(3) Stripping
(4) Steam Stripping
(5) Air Stripping
(6) Liquid/Liquid extraction
(7) Adsorption: - General
- Granular Carbon
- Powder Carbon
- Charcoal
- Zeolites/polymeric
- Ion exchange
(c) Membrane processes - General
- Microfiltration
- Ultra filtration
- Reverse Osmosis
- Pervaporation
- Electro dialysis
(d) Chemical Oxidation - Wet Air Oxidation
- U.V. Light
- U.V. Light + H2O2
- Ozone
- H2O2/Fe
- Other
(e) Thermal Oxidation - Total (Incinerators)
- Partial (Oil-Gas process)

8.4.3 Emerging Technologies
The technologies listed below are described in outline in Appendix G.
(a) Supercritical Water Oxidation
(b) Liquid Membranes
(c) Reed Beds
8.5 Process Sequences
In some cases it will not be possible or desirable to achieve the required
design objective by using a single technology, and several treatment steps
may have to be designed to operate in sequence.
In addition, the most suitable options for treating each individual AOS can
be listed as a basis for generating alternative process flow schemes which
combine the several AOS in different ways. A comparative evaluation will
then lead to a short list of preferred options. These should be assessed in
more detail by following up appropriate references and discussion with
GBHE specialists/contractors.
8.6 Economic Evaluation
Economic evaluation data obtained from sources external to the Project
Team should be treated with caution. In this first issue of the Guide no
internally generated economic assessment data has been provided.
However, some published comparative cost data has been appended (see
Appendix J) which shows the variability of costs as a function of the
specific chemical composition of each stream.
An example of the type of problem commonly met in this area are cost
comparisons which, when examined in detail, are found to apply to
different technical definitions (e.g. items of equipment are omitted or
feed/product qualities are different.)

8.7 Process Selection
The main objective at this final stage is to identify those options which
perform strongly when judged against the following criteria:
(a) Compliance with legislation.
(b) Compliance with GBHE rules and requirements.
(c) Low capital cost.
(d) Low operating cost.
(e) High reliability.
(f) Compatibility with existing and projected Site operations.
The process engineer should then justify to the Project Team his/her
selection of preferred options. It is likely that considerable Project effort
will then be applied to refine the preliminary selection referred to here in
order to select a preferred process. In some cases it may also be
necessary to reassess other factors, for example, the chemistry of the
process or the location of the plant.

APPENDIX A DIRECTIVE 76/464/EEC - LIST 1
List 1 contains individual substances which belong to the following families and
groups of substances, selected mainly on the basis of their toxicity, persistence
and bio-accumulation with the exception of those which are biologically harmless
or which are rapidly converted into substances which are biologically harmless.
(1) Organo-halogen compounds and substances which may form such
compounds in the aqueous environment.
(2) Organo-phosphorus compounds.
(3) Organotin compounds.
(4) Substances in respect of which it has been proved that they possess
carcinogenic properties in or via the aquatic environment. (Where certain
substances in List 2 are carcinogenic they are included in this category).
(5) Mercury and its compounds.
(6) Cadmium and its compounds.
(7) Persistent mineral oils and hydrocarbons of mineral origin, and for the
purposes of implementing Articles 2, 8, 9 and 14 of this Directive.
(8) Persistent synthetic substances which may float, remain in suspension or
sink and which may interfere with any use of the waters

APPENDIX B DIRECTIVE 76/464/EEC - LIST 2
List 2 contains:
(a) Substances belonging to the families and groups of substances in List 1
for which the limit values referred to in Article 6 of the Directive have not
been determined.
(b) Certain individual substances and categories of substances belonging to
the families and groups of substances listed below, and which have a
deleterious effect on the aquatic environment, which can, however, be
confined to a given area and which depend on the characteristics and
location of the water into which they are discharged.
Families and groups of substances referred to in the second indent:
(1) The following metalloids and metals and their compounds:
1 Zinc 8 Antimony 15 Uranium
2 Copper 9 Molybdenum 16 Vanadium
3 Nickel 10 Titanium 17 Cobalt
4 Chromium 11 Tin 18 Thallium
5 Lead 12 Barium 19 Tellurium
6 Selenium 13 Beryllium 20 Silver
7 Arsenic 14 Boron
(2) Biocides and their derivatives not appearing in List 1.
(3) Substances which have a deleterious effect on the taste and/or smell of
the products for human consumption derived from the aquatic
environment, and compounds liable to give rise to such substances in
water.
(4) Toxic or persistent organic compounds of silicon and substances which
may give rise to such compounds in water, excluding those which are
biologically harmless or are rapidly converted in water into harmless
substances.
(5) Inorganic compounds of phosphorus and elemental phosphorus.
(6) Non persistent mineral oils and hydrocarbons of petroleum origin.
(7) Cyanides and fluorides.

(8) Substances which have an adverse effect on the oxygen balance,
particularly: ammonia, nitrites.

APPENDIX F ESTABLISHED TECHNOLOGIES
Table of Contents
F.1 BIO TREATMENT: AEROBIC - ACTIVATED SLUDGE PROCESS
F.2 BIO TREATMENT: AEROBIC - VITOX PROCESS
F.3 BIO TREATMENT: AEROBIC - DEEP SHAFT
F.4 BIO TREATMENT: AEROBIC - BIO-TOWERS
F.5 BIO TREATMENT: ANAEROBIC PROCESSES
F.6 COAGULATION/FLOCCULATION
F.7 DISTILLATION
F.8 STRIPPING
F.9 AIR STRIPPING: PACKED COLUMNS
F.10 AIR STRIPPING: HIGEE
F.11 LIQUID/LIQUID EXTRACTION
F.12 ADSORPTION - GENERAL
F.13 ADSORPTION: GRANULAR CARBON
F.14 ADSORPTION: POWDER CARBON
F.15 ADSORPTION: BONE CHARCOAL
F.16 ADSORPTION: POLYMERIC/ZEOLITES
F.17 ADSORPTION: ION EXCHANGE
F.18 MEMBRANE PROCESSES (GENERAL)
F.19 MEMBRANE PROCESSES: MICROFILTRATION

F.20 MEMBRANE PROCESSES: ULTRAFILTRATION
F.21 MEMBRANE PROCESSES: REVERSE OSMOSIS
F.22 MEMBRANE PROCESSES: PERVAPORATION
F.23 MEMBRANE PROCESSES: ELECTRODIALYSIS
F.24 CHEMICAL OXIDATION: WET AIR OXIDATION (WAO)
F.25 CHEMICAL OXIDATION: U.V. LIGHT
F.26 CHEMICAL OXIDATION: U.V. LIGHT + H202
F.27 CHEMICAL OXIDATION: OZONE
F.28 CHEMICAL OXIDATION: H2O2/Fe (FENTON'S REAGENT)
F.29 CHEMICAL OXIDATION: OTHERS
F.30 TOTAL THERMAL OXIDATION: INCINERATION
F.31 PARTIAL THERMAL OXIDATION: OIL-GAS PROCESS

F.1 BIO TREATMENT: AEROBIC - ACTIVATED SLUDGE PROCESS
F.1.1 Introduction
Aerobic biological waste water treatment is the process by which
microorganisms consume biodegradable organic compounds and free
oxygen to produce cell growth, CO2 and water.
Bio treatment can only destroy biodegradable compounds and therefore
those chemicals which are not biodegradable (hard COD) will pass
through and will require additional treatment. Not all the biodegradable
material is oxidized and the BOD5 leaving the treatment beds depends on
the design of the process, the technology employed and the residence
time, and can vary from 5 to 40% of the original BODs.
F.1.2 Process Description
Several types of bio treatment processes have been operated over the
years. Differentiation between these requires a careful assessment of cost
and performance on a project by project basis.
A bio treatment process may include the following additive stages:
(a) Primary treatment:
(1) An equalization stage to minimize concentration and
temperature fluctuations (typical operating temperature 10 to
37°C)
(2) A pH adjustment and nutrients dosing stage to prepare the
feed for the process. (typical pH range 5.5 to 9).
(3) A Suspended Solids removal stage.
(b) Secondary treatment:
(1) The aeration tanks which are agitated to maintain the
biomass in suspension and where air or oxygen is injected.
The sizes of the tanks depend on the stream mass flow, the
type and concentration of chemicals present and the exit
BOD/COD levels required (i.e. standards and legislation).

(2) A sedimentation stage to separate the biomass from the
water and allow recycle of the biomass to the aeration tanks.
(3) A sludge thickening stage. This is applied to surplus sludge
to reduce its water content to a level suitable for further
treatment or landfill.
(c) Tertiary treatment:
Removal of specific organic or inorganic pollutant such as hard
COD/metals and excess nutrients (phosphorus and nitrogen
compounds if they have not been removed in the
nitrification/ denitrification section of a secondary treatment).
(d) Sludge disposal:
An appropriate sludge disposal stage: for example, landfill, land
spread, incineration, digestion in aerobic or anaerobic digesters or
Wet Air Oxidation.
F.1.3 Process Requirements/Limitations
(a) A substantial amount of land is required to locate the equipment,
although it can be reduced by using Deep Shaft and similar "tower"
processes.
(b) Electric power is required to ensure adequate mixing/the
` suspension of the solids if necessary and oxygen/air mass transfer.
There are several generic and proprietary methods for dispersing
the air and maintaining solids suspension (e.g. surface aerators,
liquid jet aerators, fine bubble diffusers, venting aerators, etc.). The
total power requirement is one of the main factors in the choice of
process. Typical values are 0.05 kW/m3
with an oxygen transfer
capability of 2 kgO2/kW.h.
(c) In the absence of a specific treatment stage:
(1) Heavy metals will either remain dissolved in the water or will
accumulate in the biomass and may create subsequent
sludge disposal problems.

(2) The non-biodegradable chemicals will not be oxidized, and if
allowed to remain in the effluent may result in toxic
effect/COD problems in receiving waters.
] (d) The performance of a conventional activated sludge bio treatment
plant can be improved by the addition of powdered activated
carbon. This technology is well established and marketed as the
PACT process by Zimpro Passavant. The main benefits derived
from the combined adsorption/biological oxidation are:
(1) It buffers the system against shock loads of biologically toxic
or inhibitory compounds.
(2) Improved removal of compounds which exhibit only partial or
slow biodegradability.
(3) Improved COD reduction and color removal by adsorption of
Refractory Organics.
(4) Increased hydraulic capacity of an existing facility.
(5) Reduced VOC losses from the aeration basin. However,
VOC could be present in the off-gas from the Wet Air
Regeneration process.
(6) Improved sludge settling capacity.
The choice of carbon is important, but generally speaking the
cheaper "low" activity waste water carbons are more commonly
used.
The economics and elegance of the PACT process may be
improved by adopting Wet Air Regeneration (WAR) of the spent
carbon contained in the surplus biomass. In this manner, excess
biomass is oxidized (the high COD providing autogenous operation
of the reactor) and contained carbon may be regenerated for
recycle. Virgin carbon make-up is required to compensate for
physical losses and deterioration of carbon activity on repeated
regeneration.

(e) The amount of sludge produced per tonne of BODs is a function of
the type of process used and the operating conditions [feed to
biomass ratio (F/M)] but it ranges from about 0.5 tonne/tonne on a
dry weight basis with F/M of 1.0 down to less than 0.1 tonne/tonne
with F/M lower than 0.2.
(f) During plant shutdown periods the biomass should be sustained by
an alternative feed supply. In addition, the design should cater for
the required turndown.
(g) Start-up of a bio treatment system normally takes several days
before BOD removal is effective. In consequence, its design usually
incorporates protection against any identified risk to the biomass
health. This is usually a combination of operating procedures and
detection by analysis which enable unacceptable feed to be
dumped into holding tanks/lagoons. This material can then be
blended into the feed at an acceptable rate.
(h) Temperature influences the rate of reaction but is limited to a
maximum of 40°C in most cases.
(j) The kinetic constants of the biological reactions become dependent
on the mode of operation of the system, as well as the chemical
nature of the waste, and should be determined experimentally.
(k) Minor nutrient (e.g. Fe, K, Mg, Zn, Mn) are also required for
optimum performance.

F.2 BIO TREATMENT: AEROBIC - VITOX PROCESS
F.2.1 Introduction
The VITOX process is a bio treatment process developed by BOC for the
treatment of effluents. Its distinguishing feature is the use of oxygen
instead of air.
The operation of a VITOX process is very similar to the traditional
activated sludge process. However, BOC makes several specific claims:
(a) The use of oxygen allows the process to operate at a higher
biomass concentration "M" and therefore a smaller size biological
treatment tank is required for the same duty.
(b) In the case of existing plants, the extra capacity can be used either
to increase the overall treatment capability by maintaining the F/M
ratio or, alternatively, to reduce the final DOB of the discharge by
operating at a lower F/M.
(c) If the process is operated at low F/M ratios, then the rate of
production of excess biomass can be reduced. In some cases, this
rate can be so low that it is possible to discharge the excess
biomass mixed with the treatment effluent without exceeding the
suspended solid specification of the receiving waters.
(a) It requires a supply of oxygen at a suitable price.
(b) The VITOX process is normally designed to operate with a low F/M
ratio, high "M" concentrations and a low rate of sludge export.
(c) I t may need a larger clarifier because the high operating "M" can
produce hindered settling.
(d) The low sludge production may result in progressive build up of
inert solids (e.g. metals and inorganic salts).

F.3 BIO TREATMENT: AEROBIC - DEEP SHAFT
F.3.1 Introduction
The Deep Shaft process is a specific aerobic process utilizing air as
oxidant and developed by ICI for the treatment of effluents. Its main
difference from a traditional activated sludge process is its design as a
tower which is located underground and therefore it provides a very
compact arrangement.
Each shaft is divided into a down comer and a riser. Compressed gas is
injected into the down comer to induce liquid circulation by an air lift effect,
to create turbulence and supply oxygen to the microorganisms. (During
start-up, air is injected into the riser to establish circulation).
The good mixing, long bubble residence times and large hydrostatic head
create a high oxygen transfer rate, and so with increased availability of
nutrients the BOD degradation rate is maximized. As with conventional
processes, a treatability study is commonly needed for detailed design
purposes.
Gas bubbles disengage in the head tank at the shaft top, and the clarifier
feed is taken from here. Excess sludge is removed from the clarifier.
There are several specific claims for the Deep Shaft process:
(a) A very small land requirement for the biological bed.
(b) An intensified process due to the high hydrostatic pressure
generated at the bottom of the shaft which increases the oxygen
transfer rate.
(c) An enclosed system which can be located in sensitive areas like
building basements and proximity to domestic housing.
(d) Lower power input than traditional designs.

To date, the Deep Shaft has been operated with air, and air/oxygen
mixtures.
Anti-froth agents may need to be added to avoid frothing in the head tank.

F.4 BIO TREATMENT: AEROBIC - BIO-TOWERS
F.4.1 Introduction
The bio-tower technology is an alternative to the conventional activated
sludge plants which uses enclosed tanks of up to 30 m height instead of
open basins. This results in a more compact design and, in some cases,
lower capital and energy costs.
The aeration is provided by the injection of air into the waste water stream.
The mixture of air and waste water is then injected at several points at the
bottom of the tower to achieve uniform distribution of the air. The height of
the tower determines the hydrostatic pressure and the solubility of oxygen
at the point of injection. This results in a much higher oxygen efficiency
than that achieved by conventional activated sludge plants.
Additional claims for the bio-tower design (compared with a conventional
activated sludge process) are:
Volume of air required 20%
Energy required 40-50%
Land area required 20%
The closed tank design facilitates elimination of pollution by fumes and
aerosols.

F.5 BIO TREATMENT: ANAEROBIC PROCESSES
F.5.1 Introduction
Anaerobic treatment is a biological process in which microorganisms
convert organic compounds in the presence of water into methane, CO2,
cellular materials and other organic compounds.
Anaerobic processes do not require the introduction of air or oxygen.
Some microorganisms are able to operate both under aerobic or
anaerobic conditions while other are specifically anaerobic.
There are three basic types of reactor systems:
(a) Deep lagoons - often used as pretreatment but which can have an
odor problem.
(b) Enclosed vessels with suspended growth - with separation and
recycle of the suspended solids.
(c) Enclosed vessels with fixed growth - in which the microbial growth
is attached to solid surfaces provided in the form of packing or
particles in the case of a fluidized bed system.
Anaerobic treatment has the following characteristics:
(a) Suitable for:
(1) pretreatment of high strength waste streams;
(2) waste water sludge destruction.
(b) Low sludge production rate.
(c) Energy potential of the off-gas produced.

(d) Reaction rate is slow compared with aerobic processes and needs
higher temperatures.
(e) Anaerobic treatment can destroy some chemicals which are not
degradable by an aerobic process.
(f) Effluent from anaerobic processes usually requires further
treatment prior to discharge to receiving waters.
(g) Very sensitive to variations in incoming effluent composition and
flow rate.
(h) Sulfates in the effluents are reduced to H2S which may require
corrosion resistant materials of construction.

F.6 COAGULATION/FLOCCULATION
F.6.1 Introduction
Coagulation and flocculation are well established methods for removing
soluble and insoluble organic compounds from water and are generically
known as Physical - Chemical processes. They are mainly used prior to
biological processes to partially remove suspended solids, colloidal
particles and dissolved substances (dyes and other hard COD
compounds).
The treatment, which in most cases is specific to the organic compounds
to be removed, requires the pH to be adjusted to insure the optimum
performance of the coagulation and flocculation stages.
The coagulation process involves the addition of a coagulant to the
aqueous stream to destabilize the colloidal suspensions and allow the
organic matter to come out of solution. In most cases a flocculant is also
added to promote the formation of large flocs which can then be separated
by settling.
The most widely used coagulants are iron or aluminum salts although
synthetic cationic polyelectrolyte's can also be used. The inorganic salts
are generally used together with lime or caustic to produce a hydroxide
precipitate.
When using ferrous salts it is possible to use their reducing power to break
the azoic link in some dye molecules and render them colorless.
Coagulants are mainly synthetic organic polymers of acrylamide and
acrylic acid and, depending on their composition, can be cationic, anionic
or neutral. Natural organic polymers, starches and alginates and inorganic
coagulants, activated silica, alumino silicates and clays are also used.
The settling time required depends on the sedimentation rate of the flocs
obtained. The clear liquid is separated from the top of the settling tank and
the concentrated sludge is removed from the bottom and then further de-
watered in a pressure filter before disposal by a suitable method; normally
to landfill, depending on the toxicity of the chemicals present.

The size of the coagulation, flocculation and settling stages depends on
the nature of the physical and chemical reactions taking place and the
type, composition and quantity of the reagents used.
This process requires the addition of specific coagulating and flocculating
chemicals which need to be identified and evaluated during laboratory
trials. Depending on the coagulating chemicals used, the pH may need to
be increased to 9 or 10 using caustic or lime and then neutralized with a
mineral acid or CO2.
In most cases, for economic reasons, the process is operated to achieve
only a partial removal of the BOD and COD and is then followed by a
Biological Treatment Stage to achieve the required discharge values.

F.7 DISTILLATION
F.7.1 Introduction
Distillation as a recovery technique is generally limited to separating
compounds more volatile than water from water itself.
A distillation column consists of two sections:
(a) A stripping section below the feed entry which can be designed to
control the final concentration of volatile organics in the aqueous
product stream.
(b) A rectifying section above the feed which, combined with the choice
of reflux, allows control of the concentration of water in the
recovered organic product stream.
(a) Distillation is used for the recovery of individual organic compounds
or groups of compounds from aqueous streams only if:
(1) their concentration is high enough to make economic sense,
generally greater than 5%, and the water content of the
recovered stream is acceptable either for recycle or
subsequent processing or export;
(2) it is the most cost effective process for removal of
compounds which are highly toxic and have to be separated
to facilitate subsequent treatment of the aqueous stream or
for disposal as a concentrated stream (e.g. by incineration);
(3) relative volatility of organics with water exceeds 1.2. Below
1.2, it is generally more economic to remove high
concentrations of organics by liquid-liquid extraction (see
F.11).
(b) The overhead stream, mainly organics, may require further
treatment or purification if it is to be returned to the process.

F.8 STRIPPING
F.8.1 Introduction
The stripping process is a variant of conventional distillation, utilizing
either a reboiler for steam generation or direct injection of steam from an
outside source. Even relatively high boiling compounds can be removed
efficiently by this method, e.g. Phenol (Boiling point 182°C).
A stripping column consists of one section below the feed designed to
achieve the required low level of organics in the water.
It can operate on a batch or continuous mode.
(a) The overheads are recovered as a mixture of organics in water
which will separate into two phases if immiscible and the
distribution of the organic compounds between the organic and
the water layer will be determined by solubility levels.
(b) Both layers may need to be further treated before disposal or
recycle. In some cases the water layer can be recycled back to the
column.
(c) Removal of high boiling point components is assisted by operation
under vacuum.

F.9 AIR STRIPPING: PACKED COLUMNS
F.9.1 Introduction
Air stripping is the countercurrent contacting in a column of an AOS with a
gas stream usually air or N2, although natural gas has also been used to
strip methanol from water.
It is only useful for volatile organics, that is, compounds with a boiling point
less than 100°C. It can reduce the final COD to less than 0.001ppm and
can remove up to 99.9% of the organics present.
Air stripping is performed in packed columns and requires a substantial
volume of air which then has to be disposed of in an acceptable way to
prevent the organics reaching the environment.
If the columns are operating continuously, the packing may get fouled and
require a continuous or intermittent supply of biocide at a level of 50 to
500 ppm which will be discharged in the water.
Batch operation may need 2 columns and regular cleaning to control
fouling.

F.10 AIR STRIPPING: ICI HIGEE
F.10.1 Introduction
The Higee process intensifies mass transfer between a gas stream and a
liquid stream by means of high "g" forces generated by rotation. For
example, in this way the height of packing required to reach equilibrium for
the EDC/water system is reduced from about 0.8 m per stage in a packed
column to less than 0.06 m achieved in the Higee machine.
The packing has the form of a hollow cylinder which rotates on its axis.
The liquid is distributed on the inside surface and travels through the
packing by centrifugal force. The stripping gas is fed to the outside of the
rotating cylinder and travels through the packing counter currently with the
liquid and is discharged from the centre.
The thickness of the packing, and therefore the outside diameter of the
rotor, is a function of the number of stages required (at about 50 to 70 mm
per stage) and the axial length of the cylinder is determined by the liquid
flow.
The machine operates in the range of 100 to 1000 times terrestrial "g" and
therefore a very small volume of packing is required when compared with
a packed tower.
The standard stacked rings Sherwood correlation for the calculation of
flooding has been found to apply to the rotating packing.
Fouling of various types may develop in the packing.

F.11 LIQUID/LIQUID EXTRACTION
F.11.1 Introduction
Liquid/liquid extraction's main application is to remove organic
components which are present in high concentration (1 to 25%) and the
relative volatility to water is less than 1.2 (otherwise distillation may be
more appropriate)
An organic, low toxicity, preferably biodegradable solvent with very low
water solubility is required.
The process involves the countercurrent contact of the AOS with a water
immiscible, selective organic solvent which is then phase separated from
the treated water.
The loaded organic solvent is then separated from the contained organics
by distillation before recycling it to the extractor. A solvent purge is
normally removed for purification.
The organic solvent will be present in small amounts in the treated water
and, depending on its toxicity, solubility and cost, will have to be removed
for recovery or destruction by a suitable treatment.

F.12 ADSORPTION - GENERAL
F.12.1 Introduction
Adsorption is a well established process for the removal of organic
compounds from industrial waste waters and potable waters. Although a
variety of adsorbents are available commercially, activated carbon is by
far the most popular. This is a broad spectrum adsorbent with a wide pore
size distribution which makes it very attractive for AOS treatment.
Activated carbon is available in two basic forms, viz. powder (PAC) or
granular (GAC). PAC is the cheapest, for example, at about $2/kg
compared with $4-6/kg for a GAC of similar activity, and achieves a higher
adsorption rate but is less amenable to regeneration.
F.12.2 PAC
Fresh PAC is normally added to the aqueous waste in the last stirred tank
in a series. Then, after filtration at each stage, it is transferred through the
remaining tanks countercurrent to the AOS to achieve maximum use of
adsorptive capacity. Regeneration may not be cost effective.
F.12.3 GAC
The use of GAC in fixed beds requires less material handling than PAC.
However, the moving bed version is likely to be more problematical in this
respect. When the adsorption capacity of the carbon is exhausted, the
spent GAC is usually discharged prior to regeneration/reactivation and the
adsorber reloaded with active material. Spent GAC is usually regenerated
and reactivated in large plant using multiple-hearth furnaces.
Regeneration/reactivation losses are typically 5-10% and the
reactivated carbon has different adsorption characteristics to virgin carbon
in part due to enlarged pore sizes caused by the Pyrolysis step. A contract
regeneration/reactivation service is available (e.g. Chemviron Carbons).
Alternatively, it can be incinerated.
If on-line regeneration is feasible, for example by steam stripping, then this
may be preferred.

F.12.4 Key Points
Adsorption is used mainly for the removal of dissolved organics that are
present in small amounts and are difficult to remove by biological
methods. For a given adsorbent/adsorbate system the adsorption
capacity, as defined by the adsorption isotherm, is influenced by many
factors including temperature, solubility, pH, size of adsorbate molecule,
adsorbent pore structure, etc. but the most important factor is the
adsorbate concentration in the aqueous phase. For example, the capacity
of a GAC (expressed as weight adsorbate/weight adsorbent) is expected
to be about 45% when in equilibrium with an aqueous solution containing
2000 ppm Aniline whereas at 1-10 ppm the capacity falls to less than 1%.
The bed life will, however, be appreciable because the quantity of
adsorbate present is so small.
GAC is regenerated by four methods:
(1) Steam Stripping - applied in situations where the
molecular weight of the adsorbate
(in situ) is generally less than 200;
separation usually allows recycle of the
organic layer with the aqueous layer
discharged either to receiving waters or
to biotreatment or recycled to adsorber
feed.
(2) Chemical - e.g. caustic washing to remove Phenol.
(in situ)
(3) Solvent Extraction - e.g. elution of dyestuffs.
(in situ)
(4) Thermal - is used principally at waste water
treatment plants and usually includes
multiple-hearth furnaces. The process
includes drying, volatilization, Pyrolysis,
and reactivation stages. GAC weight
loss is typically 5-10%. Most modern
units employ afterburners operating at
1200/1300°C to destroy any dioxins that
may have been formed.

The bed size in terms of its length/diameter ratio is influenced by the
shape of the adsorption profile through the bed and whether the bed is
regenerated or used on a once-through basis. For example, the more
favorable adsorption profile achieved by chlorobenzene allows the use of
a lower L/D ratio than with dyestuffs while still achieving efficient utilization
of the carbon bed. In the case of dyestuffs adsorption the bed should be
sized for a minimum of two weeks operation on-line compared with only a
few hours for chlorobenzene, depending on the regeneration time.
Hydraulic loadings are usually in the range 1-6 m3
/m2
with the lowest
loadings selected for adsorbates that are slow to adsorb such as
dyestuffs.
Carbon adsorption is commonly used to treat AOS containing from a few
ppb to 2000!ppm of dissolved organics.
If the AOS contains suspended solids then the adsorption bed should be
preceded by a filtration stage.

F.13 ADSORPTION: GRANULAR CARBON
F.13.1 Introduction
Granular carbon is a treatment process for the removal of small amounts
of dissolved, refractory organic compounds from water. It is used when
high quality process water is required for reuse or when the organic
compounds are so toxic that they have to be removed before the effluent
water is finally discharged to receiving waters.
Granular carbon is used in fixed packed beds which operate with
continuous liquid feed until they are economically loaded, at which point
they have to be taken off-line and the carbon either regenerated or
replaced with fresh material.
Various series/parallel equipment arrangements are needed to achieve
the required technical performance and reliability.
In most cases, granular carbon is only economic if the organic compounds
can be removed and the carbon regenerated and reused several times.
The most commonly used methods of regeneration are steam stripping,
solvent extraction and partial combustion, or a combination of these.
Laboratory tests are advisable since:
(a) Some organic compound present in minor amounts in a stream may
interfere with the adsorption of the key component and drastically reduce
the efficiency of the beds.

(b) The presence of inorganic salts may cause an irreversible deactivation of
the carbon which will then have to be replaced.
(c) The reliable calculation of steady-state rate of carbon make-up to a
specific adsorption/regeneration process requires the use of practical
data. During regeneration there is always a mass loss due to attrition and
partial combustion which needs to be compensated by addition of fresh
carbon. However, a further purge and addition of carbon may be
necessary to compensate any progressive irreversible loss of adsorption
capacity.
Granular carbon is usually only suitable economically if it can be readily
regenerated.
The size of the bed has to be calculated so that it takes a reasonable time
to achieve economic loading.
F.13.4 Carbon Properties
Data sheets on carbon properties can be obtained from the following
suppliers:-
NORIT
CHEMVIRON
SUTCLIFFE SPEAKMAN

F.14 ADSORPTION: POWDER CARBON
F.14.1 Introduction
Powder carbon is more active per unit mass than granular carbon and it
can be used in both batch and continuous processes to remove impurities.
However, it requires suitable filtration equipment to separate it from the
treated liquid.
For effluent treatment it is used mainly in activated sludge processes to
adsorb the non-biodegradable components.
PAC is used in stirred tanks followed by filtration to remove trace
impurities. The spent PAC is then disposed of, according to the toxicity of
the adsorbate, by such methods as landfill and incineration.

As part of an activated sludge process (PACT) the carbon is added to the
unit and remains suspended with the sludge. Most of the carbon is
recycled to the process from the primary clarifier together with the
biomass.
Treatment of the excess sludge and contained carbon in a Wet Air
Oxidation process may enable the carbon to be recycled with benefit, in
addition to destruction of the sludge.
The process requires the handling and disposal of carbon slurries.

F.15 ADSORPTION: BONE CHARCOAL
F.15.1 Introduction
Bone Charcoal, marketed as Brimac by Tate and Lyle, contains two
separate components, an active carbon surface and a hydroxyapatite
lattice.
As a result of this surface activity, it is more commonly used for heavy
metal recovery particularly lead, iron, manganese and zinc and is used by
several U.K. water companies.
It is available in granular form and is used on a once-through basis in
equipment similar to that which utilizes GAC.
The reactivation (if required) will have to be designed to remove any
metals as well as the organic compounds present.
Other uses include color removal (e.g. humic acid and peat color) and
trace organics, fluoride etc.

F.16 ADSORPTION: POLYMERIC/ZEOLITES
F.16.1 Polymeric
As well as the ion exchange resins (see F.17) a number of non-ionic
polymeric media (e.g. polystyrene, polyacrylate) are commercially
available for use as sorbents including the Amberlite XAD-x range from
Rohm and Haas. These will absorb organic substances from aqueous
streams. However, capacities tend to be low and the resins themselves
are prone to attack by both microorganisms and aggressive media or
conditions. Their utility is thus limited.
F.16.2 Zeolites and other Molecular Sieves
Traditional alumino silicate zeolites behave in aqueous media as cation
exchangers. They will also extract some polar neutral organic molecules
(e.g. sugars) by a complexation mechanism. The more recently
discovered high silica zeolites and silica molecular sieve are hydrophobic
at high Si/Al ratios and behave as solid organic solvents. The best known
example is "Silicalite" (UOP Corporation). Such materials will extract
organic molecules from aqueous solutions, the exact partition depending
upon concentration, temperature, solubility and polarity. The unique fixed
pore size combined with a choice of chemical composition and structure
allows achievement of far higher selectivity's than activated carbon. Also,
their thermal and oxidative stabilities mean that in most cases cleanly
regenerable systems are possible. However, these materials are at
present relatively new and expensive. It is anticipated that many more
microporous inorganic sorbents will soon become available.
F.16.3 Other Inorganic Sorbents
Many simple inorganic compounds (e.g. oxides and hydroxides) have
potential as agents for removal of organics from aqueous streams. The
use of alumina to remove chlorinated hydrocarbons in this way is well
known.

F.17 ADSORPTION: ION EXCHANGE
Ion exchange resins are polymeric materials which contain specific
chemical groups capable of reacting with cations and anions and with
acidic or alkaline impurities.
Of the many types of resins available, some may be appropriate for AOS
application. However, the exchange process inevitably releases a new
substance into the aqueous stream and regeneration usually creates
further wastes except where recycle back into the chemical process
is a practical option.
This is a very specialized topic which is beyond the scope of this Guide.
However, ion exchange should be evaluated for any application which
requires the removal of small amounts of high value or toxic metals or
strongly polar refractory impurities from aqueous organic streams.

F.18 MEMBRANE PROCESSES (GENERAL)
F.18.1 Introduction
Membrane processes utilize a solid semi permeable membrane which
allows selected components of an AOS to pass through.
The type of membrane and the operating conditions determine which
components are allowed through.
There are many types of membrane which individually or in combination
can perform most of the common separations.
The driving force for mass transfer is either pressure, concentration or an
electric potential.
The pressure driven processes are classified according to the pressure
used:
(a) Low pressure (0.1 to 3 bar ) for microfiltration (MF)
(b) Medium pressure ( 2 to 10 bar) for ultrafiltration (UF)
(c) High pressure (10 to 100 bar) for reverse osmosis (RO)
In membrane processes the type of membrane chosen is only one
component of the process technology which has to be developed and
optimized specifically for each application taking into account the
characteristics of each separation problem.
The main steps (i.e. membrane selection, module design, plant hydraulic
design, operating procedure, cleaning procedure, replacement procedure)
are outlined as follows.
F.18.2.1 Membranes
The chemical composition and physical structure of the membrane is
designed to be compatible with the fluid to be treated and the separation
required.

F.18.2.2 Modules
There are several types of module design:
(a) Hollow fiber modules are assembled as a tube bundle with the AOS
flowing within the hollow fibers and the clean water collected on the
shell-side.
(b) Spiral wound modules are similar in construction to spiral wound
heat exchangers.
(c) Plate and frame modules are similar to pressure filters.
In all cases the mechanical design includes a method of accommodating
the operating pressure across the membrane.
F.18.2.3 Operating procedure
The AOS to be treated is circulated at high rate and at the required
pressure over the surface of the membrane. The solute then permeates
through the wall of the membrane. This method of operation is called
cross-flow and is designed to maintain high cross flow over the surface of
the membrane to reduce the rate of fouling.
F.18.2.4 Cleaning procedure
Although most membrane systems operate under cross-flow conditions
they still need cleaning at regular intervals. MF membranes with capillary
pores in hollow fiber form can be cleaned by back-flushing with either the
cleaned process liquid or a gas (air or N2).
MF with tortuous pores, UF and RO membranes are usually cleaned by
circulating proprietary cleaning agents in water, such as detergents, to
remove the fouling layer.
The rate of fouling determines the frequency and duration of the back-
flushing operation.

Changes in properties and composition of the AOS will also have an
influence on the frequency of cleaning.
F.18.2.5 Replacement
It is possible that degradation of the membrane may occur under
operating conditions and therefore the economic operating life of
alternative membranes should be determined by life cycle
tests as an aid to selection.
Membranes are characterized by their rejection capability which is the %
of the solute contained in the feed which remains after membrane
separation.
In most cases the membrane process has to be developed to meet the
requirements of a specific AOS. This can be a lengthy and expensive
development process.
While there are hundreds of different types of membrane capable of
performing thousands of separations there are very few off-the-peg
commercial membrane processes available for treatment of industrial
AOS.
Most commonly used membranes are fabricated from organic polymers
and therefore have an operating temperature limit and a chemical
compatibility limit.
Recent developments include the use of PEEK membranes which extends
the operating temperature range to 140+°C and the chemical resistance.
Metallic membranes made of sintered stainless steel are also available.

F.19 MEMBRANE PROCESSES: MICROFILTRATION
F.19.1 Introduction
Microfiltration is a low pressure process, (0.1 to 3 bar) which uses a
porous membrane, suitable for the separation of suspended solids and
colloidal matter and some viruses from liquid streams down to 0.2 microns
in size.
Although its main application is for product cleaning (e.g. wine or beer
clarification) it can also be used to remove suspended BOD from an AOS
to give a product water suitable for recycle.
Other applications include:
(a) Separation of oil-water emulsions.
(b) Metal recovery as colloidal oxides or hydroxides.
(c) Production of ultrapure water for the semiconductor industry.
The process is normally operated under cross-flow conditions with regular
back-flushing of the membranes using either compressed air or the filtrate.

F.20 MEMBRANE PROCESSES: ULTRAFILTRATION
F.20.1 Introduction
Ultra filtration is a medium pressure process (2 to 10!bar) which uses a
non-porous or a very fine pore membrane to achieve the separation of
suspended solids, colloidal matter and viruses from liquid streams down to
0.002 microns in size.
Although similar in operation to microfiltration, because of the smaller size
pores it allows the solvent and small solute molecules to pass through and
rejects large solute molecules (Molecular Weight > 500).
Ultra filtration membranes are usually characterized by their "molecular
weight cut-off" (MWCO) which is the MW which has a retention of 90%
under the test conditions. Although the actual performance is also a
function of the pH, molecular structure and the pore size distribution of the
membrane.
It is used to separate oil-water emulsions down to 10 to 50!ppm of oil.
However, if the initial oil concentration is more than 2% a centrifugal
pretreatment is usual.
The process is normally operated under cross-flow conditions with regular
back-flushing.

F.21 MEMBRANE PROCESSES: REVERSE OSMOSIS
F.21.1 Introduction
Processes using reverse osmosis can separate water contained in an
AOS by forcing this water through a membrane. The pressure applied is
greater than the osmotic pressure of the AOS. The separated water is
generally clean enough for recycle back into the process and the waste
concentrated in the AOS can either be sent to the next treatment stage or
recycled.
The process operates at between 10 to 100!bar and ambient temperature
and requires less energy than simple distillation to achieve a required
degree of concentration.
For organic molecules the degree of rejection varies according to the
molecular weight, initial concentration and solubility.
For example: Permasep B-9 polyamide membrane processing AOS with
an initial concentration of 500 to 2000 ppm achieves:
% rejection
Methanol 0
Ethanol 28
n-Propanol 62
iso-Propanol 75
n-butanol 65
iso-butanol 95
The process is operated under cross-flow conditions and at pressures up
to 100 bar and temperatures up to 70°C.
Several stages may be used in series or parallel to achieve the required
flow rate and final purity.
It has been used to desalinate water and treat landfill leachate. The clean
water stream produced from leachate is suitable for discharge or reuse
and the concentrated stream can be recycled back to the landfill or
disposed of in an appropriate manner.

De-ionized water for laboratory use is produced by reverse osmosis in
preference to distillation.
The membranes are very sensitive to fouling, and pretreatment of the
AOS is absolutely essential. This will include removal of fine particles,
removal of sparingly soluble salts which might precipitate out as the water
is removed and their concentration increases, and pH adjustment.

F.22 MEMBRANE PROCESSES: PERVAPORATION
F.22.1 Introduction
Pervaporation is the process of evaporation through a membrane of one
or several components of an AOS into a vapor phase and it can be used
for:
(a) Removal of volatile organics from water (Benzene, CFC's).
(b) Water reduction from AOS containing organic solvents (down to
less than 1% water).
(c) Separation of polar from non-polar compounds are being
developed (e.g. Methanol from Toluene).
It can be used as an alternative to, or in combination with, activated
granular carbon, air stripping, or conventional distillation.
The process is based on the preferential diffusion of a component of the
AOS through a non-porous membrane. The driving force is due to the
concentration difference provided by the evaporation of the components
on the low pressure side of the membrane.
The evaporation is effected by operating under vacuum or circulating a
carrier gas which vaporizes the liquid from the surface and transports the
vapor.
The heat of vaporization has to be provided via the feed liquid and a
condenser is required to condense the separated vapor.
There are several commercial installations which remove water from 80/20
ethanol/water mixtures by means of a pervaporation process (rather than
the alternative method of azeotropic distillation). In this case, the flux is a
function of the initial water concentration and can change from 1 kg/m2.h
from a solution of 1% water in ethanol to almost zero at 0.1% water.

F.23 MEMBRANE PROCESSES: ELECTRODIALYSIS
F.23.1 Introduction
When a membrane is used to fabricate channels which separate an AOS
into parallel streams and an electric field is applied, the ionic components
of the AOS separate by migration through the membrane towards the
respective electrode.
Cation and anion transfer membranes are used in the same cell.
The AOS is fed to an electrolytic cell containing alternate cation and anion
membranes which are arranged to deliver two exit streams. The AOS is
thereby separated into a dilute stream and a concentrate. The dilute
stream could be suitable for discharge into receiving waters. The
concentrate is either recycled or sent for further treatment.
Suitable cation and anion membranes are required.

F.24 CHEMICAL OXIDATION: WET AIR OXIDATION (WAO)
F.24.1 Introduction
WAO is a liquid phase oxidation process suitable for the treatment of
concentrated waste water streams and waste water sludge's including
pulp and paper industry waste liquors, biomass sludge, refinery waste
caustic liquors and AOS.
WAO can also be used to regenerate any powder activated carbon purged
with the surplus sludge from bio treatment process.
The AOS is treated in a reactor at high pressure (50 to 200!bar) and high
temperature (200 to 350°C) with air or oxygen to achieve at least a partial
cleavage of organic molecules present. It is an expensive processing step
and should only be used to do that part of the oxidation which cannot be
done economically using a biological process.
The exit stream from the WAO process is normally treated in a biological
process to arrive at the required final BOD suitable for discharge.
This process needs high pressure equipment and adequate controls for
the temperature and oxygen or air input.
The process generates organic acids which need to be neutralized to
prevent corrosion.
The off-gas produced contains CO which should be oxidized catalytically
to CO2 before discharge to atmosphere.
To minimize energy usage and achieve economic operation the
concentration of organic compounds in the AOS should be high enough to
achieve the required reactor temperature adiabatically.

F.25 CHEMICAL OXIDATION: U.V. LIGHT
F.25.1 Introduction
Ultraviolet (U.V.) light on its own is used as a tertiary treatment to destroy
all microorganisms present in water. It is also used in those cases where
chlorine is not acceptable.
In addition, there is enhanced performance of U.V. light by the addition of
either hydrogen peroxide, ozone or titanium dioxide.
The water is irradiated by passing over a U.V. source. The intensity of the
radiation and the residence time are controlled to achieve the required
dose.
The U.V. light is generated by one or several mercury vapor lamps
assembled within a stainless steel shell. The U.V. intensity is measured
and controlled and the tubes are replaced when they reach the end of
their useful life (>200 h).
In some cases the surface of the tubes gets coated with residues and it
has to be cleaned. This can be done on-line using reciprocating scrapers
which wipe over the surface at regular intervals, or off-line with an acid
wash.
This process requires clean streams because the efficiency of the U.V.
light transmission is greatly reduced by the presence of suspended or
colloidal matter.

F.26 CHEMICAL OXIDATION: U.V. LIGHT + H202
F.26.1 Introduction
The combination of U.V. light and H2O2 can destroy most organic
molecules dissolved in aqueous streams including aliphatic chlorinated
hydrocarbons, toxics and other hard COD.
The process involves the addition of the required amount of H2O2 (typically
a 5:1 molar excess) prior to irradiation with U.V. light.
The hydroxyl radicals generated are powerful oxidizing agents which can
in certain cases completely convert the organic compounds present into
CO2, salts and water.
This process is suitable for treating aqueous streams having both a low
solids content and a low organic content and can, therefore, be used
either directly on an appropriate stream or as a tertiary treatment step.
The process can produce a TOC free product stream and does not
generate any other effluents. In some cases it has been found to be
competitive with the alternative tertiary treatment processes like granular
carbon adsorption or air stripping. Both of these need further treatment
stages to deal with the secondary streams produced during operation or
regeneration.
All designs incorporate on-line cleaning of the U.V. tubes to maintain high
light transmission efficiency.

F.27 CHEMICAL OXIDATION: OZONE
F.27.1 Introduction
Ozone is a powerful oxidizing agent which is used mainly as a tertiary
treatment to destroy bacteria present in the water and in those cases
where chlorine is not acceptable.
It can also be used in conjunction with H2O2 to promote the formation of
more powerful free radicals which can be used for the destruction of
pesticides.
In some cases, ozone has been used for the final oxidation of domestic
sewage to produce disinfected water useful for irrigation or industrial use.
The process includes the production of ozone which is a highly toxic and
corrosive gas and therefore the equipment has to be designed
accordingly.
Ozone is never produced as a pure chemical but as a mixture in air or
oxygen normally at a concentration of 3% w/w in air or 6% in oxygen.
The main steps are:
(a) Ozone production:
by subjecting the oxygen in air to a high voltage silent electrical
discharge.
The air needs to be dried to less than 2!ppm of water (dew point -
70°C).
(b) Ozone dispersion:
due to its low solubility in water the appropriate agitation conditions
have to be used to maximize mass transfer.
(c) Excess ozone destruction:

due to its high toxicity the excess unreacted ozone (3 to 10% of the
initial amount) has to be diluted or thermally decomposed before it
is discharged into the atmosphere.
Good process control is required to insure optimum operation of the
system and to minimize energy usage.
The "Occupational Exposure Limit" for ozone is 0.1 ppm (calculated as an
8 hour time-average concentration).
It may not be suitable for AOS containing VOCs which can be stripped out
during the process.

F.28 CHEMICAL OXIDATION: H2O2/Fe (FENTON'S REAGENT)
F.28.1 Introduction
In circumstances where the AOS contains relatively low concentrations of
COD (less than 2000 ppm) and recovery cannot be justified, then the use
of peroxide/iron as a chemical oxidant may prove attractive. Work by
FCMO, Zeneca has shown for a range of substrates derived from
benzene/toluene/halogenated aliphatics, that:
(a) Most of the aromatic substrates examined were amenable to
removal by oxidation with peroxide/iron, under acid conditions.
(b) Halogenated aliphatic substrates were resistant to oxidation.
(c) Destruction of substrate was accompanied by a reduction in COD,
typically by 30-75% of the starting value. The BOD also reduced
substantially except in the case of benzene where the BOD
approximately doubled.
The peroxide charge required to achieve substantial removal of one mole
of substrate is typically 5-10!moles, catalyzed by 0.15-0.5!moles ferrous
iron.
The rate of substrate destruction is specific to its molecular structure and
therefore should be determined by experiment.

F.29 CHEMICAL OXIDATION: OTHERS
F.29.1 Chlorine
Chlorine is a strong oxidant and the most commonly used reagent for the
disinfection of water.
Chlorine also reacts with any organic matter or ammonia/ammonium ion
present.
F.29.2 Chlorine Dioxide
Chlorine dioxide is a strong oxidant. There are several commercial
processes for making it, most of which use sodium chlorite as the starting
point. It is used mainly as a bleaching agent but there are some
environmental applications. One example is aqueous effluents containing
between 100 and 1000 ppm of phenol. Unlike elemental chlorine, chlorine
dioxide does not form organic chlorine compounds when it oxidizes
organic compounds. The economics can be attractive where the need is
for oxidation "on demand" on a modest scale. Degussa is one system
supplier.
F.29.3 Sodium Hypochlorite (4)
Aqueous sodium hypochlorite is a well established process for the
oxidation of organic matter in water. The main advantage is low cost - it's
probably the cheapest oxidant, other than air. The main disadvantage is
the tendency of this process to generate organic chlorine compounds.
Scrubbing liquors from VOC and odor treatment plants can be treated
this way.
F.29.4 Lime, Caustic, Sulfides
Lime, caustic, sulfides are commonly used in the precipitation of metals.
F.29.5 Acids/Alkalies
Acids/alkalies are used for the neutralization of waste water. This
operation often turns out to be more difficult to achieve within budget than
expected at first assessment and advice should be sought.

F.29.6 Aluminum Sulfate, Ferric Chloride, Lime, Sodium Aluminate
Aluminum sulfate, ferric chloride, lime, sodium aluminate are used to
precipitate phosphorus compounds from aqueous streams.
F.29.7 Sulfur Dioxide
Sulfur dioxide is used for the removal of chlorine from aqueous streams.
F.29.8 OXISPEC
OXISPEC is a process provided by JMC for the catalytically enhanced
oxidation of AOS containing up to 1% w/w organics. The oxidants used
are sodium hypochlorite, hydrogen peroxide, ozone and the catalyst is
heterogeneous. Operating conditions are modest.

F.30 TOTAL THERMAL OXIDATION: INCINERATION
F.30.1 Introduction
Incineration is a well established method for the destruction of organic
components. When the concentration of organics in an AOS is higher than
50%, the combustion is self-sustaining and it does not need
supplementary fuel.
To prevent excessive NOx formation, most modern incinerators operate
with water injection into the low temperature second combustion chamber.
In some cases very dilute solutions < 5% organic can be disposed of by
injection into this chamber instead of water.
The use of a custom-built incinerator for the destruction of a specific AOS
is very expensive and should only be considered if no other practicable
alternative is available. However, there are examples of the use of power
plants, steam generators or fired process heaters to dispose of unwanted
organic components and at the same time recover the calorific value.
Such disposal requires very careful consideration.
The main requirement is to make the AOS as near compatible with the
capabilities of the existing equipment as is practicable. This may involve
concentrating the AOS, or blending it with existing fuel supply, adding
other fuels to achieve a homogeneous mixture. To minimize interference
with the process heater operation it is common to design one of the burner
guns to operate using the organic residues while the rest are operated
with the normal fuel. The residues are stored in one or several tanks
according to their composition and are then fired in campaigns when the
rest of the plant is operating.
Special waste may require custom designed incinerators to meet EA
Authorization requirements. This is the case for chlorine containing
organics which can form dioxins during incineration and require a second
combustion stage operating at about 1200°C to insure complete
destruction. NOx abatement may then be necessary.

Rotary kilns can be used to incinerate liquids, sludge's and solids.
The presence of metals in the feed may be a problem because they can
react with the refractory lining and shorten its life.
Heat recovery is sometimes implemented as part of the incinerator design
in which case if the heat recovered in the incinerator is a substantial
proportion of the process heat input it is very important that the reliability
of the incinerator installation matches the process requirements. Most
incinerator installations include particulate removal equipment to remove
solids from the combustion gases.
If present in the combustion gases, volatile metal compounds, P2O5, Br,
SO2 etc. will probably have to be removed. This can be done using a wet
or dry scrubber. Dry systems use a bag house for removal of particulates.
For acid gas absorption, dry reagent is either blown directly into the
bag house or injected as a slurry into a spray tower which precedes the
bag house. Wet systems use a venturi scrubber for particulate removal
and an acid gas absorber, typically a vertical counter flow packed tower to
remove the acid gases. A back-up filtration or electrostatic precipitation
stage is likely to be required. All these methods are likely to generate a
need for further processing in order to minimize the ultimate disposal
problem.
In some locations the visible steam plume produced by the incinerator
may also have to be removed either by reheating the combustion gases
after scrubbing or by dilution with air/inert gas streams.
Specific material recovery processes are available in which a combustion
process is used to convert part of the AOS into its basic inorganic
components which can then be used to reconstitute either the original
material in a usable form or some other product. For example, the
Acid Recovery Process in a methyl methacrylate plant uses oxygen to
combust a dilute stream of waste sulfuric acid contaminated with organic
impurities. The resulting SO2 is recovered from the combustion gases,
reoxidized to SO3 and then absorbed in water to regenerate the sulfuric
acid which is recycled within the process.

F.31 PARTIAL THERMAL OXIDATION: OIL- GAS PROCESS
F.31.1 Introduction
Partial oxidation is a well established process for the production of
mixtures of CO and H2 by partial combustion of organic compounds in the
presence of a limited amount of O2 and a moderator (either water or
carbon dioxide).
In the absence of a catalyst, the preheated feeds react adiabatically in the
combustion section of the reactor at 30-100 bar and 1200-1500°C. The
hot gas mixture produced is quenched either by direct contact with water
or by indirect heat exchange.
Most liquid organic residues including those containing free water can be
used as feed.

APPENDIX G EMERGING TECHNOLOGY
Table of Contents
G.1 SUPERCRITICAL WATER OXIDATION (SCWO)
G.2 LIQUID MEMBRANES
G.3 REED BEDS

G.1 SUPERCRITICAL WATER OXIDATION (SCWO)
G.1.1 Introduction
SCWO technology is used to totally oxidize all organics present in an AOS
to CO2 and water. It operates in the supercritical region of water where all
mixtures of water with organic compounds are completely miscible and
react with the oxygen in less than one minute.
G.1.2 Process Description
AOS is heated under a pressure of 300 bar to a temperature in excess of
400°C with the addition of air.
Heat integration is required to minimize energy consumption.

G.1.3 Process Requirements/Limitations
This technology is expensive and its use will be restricted to the removal
of hazardous, refractory materials.

G.2 LIQUID MEMBRANES
G.2.1 Introduction
Liquid membranes allow the removal of water soluble organics from AOS
as an aqueous concentrate. This recovery technique can potentially be
used when conventional solvent extraction of dilute AOS stream is
uneconomic.
The membrane system has to exist as a liquid phase and is specifically
formulated so it can selectively extract the desired chemical(s) from one
aqueous stream (the AOS waste water) and concentrate it in another
aqueous phase (the strip phase). This enables the reuse or recycle of
the extracted chemical or, alternatively, its disposal or treatment as a
stream of lower volume.
There are two types of liquid membrane:
(a) Emulsion membranes
In emulsion membranes, clean water is dispersed as micro-droplets
in the organic continuous phase which forms the membrane. This
emulsion membrane phase can be used as an extractant in
equipment similar to traditional agitated liquid/liquid extraction plant.
During the extraction of AOS, under the effect of the agitation the
emulsion membrane splits itself into small droplets (still containing
the water micro-droplets inside). The organic compounds contained
within the AOS dissolve in the membrane organic phase and then
transfer to the water micro-droplets.
After the extractor the emulsion membrane is phase separated from
the AOS. The emulsion is then broken to form an aqueous strip
phase which is readily separated from the organic continuous
phase either for disposal, recycle or further treatment. The
membrane layer is then re-emulsified with clean water and reused.

(b) Fixed membranes
The membrane is supported in a porous inert substrate (e.g. a
hollow fiber). This is known as a Supported Membrane.
Of the two types, the Emulsion Liquid Membrane has the most commercial
potential because of the high surface area of membrane that can be
achieved when forming and dispersing the emulsion (1000-3000 m2
/m3
).
G.2.3 Process Requirements/Limitations
The process requires:
(a) A driving force for mass transfer.
(b) Suitable emulsion stability, i.e. it does not coalesce when in contact
with the feed phase and yet can subsequently be coalesced to
release the strip phase.
(c) The organics concentration in the AOS should be well below
saturated solubility level.
The process is limited by:
(1) The presence of solids.
(2) Entrainment of feed in the emulsion and osmosis of water into the
emulsion. (Hence controlled contacting, good emulsion settling and
short contact times are preferred).
(3) Any accumulation of trace impurities in the liquid membrane which
prevents the system from functioning properly. However, a purge
could be removed and purified prior to reuse.

G.3 REED BEDS
G.3.1 Introduction
Reed beds are becoming accepted as an alternative to biological
treatment and have been used in many small size communities and
industrial applications for the destruction of biodegradable waste.
The reed beds are constructed by removing the soil up to a depth of 1.5 m
and installing an impermeable polypropylene membrane and refilling with
suitable agricultural soil up to a height of 1 m. The reeds are then planted
and allowed to grow.
The AOS is percolated through the beds at such a rate that the effluent
achieves the required specification.
The feed liquid is distributed from an inlet manifold, passes through the
reed bed and is then collected and discharged to receiving waters. The
level is maintained at 20 cm below the surface to provide a non-flooded
bed.
Oxygen is transferred by the plants to the roots and supports the attached
colonies of bacteria. The plant root system enables the flow of water through the
bed.

APPENDIX H PROPRIETARY/LESS COMMON TECHNOLOGIES
Table of Contents
H.1 INTRODUCTION
H.2 PRECIPITATION
H.3 SOLIDIFICATION
H.4 METEX
H.5 BIOKOP
H.6 A-B PROCESS
H.7 BACTERIA - SPECIAL
H.8 BIOSORPTION
H.9 BIOBOR HSR
H.10 BIOSTYR
H.11 CAPTOR
H.12 CARROUSEL
H.13 LINDOX
H.14 LINPOR
H.15 OTTO AQUA-TECH HCR
H.16 UNOX
H.17 ACIMET
H.18 ANTHANE/ANODEK
H.19 BIOTHANE
H.20 LARAN
H.21 UHDE/SCHWARTING
H.22 OXIDATION BY PERMANGANATE
H.23 OXIDATION BY PHOTOCATALYSIS
H.24 InTox .

H.25 KENOX
H.26 MODAR
H.27 ULTROX
H.28 VerTech
H.29 WINWOX AND WOX .
H.30 ZIMPRO
H.31 SPRAY ROASTING (SPRAY CALCINATION)
H.32 PLASMA PROCESSING
H.33 ELECTROCHEMICAL PROCESSES
H.34 CRYSTALLIZATION

H.1 INTRODUCTION
The information in this Appendix has been extracted from the document
produced for GBHE.
In the brief descriptions which follow, each technology/process is
annotated with a number between (1) and (4) giving an indication of
GBHE's current perception of the commercial status.
The key is as follows:
(1) At a development stage as far as the waste market is concerned.
(2) Commercially available for up to a few years but not yet in
widespread use for waste.
(3) Commercially available for a considerable time but either never
achieved widespread use or are in decline.
(4) In widespread use.
It should be emphasized that these numbers refer to waste treatment. For
instance, a process identified as (1) or (2) might be in widespread use in
another field such as potable water. The distinction between (2) and (3) is
an attempt to identify within processes in limited commercial use those
which could be emerging with a future as opposed to mature ones in
decline.
H.2 PRECIPITATION (4)
Precipitation is usually achieved by addition of alkali to neutralize acidic
waste, followed by filtration with dumping of the cake and discharge of the
filtrate into sewer if possible. Flocculation as practiced in the water
industry is a special case. Suitable for effluents from chemical and
metallurgical operations - inorganic and organic acids and anions, metals
and cyanides (e.g. Pickle liquors, metal finishing liquids). The main
advantage is cheapness. Practiced for many years. A relatively recent
development in flocculation is the use of a magnet to remove flocculant
precipitates which have been caused to adhere to granules of magnetite
(the Sirofloc process).

H.3 SOLIDIFICATION (3)
Conversion of aqueous wastes to solids which can be land filled. Can vary
from simple physical entrapment to more complex molecular caging. In the
simpler concepts, proprietary additives are used, usually based on cement
or silicates. Effluents should have neutral pH. Organic materials generally
unsuitable. Some inorganics with high levels of dissolved salts also
unsuitable as setting is inhibited. Developed since the 1960s, mainly in the
U.S.A..
There are many doubts about the approach - particularly on softening with
age with release of soluble constituents. In particular, the presence of
organic compounds can weaken the solids. The commercial operating
process is fairly widely used in Europe. (Over 80 techniques exist in the
U.S.)
H.4 METEX (2)
A process for extracting heavy metals from industrial waste waters by
adsorption on activated sludge under anaerobic conditions. It is operated
in an upflow, cylindrical reactor having a conical separation zone at the
top. Particularly suited to the removal of heavy metals from waste water
with organic loads which are difficult to handle by conventional methods
such as ion exchange or electrolysis. Sludge containing concentrated
heavy metals has to be disposed of. Developed by Linde AG, originally for
removing dissolved copper from winemaking wastes. Piloted on synthetic
wastes containing other metals (Ni, Cr, Zn, Hg) and typical organics such
as tartrate, citrate, and glycine. The Institute of Gas Technology, Chicago,
has developed a similar process.
H.5 BIOKOP (2)
A process for treating liquid effluents containing wastes from organic
chemical manufacture and also domestic sewage. It combines aerobic
fermentation, in special reactors known as Biohoch reactors, with
treatment by powdered activated carbon. Low space requirement with
energy saving due to high oxygen utilization. More complex and needs
more control than traditional technology. Developed originally for treating
the effluent from the Griesheim works of Hoechst AG, it was engineered
by Uhde GmbH and is now offered by that company.

H.6 A-B PROCESS (2)
This process stands for Adsorptions-Belebungsverfahren, German,
meaning Adsorption-Activation process. A two-stage, aerobic activated
sludge process for treating sewage and industrial wastes. The first (A)
stage is highly loaded, the second (B) low-loaded. Such a system can
cope with sudden changes in the quantity and quality of effluent feed.
Suitable for high BOD, non-biotoxic wastes, both municipal and industrial.
A small land area is required and the capital cost is lower than that of
conventional activated sludge plant because fewer stages are required.
Relatively low energy consumption. Developed in 1983 by B Bohnke at
the Technical University of Aachen and subsequently engineered by
Esmil.
H.7 BACTERIA - SPECIAL (3)
Use of bacteria which are specially adapted to metabolizing particular
substrates. Developed in the 1970s, to improve the performance of
activated sludge plants when specific materials were present (e.g.
hydrocarbons) which were difficult for the normal spectrum of
microorganisms to metabolize. Often referred to as bioaugmentation.
Have not achieved mainstream use. The economics are contentious.
Usually supplied freeze-dried. Suppliers include International
Biochemical's Ltd and a variety of importers of products from the US.
H.8 BIOSORPTION (1)
A process for removing metals and some organic compounds from
aqueous solution by biosorption on suitable microorganisms. Biotechna
Ltd has been prominent in this field. Development started in about 1984.
First patents were filed in 1987. They work with Graesser Contactors and
organisms are grown in a helical reactor called a "Biocoil". These include
bacteria, algae, fungi and yeasts. Desulfovibrio, a sulfur reducing bacteria,
is one example. More recently, Archaeus Technology Group has been
promoting its Arcasorb range.

H.9 BIOBOR HSR (2)
An intensification of the classic activated sludge aerobic approach. Uses
compressed air into a tower with moving perforated disc internals. HSR
stands for Hubstrahlreaktor which translates to reciprocating jet reactor.
Closed reactor giving odor control. Agitation gives high rate of
oxygenation. Short residence time/relatively small volume. Doesn't take up
much space. Low surplus sludge production. Developed by Borsig GmbH
and now being commercialized. A mobile test rig can be rented. Claimed
to be economic for rigorous treatment of wastes with very high
BOD/COD levels.
H.10 BIOSTYR (2)
An immersed biological filtration approach using a fixed biomass. The
microbiological organisms are trapped within rigid, lighter-than-water
porous polystyrene granules. The effluent flows upward through a bed of
these granules and air is injected at the base of the bed. Suitable for both
dilute and concentrated effluents containing dissolved non-toxic organic
matter. Compact with high performance in a single stage and no final
clarification needed. Developed in France by OTV S.A. and licensed in the
U.K. through General Water Processes Ltd.
H.11 CAPTOR (2)
A modification of the activated sludge system in which the microorganisms
are retained in a reticulated, flexible polyether foam. Excess sludge is
periodically pressed out mechanically. Particularly suited to concentrated
effluents with high BOD and COD from food processing plants and the
like. Occupies only 20% of the land area occupied by conventional
activated sludge plant. Invented at UMIST and now offered by Simon
Hartley.
H.12 CARROUSEL (2)
An unconventional aerobic treatment system for sewage and industrial
effluents, providing efficient oxygenation, mixing, and quiescent flow in an
elliptical aeration channel fitted with baffles. Suitable for effluents with
moderate loadings of non biotoxic organic materials. Capital cost lower
than that of conventional activated sludge plant because fewer stages are
required. Low power requirements. Claimed to provide buffer against
shock loading. Developed in Holland by DHV and now licensed in the U.K.
by Esmil Ltd.

H.13 LINDOX (3)
A variation of the activated sludge process, using industrial oxygen (90-
98%) instead of air. The liquor passes through several closed tanks in
series and the oxygen is absorbed through the surface of the liquor. Can
treat wastes having high nitrogen contents, e.g. those from meat
processing plants. Occupies less space than conventional activated
sludge plants. Totally enclosed so no odors. More complex to operate and
maintain than conventional plant. Developed by Linde AG in the 1970s
and first operated at a meat rendering plant in Oberding in 1974. Closely
related to the Unox process. Claimed to be viable for the more difficult and
variable effluents, such as from the food industry, with very high oxygen
demand and potential problems with sludge bulking.
H.14 LINPOR (3)
Uses an open-pore plastic foam for retaining the biomass. Suitable for
high BOD, non-biotoxic effluents - particularly really concentrated ones. Its
use enables the capacity of an activated sludge plant to be increased
without adding extra tanks. Good results where sludge bulking might
be a problem. More complex than conventional plant. Invented at the
Technische Universitat, Munich, and further developed by Linde AG.
Initiated by the demand for nitrification in the activated sludge process
calling for large treatment volumes.
H.15 OTTO AQUA-TECH HCR (2)
An intensification of the classic activated sludge aerobic approach. HCR
stands for high capacity reactor. Uses a vertical loop reactor aerated from
the top by a two-phase air jet in conjunction with a sedimentation facility.
Closed reactor giving odor control. The means of aeration is claimed to
give very high mass transfer rates between microorganisms and the
supplied substrate. Doesn't take up much space. Reduced surplus sludge.
Total cost in use claimed to be lower than activated sludge.
Fundamental research at the Institute for Thermic Processing at the
Technical University of Clausthal-Zellerfeld. Developed and engineered by
Otto. First commercial installation 1989. Eleven plants have now been
installed in Germany and Italy on wastes from dairies, abattoirs,
yeast processing, printing ink manufacture, olive oil refining and landfill
leachate.

H.16 UNOX (3)
A variation of the activated sludge process based on the use of oxygen
instead of air, in closed reaction tanks. The preferred source of oxygen
depends on the size of the plant; small plants use liquid oxygen; medium-
sized plants use the pressure-swing process, and large plants have
cryogenic generators. Occupies less space than conventional activated
sludge plants. Totally enclosed, so no odors. Accepts large swings in
oxygen demand. More complex than conventional activated sludge -
needs higher standard of operation and maintenance. Capital
costs lower and operating costs higher than conventional activated sludge
plants. Developed by Union Carbide Corporation in the late 1960s and
now licensed to a number of other companies including Wimpey
Engineering in the U.K.. Similar to the Lindox process.
H.17 ACIMET (1)
A two-stage, anaerobic digestion process for treating municipal waste
waters. In the first stage, organic matter is decomposed to a mixture of
acids, aldehydes and alcohols. In the second, the carbon in this mixture is
anaerobically converted to methane. Suitable for wastes containing large
amounts of cellulose as well as municipal wastes. Designed primarily to
produce gas for fuel. Invented in 1974 by S Ghosh and D L Klass at the
Illinois Institute of Gas Technology, Chicago. First commercialized in 1991
by IGT and DuPage County, Illinois, at the Woodridge-Greene Valley
Wastewater Treatment Plant.
H.18 ANTHANE/ANODEK (3)
A two-stage process for generating methane by the anaerobic
fermentation of industrial organic wastes. The process is designed
basically for producing a fuel gas and is said to be suitable for
effluents containing up to 40 g/l COD. Higher loading rates and shorter
hydraulic residence times than conventional digestion are claimed.
Invented by the Institute of Gas Technology, Chicago. Engineered by the
Studiebureau O. de Konickx, (ODK) Belgium, and commercialized since
1977. Now offered by ODK's U.S. affiliate VIMAG Inc.

H.19 BIOTHANE (4)
An anaerobic digestion system for treating industrial organic wastes. The
reactor contains an upflow sludge blanket and is operated at about 35°C,
the heat being provided by burning some of the product gas which
contains 70% methane. It is usually necessary to add nutrients such as
urea and iron. Particularly suited to food industry wastes. Occupies a
relatively small land area. Essentially a pretreatment usually followed by a
secondary aerobic stage. Developed in the early 1970s in Holland by
Centrale Suiker Maatschappij; in 1984, Gist-Brocades nv (Delft) acquired
the rights and subsequently licensed the process in the U.K. to Esmil Ltd.
In 1990, more than 70 units had been built, worldwide, for a variety of
industries.
H.20 LARAN (2)
An anaerobic process for treating industrial waste waters, generating
methane for use as fuel. The process uses a fixed-bed loop reactor.
Shock loads can be accommodated. Short retention times and good
nitrification are claimed. Developed by Linde AG, Munich, in the early
1980s. European patent 161,469. First piloted at a dairy in 1983. Viable as
a pretreatment for wastes with a high level of organic pollution prior to an
aerobic "polishing" step.
H.21 UHDE/SCHWARTING (2)
An anaerobic fermentation process for treating aqueous wastes containing
high concentrations of organic materials. Two fermenters are used,
operated at different temperatures and acidities. In the first, insoluble
materials are brought into solution and most of the organic matter is
converted to acids and alcohols. In the second, methane and carbon
dioxide are produced. Developed in 1982 in Germany by Geratebau
Schwarting AG and the Fraunhofer Institute for Boundary Layer
Research; engineered and offered by Uhde GmbH. Three plants have
since been built in Germany and one in Portugal, all for the food industry.
As with anaerobic processes generally, the value of the gas generated is
important.

H.22 OXIDATION BY PERMANGANATE (3)
This is often used for removing trace colors and odors from potable water,
so it could be considered for removing traces of toxic materials from
effluents too. In general, oxidation by permanganate is between 2 and 3
times as expensive as oxidation by chlorine so it would not be economic
for removing more than trace amounts except for very specific
applications.
H.23 OXIDATION BY PHOTOCATALYSIS (1)
Photocatalysis, using titanium dioxide catalyst and sunlight. Will treat
compounds that are hard to oxidize in other ways, e.g. dioxins, if present
in very dilute form. The photocatalytic properties of titanium dioxide have
been known for many years but it has only been seriously considered for
practical use during the last ten. Sandia National Laboratories and the
Solar Research Institute, U.S.A., have demonstrated its usefulness for
treating groundwater containing chlorinated hydrocarbons and predict its
commercial adoption by 1995. There has been a lot of academic
research but only one, modest, device has been marketed. This is the
Nulite reactor from Nutech Environmental in Canada.
H.24 InTox (1)
The InTox process uses established wet air oxidation principles in a pipe
reactor autoclave (230-280°C, 120 bars). The pipe is 2-4 km long and 2.5-
10 cm in diameter. The technology is based on an aluminum extraction
process developed in Germany in the 1960s by VAW and Lurgi. The
process was promoted in the U.K. during 1991 for waste treatment by
InTox Corporation Limited. This is believed to be a group of individuals
basing their promotion on a unit operated by Chemcontrol A/S in Denmark
- the unit pictured in InTox literature. InTox claimed a higher degree
of waste destruction than other wet air oxidation variants and also
relatively low capital and operating costs.
However, InTox ceased its promotion in late 1991. Apparently, the
Chemcontrol unit is no longer operational and has been dismantled. In
1995 no information on the InTox process or InTox Corporation could be
found. Lurgi (UK) Ltd have no knowledge of the process.

H.25 KENOX (2)
The Kenox wet air oxidation process is offered by the Kenox Corporation
of Ontario. This is a small company formed by some individuals who came
together in 1983 to develop a system using a different reactor design from
that used by Zimpro. Kenox became part of Environmental Technologies
Investments of Toronto in 1991.
Kenox claims that its reactor operates in a much more dynamic regime
with a high circulation rate giving very much higher mass transfer of
oxygen. For a given duty, its operating temperature and pressure (250°C,
700 psi) are lower than those of Zimpro. Kenox also claims that, overall,
corrosion is less, total operating costs dramatically less and that when
items of plant have to be replaced they can easily be sourced locally
whereas Zimpro requires various specialized items to be sourced directly
from the company. Until recently, the only unit in operation was of 12
gallons per minute capacity dealing with the washing wastes from a large
steel drum reconditioning plant in Toronto.
A breakthrough for Kenox was an agreement with Leigh Environmental in
1991 giving Leigh exclusive rights to use and market the Kenox
technology in the U.K.. Leigh announced a merchant facility which is being
installed at Small Heath in the Midlands. This is designed for 50,000 tpa of
difficult organic wastes from the pesticide, chemical and pharmaceutical
industries. This is being commissioned now and Leigh has said that, upon
the successful completion of this exercise it will build three more merchant
units in different parts of the country.
H.26 MODAR (2)
Modar Supercritical Water Oxidation (SCWO) Technology was invented in
1980 by M Modell, a professor of chemical engineering at MIT. It was then
developed through the 1980s being piloted at the SKF Laboratories in
1985 and then at CECOS, a waste treatment company in Niagara Falls,
in 1986. A larger capacity plant for CECOS has been designed but has not
yet gone ahead. SCWO should still be classed as an emerging
technology.
The principle is that water above its critical point is an effective solvent for
organic compounds and also gases including oxygen are completely
miscible. Hence, a homogeneous single phase results where the organic
compounds and oxygen can react rapidly without interfacial mass transfer
limitations. Particularly suitable for 1-30% toxic organics in water.

With operations at above the critical point of water (374°C and 22.13 MPa
pressure) - typically 620°C and 23.5 MPa - the engineering and materials
of construction challenges are severe. However, for more than two years
the worldwide exclusive license has been in the hands of ABB Lumus
Crest Inc which gives the potential for heavyweight support. Indeed, ABB
Lumus Crest claims to have "invested" about $2 million over the past two
years in the development of the technology and has now completed two
basic engineering packages for modest sized plants of 5,000 and 20,000
gallons per day respectively. The potential prize for ABB Lumus Crest is a
more acceptable alternative to incineration with operating costs which
could be a tenth of those of conventional incineration.
H.27 ULTROX (1)
Combined UV-Ozone-Hydrogen peroxide oxidation approach. Effluents
should be free from particles or cloudiness and fairly dilute - concentration
of organic to be destroyed initially in the range 20-30,000 ppm. Reduces
total organic carbon to low parts per billion and will treat compounds that
are hard to oxidize in other ways, e.g. halogenated organics. End products
are CO2 and halide ion. Developed since the 1970s by Ultrox International
and demonstration tests on 15 various effluents published. Tested on
large scale in California in 1989, results well documented.
H.28 VerTech (2)
VerTech Treatment Systems BV of the Netherlands is promoting a system
which uses conditions in the typical wet air oxidation range (i.e. 270°C and
10 MPa). However, VerTech describes the system as subsurface
oxidation since it relies on a vertical pipe about one mile deep with
pressure being created at the bottom by the weight of the liquid above it.
The vertical shaft is drilled conventionally and encased in cement after
which two concentric special quality steel tubes are suspended in it.
Oxygen rather than air is normally advocated as the oxidizing agent.
Although the company says that there is potential use of the system for
industrial organic waste, a large volume throughput is required - a
minimum of the order of 100 gallons per minute. This rules it out of most
industrial waste applications. VerTech is concentrating its promotion on
sewage sludge treatment with large volume flows with up to 10% solids.
The operating experience is based on a system installed at Longmont,
Colorado in 1985. About a year ago, a unit for the Veluwe Water Board at
Apeldoorn in the Netherlands was announced.

H.29 WINWOX AND WOX (2)
Catalyzed oxidation by hydrogen peroxide. Winwox has been developed
since 1987 by the Winfrith Technology Centre (part of the U.K. Atomic
Energy Authority) as a method of destroying ion exchange resins
containing radioactive isotopes. A pilot plant for handling 200 kg batches
containing 300 g/kg solids was built in 1989. WOX has similarly been
developed by ASEA Atom, Sweden. Now being promoted for hazardous
aqueous/organic wastes more generally. Advantages are mild conditions,
small amount of secondary effluent and ordinary materials of construction.
Capital costs relatively low but hydrogen peroxide costs high, hence likely
to remain specific to specialized hazardous wastes.
H.30 ZIMPRO (4)
The Zimpro wet air oxidation process was introduced by J F Zimmerman
in the U.S.A.. in 1954 and for many years was known as the Zimmerman
wet incineration process. It has had a somewhat chequered ownership
history but latterly has been offered by Zimpro Passavant Environmental
Systems Inc under the Zimpro name. Zimpro Passavant became part of
the Black Clawson Company late in 1990.
Over the last 35 years, more than 200 Zimmerman/Zimpro wet air
oxidation units have been installed around the world. Many of these have
been for the treatment of pulp and paper industry waste liquors, sewage
sludge and refinery waste caustic liquors. Experience on general industrial
aqueous effluents containing organics is clearly more recent but the
accumulated generic engineering and operational experience on the 200+
units is unrivalled. Zimpro has to be regarded as the current market leader
in wet air oxidation.
Typically operates at 280°C and 1700 psi. Sterling Organics are installing
a unit with a design flow of 30 gallons per minute in Northumberland. This
will remove para amino phenol from waste water generated in
paracetamol manufacture.

H.31 SPRAY ROASTING (SPRAY CALCINATION) (3)
Injection of liquid waste into a hot combustion chamber which may or may
not contain a fluidized bed of inert material. Suitable for aqueous wastes,
which may be strongly acid or alkaline, containing dissolved organic
and/or inorganic compounds, e.g. steel pickling liquor containing
hydrochloric acid and ferrous chloride; liquor from limonite beneficiation;
caustic waste from oil refineries. A established process, often associated
with hydrochloric acid recovery. Suppliers of systems include Babcock
Woodall, Duckham and Copeland Systems Inc.
H.32 PLASMA PROCESSING (1)
A plasma is a gas in which some of the gas molecules are ionized to form
positive ion and electron pairs and thus conducts electricity. Thermal
plasmas based on arc discharge operate at very high temperatures,
typically greater than 5,000°C. Waste is injected into the plasma arc and
dissociation takes place sometimes with incineration if additional air or
oxygen is introduced. Suitable for effluents containing virtually any
organics and some inorganics. Particular attention is needed to rapid
quenching after the plasma Pyrolysis to prevent chemical re-combination.
Westinghouse has made a big effort to commercialize plasma technology
for waste destruction with little success. EA Technology at Capenhurst is
developing a system. Other suppliers/ developers include Arc
Technologies Co, U.S.A., CSIRO, Australia and Tetronics Ltd.
H.33 ELECTROCHEMICAL PROCESSES (3)
Such processes include both those where oxidation or reduction of the
substrate occur at an electrode, and those where a particular metal ion in
a particular valence state is an intermediary. In principle, any aqueous
solute which can be oxidized or reduced can be considered as a
candidate for such a process. Large scale electrochemical technology
goes back almost a century in the chloralkali industry but other
applications have been slow - held back by lack of electrochemical
expertise, limited access until recently to "off the shelf" pilot reactors and
general perception of high cost. EA Technology (former ERDC) has been
successful with specific packages such as the Chemelec cell for
recovering metal and the CEER process for regenerating etchant with
copper recovery from printed circuit board production.

The use of Ag2+
(the so-called "silver bullet" process) arose from work at
a European plant where this oxidant was used to solubilize plutonium
dioxide. It was then discovered that this oxidant also oxidized cellulose
tissues to carbon dioxide. Relatively exotic and still under development.
The electrochemical approach is generally particularly suitable for dilute
effluents. Very powerful oxidants can be produced (e.g. Ag2+
).
Electrochemical processes are generally regarded as expensive in energy
and capital and the economics depend on recovered materials or other
specific factors. Small reactors and general know-how are available from
EA Technology and their licensee Electrocatalytic, and Electrocell AB.
AEA Technology is promoting the "silver bullet" process.
H.34 CRYSTALLISATION (2)
Removal of solutes from water or organic solutions by crystallization,
either by evaporation or by cooling. Cooling is sometimes done by adding
a cold liquid such as petrol or liquid carbon dioxide. Suitable for "clean"
solutions - complex mixtures can be hard to crystallize. Ideally there
should be some value in the solute or solvent. Widely used in the chemical
industry, e.g. to remove ferrous sulfate from sulfuric acid residues from the
sulfate process for making titanium dioxide.

APPENDIX J COMPARATIVE COST DATA
J.1 EXAMPLE 1
Aqueous stream containing 2 to 3% TOC including CN compounds, inorganic
salts such as ammonium sulfate, methylene chloride, benzene as well as some
solids and heavy metals.
REFERENCE: 4
ŧ Widely practiced in the U.S.A. However, it may not be acceptable in the
future.
§ This process still requires further technical development.

J.2 EXAMPLE 2
Aqueous stream containing 200 to 500 ppm TOC including benzene,
toluene, ethylbenzene and xylene.
REFERENCE: 4

J.3 EXAMPLE 3
Aqueous stream containing 5 to 10 ppm TOC including TCE and PCB's.
REFERENCE: 4
J.4 INDICATIVE COST DATA (1993)
CAPITAL COST OF A BIO TREATMENT PLANT: $1.0M to
1M/(tonne/day) of BOD
COST OF LANDFILL: $50 to $132/tonne
COST OF CONTRACT INCINERATION: General Waste: $250 to
$3,3000/tonne Laboratory
Waste: up to
$16,500/tonne
(Cost expected to increase by a minimum of 30%/year)

PRACTICAL GUIDE ON THE SELECTION OF PROCESS TECHNOLOGY FOR THE TREATMENT OF AQUEOUS ORGANIC EFFLUENT STREAMS

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PRACTICAL GUIDE ON THE SELECTION OF PROCESS TECHNOLOGY FOR THE TREATMENT OF AQUEOUS ORGANIC EFFLUENT STREAMS