An Introduction to Brine Waste

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An Introduction to Brine Waste
Christos Charisiadis 2014

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Contents
1. Introduction 4
2. Feedwater intake and environmental impacts 4
3. Characteristics of desalination brine 6
3.1 Multi-Stage Flash Desalination (MSF) 6
 3.1.1 Seawater Intake 6
 3.1.2 Discharge of Brine Containing Additives 6
 3.1.3 Physical Properties of Brine 8
 3.1.4 Biocides 8
 3.1.5 Antiscalants 9
 3.1.6 Antifoaming Agents 12
 3.1.7 Corrosion Inhibitors and Corrosion Products 13
3.2 Multi-Effect Distillation Desalination (MED) 14
 3.2.3 Physical Properties of Brine 16
 3.2.6 Antifoaming Agents 18
 3.2.7 Corrosion Inhibitors and Corrosion Products 19
3.3 Reverse Osmosis (RO) 19
 3.3.4 Coagulants 21
 3.3.6 Membrane Cleaning Agents 22
 3.3.7 Corrosion Products 23
 3.3.8 Dechlorination 23
4. Receiving coastal environment 24
4.1 Discharge Mode 24
4.2 Receiving Environment 25
4.3 Discharge and Site Variability 27
4.4 Bathymetry and Gravity Currents 27
5. Brine disposal; A look at the possible options 29

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5.1 Inland plants 29
 5.1.1 Deepwell injection 29
 5.1.2 Evaporation ponds 31
 5.1.3 Solar ponds 33
 5.1.4 Zero Liquid Discharge (ZLD)/ Degremont 34
5.2 Coastal options; Disposal strategies and near field effects 37
 5.2.1 Coastal hydrodynamic concept 38
 5.2.2 Disposal Alternatives 38
6. Summary & Conclusions 42

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1. Introduction
Available supply of good quality water for drinking water and industrial has met a
steep increase primarily because of high demand and severe droughts. As a result
many companies are looking into brackish and seawater to satisfy these demands.
These sources typically require a treatment process that generates concentrated
brine as a liquid residual. Due to increasingly strict regulations, conventional brine
waste management strategies such as surface water discharge, deep well injection
or discharge to wastewater treatment facilities may not be feasible in the near
future.
Brine is a very loose term in water treatment. When it comes to desalination, brine
is the liquid residue generated by the treatment process. It contains high
concentrations of sodium chloride and other dissolved salts. This brine can either be
disposed of without any additional treatment or minimized prior to disposal.
2. Feedwater intake and environmental impacts
The selection of the seawater intake system depends on the raw water source, local
conditions, and plant capacity. The best seawater quality can be reached by beach
wells, but in these cases the amount of water that can be extracted from each beach
well is limited by the earth formation, and therefore the amount of water available
by beach wells is very often far below the demand of the desalination plant. For
small and medium reverse osmosis plants, a beach well is often used.
For seawater with a depth of less than 3 m, short seawater pipes or an open intake
are used for large capacities. Long seawater pipes are used for seawater with depths
of more than 30 m.

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The seawater intake may cause losses of aquatic organisms by impingement and
entrainment. The effects of the construction of the intake piping result from the
disturbance of the seabed which causes re-suspension of sediments, nutrients or
pollutants into the water column. The extent of damage during operation depends
on the location of the intake piping, the intake rate and the overall volume of intake
water.
The second impact category is linked to the demand of energy and materials
inducing air pollution and contributing to climate change. The extent of impact
through energy demand is evaluated by life cycle assessment, LCA. The impacts
of this category can be mitigated effectively by replacing fossil energy supply by
renewable energy and using waste heat from power generation for the thermal
processes.
The third impact category comprises effects caused by the release of brine to the
natural water body. Effluents from desalination are not merely concentrated salts,
but include a variety of chemicals that come from the reverse osmosis process, such
as antiscalants and antifoulants, including chlorine and other disinfection by-
products that may be toxic, as well as chemicals present in the intake water. These
additives and their by-products can be toxic to marine organisms, persistent
and/or can accumulate in sediments and organisms.
Also the elevated salinity of the concentrate can cause it to behave differently than
traditional wastewater, stormwater and cooling water plumes. When the effluent
density exceeds that of the ambient seawater, the plume could settle on the ocean
floor and spread as a density current, resulting in increased exposure to bottom-
dwelling marine life. The elevated concentration of salts and other constituents in
these discharges may result in adverse impacts to sensitive components of the
ecosystem.
Apart from the chemical and
physical properties the
impact of the brine depends
on the hydrographical
situation which influences
brine dilution and on the
biological features of the
discharge site. For instance,
shallow sites are less
appropriate for dilution than
open-sea sites and sites with
abundant marine life are
more sensitive than hardly

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populated sites. But dilution can only be a medium-term mitigation measure. In the
long run the pre-treatment of the feed water must be performed in an
environmentally friendly manner. Therefore alternatives to conventional chemical
pre-treatment must be identified.
3. Characteristics of desalination brine
The environmental impacts of seawater desalination will be discussed
separately for each technology because of differences in nature and magnitude
of impacts. The technologies regarded here are MSF, MED and RO.
3.1 Multi-Stage Flash Desalination (MSF)
3.1.1 Seawater Intake
Due to their high demand of cooling water, MSF desalination plants are
characterized by a low product water conversion rate of 10 to 20 %. Therefore the
required volume of seawater input per unit of product water is large, i.e. in the case
of a conversion rate of 10 %, 10 m³ of seawater are required for 1 m³ of produced
freshwater (see Figure 6-1). Combining the high demand of seawater input in
relative terms with the high demand of seawater input in absolute terms due to the
large average MSF plant size the risks of impingement and entrainment at the
seawater intake site must be regarded as high. Therefore, the seawater intake must
be designed in a way that the environmental impact is low.
3.1.2 Discharge of Brine Containing Additives
The discharge of brine represents a strong impact to the environment due to its
changed physical properties, i.e. salinity, temperature and density, and to the
residues of chemical additives or corrosion products. In MSF plants common
chemical additives are biocides, anti-scalants, antifoaming agents, and corrosion
inhibitors. The conditioning of permeate to gain palatable, stable drinking water

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requires the addition of chlorine for disinfection, calcium, e.g. in form of calcium
hydroxide, for remineralisation and pH adjustment. In case of acidification as pre-
treatment removal of boron might be necessary.
Figure 6-2 shows where the chemicals are added, and indicates the concentrations
as well as the characteristics of the brine and its chemical load.

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3.1.3 Physical Properties of Brine
The physical parameters of the brine are different compared to the intake seawater.
During the distillation process the temperature rises and salt accumulates in the
brine. Taking the reference process (Figure 6-1) with a conversion rate of approx. 10
% (related to the seawater flow) as example the salinity of the brine rises from 45 g/l
to 67.5 g/l (Figure 6-3). Brine and cooling water temperature rises by 9 and 7.5 K,
respectively. Salinity of the brine is reduced by blending with cooling water, but still
reaches a value of 5.4 g/l above ambient level. The resulting increase of density is
small what can be attributed to balancing effects of temperature and salinity rise. In
general, the increase of the seawater salinity in the sea caused by solar evaporation
is normally much higher than by desalination processes. However, the brine
discharge system must be designed in a way that the brine is well distributed and
locally high temperature and salinity values are avoided.
3.1.4 Biocides
Surface water contains organic matter, which comprises living or dead particulate
material and dissolved molecules, leads to biological growth and causes formation of
biofilm within the plant. Therefore the seawater intake flow is disinfected with the
help of biocides. The most common biocide in MSF plants is chlorine. A
concentration of up to 2000 μg/l in the seawater intake flow is sustained by a
continuous dosage. Chlorine reacts to hypochlorite and, in the case of seawater,
especially to hypobromite. Residual chlorine is released to the environment with the
effluents from cooling and distillation where it reaches values of 200-500 μg/l,
representing 10-25 % of the dosing concentration. Assuming a product-effluent-ratio
of 1:9 the specific discharge load of residual chlorine per m³ of product water is 1.8-
4.5 g/m³. For a plant with a desalination capacity of 24,000 m³/day, for instance, this
means a release of 43.2-108 kg of residual chlorine per day.
Further degradation of available chlorine after the release to the water body will
lead to concentrations of 20-50 μg/l at the discharge site. Chlorine has effects on the
aquatic environment because of its high toxicity, which is expressed by the very low
value of long-term water quality criterion in seawater of 7.5 μg/l recommended by
the U.S. Environmental Protection Agency and the predicted no effect concentration
(PNEC) for saltwater species of 0.04 μg/l determined by the EU environmental risk
assessment. In Figure 6-4 the occurring concentrations near the outlet and at a
distance of 1 km are compared to ecotoxicity values determined through tests with
different aquatic species and to the EPA short term and long-term water quality
criteria. It is striking that most of the concentrations at which half of the tested
populations or the whole population is decimated at different exposure times or
show other effects are exceeded by the concentrations measured near the outlet
and even at the distance of 1 km.

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Another aspect of chlorination is the formation of halogenated volatile liquid
hydrocarbons. An important species is bromoform, a trihalomethane volatile liquid
hydrocarbon. Concentrations of up to 10 μg/l of bromoform have been measured
near the outlet of the Kuwaiti MSF plant. The toxicity of bromoform has been proven
by an experiment with oysters which have been exposed to a bromoform
concentration of 25 μg/l and showed an increased respiration rate and a reduced
feeding rate and size of gonads. Larval oysters are even more sensitive to
bromoform, as significant mortality is caused by a concentration of 0.05-10 μg/l and
acute, 48 h exposures.
3.1.5 Antiscalants
A major problem of MSF plants is the scale formation on the heat exchanger surfaces
which impairs heat transfer. The most common scale is formed by precipitating
calcium carbonates due to increased temperatures and brine concentration. Other
scale forming species are magnesium hydroxide calcium sulphate, the latter being
very difficult to remove as it forms hard scales. Therefore sulphate scaling is avoided
in the first place by regulating the operation parameters temperature and
concentration in such a way that the saturation point of calcium sulphate is not
reached. Calcium carbonates and magnesium hydroxides, again, are chemically
controlled by adding acids and/or antiscalants.
In the past, acid treatment was commonly employed. With the help of acids the pH
(acidity value) of the feed water is lowered to 2 or 3 and hereby the bicarbonate and
carbonate ions chemically react to carbon dioxide which is released in a

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decarbonator. Thus, the CaCO3 scale forming ions are removed from the feed water.
After acid treatment the pH of the seawater is re-adjusted. Commonly used acids are
sulphuric acid and hydrochloric acid, though the first is preferred because of
economic reasons. High concentrations and therefore large amounts of acids are
necessary for the stoichiometric reaction of the acid.. Apart from a high consumption
of acids further negative effects of using acids are the increased corrosion of the
construction materials and thus reduced lifetimes of the distillers as well as handling
and storage problems. The negative effects mentioned above have led to the
development of alternatives: Nowadays antiscalants are replacing acids during
operation. But before talking about antiscalants, the use of
acids as cleaning agents needs to be mentioned because that’s when significantly
acidic effluents occur. During this periodic cleaning procedure the pH is lowered to
2-3 by adding citric, sulfamic or sulphuric acid, for instance, to remove carbonate
and metal oxide scales. In this context Mabrook (1994, in /Lattemann and Hφpner,
2003/) explained an observed change in density and diversity of marine organisms
by a decreased pH of 5.8 compared to 8.3 in coastal waters. Eco-toxic pH values
range from 2-2.5 for starfish (LC50, HCl, 48 h) to 3-3.3 for salt water prawn (LC50,
H2SO4, 48 h) and show the sensitivity of marine organisms to low pH values. Little
mobile organisms, like starfish, are especially affected by an acid plume as they
cannot avoid this zone. To mitigate these possible effects the cleaning solution
should be neutralized before discharge or at least blended with the brine during
normal operation.
An antiscalant can suppress scale formation with very low dosages, typically below
10 ppm. Such low dosages are far from the stoichiometric concentration of the
scaling species. Hence inhibition phenomena do not entail chemical reactions
and stem from complex physical processes involving adsorption, nucleation and
crystal growth processes. Scale suppression in the presence of minute
concentrations of antiscalants is believed to involve several effects:
 Threshold effect: An antiscalant can slow down the nucleation process
occurring in a supersaturated solution. Thereby, the induction period, which
precedes crystal growth, is increased. The inhibition effect of anti-scalants is
based on their ability to adsorb onto the surfaces of sub-microscopic crystal
nuclei, which prevents them from growing any further or, at least,
substantially slows down the growth process. Since anti-scalant molecules
with a low molecular weight are more mobile, the extension of the induction
period is more pronounced with molecules of comparatively low molecular
weight.
 Crystal distortion effect: Adsorbed antiscalant molecules act to distort the
otherwise orderly crystal growth process. A different degree of adsorption
and retardation of the growth process on different crystal faces results in

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alteration of the crystal structure. The scale structure can be considerably
distorted and weakened. The distorted crystals are less prone to adhere to
each other and to metal surfaces. When crystallisation has started either
further growth is inhibited or the precipitates form a soft sludge that can be
easily removed rather than hard scales.
 Dispersive effect: Antiscalants with negatively charged groups can adsorb
onto the surfaces of crystals and particles in suspension and impart a like
charge, hence repelling neighbouring particles, thereby preventing
agglomeration and keeping the particles suspended in solution.
 Sequestering effect: Antiscalants may act as chelating agents and suppress
the particle formation by binding free Ca2+
or Mg2+
ions in solution. Anti-
scalants with strong chelating characteristics cannot work at the sub-
stoichiometric level, as the anti-scalant is consumed by the scale-forming
ions. Sequestration is affected by chemicals that require relatively high
concentrations and is not a physical inhibition effect.
Polyphosphates represent the first generation of antiscalant agents with
sodium hexametaphosphate as most commonly used species. A procedural
disadvantage is the risk of calcium phosphate scale formation. Of major concern
to the aquatic environment is their hydrolytic decomposition at 60°C to
orthophosphate which acts as a nutrient and causes eutrophication. The
development of algae mats on the water body receiving the discharge could
be ascribed to the use of phosphates. Because of these reasons they have partly
been substituted by thermally stable phosphonates and polycarbonic acids, the
second generation of antiscalants. Where phosphates have been replaced by these
substances the problem of algae growth could be solved completely.
Main representatives of polycarbonic acids are polyacrylic and polymaleic acids.
Especially polyacrylic acid has to be dosed carefully if precipitation is to be avoided.
The reason for this is that, at lower concentrations, it enhances agglomeration and
therefore also serves as a coagulant in RO plants (see below). Discharge levels of
phosphonates and polycarbonic acids are classified as non-hazardous, as they are
far below concentrations with toxic or chronic effects. They resemble naturally
occurring humic substances when dispersed in the aquatic environment which
is expressed by their tendency to complexation and their half-life of about one
month, both properties similar to humic substances. Though they are generally
assumed to be of little environmental concern, there is a critical point related to
these properties. As they are rather persistent they will continue to complex metal
ions in the water body. Consequently, the influence on the dissolved metal
concentrations and therefore metal mobility naturally exerted by
humic substances is increased by polymer antiscalants. The long-term effect induced
hereby requires further research.

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Experimental data on the bioaccumulation potential of polycarboxylates are not
available. However, polymers with a molecular weight > 700 are not readily taken up
into cells because of the steric hindrance at the cell membrane passage. Therefore a
bioaccumulation is unlikely. Copolymers have a favourable ecotoxicological profile.
Based upon the available short-term and long-term ecotoxocity data of all three
aquatic trophic levels (fish, daphnia, algae) for a variety of polycarboxylates, it is
considered that exposure does not indicate an environmental risk for the
compartments water, sediment and sewage treatment plants.
A MSF plant with a daily capacity of 24,000 m³ releases about 144 kg of antiscalants
per day if a dosage concentration of 2 mg per litre feedwater is assumed. This
represents a release of 6 g per cubic meter of product water.
3.1.6 Antifoaming Agents
Seawater contains dissolved organics that accumulate in the surface layer and are
responsible for foaming. The use of antifoaming agents is necessary in MSF plants,
because a surface film and foam-increase the risk of salt carry-over and
contamination of the distillate. A surface film derogates the thermal desalination
process by increasing the surface viscosity. An elevated
surface viscosity hampers deaeration. Furthermore, if the surface tension is too high,
brine droplets will burst into the vapour phase during flashing. Deaeration is
essential for thermal plants as it reduces corrosion; salt carry-over with brine
droplets must be avoided for a clean distillation.
As the antifoaming agents are organic substances, too, they must carefully be
chosen and dosed. Blends of polyglycol are utilized, either containing polyethylene
glycol or polypropylene glycol. These substances are generally considered as non-
hazardous and low discharge concentrations of 40-50 µg per litre of effluent further
reduce the risk of environmental damage. However, highly polymerized
polyethylene glycol with a high molecular mass is rather resistant to
biodegradation. On this account it has been replaced in some industrial
applications by substances, such as dialkyl ethers, which show a better
biodegradability. Addition of usually less than 0.1 ppm of an antifoaming agent is
usually effective. Concentrations in the discharge were found to be half this level,
which is mainly due to mixing of brine with cooling water.While the brine contains
residual antifoaming agents, the cooling water is not treated and thereby reduces
the overall discharge concentration.
Under the assumption of a product-feedwater-ratio of 1:3 and 0.035-0.15 ppm
dosing 0.1-0.45 g per cubic meter of product water are released.

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3.1.7 Corrosion Inhibitors and Corrosion Products
An important issue for MSF plants is the inhibition of corrosion of the metals
the heat exchangers are made of. The corrosive seawater, high process
temperatures, residual chlorine concentrations and corrosive gases are the reason
for this problem. Corrosion is controlled by the use of corrosion resistant materials,
by deaeration of the feed water, and sometimes by addition of corrosion inhibitors .
Especially during acidic cleaning corrosion control by use of corrosion inhibitors is
essential for copper-based tubing. In a first step oxygen levels are reduced by
physical deaeration. The addition of chemicals like the oxygen scavenger sodium
bisulfite can further reduce the oxygen content. Sodium bisulfite should be
dosed carefully as oxygen depletion harms marine organisms.
Corrosion inhibitors generally interact with the surfaces of the tubes. Ferrous
sulphate, for example, adheres to the surface after having hydrolized and oxidized
and hereby protects the alloy. Benzotriazole and its derivates are special
corrosion inhibitors required during acid cleaning. They possess elements like
selenium, nitrogen, sulphur and oxygen with electron pairs which interact with
metallic surfaces building a stable protective film. However, it is assumed
that in the end the major amount is discharged with the brine. Due to the slow
degradation of benzotriazole, it is persistent and might accumulate in sediments if
the pH is low enough to allow adsorption to suspended material. Acutely toxic
effects are improbable because the expected brine concentrations are well below
the LC50 values of trout and Daphnia magna. Still the
substance is classified as harmful for marine organisms. The release of benzotriazole
per cubic metre product water, corresponding to a continuous dosage of 3-5 ppm to
the feed water, amounts to 9-15 g.
The most important representative of heavy metals dissolved from the tubing
material is copper, because copper-nickel heat exchangers are widely used. In brines
from MSF plants it represents a major contaminant. Assuming a copper level of 15
ppb in the brine and a product-brine-ratio of 1:2, the resulting output from the
reference MSF plant with a capacity of 24,000 m³/d is 720 g copper per day.
Generally, the hazard to the ecosystem emanates from the toxicity of copper at high
levels. Here, levels are low enough not to harm the
marine biota, but accumulation of copper in sediments represents a latent risk as it
can be remobilised when conditions change from aerobic to anaerobic due to a
decreasing oxygen concentrations. To illustrate the latent risk posed by discharge of
untreated brine Figure 6-5 compares reported discharge levels to eco-toxicity values
and the EPA water quality criteria. The eco-toxicity values have been derived from
values which have been determined during tests with
copper sulphate under the assumption that copper sulphate is of less concern for

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saltwater organisms. Diluting discharge water with cooling water does not produce
relief as reported levels are still above water quality criteria and total loads stay the
same.
3.2 Multi-Effect Distillation Desalination (MED)
The flow rate of the cooling water which is discharged at the outlet of the final
condenser depends on the design of the MED distiller and the operating conditions.
In the case of a conversion rate of 11 % (related to the seawater intake flow), 9 m³ of
seawater are required for 1 m³ of fresh water (Figure 6-6). Due to the smaller unit
sizes the seawater intake capacity for a single MED unit would be lower than for a
single MSF unit, but in the majority of cases the required distillate production is
reached by installing several units in parallel. Thus, the seawater
intake capacity for MED plants and MSF plants would be similar. Nevertheless, the
potential damage caused by impingement and entrainment at the seawater intake
must be regarded as high.

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changed physical properties and to the residues of chemical additives or corrosion
products. In MED plants common chemical additives are biocides, antiscalants,
antifoaming agents at some plants, and corrosion inhibitors at some plants. The
conditioning of permeate to gain palatable, stable drinking water requires the
addition of chlorine for disinfection, calcium, e.g. in form of calcium hydroxide, for
remineralization and pH adjustment. Figure 6-7 shows where the chemicals are
added and at which concentrations as well as the characteristics of the brine and its
chemical load.

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3.2.3 Physical Properties of Brine
The physical parameters of the brine are different compared to the intake seawater.
During the distillation process the temperature rises and salt accumulates in the
brine. Taking the reference process (Figure 6-6) with a conversion rate of approx.
11.2 % as example the salinity rises from 45 g/l to 66 g/l (Figure 6-8). Brine and
cooling water temperature rises by about 14 and 10 K, respectively. Salinity of the
brine is reduced by blending with cooling water, but still reaches a value of 5.6 g/l
above ambient level. The resulting decrease of density is very small what can be
attributed to balancing effects of temperature and salinity rise.
3.2.4 Biocides
biofilm within the plant. Therefore both the feed water and the cooling water are
disinfected with the help of biocides. The most common biocide in MED plants is
chlorine. A concentration of up to 2000 µg/l is sustained by a continuous dosage.
Chloride reacts to hypochlorite and, in the case of seawater,
especially to hypobromite. Residual chloride is released to the environment with the
brine where it reaches values of 200-500 µg/l, representing 10-25 % of the dosing
concentration. Assuming a product-effluent-ratio of 1:8 the specific discharge load of
residual chlorine per m³ of product water is 1.6-4.0 g/m³. For a plant with a daily
desalination capacity of 24,000 m³, for instance, this means a release of 38.4-96.0 kg
of residual chlorine per day. The effects of chlorine are described in 3.1.2.

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3.2.5 Antiscalants
A major problem of MED plants is the scale formation on the heat exchanger
surfaces which impairs the heat transfer. The most common scale is formed by
precipitating calcium carbonates due to increased temperatures and brine
concentration. Other scale forming species are magnesium hydroxide, and
calcium sulphate, the latter being very difficult to remove as it forms hard scales.
Therefore sulphate scaling is avoided in the first place by regulating the operation
parameters temperature and concentration in such a way that the saturation point
of calcium sulphate is not reached. Calcium carbonates and magnesium hydroxides,
again, are chemically controlled by adding acids and/or antiscalants.
In the past, acid treatment was commonly employed. With the help of acids the pH
(acidity value) of the feed water is lowered to 2 or 3 and hereby the bicarbonate and
carbonate ions chemically react to carbon dioxide which is released in a
decarbonator. Thus, the CaCO3 scale forming ions are removed from the feed water.
After acid treartment the pH of the feed water is re-adjusted. Commonly used acids
are sulphuric acid and hydrochloric acid, though the first is
preferred because of economic reasons. High concentrations and therefore large
amounts of acids are necessary for the stoichiometric reaction of the acid. Apart
from a high consumption of acids further negative effects of using acids are the
increased corrosion of the construction materials and thus reduced lifetimes of the
distillers as well as handling and storage problems. The negative effects mentioned
above have led to the development of alternatives: Nowadays antiscalants are
replacing acids during operation. But before talking about antiscalants, the use of
acids as cleaning agents needs to be mentioned because that’s when significantly
acidic effluents occur. During this periodic cleaning procedure the pH is lowered to 2-
3 by adding citric or sulfamic acid, for instance, to remove carbonate and metal oxide
scales. In this context Mabrook explained an observed change in density and
diversity of marine organisms by a decreased pH of 5.8 compared to 8.3 in coastal
waters. Ecotoxic pH values range from 2-2.5 for starfish (LC50, HCl, 48 h) to 3-3.3 for
salt water prawn (LC50, H2SO4, 48 h) and show the sensitivity of marine organisms to
low pH values. Little mobile organisms, like starfish, are especially affected by an acid
plume as they cannot avoid this zone. To mitigate these possible effects the cleaning
solution should be neutralized before discharge or at least blended with the brine
during normal operation.
The mode of action of antiscalants is described in 3.1.2. They react substoichio-
metrically which is the reason why they are effective at very low concentrations.
Polyphosphates represent the first generation of antiscalant agents with sodium
hexametaphosphate as most commonly used species. A procedural disadvantage is
the risk of calcium phosphate scale formation. Of major concern to the aquatic

18
environment is their hydrolytic decomposition at 60°C to orthophosphate which acts
as a nutrient and causes eutrophication. The development of algae mats on the
water body receiving the discharge could be ascribed to the use of phosphates.
Because of these reasons they have partly been substituted by thermally stable
phosphonates and polycarbonic acids, the second generation of antiscalants. Where
phosphates have been replaced by these substances the problem of algae growth
could be solved completely. Main representatives of polycarbonic acids are
polyacrylic and polymaleic acids. Especially polyacrylic acid has to be dosed carefully
if precipitation is to be avoided. The reason for this is that, at lower
concentrations, it enhances agglomeration and therefore also serves as a coagulant
in RO plants. Discharge levels of phosphonates and polycarbonic acids are classified
as non-hazardous, as they are far below concentrations with toxic or chronic effects.
They resemble naturally occurring humic substances when dispersed in the aquatic
environment which is expressed by their tendency to complexation and their half-life
of about one month, both properties similar to humic substances. Though they are
generally assumed to be of little environmental concern, there is a
critical point related to these properties. As they are rather persistent they will
continue to complex metal ions in the water body. Consequently, the influence on
the dissolved metal concentrations and therefore metal mobility naturally exerted
by humic substances is increased by polymer antiscalants. The long-term effect
induced hereby requires further research.
A MED plant with a daily capacity of 24,000 m³ releases about 144-288 kg of
antiscalants per day if a dosage concentration of 2-4 mg per litre feedwater is
assumed. This represents a release of 6 g per cubic meter of product water.
3.2.6 Antifoaming Agents
MED plants also use antifoaming agents, but compared to MSF plants, it’s less usual.
The use of antifoaming agents can be necessary if foam forms in the presence of
organic substances concentrated on the water surface which derogates the
thermal desalination process by hampering the falling film flow onto the horizontal
evaporator tubes and thus the wetting of the tubes.
As the agents are organic substances, too, they must carefully be chosen and dosed.
Blends of polyglycol are utilized, either containing polyethylene glycol or
polypropylene glycol. These substances are generally considered as non-hazardous
and low discharge concentrations of 40-50 µg/l per litre brine further reduce the
risk of environmental damage. However, highly polymerized polyethylene glycol
with a high molecular mass is rather resistant to biodegradation. On this
account it has been replaced in some industrial applications by substances, such
as dialkyl ethers, which show a better biodegradability.

19
Under the assumption of a product-feedwater-ratio of 1:3 and 0.035-0.15 ppm
dosing 0.1-0.45 g per cubic meter of product water are released.
3.2.7 Corrosion Inhibitors and Corrosion Products
The corrosion inhibitors that are used in MSF plants are also necessary in MED
plants. However, it is assumed that the copper load is smaller compared to MSF
plants as operation temperatures are lower and piping material with lower copper
contents are used, such as titanium and aluminium-brass.
3.3 Reverse Osmosis (RO)
The conversion rate of RO processes ranges between 20 and 50 % /Goebel 2007/,
signifying an intake volume of less than 5 m³ of seawater per cubic meter of
freshwater. Therefore, compared to the thermal processes the mechanical process
of RO requires significantly less intake water for the same amount of product water.
Consequently the loss of organisms through impingement and
entrainment is lower. The flows, shown in Figure 6-9, result from a conversion rate
of 33 %.
changed physical properties and to the residues of chemical additives or corrosion
products. In RO plants common chemical additives are biocides, eventually acids
if not yet substituted by antiscalants, coagulants, and, in the case of polyamide
membranes, chlorine deactivators. The conditioning of permeate to gain palatable,
stable drinking water requires the addition of chlorine for
disinfection, calcium, e.g. in form of calcium hydroxide, for remineralization and pH
adjustment. Figure 6-10 shows where the chemicals are added and at which
concentrations as well as the characteristics of the brine and its chemical load.

20
Physical Properties of Brine
The salinity of the brine is increased significantly due to high conversion rates of 30
to 45 %. The conversion rate of 32 % of the process presented in Figure 6-9 leads to a
brine salinity of 66.2 g/l (Figure 6-11). As the temperature stays the same during the
whole process, also density increases significantly from 1028 g/l to 1044 g/l. If the
RO process is coupled with electricity generation and the effluent streams are
blended, the warmed cooling water from the power plant reduces the overall
density slightly compared to the ambient value and the overall salinity is almost
reduced to the ambient level.
3.3.3 Biocides
biofilm within the plant.
Therefore the RO feed water is disinfected with the help of biocides. The most
common biocide in RO plants is chlorine. A concentration of up to 1000 µg/l is

21
sustained by a continuous dosage. Chloride reacts to hypochlorite and, in the case of
seawater, especially to hypobromite. In RO desalination plants operating with
polyamide membranes dechlorination is necessary to prevent
membrane oxidation. Therefore the issue of chlorine discharge is restricted to the
smaller portion of plants which use cellulose acetate membranes. Regarding these
plants residual chlorine is released to the environment with the effluents where
it reaches values of 100-250 µg/l, representing 10-25 % of the dosing
concentration. Assuming a product-effluent-ratio of 1:2 the specific discharge load of
residual chlorine per m³ of product water is 0.2-0.5 g/m³. For a plant with a daily
desalination capacity of 24,000 m³, for instance, this means a release of 4.8-12 kg of
residual chlorine per day. Again, the problem of chlorine discharge is restricted to
plants with cellulose acetate membranes. In contrast, the release of chlorination by-
products is an issue at all RO plants regardless of the material of their membranes,
as by-products form up to the point of dechlorination. The effects of chlorine are
described in 3.1.2.
3.3.4 Coagulants
The removal of suspended material, especially colloids, beforehand is essential for a
good membrane performance. For this purpose coagulants and polyelectrolytes
are added for coagulation-flocculation and the resulting flocs are hold back by dual
media sand-anthracite filters. Coagulant substances are ferric chloride, ferrous
sulphate, and ferric chloride sulphate or aluminium chloride. To sustain the
efficiency of the filters, they are backwashed regularly. Common practice is to
discharge the backwash brines to the sea. This may affect marine life as
the brines are colored by the coagulants and carry the flocs (see Figure 6-12). On the
one hand the decreased light penetration might impair photosynthesis. On the
other hand increased sedimentation could bury sessile organisms, especially corals.
The dosage is proportional to the natural water turbidity and can be high as 30 mg/l.
This extreme dosage results in a specific load of 90 g per m³ of product water and a
daily load of a 24,000 m³/d plant of 2200 kg which adds to the natural turbidity.
Polyelectrolytes support the flocculation process by connecting the colloids. Possible
substances are polyphosphates or polyacrylic acids and polyacrylamides respectively,
which are also used as antiscalants. The concentration decides whether they have a
dispersive or coagulative effect. Compared to their use as antiscalants the dosage of
polyelectrolytes is about a tenth of the concentration required for dispersion. These
substances are not toxic; the impact they cause is connected to the increased
turbidity. A dosage of 500 µg/l implies a discharge of 1.5 g per m³ of
product water and a daily load of a 24,000 m³/d plant of 36 kg which adds to the
natural turbidity.

22
3.3.5 Antiscalants
The main scale forming species in RO plants are calcium carbonate, calcium sulphate
and barium sulphate. Acid treatment and antiscalant dosage are used for scale
control. Here, sulphuric acid is most commonly used and dosed with a range of 30-
100 mg/l. During normal operation the alternative use of antiscalants, such as
polyphosphates, phosphonates or polycarbonic acids, has become very common in
RO plants due to the negative effects of inorganic acid treatment explained in 3.1.2.
As it is explained there, these antiscalants react substoichiometrically and therefore
low concentrations of about 2 mg/l are sufficient.
A RO plant with a daily capacity of 24,000 m³ releases about 144 kg of antiscalants
per day if dosage concentration of 2 mg per litre feedwater and product-feedwater-
ratio of 1:3 are assumed. This represents a releaseof 6 g per cubic meter of product
water.
3.3.6 Membrane Cleaning Agents
Apart from acid cleaning, which is carried out with citric acid or hydrochloric acid,
membranes are additionally treated with sodium hydroxide, detergents and
complex-forming species to remove biofilms and silt deposits.
By adding sodium hydroxide the pH is raised to about 12 where the removal of
biofilms and silt deposits is achieved. Alkaline cleaning solutions should be
neutralized before discharge, e.g. by blending with the brine.
Detergents, such as organo-sulfates and -sulfonates, also support the removal of dirt
particles with the help of both their lipophilic and hydrophilic residues. Regarding
their behaviour in the marine environment, organo-sulfates, e.g. sodium
dodecylsulfate (SDS), and organo-sulfates, e.g. sodium dodecylbenzene sulfonate
(Na-DBS), are quickly biodegraded. Apart from the general classification of
detergents as toxic no further information is available on toxicity of NaDBS, but it’s
assumed to be relatively low once the decomposition has started with cutting off the
hydrophilic group. In contrast, LC50 for fish, Daphnia magna and algae are available
in the case of SDS confirming the categorization as toxic substance. But, again, fast
degradation reduces the risk for marine life. This risk could be further reduced by
microbial waste treatment which destroys the surface active properties and
degrades the alkyl-chain.
Complex-forming species, such as EDTA (Ethylendiamine tetraacetic acid) are
employed for the removal of inorganic colloids and biofouling. From comparing the
calculated maximum estimate of discharge concentration (46 mg/l) and an LC50 for
bluegill (159 mg/l, 96 h) it can be deduced that in the case of EDTA direct toxicity is
of minor concern. In contrast, persistent residual EDTA in the marine environment

23
might provoke long-term effects in connection with its chelating and dispersing
properties. Consequences of increased metal solubility and mobility and thereby
reduced bioavailability still need further investigation. Generally, total amounts are
of bigger interest than concentrations.
During the periodic membrane cleaning process also further disinfectants such as
formaldehyde, glutaraldehyde, isothiazole, and sodium perborate, are used. These
substances are toxic to highly toxic and reach toxic concentrations if discharged all at
once. Therefore deactivation should be compulsory. Several deactivation substances
are available: formaldehyde can be deactivated with hydrogen peroxide and calcium
hydroxide or sodium hydroxide and isothiazole is neutralized with sodium bisulfite.
Sodium perborate has to be handled carefully as it breaks down to sodium borate
and hydrogen peroxide. The latter is the actual biocide and therefore may not
be overdosed, also for reasons of membrane protection as it has an oxidizing effect.
3.3.7 Corrosion Products
In RO plants corrosion is a minor problem because stainless steels and non-metal
equipment predominate. There are traces of iron, nickel, chromium and
molybdenum being released to the water body, but they do not reach critical levels.
Nevertheless, an environmentally sound process should not discharge heavy metals
at all; therefore alternatives to commonly used material need to be found.
3.3.8 Dechlorination
The removal of chlorine is performed with sodium bisulfite, which is continuously
added to reach a concentration three to four times higher than the chlorine
concentration, the former amounting to 1500-4000 µg/l. The corresponding amount
per cubic metre of product water is 4.5-12 g/m³. As this substance is a biocide itself
and harms marine life through depletion of oxygen, overdosing should be prevented.
Alternatively sodium metabisulfite is used.

24
4. Receiving coastal environment
4.1 Discharge Mode
The mode of discharge controls the physical properties of the discharge plume, the
most significant of which is the net buoyancy of the plume. There are three principal
discharge modes to be considered: 1) positively buoyant combined discharges that
blend concentrate with thermal or wastewater effluents using existing
infrastructure, 2) negatively buoyant discharge using dedicated brine discharge
infrastructure, and 3) sometimes or weakly-negatively buoyant combined discharge
when brine is the predominant effluent constituent. Each of these discharge modes
will interact differently with the receiving environment, producing different near
field different characteristics and dimensions in both the near and far fields.
Fig.5.1 Factors influencing discharge site scenarios.

25
4.2 Receiving Environment
The physical boundaries, oceanography, and geomorphology of the receiving
environment affect the fate of the plume and also determine the nature of the
biological communities potentially affected by the discharge. Key boundary
conditions that should be considered include coastal type, bathymetry and coastal
structures, sediment properties, and water mass properties (salinity and
temperature). The coastal type includes collision coasts, which are exposed open
coastlines that are accompanied by either sandy or rocky intertidal and subtidal
habitats. The geomorphology of both the sandy and rocky collision coastal types
creates high-energy coastal environments with vigorous ambient mixing and
advection that contributes to rapid dilution that limits dispersion and accelerates
extinction of brine discharge plumes.
Concentrate releases into the open ocean will be influenced by different currents as
a function of the depth (i.e., location) of the discharge. The three primary circulation
regimes that can be expected in the coastal setting are shown in Figure 5-1: 1) surf
zone, 2) inner shelf, and 3) deep waters. These regimes are distinguished by the
different processes that dominate their currents. The surf zone is that shallow water
province at the shoreline in which currents are dominated by the effects of breaking
waves. The inner shelf is that region from the surf zone to the offshore location
where incident waves begin to refract and shoal and where surface and bottom
boundary layers (also known as Ekman layers) first intersect. Finally, the deep water
is the offshore region for which surface and bottom boundary layers exist but the
bulk of the flow is dominated by the geostrophic acceleration balance between
horizontal pressure gradients and the effect of Earth's rotation (i.e., the Coriolis
acceleration). The exact depths that determine the boundaries between the three
offshore regimes vary from place to place and, at one location, in time. The
boundary between the surf zone and the inner shelf is around 10 m and between the
inner shelf and the deep water is around 30 m.

26
Geomorphology also influences the resident biological communities of a particular
coastal environment. Open coasts with sandy environments support soft-bottom
habitat species (particularly benthic macroinvertebrates), while rocky coasts provide
substrate for kelp-based marine communities. Rocky coasts support tide pool
environments, and kelp beds and sea grasses in the offshore environments, both of
which are often protected. Estuarine embayments are generally complex and highly
productive ecosystems, likely to have tidal marshes in the intertidal zone, which is
another sensitive habitat type protected. The subtidal areas of embayments are
generally nurseries for a variety of juvenile fish species and are considered to be
sensitive habitats.
Forcing Functions
Forcing functions affect the strength of ocean mixing, ventilation and available
dilution volume in shallow water, including: waves, currents, ocean water levels
(tides and sea level anomalies), and winds. Movement of material in inner shelf and
surf zone, including the average and low-frequency movements, is controlled by the
waves approaching the beach and the shape of the bottom. Waves striking the
beach at an oblique angle drive mean currents up or down the beach (cross-shore
currents) and parallel to the beach (long-shore currents) as a function of the
incidence angle. When waves approach the beach straight on, local rip currents are
more common, which are associated with complex circulation cells that control the
amount of mixing with waters outside the surf zone. Hence, any assessment or
monitoring of a shoreline (i.e., surf zone) discharge must include local wave statistics
and bathymetry data.
Of the three current regimes, the inner shelf has received the least amount of study.
By definition, it is a transition region between the surf zone and deep waters. In
recent years it has been recognized that the inner shelf is a critical region with
regard to cross-shore exchange of material and better characterization of inner shelf
dynamics has been shown. A good review of the important dynamics in the inner
shelf is given by Lentz and Fewings (2012).
The deep water currents outside the inner shelf are a combination of flow driven by
local winds and geostrophic currents. Accurate modeling of velocity statistics for a
given location can be difficult because, in all cases, flow is highly dependent on the
conditions at the boundary of any local model. (For a review of numerical ocean
circulation models see Miller 2007). Direct measurements in the region may be
adequate to describe the velocity variability if the data records are appropriately
long. Care must be taken, however, to focus model results and observations on the
local bottom currents when assessing the fate of concentrate in a negatively buoyant
plume. In particular, deep water bottom currents will include the effects of the
frictional bottom Ekman (boundary) layer.

27
4.3 Discharge and Site Variability
None of the initial conditions, forcing functions or the boundary conditions of the
far-field are constants over time, and consequently the dilution and dispersion of
concentrate discharge can have considerable variability, which complicates the
determination of "natural" conditions and prediction of discharge dispersion. There
may be short-term or seasonal changes in RO operations resulting in variations in the
concentrate discharge rates, salinities and temperatures. On the other hand, the
temporal variation in boundary conditions and forcing functions of the far field
receiving water can vary over a vast range of time scales that are related to
geophysical, atmospheric, and climatic processes, including: diurnal variations
related to tides, solar heating and coastal winds, monthly variations related to tidal
spring/neap cycles, semi-annual variability related to summer/winter equilibrium
transitions, and longer term variability related to climate (e.g., El Nino/Southern
Oscillation (ENSO)). Variations in salinity, climate, and bathymetry are discussed here
to illustrate some of the most important factors.
Salinity
Ocean salinity variation exerts a modulating effect on the impact of sea salts
discharged from a desalination plant. The RO process produces a concentrated sea
water reject (brine) that is a fixed multiple of the instantaneous source-water salinity
(generally 1.8 to 2 times ambient). However, the ambient ocean salinity has
considerably different degrees of variability. So a water quality objective for salinity
should not be a fixed limit in terms of absolute salinity units. Rather, a water quality
objective should be stated in terms of some relative measure of deviation from
natural background, such as % deviation from background or a minimum initial
dilution producing equivalent results.
Ocean climate
The plume dilution and dispersion processes in the far field are influenced by ocean
temperature, salinity and the wave climate. These features vary as a result of
seasonal weather cycles and can also be severely modified by global ocean climate
events.
4.4 Bathymetry and Gravity Currents
The dynamics of negatively buoyant plumes are fundamentally different that those
of positively buoyant plumes. The fate of positively buoyant plumes is primarily
controlled by background currents, density stratification, and wave or wind-induced
mixing. They will either reach the water surface or be trapped by ambient
stratification. Negatively buoyant plumes, on the other hand, will generate density
(i.e., gravity) currents along the seabed by virtue of their density anomaly compared

28
with the ambient bottom waters. The magnitude of these density currents will
depend on the magnitude of the density anomaly and the bottom slope.
There may be environmental concerns with respect to density currents, however.
The presence of rocky outcrops and reefs offshore from the discharge site may block
the offshore dispersion of brine by gravity. Therefore, discharge sites with
bathymetric barriers (offshore rocky reefs and outcrops) should be avoided with
negatively buoyant discharges. Depending on the mixing rates with ambient waters
outside of the density layer, the dissolved oxygen (DO) supply to the density layer
may not meet the net oxygen demand of the benthic fauna within the layer. In this
case, DO will decrease over time and, if the layer persists long enough, hypoxia or
anoxia within the bottom layer can produce lethal effects in the far field well away
from the discharge. This is unlikely to occur with a well-designed discharge, however.
Many factors control the development of hypoxia or anoxia, including the
stratification between the ambient waters and the density layer, the thickness of the
layer, the water depth, the slope of the bottom, the strength of the wind, the
vertical velocity shear across the layer, and the height of the surface waves. The
general situation and many of these factors are addressed in the excellent study by
Hodges et al. (2011).
Other far field bathymetric features to be avoided for the siting of a negatively
buoyant brine discharge are bathymetric depressions (hollows). These are not
generally features found along the exposed open coast of California, but can be
common in embayments, either from natural shoaling effects or from man-induced
activities such as the dredging of navigation channels and berthing areas. When such
features are located in embayments with low mixing, a bathymetric depression can
fill with brine and displace the lighter ambient seawater from the depression. This
situation can result in stratification and stagnation of the bottom layer, leading to
hypoxia and increased exposure of the benthos to the plume contaminants. Sites
with topographic depressions should be avoided as locations for negatively buoyant
discharges.

29
5. Brine disposal; A look at the possible options
5.1 Inland plants
The major strategies for brine disposal at inland sites are limited to three general
categories;
1) Deep Well Injection
2) Evaporation Ponds and
3) Solar Ponds.
Several other systems for utilization of waste brine have been proposed, which
include, among others, irrigation of salt tolerant plants (halophytic crops) and brine
shrimp harvesting. Such approaches have been limited and are certainly not
applicable to very large volumes of wastewater. Recovery of inorganic salts with
potential commercial value has also been suggested, but construction of chemical
separation facilities would indeed result in a costly venture. It is important to
recognize the prime mission of any desalination facility, which is to upgrade water
quality - not to market by-products. To date, proposed by-product recovery systems
have not demonstrated economical viability and it seems likely that the cost of by-
product recovery would far exceed the cost of the principal product – water.
A system known as zero discharge has also been used in certain situations where
waste brine streams are relatively small and available land is limited. This technology
has generally been applied to wastewater disposal from power plants, oil refineries
and certain mining operations. The final stage of such a system involves thermal
evaporation, subsequently providing a solid residue. Energy requirements are large
and overall economics unfavorable for handling large brine volumes.
5.1.1 Deepwell injection
Deep well injection is presently applied worldwide for disposal of industrial,
municipal and liquid hazardous wastes . In recent years this technology has been
given serious consideration as an option for brine disposal from land based
desalination plants. Deep well injection has been applied successfully for brine
disposal from several membrane plants in Florida. Injection wells may vary in depth
from a few hundred feet to several thousand feet depending on geological
considerations at the selected site. Several factors contribute to the overall
performance and reliability of an injection well. In general, however, this method of
brine disposal is considered the most cost effective as compared with other systems
in practice for land based desalination plants.

30
The nature of subterranean strata
must be carefully considered in
selecting a suitable well location.
Most stratifications consist of
sand (porous medium) and shale
(confining layers). Mathematical
models, are used to determine
the permeability and solution
confinement capability of strata
with different ratios of sand to
shale. They are primarily
applicable to hazardous waste
disposal, can also be used as a
model for deep well injection of
any concentrate where
inadequate waste solution
transport and confinement
could result in contamination of
surface and groundwater
resources.
A measure of the effects of
plugging and damage to
subterranean formations on
injection well performance was
expressed by injectivity (I),
defined as the ratio of injection rate (q) to the difference between well flowing
pressure (Pwf) and the average formation pressure (Pr) given by the following
equation.
I = q / (Pwf - Pr) (1)
Injectivity is impacted by several factors, which include the chemical and physical
quality of the injected fluid, injection rate and pressure, as well as the nature and
physical properties of subterranean strata. One of the most important constraints on
stable injectivity is the presence of suspended solids in the injection fluid. Frequent
measurements of total suspended solids (TSS) are required to insure steady well
performance. High TSS in process fluids, low injection rate, low injection pressure,
and low porosity and permeability of the well strata all contribute to rapid well
plugging and diminished injectivity.

31
Deep well injection is a reasonable method for brine disposal provided that long-
term operation can be maintained, in order to dispose of large volumes of process
fluid. Drawbacks of this technology are:
1) selection of a suitable well site;
2) costs involved in conditioning the waste brine
3) possibility of corrosion and subsequent leakage in the well casing;
4) seismic activity which could cause damage to the well and subsequently result in
ground water contamination; and
5) uncertainty of the well half-life which can only be estimated using mathematical
simulation techniques.
5.1.2 Evaporation ponds
Evaporation pond technology is practiced primarily in the Middle East and to a lesser
extent in arid regions of Australia. At this time, it is probably the most widespread
method of brine disposal from inland-based desalination facilities. This disposal
system is especially effective in regions with low rainfall, and where climatic
conditions are favorable for steady, and relatively rapid evaporation rates. In
addition, desalination plants are often sited at locations where the cost of adjacent
level land is relatively low.
The pond open surface area (A) and minimum pond depth (d) can be estimated from
A = (V x f1) / Eave (2)
d = Eave x f2 (3)
where V is volume of reject water, Eave is evaporation rate, f1 is an empirical safety
factor to allow for lower than average evaporation rate and f2 is an empirical factor

32
that accounts for the length of the winter season. The designer of evaporation ponds
must carefully consider the surface area, depth and freeboard of such installations,
since these factors are determined by rates of concentrate discharge relative to
surface evaporation rates. It is noted that freeboard is especially difficult to estimate
since it depends on average rainfall and wind velocity in the pond area. It is clear
from the above relationship that the area needed is directly proportional to volume
of reject water and inversely proportional to the evaporation rate. Although other
empirical factors and relations have been suggested for calculating the impact of
brine salinity on surface evaporation rates, in the judgment of the authors of this
report, evaporation pond design optimization could be best developed
experimentally by circulating typical model brine solutions through small
evaporation ponds.
The principal environmental concern associated with evaporation pond disposal is
pond leakage, which may result in subsequent aquifer contamination. All current
installations are lined with polyethylene or various other polymeric sheets. Liner
installation must be carried out with care since sealing of joints is critical in order to
prevent leakage. Double lining is strongly recommended with leakage sensing probes
installed between layers of pond lining.
A system for enhancement of evaporation pond performance has recently been
developed at Ben Gurion University in Israel. This new technology described as the
WAIVER process involves periodic circulation of pond brine over “wetable surfaces,”
designed to increase the effective evaporative surface area. This results in enhanced
evaporation, which, of course, also depends on wind speed and direction in addition
to relative humidity. It has been estimated in this study that evaporation rates can
be increased by 50% in a typical Middle East dry climate. If proven effective in
practice, evaporation pond size could be significantly reduced.
Existing literature indicates that application of evaporation ponds is a relatively
simple and straightforward method of brine disposal. This technology, however, is
limited to relatively small desalination plants (less than 5MGD) and generally

33
restricted to arid climatic conditions. Capital costs arise primarily from acquisition of
land.
5.1.3 Solar ponds
Development of salt
gradient solar ponds as a
renewable energy source
began in Israel more than
thirty years ago. Although
limited in scope,
successful power
generation by this
technology has been
demonstrated primarily in
arid and semi-arid parts of
the world. Recent
technical papers have also appeared, describing experimental studies in Italy and
Switzerland, in which solar ponds are coupled with thermal desalination systems. In
these experimental studies, the pond is used as a heat source for small multistage
flash evaporator units. Ongoing solar pond studies at the University of Texas involve
power generation and thermal desalination coupled with brine disposal for recharge
of the bottom (hot) layer of the pond.
Perhaps one of the most innovative system for utilization of solar ponds is an
experimental study, conducted by the California Department of Water Resources at
Los Banos, CA. in the early 1980’s, which developed an integrated system for
membrane desalination coupled with brine disposal. A salt gradient solar pond
provided hot water cycled through a dual media heat exchanger, driving a turbine
for electric power generation. The power was then utilized for electrically driven
pumps to provide necessary pressure for reverse osmosis desalination of agricultural
drainage water. The resulting RO concentrate was then injected into the hot bottom
layer of the solar pond. The overall objective of this system was to provide for brine
disposal, heat recovery, and salinity augmentation of the solar pond. Unfortunately,
the Los Banos desalting operation was shut down in 1986 as a result of an EPA order
for termination of agricultural drainage, which provided feed water for this
experimental facility.

34
5.1.4 Zero Liquid Discharge (ZLD)/ Degremont
The ZLD System removes dissolved solids from the wastewater and returns distilled
water to the process (source). Reverse osmosis (membrane filtration) may be used
to concentrate a portion of the waste stream and return the clean permeate to the
process. In this case, a much smaller volume (the reject) will require evaporation,
thus enhancing performance and reducing power consumption. In many cases,
falling film evaporation is used to further concentrate the brine prior to
crystallization.
Falling film evaporation is an energy
efficient method of evaporation,
typically to concentrate the water up to
the initial crystallization point. The
resultant brine then enters a forced-
circulation crystallizer where the water
concentrates beyond the solubility of the
contaminants and crystals are formed.
The crystal-laden brine is dewatered in a
filter press or centrifuge and the filtrate
or centrate (also called “mother liquor”)
is returned to the crystallizer. The
collected condensate from the
membranes, falling film evaporator and
forced-circulation crystallizer is returned to the process eliminating the discharge of
liquids. If any organics are present, condensate polishing may be required for final
cleanup prior to reuse.

35
Pretreatment: In the majority of cases, it is more costeffective to remove
contaminants prior to evaporation/ crystallization. This pretreatment step often
includes limesoda softening which requires clarifiers to remove calcium and
magnesium compounds.
Membrane Filtration: Where possible, membrane filtration such as reverse osmosis
can be used to treat the wastewater. The permeate (clean water) is reused in the
process and the reject/concentrate is sent on to evaporation.
Evaporation: When a significant amount of water needs to be evaporated prior to
the crystallization step, pre-concentration in a falling film evaporator is the most
efficient solution. These evaporators require less heat/power per unit of water
evaporated.
Crystallization: The crystallizer is the heart of the ZLD process. Typically, forced-
circulation crystallizers are used, which evaporate the water past the crystallization
point. Crystals are mechanically dewatered and the resulting filtrate/ centrate is
returned to the crystallizer. The crystallizer usually requires corrosion resistant
materials due to the extremely high salt concentrations present. In some cases, part
of the crystallization can be achieved by spray driers to overcome high solubility of
certain salts. The clean condensate is returned to the process for reuse and the
dewatered crystals are transported off-site for reuse or disposal. This crystallization
process is extremely sensitive to the wastewater chemistry as the ions present will
determine the boiling point elevation which has a major impact on the power
consumption, impacting both capital and operating costs.
Solids Recovery: Sludge generated by the pretreatment phase, is generally
mechanically dewatered in a plate-and-frame filter press. A solids concentration of
20-50% dry solids can usually be achieved and the filtrate is simply recycled back to
the beginning of the pretreatment system. The crystals from crystallization phase
can also be mechanically dewatered, but corrosion resistant materials are usually
necessary due to the high salt concentrations present. The crystals can be dewatered
in a filter press (belt or recessed chamber) or centrifuge and as a result, much higher
solids concentrations can be achieved. The filtrate (or centrate) is then returned to
the crystallizer.
System Enhancements
Multiple Effects: Evaporation processes such as falling film evaporators can be
installed in series such that the water vapour from one is reused in the next. In this
way, the efficiency of the evaporation process can be increased and almost doubled,
tripled, etc. based on the number of evaporator effects installed. This increases the

36
capital cost of the system, but it is more economical for larger flow operations based
on the energy saved.
Waste Heat Usage: Economics are enhanced when waste heat found in most
industrial applications can be productively reused in the ZLD design. This can take
the form of dryer exhaust gas or low pressure return steam. The evaporator designs
can make use of these ‘waste’ heat sources, significantly saving on energy
requirements.
Integration Effects: The chemistry of ZLD systems is very complex. The waste
streams from the different zones are very interdependent. Having a single point of
contact for the entire system is therefore crucial.
Mechanical Vapor Recompression: For some applications, turbofans or high speed
compressors can be more economical by reducing the steam usage with electricity.
Water vapor produced in the evaporator or crystallizer can be compressed and
reused as the heating source. Depending on the boiling point elevation of the
wastewater, single- or multi-stage vapor compression systems can be used. MVR
systems are typically implemented where high evaporation rates are necessary.
A ZLD system is potentially more cost-effective when the nearest discharge location
(surface water or sewer) is far from the conventional treatment plant, since the ZLD
system eliminates the need for long conveyance lines.
The disadvantage of such a system is the potentially higher capital costs for
treatment equipment and more complex operations. A brine ZLD system uses heat
to force the majority of the water to evaporate quickly, leaving behind thick slurry
that can be sent to a small evaporation pond for final solar drying or mechanical
dewatering. Figure 1 shows examples of the brine condition before and after the
processes.

37
There are three general types of equipment for a brine ZLD system:
• Brine concentrator – Also known as a brine evaporator. The concentrator reduces
the original brine volume by 95 to 98%, and effluent is a two-phase solution – a high
TDS liquid and crystalline salt particles.
• Brine crystallizer – This further heats the concentrated solution from a
concentrator to reduce the liquid to slurry that consists of highly saline free liquids
and solid crystalline salt particles.
• Spray dryer – Alternative to the crystallizer that uses heat and forced air. ZLD
systems for brine applications are complex and energy intensive mechanical systems
with lifecycle costs on the same order as the desalination process itself. Such
systems have been used for decades in the pulp, petrochemical and power
industries. Given the costs, ZLD systems have rarely been used in municipal
applications in the United States.
However, ZLD systems will be used more frequently as salinity control and water
recovery become more pressing issues. Given the cost of this equipment, alternative
processes and brine minimization treatment equipment have been developed as
ways to reduce the costs of evaporating the brine. A major research and
development effort has been initiated by the water industry to develop new
methods to reduce the brine stream so that the ZLD systems can be smaller and less
expensive to install and operate.
5.2 Coastal options; Disposal strategies and near field effects
For a direct discharge of brine, the use of a diffuser is preferred. For flows typical of
major desalination plants, a multiport diffuser will probably be required that results
in high dilutions and rapid reductions of salinity in the near field. The diffuser should
be designed so that the jets do not impact the water surface and the effects of jet
merging should be carefully modeled (see later discussion of modeling techniques).
For co-discharges with power plant cooling water, existing shoreline surface
discharges, multiport diffusers, or single-port risers can probably be used. In most
cases, however, near field dilution alone may not suffice to meet water quality
standards and in-pipe dilution will also be needed. If the discharge is negatively
buoyant, the dilution from horizontal nozzles must be carefully evaluated to ensure
adequate initial dilution. Small amounts of concentrate can probably be discharged
through existing municipal wastewater outfall diffusers. However, the dilution must
be re-evaluated to account for the change in effluent density and flow rates, and
carefully evaluated if negatively buoyant.

38
5.2.1 Coastal hydrodynamic concept
It is important to understand the distinctions between near field, mixing zones, and
other related terms that are often associated with wastewater discharges. The near
field is a hydrodynamic, or physical, concept. It is the region where mixing of the
effluent is influenced and affected by discharge parameters. The physical processes
are primarily entrainment caused by shear between the buoyant jet (either
positively or negatively buoyant), an internal hydraulic jump where the plume
impacts a boundary (e.g., sea floor) or water surface and transitions to horizontal
flow, and entrainment in the horizontally spreading layer. The near field ends where
the self-induced turbulence collapses under the influence of the induced density
stratification. The layer then spreads as a density current of some finite thickness.
Ultimately, ambient diffusion due to oceanic turbulence is responsible for most
mixing and dilution; this region is known as the far field. The rate of mixing and
dilution in the far field is much slower than in the near field. A mixing zone is a
regulatory concept that will generally encompass most, or all, of the near field.
The near field characteristics of negatively buoyant discharges are primarily
determined by the orientation of the discharge port or nozzle to the horizontal, the
jet exit velocity, and the density difference between the effluent and receiving
water. Flowing currents will generally increase the dilution in the near field. For
larger discharges a multiport diffuser consisting of many nozzles will be needed. In
that case, an additional parameter is the port spacing and orientation of the diffuser
axis to the prevailing currents.
5.2.2 Disposal Alternatives
Examples of common concentrate discharge scenarios are shown in Figure 6-1.
Concentrates can be disposed of in several ways. They can be discharged as a surface
stream at the shoreline, co-mixed (and pre-diluted) with other effluent such as
municipal wastewater or power plant cooling water, or directly into the ocean as a
“pure” brine stream. For shoreline surface discharges (Figures 6-1a and b), the near
field results primarily from entrainment into the surface layer (for a positively
buoyant flow), or the bottom density current (for a negatively buoyant flow). This
entrainment is dependent on the source velocity, as entrainment due to the
spreading density currents is quite slow. Also, the density stratification reduces
vertical mixing in the far field. Because of these effects, near field dilution is quite
small, of order 5 times or less.

40
Shoreline discharge of raw (negatively buoyant) concentrate (Figure 6-1a) will result
in a density current that runs down the bottom slope. Because the resulting density
stratification inhibits vertical mixing, dilution is relatively small and benthic
organisms could be exposed to relatively high salinities. Shoreline disposal of pure
concentrate by this means in California is discouraged.
Co-discharge is another disposal strategy that involves diluting the concentrate to
below potentially toxic levels prior to discharge into the receiving water body. This
strategy involves blending brine with an existing effluent stream to achieve what is
referred to as in-the-pipe dilution or in-plant dilution. Co-discharge is permitted by
California water quality regulations and is currently used by several facilities.
Shoreline discharges are practical if co-discharged with a much larger flow for pre-
dilution, such as power plant cooling water. In this case, the effluent is likely to be
positively buoyant because of the elevated temperature of the cooling water (Figure
6-1b).
There are two common means for achieving in-plant dilution: 1) co-locating the
desalination plant with a wastewater plant, in which the dilution water is generally
of very low salinity; or 2) colocating the desalination plant with a power plant where
the dilution water is cooling water taken from the receiving water body, typically the
ocean. Dilution with wastewater produces a discharge salinity lower than ambient
seawater, even at relatively low wastewater discharge rates because the treated
effluent is fresh water. This is a means of reducing or eliminating hypersalinity
impacts on marine life from brine discharge.
Concentrates that are blended with other effluents are typically discharged though
existing ocean outfalls and diffusers (Figure 6-1c). Discharge through an existing
outfall and diffuser will generally be at “low” pressure, i.e. the jet exit velocity is
relatively low and the jet momentum flux will be quite small. If the effluent is
positively buoyant as a result of the elevated effluent temperature, the jets will
ascend towards the surface. If the ambient stratification is strong enough the plumes
will be trapped below the water surface, if not the plumes will reach the water
surface. The near field is primarily the rising plume region and has dispersion
characteristics similar to other buoyant plumes currently addressed in the Ocean
Plan. Because multiport diffusers for positively buoyant effluents are predominantly
horizontal, they may not be suitable for a negatively buoyant discharge and will have
to be carefully evaluated. A possible solution is to open more ports on the diffuser
and fit the portswith variable-area check valves which give higher velocity at low
flow rates. Again, the dilution must be carefully modeled and evaluated.
For co-discharge though a single large vertical riser (such as used for some power
plants) the exit dimensions may be very large, such as a square opening 25 ft on side,
which is comparable to the local water depth. In that case, the initial dilution can be

41
quite small and mixing in the spreading layer should be incorporated into the near
field. These types of discharges should include in-pipe dilution of the brine with
larger flows of seawater in order to achieve adequate dilution of the brine within the
mixing zone.
The use of seawater to achieve in-plant dilution requires a much larger volume,
relative to municipal wastewater effluent, to achieve a comparable level of reduction
in the salinity of the brine discharge. The intake of seawater used for in-plant
dilution (e.g., as power plant cooling water) causes additional mortality to marine
organisms through velocity shear and turbulence in the confined flows through
pumps and impellors of the (older design) once-through sea water circulation
systems. However, recent work on hydroelectric turbines by Cada (2001) and Cada et
al. (2006) has shown pump-induced turbulence mortality can be reduced by
employing low speed impellors after the Kaplan turbine and Archimedes screw
pump that reduce the shear stresses on entrained organisms to levels they can
tolerate. Low-stress water wheel technologies are also being considered as
alternatives to seawater circulation pumps of legacy power plants to reduce impacts
on marine life. The practicality of these technologies for the applications considered
here remains to be demonstrated, however.
The final case is direct discharge of negatively buoyant brine concentrate by means
of high velocity jets inclined upwards. This could be either a single jet for a small
discharge or a multiport diffuser for larger discharges. Multiport diffusers are used
for the Perth and Sydney (Australia) desalination plants. The high jet velocities result
in entrainment of ambient seawater into the jets and rapid dilution and reduction of
salinity. The processes are illustrated in Figure 6-2. Dilutions exceeding 30:1 can be
readily accomplished by such a diffuser.
A multiport diffuser with multiport “rosette” risers is shown in Figure 6-3. In this
example, the rosettes each consist of four nozzles. Other diffusers may have the
nozzles distributed uniformly along one or both sides of the diffuser.

42
In turbulent environments, physical damage can occur to delicate eggs and larvae.
The effect of turbulence on larval mortality was studied in the field by Jessopp
(2007), who found that even turbulent tidal flows produce significantly increased
mortality to thin-shelled veligers of gastropods and bivalves. While there is presently
no known published evidence of mortality to marine species for diffuser jets, the
cause and effect relations demonstrated by prior studies certainly raises that
possibility. Threshold shear stress tolerances of marine organisms to diffuser
discharges could be established by combining data from laboratory tests,
computational fluid dynamics modeling, and field studies of diffuser systems.
6. Summary & Conclusions
Available technologies for brine disposal

43
Future technologies,
In summary:
• There are no ‘residuals-free’ treatment processes. While some residuals streams
are more difficult and costly to dispose of than others, the disposal of residuals
should be considered from the beginning of the project.
• The contaminants requiring treatment may not be those most difficult to dispose.
Residual disposal should consider the full spectrum of contaminants in the source
water, not just those being treated.
• If surface water or sewer discharge is not feasible, the cost and complexity of
residual disposal can equal that of treatment for high pressure membrane systems.
This economic reality must be addressed in the funding for the project.

44
• Because of the high cost and complexity of brine disposal, the selection of the
disposal method may dictate the selection of the treatment process.
• Brine management is a dynamic field that’s rapidly changing as vendors try to fill
the void.

An Introduction to Brine Waste

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An Introduction to Brine Waste