Final Design Document 1

Table of Contents
List of Figures……………………………………………………………………………iii
List of Tables……………………………………………………………………………..iv

1. Problem Formulation .............................................................................................................. 1
1.1 Introduction ........................................................................................................................... 1
1.2 Objective ............................................................................................................................... 1
2. Problem Analysis and Literature Review ............................................................................... 1
2.1 Introduction ........................................................................................................................... 1
2.2 Problem Analysis .................................................................................................................. 1
2.2.1 The Input ........................................................................................................................ 2
2.2.2 The Output ..................................................................................................................... 2
2.2.3 Solution Variables .......................................................................................................... 2
2.2.4 Criteria ........................................................................................................................... 3
2.2.5 Usage.............................................................................................................................. 4
2.2.6 Production Volume ........................................................................................................ 4
2.3 Introduction to Literature Review ......................................................................................... 4
2.3.1 Flush toilets, dry toilets, and Composting Toilets. ........................................................ 4
2.3.2 Known Conditions of Project Location ......................................................................... 4
2.3.3 Client Stipulations.......................................................................................................... 5
2.3.4 Composting Conditions ................................................................................................. 5
2.3.4.1 Temperature ............................................................................................................ 5
2.3.4.2 Moisture .................................................................................................................. 5
2.3.4.3 Aeration................................................................................................................... 6
2.3.5 Additives ........................................................................................................................ 6
2.3.6 Quality of Compost End Product ................................................................................... 6
2.3.6.1 Importance of Air Flow .......................................................................................... 6
2.3.6.2 Benefits of Urine Inclusion ..................................................................................... 7
2.3.6.3 Other Important Factors .......................................................................................... 7
2.3.7 Pathogen Concerns in Fecal Compost ........................................................................... 7
2.3.7.1 Thermophilic Composting ...................................................................................... 7
2.3.7.2 Specific Temperature Requirements ....................................................................... 7
2.3.8 Odor ............................................................................................................................... 8

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2.3.8.1 Smell diagnostics .................................................................................................... 8
2.3.8.2 Vent Airflow ........................................................................................................... 8
2.3.8.3 Venting .................................................................................................................... 9
2.3.9 Toilet designs ................................................................................................................. 9
2.3.9.1 Composting Privy ................................................................................................... 9
2.3.9.2 Compost Toilet with Axial Rotation ..................................................................... 10
2.3.9.3 Drum Privy............................................................................................................ 10
2.3.9.4 Sunfrost Batch Composting System ..................................................................... 11
2.3.10 Local Laws and Codes ............................................................................................... 11
3. Alternative Design Solutions ................................................................................................ 12
3.1 Introduction ......................................................................................................................... 12
3.2 Brainstorming ..................................................................................................................... 12
3.3 Alternate Designs ................................................................................................................ 12
3.3.1 Sunfrost ........................................................................................................................ 12
3.3.1.1 High Chair ............................................................................................................. 13
3.3.1.2 Cork Screw Mixer ................................................................................................. 13
3.3.1.3 Rolling Dolly ........................................................................................................ 14
3.3.1.4 Crank Mixer .......................................................................................................... 15
3.3.2 Biolet ............................................................................................................................ 16
3.3.3 Axial Rotation .............................................................................................................. 17
3.3.4. Composting Privy ....................................................................................................... 18
3.3.5 Anaerobic Digester ...................................................................................................... 19
4. Decision Phase .......................................................................................................................... 20
4.1 Introduction ......................................................................................................................... 20
4.2 Criteria Definitions ............................................................................................................. 20
4.3 Solutions ............................................................................................................................. 21
4.4 Decision Process ................................................................................................................. 22
4.5 Final Decision Justification................................................................................................. 23
5. Specification of Solution.......................................................................................................... 23
5.1 Introduction ......................................................................................................................... 23
5.2 Solution Description ........................................................................................................... 23
5.2.1 The Waste Containers .................................................................................................. 23
5.2.2 Barrel Lids ................................................................................................................... 25
5.2.3 Ventilation.................................................................................................................... 26

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5.2.4 Step Box ....................................................................................................................... 27
5.3 Cost Analysis ...................................................................................................................... 27
5.3.1 Design Costs ................................................................................................................ 27
5.3.2 Construction Cost......................................................................................................... 28
5.3.3 Maintenance Cost......................................................................................................... 28
5.4 Implementation Instructions ............................................................................................... 29
5.4.1 Overview ...................................................................................................................... 29
5.4.2 Barrel setup .................................................................................................................. 29
5.4.3 Stage One ..................................................................................................................... 30
5.4.4 Stage Two .................................................................................................................... 30
5.4.5 Stage Three .................................................................................................................. 30
5.4.6 Emptying and Cleaning................................................................................................ 30
5.5 Prototype Performance........................................................................................................ 30
6. Appendices ................................................................................................................................ 31
Appendix A – Brainstorming Notes ......................................................................................... 31
Appendix B - References .......................................................................................................... 37

List of Figures
Figure 1: Black Box Model............................................................................................................. 1
Figure 2: Diagram of the Sunfrost Design .................................................................................... 14
Figure 3: Diagram of the Rolling Dolly Design ........................................................................... 15
Figure 4: Diagram of the Crank Mixer Design ............................................................................. 16
Figure 5: Diagram of the Biolet Design ........................................................................................ 17
Figure 6: Diagram of the Axial Rotation Design .......................................................................... 18
Figure 7: Diagram of the Composting Privy Design .................................................................... 19
Figure 8: Diagram of the Anaerobic Digester Design .................................................................. 20
Figure 9: Inside view of Barrel ..................................................................................................... 24
Figure 10: Outside view of Barrel ................................................................................................ 24
Figure 11: Stage One Lid .............................................................................................................. 25
Figure 12: Stage Two and Three Lid ............................................................................................ 26
Figure 13: System Layout ............................................................................................................. 26
Figure 14: Project Hours Pie Chart ............................................................................................... 27

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List of Tables

Table 1: Composting Privy Pros and Cons ................................................................................... 10
Table 2: Compost Toilet with Axial Rotation Pros and Cons ...................................................... 10
Table 3: Drum Privy Pros and Cons ............................................................................................. 11
Table 4: Sunfrost Batch Composting System Pros and Cons ....................................................... 11
Table 5: Delphi Method Chart ...................................................................................................... 22
Table 6: Materials Cost ................................................................................................................. 28
Table 7: Maintenance Cost ........................................................................................................... 29
Table 8: Usage Costs .................................................................................................................... 29

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1. Problem Formulation
1.1 Introduction
The first phase of the design project is to create a Black Box model this is shown in Figure 1.
The Chocolate Factory, along with the help and cooperation of the CCAT will be able to create a
composting toilet that will be used by the people residing in the CCAT house.

INPUT: OUTPUT:
No useable system to A useable system to
demonstrate and educate BLACK BOX demonstrate and educate
public of a composting public of a composting
toilet at the CCAT house. toilet at the CCAT house.

Figure 1: Black Box Model

The Black Box model above is the first step in determining what how our design project is going
to contribute to the CCAT house.

1.2 Objective
Our objective is to design and implement a useable composting toilet that will be added to the
infrastructure of the CCAT house, which will demonstrate and educate the public about a
composting toilet system.

2. Problem Analysis and Literature Review
2.1 Introduction
The design problem is to design and install a working composting toilet for the CCAT house to
use and educate visitors about composting toilets. The problem analysis states the input variables
and their constraints, the output variables and their constraints, the solution variables and their
restrictions, and the criteria and their constraints used to judge designs. The Literature Review
will show the information relevant to building a composting toilet.

2.2 Problem Analysis

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2.2.1 The Input

CCAT is currently using freshwater to discard fecal matter wasting water and nutrients.

Input Variables:
 CCAT resident knowledge of composting.
 CCAT visitors knowledge
 Users for the toilet
 Range of ambient temperature
 Materials

Constraints:
 CCAT residents have enough knowledge to properly use the toilet
 No knowledge of composting toilets or experience with composting toilets
 Less than or equal to three users
 Between 50-70°F
 High fecal contents

2.2.2 The Output

A useable composting toilet system, at the CCAT house, which helps demonstrate and educate
public about composting toilets.

Output Variables:

 CCAT resident knowledge about composting toilet
 CCAT visitors’ knowledge
 Compost quality
 Material

Constraints:
 CCAT residents have enough knowledge to properly use the toilet
 Knowledge and/or experience is gained
 No longer hazardous waste
 Low fecal content

2.2.3 Solution Variables

Solution Variables:
 Compost per cycle
 Size

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 Ventilation
 Composting process
 Human interaction
 Type of thermal measurement

Restrictions:
 Moveable by two people
 Must fit in 6’ by 10’ storage room
 Must vent to outdoors through exterior ceiling vent
 Process must be aerobic to efficiently change into compost
 No direct exposure to unprocessed compost
 Must be able to measure mass temperature

2.2.4 Criteria

The criteria are ranked in order of importance and will be used to rank the potential designs. The
constraints are the minimal requirement for specific criteria.

Criteria:
1. Composting effectiveness
2. Safety
3. Odor
4. Cost
5. Difficulty of management
6. Grossness of management
7. Minimize space used
8. Positive presentation
9. Ease of construction
10. Resource appropriateness

Constraints:

1. Must produce compost
2. Must kill harmful pathogens
3. No unacceptable odors released into living areas
4. Less than 325 dollars
5. Work must be reasonably accomplished by two people
6. No direct exposure to waste required
7. Must fit and function in the given area
8. Unconstrained
9. Must be built within our abilities
10. Client’s mission

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2.2.5 Usage

The system will be used daily by the three residence of the CCAT house.

2.2.6 Production Volume

One final solution of a composting toilet will be made.

2.3 Introduction to Literature Review
The purpose of the Literature Review is to provide the group with background knowledge which
will be sufficient in the process of determining and completing the design project. The topics
within the literature review range from various types of composting toilets to what is required for
appropriate composting conditions.

2.3.1 Flush toilets, dry toilets, and Composting Toilets.

Flush toilets, using water as a carrying medium, take human waste and carry it to a central
location for processing. This practice leads to water pollution and wastes nutrients that are
excreted, mainly nitrogen (Stoner 1977). A dry toilet is a toilet that will accept human waste and
store it, without the addition of water. One example of a dry toilet is pit toilet, such as an
outhouse. A composting toilet is another form of a dry toilet; however, with a composting toilet
the human waste is turned into compost, which can then be used as a soil amendment for plants.
The purpose of a composting toilet is to reduce or eliminate water contamination and to reuse
human waste as a soil amendment (Stoner 1977).

2.3.2 Known Conditions of Project Location

The composting toilet that will be designed is to be used in a two-story home in Arcata,
California, on the campus of Humboldt State University. Humboldt County is a moderate climate
with heavy precipitation and high relative humidity. There is to be three people using the
composting system (Haskett 2009). According to Professor Minnis of Pace University a study
has shown that the average human excrement output is 120 grams per day of feces and 1.1 liters
of urine per day (Minnis). Therefore an estimate of 360 grams of solid waste per day will enter
the system. If urine is disposed of through the system to be designed it will require the inclusion
of an estimated 3.3 liters per day. A toilet is already in place in the upper story of the home with
an uncompleted chute leading down to a storage room in the basement. This same room will be
available for the use of the composting system (Haskett 2009). A space of five feet by six feet
with nine vertical feet is available (Haskett 2009). Access to this room is through a hallway. The
room touches one exterior wall. It is likely that a location outside the building could be made
available for fully or mostly processed compost (Haskett 2009).

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2.3.3 Client Stipulations

The users of this composting toilet system need a design that will be effective in function,
production, and demonstration of an appropriate technology. Minimal human interaction
required to operate the system on a day to day basis is ideal. Energy consumption should be low
or non-existent. The work required to move the system and remove the compost should be safe,
simple, and not require difficult work (Haskett 2009).

2.3.4 Composting Conditions

The conditions inside the composting toilet will determine to a large extent the overall
effectiveness of the system. The conditions will determine: how long it will take to complete the
process, how safe the final product will be, and the smell produced by the system. The
conditions of a compost pile are all interconnected and one condition will affect the others
(Jenkins 2005). There are many different types of microorganisms that live in the compost that
are responsible for the decomposition process (Jenkins 2005). Making sure these organisms
have enough oxygen for the process to remain aerobic is significant. Decomposing releases heat
which is important for making the process continue quickly and also necessary to kill harmful
pathogens (Stoner 1977). The ratio of carbon to nitrogen (C:N) should remain high, around 30:1,
to help the pile heat up and keep odors from nitrogen compounds minimal (Leary 2007).

2.3.4.1 Temperature

The organisms in a compost pile thrive in various different temperatures, which make some more
potent than others. Mesophiles live at medium temperatures between 68- 113ºF (20-45ºC).
Thermophiles thrive above 113ºF (45ºC). psychrophiles grows best at temperatures around 59ºF
(15ºC) (Jenkins 2005). Compost temperatures must rise significantly above the temperature of
the human body (37ºC or 98.6ºF) in order to begin eliminating disease-causing organisms
(Jenkins 2005).

2.3.4.2 Moisture

Moisture is necessary for the decomposition process and a dry pile of compost will take longer to
break down (Jenkins 2005). Too much water in the compost pile will displace oxygen and
prohibit aerobic conditions (Stoner 1977). The loss of aerobic conditions due to too much water
would lead to an unproductive mass that could not be used as compost. The moisture content of
compost should be around 65% (Jenkins 2005). Organic wastes with good moisture contents
should feel damp, but not soggy (Stoner 1977). The average human excretes 1.0 liter per day of
urine at 95% water and 200 grams of feces per day at 72% water (Stoner 1977). Evaporation
will remove some of the extra water, but a carbon based bulking agent is necessary to absorb
moisture (Van der Ryn 1978).

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2.3.4.3 Aeration

Oxygen and proper aeration is critical for aerobic conditions. Not enough oxygen will cause
anaerobic conditions, which causes slower decomposition, foul odors, and may cause the
compost to not produce enough heat to kill all harmful pathogens (Jenkins 2005). Aeration
should provide adequate oxygen and oxygen distribution throughout the compost. Aerating the
system will involve vents for fresh air, airflow around pile, adding a bulking agent to create air
pockets, insuring proper moisture levels, and mixing or turning the pile (Van der Ryn 1978).
Some composting toilet designs have vents that are underneath, or buried, to increase airflow to
the bottom of the pile. If the compost is kept in a hard to access container, such as a 55-gallon
drum, mixing the pile can be difficult. Some solutions to this problem involve spinning or
rotating the drum, using a stirring mechanism, or removing the contents of the drum for final
composting (Stoner 1977).

2.3.5 Additives

Bulking materials are an essential part of a composting toilet’s process, to insure decomposition
is done correctly and safely. For the best compost we must add a sufficient amount of carbon-
based bulking material (Jenkins 2005). This will allow the compost to have proper moisture
levels and be able to decompose correctly. Possible bulking materials include: sawdust, peat
moss, straw, or weeds. Another possible factor to the compost additives is urine, if both feces
and urine are in the system that will require more organic material to help break down the extra
nitrogen entering the system. Before using the composting chamber, it should be partially filled
with bulking material and completed compost in order to create an absorbing system and start the
composting process. Not only can bulking materials are added to the compost, food scraps, egg
shells, paper and cardboard, lawn clippings and other small garden trimmings, clothes from
natural fibers and disposable cotton diapers and tampons (without the plastic tags) could also be
added if desired (Composting Toilet World 2009). Chemicals and other non-organic items
should not be added to the toilet (Van der Ryn 1978).

2.3.6 Quality of Compost End Product

Compost from human excrement is of great value for use in agriculture. Composted human
waste, especially if urine is included, can have a nutrient content equal to that of chemical
fertilizers (Oikos 2009). A very high percentage of valuable minerals taken in with food
consumption will be available in the final product for use by the plants on which it is
distributed. Nitrogen is recycled less efficiently during this process than other minerals, but still
a significant percentage is made available for reuse by plant life (Sunfrost 2004).

2.3.6.1 Importance of Air Flow

To promote nitrogen retention it is important to allow for sufficient oxygen exposure to the mass
because with little oxygen much of the nitrogen will be converted to ammonia (NH3) and lost
(Anonymous 1993, 2009). Sustaining aerobic composition, done by allowing significant airflow,
also promotes the survival of beneficial microorganisms (Anonymous 1993, 2009).

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2.3.6.2 Benefits of Urine Inclusion

There is very significant mineral and nutrient presence in human urine. In the overall waste
output of humans urine contains the majority of Phosphorus, Potassium and Nitrogen. Between
fifty and ninety percent of these nutrients expelled by humans is held in the urine (Maurer 2003).
These particular elements are very important in a fertilizing product; making inclusion of urine in
the composting process is a significant benefit (Sunfrost 2004).

2.3.6.3 Other Important Factors

Among many different criteria for compost quality is the concern about of sharp or large non-
organic materials. Also considered essential is a proper C:N ratio in the finished product. A
good method for promoting balance is to mix plant matter, high in carbon, with a manure-based
compost, which is often high in nitrogen (California Integrated Waste Management Board).

2.3.7 Pathogen Concerns in Fecal Compost

There are dangerous amounts of bacteria and other potentially dangerous microorganisms in
fecal matter, especially that of humans. Human excrement can contain numerous bacteria,
viruses, and parasites (Kaiser 2006). Before the composting process there are serious concerns
about the health risks of handling, storing or spreading human excrement. Through the processes
that occur during composting these potentially harmful pathogens can be eliminated with
sufficient effectiveness to make the use of the resulting compost safe (Jenkins 1994). Human
pathogens are not adapted to prolonged life outside the human body. A very effective method
for eliminating pathogens in human excrement is sustaining a temperature high enough to
promote thermophilic bacterial activity (Jenkins 1994). The required temperature for effective
thermophilic activity is above 1130 F (Oikos 2009).

2.3.7.1 Thermophilic Composting

The key process that which destroys pathogens is thermophilic composting, which is the heating
up of the material due to the natural composition process. When certain temperatures are
reached and sustained nearly all harmful pathogens will be eliminated. According to Dr. T.
Gibson, Head of the Department of Agricultural Biology at the Edinburgh and East of Scotland
College of Agriculture, evidence shows that a few hours at 120 degrees Fahrenheit would
eliminate [pathogenic microorganisms] completely. There should be a wide margin of safety if
that temperature were maintained for 24 hours (Jenkins, 2005). Compost piles will heat up and
Jenkins states in his Humanure Handbook that a properly prepared mass of compost will reach
the necessary thermophilic temperature on its own (Jenkins, 2005).

2.3.7.2 Specific Temperature Requirements

A report connected with Penn State University, shows the results of a laboratory test on compost
regarding the elimination of specific pathogens with human health concerns. When L.
Monocytogenes, Salmonella, and E. coli were introduced to compost the results showed that
these were virtually eliminated with particular temperatures over respective time periods. With

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1200 F for 36 hours, 1300 F for 8 hours, or 1400 F for one hour, all three organisms were
deactivated (Weil, Beelman, and LaBorde).

2.3.8 Odor

Odor and smell of human waste is a concern to people using a composting toilet. The smell
comes from the gases released by decaying organic matter (Van der Ryn 1978). The main
odorous gases are: organic sulfides, hydrogen sulfides, ammonia and other nitrogen compounds
(Leary 2007). The most common source of foul odors from decomposing fecal matter is organic
sulfides, which can be detected at low concentrations (Leary 2007). Organic sulfides are
produced with or without oxygen; however they will decompose further to other less odorous
compounds under aerobic conditions. Under anaerobic conditions the concentration of organic
sulfides can be ten or more times higher than under aerobic condition (Leary 2007). Most of the
nitrogen that is released from the decomposing fecal matter is released in the form of ammonia
gas. Ammonia gas occurs under both aerobic and anaerobic conditions but is produced in greater
concentration when the C:N ratio is 20:1 or lower. Raising the pH will also increase the amount
of ammonia gas produced. The smell of ammonia can be detected at low concentrations;
however it is not as foul as the organic sulfides and will also dissipate quickly (Leary
2007). Other nitrogen compounds that are released are amines and indoles. These nitrogen
compounds have a putrid or decaying flesh smell. Amines and indoles are produced under both
aerobic and anaerobic conditions but under aerobic conditions they will continue to decay. They
are also produced in greater quantity when the C:N ratio is 25:1 and lower (Leary 2007).

2.3.8.1 Smell diagnostics

Smell can give insight into how well the composting process is functioning. The most efficient
way to deal with odor is to make sure the process remains aerobic (Obleng and Wright 1987). If
the compost pile is too moist, or does not have adequate aeration, the process will become
anaerobic and there will be a strong foul odor. Adding a bulking agent will absorb moisture and
allow for more air pockets in the pile. Mixing or turning the pile also increases oxygen levels
(Van der Ryn 1978). If the C:N ratio is lower than 20:1, there will be a stronger smell from
ammonia and the other nitrogen compounds. Adding more of a carbon based bulking agent or
limiting the amount of urine going into the system will raise the C:N ratio and lower the smell of
ammonia and other nitrogen compounds (Stoner 1977).

2.3.8.2 Vent Airflow

A vent needs air flowing over the opening in order to create a pulling effect that will suck air out
of the vent. If the vent goes up through the roof, the vent opening should be located in a place
that gets adequate airflow. Chimneys, other vents, and tall trees can affect air flowing over vent
opening (Stoner 1977). Bends in the pipe and sudden changes in the pipe diameter can also
cause reduced airflow through the system (Pescot and Price 1982). There should be an air intake
vent in the system to supply the compost with fresh air for oxygen. This vent should supply the
bottom of the pile with oxygen. Air being sucked out of the top vent should then suck air in
through the lower vent. Not enough airflow through the system can cause odors to back up and

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leak into the bathroom. To increase airflow an electric fan can be installed in the roof vent,
sucking air out of the composting chamber (Stoner 1977). Some vent tops can maximize the
venture effect by their shape and increase air flow by up to 40% of a straight pipe opening
(Pescot and Price 1982). The venting system needs to be designed so that the chamber is at a
lower pressure than outside, which will insure air is sucked into the chamber rather than leaking
out (Stoner 1977).

2.3.8.3 Venting

The system will need to be vented for two reasons, gases will be given off during the
decomposing process, including water evaporation, and oxygen will need to be present for the
process to work efficiently. The system should be sealed so that the only ways into the
composting compartment is from the toilet or through vents. The toilet seat lid should be lined
with a sealer, like rubber, and be kept shut. The vents should have mesh screens small enough to
keep out small flies. All vents should also be hooded so that water cannot get in and minimize
sunlight to avoid flies (Van der Ryn 1978). For odor control purposes, the vents should be
placed away from people, for example above the roof. Venting away from people will allow the
odorous compounds given off by the composting process to dissipate and reduce odor (Leary
2007). Gases rise, so a vent should be placed high in the composting compartment, even higher
than the toilet seat if possible, to avoid gases escaping through the toilet seat (Stoner 1977).

2.3.9 Toilet designs

Several different designs of composting toilets exist; the following sections contain information
on Composting Privy, Compost Toilet with Axial Rotation, Drum Privy, and Sunfrost Batch
Composting System.

2.3.9.1 Composting Privy

One design, the Farallones Composting Privy by Sim Van der Ryn in The Toilet Papers. This
toilet, or privy, consists of a lower chamber, built out of bricks 3'4” tall on a 4'x'8' concrete
slab. The front wall is not built out of brick to allow access. This lower chamber is divided into
two compartments, with the idea that one compartment is being used as the toilet, while the other
compartment has been filled and is composting. The top of the chamber has a 2”x4” wood frame
on which a 1/2” sheet of plywood can be attached, which will serve as the toilet room floor. This
plywood sheet should have a hole cut in the floor over each sub section (or you could cut one
hole, and just rotate the plywood sheet half a turn when one section is filled). The privy also
needs a 10” diameter vent to allow gases and water evaporation to escape. The brick sub frame
should be lined with a strip of wood (2”x6”) or weather stripping so that the system can be
sealed. Each chamber should have a 6” high lip (brick or concrete) to avoid water from seeping
out. Each chamber should have both an outside wood panel door and a chicken wire baffle,
placed on top of the 6” lip so that the compost does rest upon the wood panel door. The wood
panel door should have a venting strip cut in the bottom. All vents should have a wire or mesh
screen to keep bugs and animals out and should also have a hood over the vent to keep rain out
and sunlight out, to discourage flies. Toilet seat cover should seal and be kept closed. If climate
is too cold to allow piles to heat up, add an insulator, plywood for example (Van der Ryan 1978).

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Table 1: Composting Privy Pros and Cons

Pros Cons
Simple Requires a structure external to house. (Can be
connected to house, but must have clear access
to front)
Easy to use, maintain, and easy access to Depending on how long composting process
compost. takes, may require additional storage areas
Sufficient size for family of four

2.3.9.2 Compost Toilet with Axial Rotation

The Compost Toilet with Axial Rotation combines the composting unit and toilet into one
structure. The top of the unit has a typical toilet seat feeding directly into the composting
area. Inside the unit is a horizontal drum with an axial shaft inside. This shaft connects to a
simple gear and crank to allow for easy rotation of the mass inside. This rotation promotes
aeration and moisture uniformity. The drum is not solid, allowing for air intake and for excess
water to leave the mass. A separate chamber will collect excessive moisture and allow efficient
evaporation. Another separate chamber inside the compact unit is used for final processing of
the compost. By rotating the drum in the direction opposite that used for aeration about one third
of the drums capacity is released into an isolated area. No longer in contact with fresh excrement
this material will compost to the point that it can be safely handled and removed (Tinseth 2002).

Table 2: Compost Toilet with Axial Rotation Pros and Cons

Pros Cons
Compact design easily fits into available space Low capacity
Low amount of operation work required Compost handled in lavatory area
Drum rotation good technique for proper Final Compost near fresh waste
conditions

2.3.9.3 Drum Privy

The drum privy is a toilet design that uses a 55-gallon drum to collect the excrement and store it
to allow for composting. The drum is set on a scissor jack on a rolling cart underneath the floor
of the toilet room. The drum is then jacked up so that it is sealed against the floor of the toilet
room. The toilet should be a plastic lined tube that tapers out going from the seat to the floor and
protrudes through the floor about an inch. The final diameter must be smaller than the drum
diameter so that it will fit inside the drum. There should be a 4-6” pipe venting from the toilet
through the roof. Vent should be painted black to increase airflow and have a mesh screen and
hood on top. In colder climates the pipe should be insulated to avoid condensation from dripping
down the pipe. The drum should have a 2” diameter hole 2” from the bottom. A polyvinyl
(PVC) venting pipe shaped, as a “U”, should be placed through this hole. The pipe should
extend up the side of the drum to the top both inside and out. The half of the vent pipe that is
inside the drum should be perforated all the way down to the bottom and capped at the top. The

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half outside the drum should have a mesh screen to keep bugs out of the system. For
composting, paint drums black to increase heat absorbed from sun. Drums should be rolled each
week to stir compost and increase aeration. Contents of drums can also be dumped out to
compost outside. (Van der Ryn 1978)

Table 3: Drum Privy Pros and Cons

Pros Cons
Simple and cheap Adequate aeration can be a problem
Drum makes for easy transport and storage Requires ability to move full 55-gallon drums
Aeration Weekly work is required for rolling the drums

2.3.9.4 Sunfrost Batch Composting System

The Sunfrost Batch Composting System is the type that was previously used in the CCAT
house. The Sunfrost composter incorporates a 55-gallon drum as the main container. The
system is insulated, sealed and connected to a toilet through a simple vertical chute. The drum
was designed to be filled to a desired capacity and then removed from the toilet so that the
composting process can take place without more excrement being added. It is necessary to have
at least two barrels for the system to continuously function. The system has a grate above the
bottom of the barrel so that liquid that leaches to the bottom will escape. A simple hand pump is
then used to recycle the liquid to the top of the mass. Before pumping the liquid, a proportionate
amount of dry additive can be placed on the top of the pile to attain a proper moisture level. To
promote aeration a mesh screen lines the hole barrel inside to create air passage around the entire
mass. The system also includes a simple hand mixer to stir the pile. An air intake funnels the
fresh air to the bottom while the exhaust pulls air from the top, promoting aeration and
effectively reducing odor. A low power DC or AC fan is used to ensure proper airflow (Sunfrost
2005).

Table 4: Sunfrost Batch Composting System Pros and Cons

Pros Cons
Many components already in possession, low Regular human interaction required
cost
Size and Capacity both suited to location Necessity of at least two systems
Low energy use

2.3.10 Local Laws and Codes

At this point there are no laws or building codes regarding composting toilets in either the city of
Arcata or the state of California. According to Dean Renfer, Building Official for Arcata, there
has never been a permit issued for a composting toilet or officially approved by the Building
Department in Arcata. Mr. Renfer also said that composting toilet systems are not part of the
California plumbing code (Renfer, 2009).

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3. Alternative Design Solutions

3.1 Introduction
After analyzing the problems at hand and researching for a literature review on the problem our
team has gained knowledge on the subject and various ways others have created a solution for
composting human waste. Using that acquired knowledge and ideas gathered using group
brainstorm sessions we have arrived at a number of alternative solutions, which have the
potential to solve our problem.

3.2 Brainstorming
Our group conducted a number of brainstorming sessions in order to produce ideas that could
lead to entirely new solution methods or to improve upon solutions already known to the group.
The first brainstorm we did was an open structure in which we sought ideas applying to the
entire project. There were many and diverse suggestions that did lead to solution alternatives for
our problem. Other brainstorming sessions were held with just a single specific solution variable
per session. In narrowing the scope of the problem we were able to arrive at many more ideas
that had not come up in the previous, less focused brainstorms. These idea sessions played a key
role in producing the alternative solutions that are shown here. The actual written record of the
brainstorms is shown in Appendix A.

3.3 Alternate Designs
Below is a list of the alternate designs we came up with for our composting toilet system.

 Sunfrost
 Sunfrost Design with Toilet Chute
 Rolling Dolly
 Crank Mixer
 Biolet
 Axial Rotation
 Composting Privy
 Anaerobic Digester

3.3.1 Sunfrost

The Sunfrost Design is the composting toilet developed by Larry Schlussler, and was previously
used in the CCAT house, except with a chute adaptation to place the toilet seat in the upper
bathroom. This design is the basis for the Sunfrost design with Toilet Chute, Rolling Dolly, and
Crank Mixer.

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3.3.1.1 High Chair

With the high chair model you would basically have a barrel that would hold the fecal matter and
the user would climb up onto the barrel and sit down on the lid or toilet seat just like any other
ordinary toilet and go to the bathroom on top the barrel which would then hold all of the bulking
material and fecal matter beneath the actual toilet. Or in other words a toilet seat directly over a
barrel.

3.3.1.2 Cork Screw Mixer

The three-barrel system with corkscrew stirring is closely based on a system previously
employed at the CCAT House. The toilet is located in the second floor restroom directly above
the space that contains the barrel containment systems. One barrel at a time is connected to the
toilet by a waste chute roughly ten inches in diameter. The chute passes through a hole in the lid
of that barrel fitting tightly and sealed to be airtight. Each barrel is lined inside its vertical walls
with a rigid metal screen that keeps the waste mass from touching the sides of the barrels and
leaves a gap to allow airflow around the whole mass. Six inches above the base of the barrel is a
circular grate and screen that keeps the solid waste above the floor of the barrel. This grate
allows excess moisture to flow down out of the solid waste, preventing the mass from having a
higher than desired moisture content. The space below the grate also allows for airflow. A
simple manual crank pump has a down pipe reaching to the bottom of the barrel allowing the
excess fluid to be pumped back onto the solid mass; usually after some dry carbon based matter
such as saw dust has been added, allowing easy control of the moisture percentage in the mass.
A narrow pipe enters the lid of the barrel and extends to the level of the bottom grate. Through
this pipe fresh air flows into the container near the bottom so that it must pass through or around
the waste mass to reach the exit vent which is out of the lid of the barrel. In each barrels exit
vent is a low wattage fan to ensure airflow in the correct direction. Also in the lid of each barrel
is a small hole, which allows for the passage of a thin steel rod with a corkscrew shape on the
end that is used to mix up the waste mass to promote aeration throughout the mass. Each
container will have one of these corkscrews so there is no need to pull the soiled rod into the
open.

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Figure 2: Diagram of the Sunfrost Design

3.3.1.3 Rolling Dolly

The Rolling Dolly mixer design is a marriage between the Sunfrost and axial rotating design.
The system works exactly like the Sunfrost design, but no stirring rod to aerate the composting
pile will be used. The toilet seat in the bathroom fits over a chute that leads down into the
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storage room. The chute is a straight plastic tube that stops 1 foot right above the 55 gallon
barrel and attach to the lid with a chute extension that can be slid up and down to attach to the
barrel lid. The lid is sealable and should stay on the barrel at all times of the composting
process. The vent coming from the lid is detachable. Both the ventilation hole and chute
opening can be closed so that no material can fall out while mixing. To mix and aerate the
system, the rolling dolly will tilt the barrel at an angle of 30° to the floor and then the barrel can
be manually spun. The lid will have to be detached from the vent and chute. The dolly has a
large plate on the bottom and a track system with wheels on the side to allow the barrel to be
spun once it is reclined. The dolly has a stand so that it is secured once it is reclined. The barrels
are placed on a cart with wheels so that they can be easily moved and also rotate freely on the
dolly. There will be three barrels; one receiving raw material and two being stored for
composting. Each barrel is lined with a wire mesh on the inside to create a gap between the
barrel wall and the material and allow air flow all around the pile. The air inlet will be a pipe
that goes to the bottom of the barrel to increase airflow all around the pile. This air inlet pipe
also doubles for the pump attachment to suck water from the bottom of the barrel. Each barrel
needs to be mixed by using the dolly each week. The barrels go through a step every 3 months.
The barrels first collect raw waste for 3 months then stored for 6 months in the storage room to
allow for composting.

Figure 3: Diagram of the Rolling Dolly Design

3.3.1.4 Crank Mixer

The three-barrel system with corkscrew stirring is closely based on a system previously
employed at the CCAT House. The toilet is located in the second floor restroom directly above
the space where the barrel containment systems are located. One barrel at a time is connected to
the toilet by a waste chute roughly ten inches in diameter. The chute passes through a hole in the

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lid of that barrel fitting tightly and sealed to be air tight. Each barrel is lined inside its vertical
walls with a rigid metal screen that keeps the waste mass from touching the sides of the barrels
and leaves a gap to allow airflow around the whole mass. Six inches above the base of the barrel
is a circular grate and screen that keeps the solid waste above the floor of the barrel. This grate
allows excess moisture to flow down out of the solid waste, preventing the mass from having a
higher than desired moisture content. The space below the grate also allows for airflow. A
simple manual crank pump has a down pipe reaching to the bottom of the barrel allowing the
excess fluid to be pumped back onto the solid mass; usually after some dry carbon based matter
such as saw dust has been added. This allows for user control of the moisture percentage in the
mass. A narrow pipe enters the lid of the barrel and extends to the level of the bottom grate.
Through this pipe fresh air flows into the container near the bottom so that it must pass through
or around the waste mass to reach the exit vent which is out of the lid of the barrel. In each
barrels exit vent is a low wattage fan to ensure airflow in the correct direction. Sixteen inches
above the grate is a shaft mounted the wall of the barrel and passing through the center to the
other side where it passes through the barrel wall to connect to a hand crank. Mounted to the
shaft is a circular steel member that will spin along the axis of the shaft, reaching down into the
waste mass and stirring it up. This mechanism breaks up the mass and promotes aeration. In the
lid of each barrel is a four inch square whole covered and sealed by a piece of fiberglass. These
windows allow the user to see the level of waste and the progress of composting without needing
to open the lids or expose the waste at all.

Figure 4: Diagram of the Crank Mixer Design

3.3.2 Biolet

In figure 3.2 is the design of a closed composting toilet system. Figure 3.2 is fairly advanced
with a motor for stirring the compost and also a fan and heater installed to help aerate the
compost to create the best humus. This is one of the standard Biolet systems the majority of these

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systems will have a heater and a fan; some may have the electronic mixer where others may need
to be manually mixed.

Figure 5: Diagram of the Biolet Design

3.3.3 Axial Rotation

This design has an outer shell that is solid and non porous. Inside the outer shell is a drum that
on the top, bottom and the circular walls is made of a metal screen material that allows the flow
of fluids and air in and out of the solid waste mass contained inside. On the side of the barrel is a
door that opens to allow the incoming waste into the barrel. This door is designed to close when
the barrel is to be rotated so that the mass does not spill out of the barrel into the outer container.
Below the screen barrel is a space in the outer container to which any excess fluids in the waste
mass flows. An air intake brings fresh air into the container and an exit vent containing an
electric fan sustains airflow in the proper direction. The excess moisture in the bottom of the
container evaporates preventing the solid waste mass from containing too much moisture for
aerobic composting.

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Figure 6: Diagram of the Axial Rotation Design

3.3.4. Composting Privy

In figure 3.6 is the layout of a composting privy. A basic composting toilet in which you have a
hole on top of a box or compartment in which the feces fall into the compartment along with the
bulking material. It is in this compartment where the composing occurs with the breaking down
of the feces into organic material. The compost will need to be attended to from an outside back
door where you will be able to aerate and remove the compost when necessary.

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Figure 7: Diagram of the Composting Privy Design

3.3.5 Anaerobic Digester

This system uses a 55-gallon drum as the storage tank and digester. The drum is placed outside
for safety and odor purposes. Inside the bathroom there is a wood box with a toilet seat on top.
Inside the box there is a five gallon bucket to collect the human waste. This bucket is then taken
outside and dumped into the digester. The lid of the digester is completely sealed but has a hatch
that can be opened to allow adding more waste material (feces, toilet paper, and urine) into the
digester. The lid of the digester is dome shaped, with a gas valve at the top. The biogas that is
produced from the anaerobic process inside the digester is lighter than air and collects at the top

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of the dome. The gas valve is connected to a hose or pipe that passes the gas through a medium
bucket. The gas is bubbled through water and collected at the top where another pipe connects to
a storage container. The storage container is a deflated large inner tube. After the barrel has
been sitting without any raw material added for 6 months the decomposing process will be done
and there will no longer be an odor. The sludge can then be dumped out into a separate compost
pile and composted to insure pathogen destruction. There are three separate barrel systems in
use. Each barrel is coated with an erosion resistant paint, inside and out. No mixing is
necessary for raw material and there should be enough water in the barrel to make the material
into sludge.

Figure 8: Diagram of the Anaerobic Digester Design

4. Decision Phase
4.1 Introduction
In the decision phase the alternative solutions are judged based on the criteria to find the best
solution for the project. We used the Delphi method in order to quantify our opinions for each
alternative solution, and narrowed our solutions down to two designs. These two designs were
then discussed with the residents of CCAT to come to our final solution.

4.2 Criteria Definitions
In order that we as a team and any observers understand what each criterion means and how it
should be weighted toward our decision we have defined them in this section. These criteria are
the same as we determined in Section II to be applicable to our project solutions.

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Composting Effectiveness: How well the system turns raw organic waste into an effective and
usable composting soil.

Safety: How much the system exposes users and staff to raw material that is potentially harmful.
The maintenance of the system should not require hazardous work.

Odor: How much the system releases odorous gases into the living or work space at CCAT.
This incorporates how well the system is vented and sealed and how well the composting process
is maintained.

Cost: The cost includes all initial costs to build and set up the system and maintain the system.

Difficulty of Management: Minimal effort to maintain and empty the system and also considers
how frequently the work will need to be done. Work includes aerating the compost pile and
removing finished compost from the system.

Grossness of Management: The up keep of the system should not be unpleasant. Minimal to
no exposure to waste matter is required to keep the system in proper working order.

Positive Presentation: How well the system shows a composting toilet as an appropriate
technology. The system should have the appearance of being easy to use to encourage the use of
a composting toilet at other locations.

Ease of Construction: How many hours of construction the system will require and that
construction can be accomplished with the skills available to Team Universe.

Resource Appropriateness: The resources used for the system match with the CCAT mission
of using local and reused or recycled materials.

4.3 Solutions
These are the solutions that we will be judging. For a more details on each design refer back to
Section 3.

 Sunfrost
 Sunfrost design with toilet chute
 Rolling dolly
 Crank mixer
 Biolet
 Axial rotation
 Composting privy
 Anarobic digester

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4.4 Decision Process
The process we used to arrive at our solution was the Delphi method. We first determined a
weight value for each of the criteria as a group. The values ranged from zero to ten with zero
being no concern to ten being of critical concern to the final solution. Next we assigned a value
for how well each design fulfilled the individual criteria. Zero meaning the design did not
address the criteria and fifty meaning the design had outstanding design features for that
criterion. When we disagreed we would debate the pros and cons and come to an agreement
about the scores. Then each score was multiplied by the criteria weight, and all weighted scores
were added up for each design. From these totals we could see how each design ranked in
comparison to the other designs. Refer to Table 5 to see the weight for each criteria and the
ranking of each design.

Table 5: Delphi Method Chart

Criteria Weight Sunfrost Sunfrost Crank Rolling Axial Anerobic
Schute no Schute Dolley Rotation Digestion
Composting
Effectiveness 10 45 450 45 450 43 430 35 350 45 450 10 100
Safety
10 40 400 42 420 45 450 30 300 45 450 20 200
Odor
10 38 380 40 400 42 420 35 350 42 420 25 250
Cost
8 40 320 45 360 32 256 30 240 15 120 10 80
Difficulty of
management 7 32 224 35 245 40 280 28 196 38 266 30 210
Grossness of
management 7 32 224 35 245 40 280 32 224 40 280 30 210
Positive
presentation 7 40 280 35 245 40 280 35 245 40 280 40 280
Ease of
Construction 6 35 210 42 252 30 180 30 180 10 60 10 60
Resource
appropriateness 6 40 240 42 252 38 228 35 210 30 180 30 180
Total: 2728 2869 2804 2295 2506 1570

The Delphi method chart in Table 5 shows the weight of each criterion and the scores for the
designs in regards to these criteria.

From the Delphi method, we narrowed out solutions down to two designs; the Sun Frost design
and the Sun Frost with Toilet Chute design. We discussed the pros and cons for each of these
two designs with the CCAT residents. The CCAT residents voiced opinion that they would
prefer the Sun Frost design based on concerns for the cleaning of the toilet chute in the other
design.

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4.5 Final Decision Justification
Our decision for the final solution is the Sun Frost design. We came to this decision from
narrowing down our solutions using the Delphi method and discussing the remaining solutions
with the CCAT residents. The Sun Frost design was in fact the solution alternative with the
highest score using the Delphi method. There are positives to the Sun Frost with Toilet Chute
Design that were appealing and made it a strong option. However, there were also significant
concerns for the toilet Chute design that were highly weighted both by our team and the clients.
Amongst our team members and CCAT we came to a consensus that the Sun Frost design was
the best suited for our situation.

5. Specification of Solution

5.1 Introduction
Section 5 of the design document has a description of all the aspects of the final solution, which
was selected in Section 4. A detailed description of the Sunfrost Composting toilet that Team
Universe will construct including: ventilation, barrel, and step box layouts. Along with a list of
costs, this will include: the implemental costs, maintenance costs, and construction time. Section
5 will conclude with implemental instructions to help the user of the system with proper
practices to use the composting toilet.

5.2 Solution Description

The Solution Description will cover 4 sub-sections including: the waste containers, barrel lids,
ventilation, and the step box. Which all have brief descriptions and along with some user
instructions as a part of our solution in the following sections.

5.2.1 The Waste Containers

The human excrement composting system to be placed in the CCAT house will utilize three 55-
gallon steel barrels as the waste containers. Each barrel will be filled with a drum liner, made of
thick, durable plastic sheeting, formed specifically to fit inside the barrels used. The plastic liner
forms neatly to the inner walls of the barrel and covers the bottom, as seen in Figure 9. By
keeping the waste away from the steel walls, the liners eliminate concern of corrosion and
promote easy cleaning after the removal of finished compost. Around the outside of each barrel
is an insulation jacket, as can be seen in Figure10. This insulation keeps heat generated by
microorganisms in the compost mass inside the barrel. Each of the three barrels is fixed to a
round wooden base, which has five evenly spaced steel castors to allow for easy moving over
smooth surfaces. Located at the bottom of each barrel is steel grate upon which is a fine steel
mesh is attached. The grate and mesh together prevent solid waste from reaching the bottom of
the barrel and create a cavity, in which excess fluid in the mass can escape, and which allows for
airflow towards the bottom of the mass. The grate is held 2.5 inches above the floor of the barrel
by four pieces of three-inch PVC pipe. In each barrel there is a two-inch PVC pipe, shown in

23

Figures 9 and 10, which extends one inch above the lid, down through the steel grate to a point
just one inch above the floor of the barrel. Each pipe is held in place by the hole in the grate and
the hole in the lid that it fits through. The function of this pipe is to allow the down pipe of the
hand crank pump to reach the fluid at the bottom of the barrel without contacting the solid waste.
Also in each barrel is a steel hand mixer with corkscrew tip, shown in Figure 9, used to stir the
compost mass.

Figure 9: Inside view of Barrel

Figure 10: Outside view of Barrel

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5.2.2 Barrel Lids

In each stage the barrel has a specific barrel lid. Upon each barrel container is a laminated
wooden lid that performs multiple functions. The lids are covered on each face by laminate for
ease of cleaning and to keep the wood from absorbing moisture. The edge of each lid is heavily
painted for the same purposes. Just one lid has a hole and toilet seat for use on the barrel
currently receiving waste. This lid, shown in Figure 11, will remain located in the bathroom
upon the barrel in use. The toilet seat is placed in a location selected for comfort and ease of use.
A hole in the lid under the seat is cut larger than the inner size of the seat to minimize the risk of
soiling the lid during use. Connected to the same hole is a one-half inch diameter strip, shown in
Figure 11, cut five inches long away from the whole to allow the stir rod to be kept in the barrel
and allow it to be used in the large entrance hole. In the other two lids there is also a large hole,
Figure 12, which allows for the use of the stir rod. Each of these holes is covered by a fitted
piece of Plexiglas to minimize any odor escaping. There is also a notch in each of these
Plexiglas pieces to allow the stir rod to stay in place. All three barrels have two holes for use by
the hand crank as seen in Figures 11 and 12. To the bottom of all three barrel lids is fixed a four-
inch duct fan, Figure 12, above which is a four-inch hole cut in the lid to allow air flow out of the
barrel. The hole above the fan is cut to allow the four inch PVC pipe fixed to each duct hose to
fit tightly in place and create a quick disconnect for the vent system, as seen in Figure 12.

Figure 11: Stage One Lid

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Figure 12: Stage Two and Three Lid

5.2.3 Ventilation

The ventilation for our system is composed of flexible PVC tarpaulin canvas, which is a
lightweight, highly flexible duct that will improve the efficiency of ventilation. The ventilation
tubing has been installed in: the downstairs bathroom, about 18 feet; the downstairs storage
room, about 40 feet. There was also a pre-existing metal duct which travels from downstairs to
the roof of the top story. For the ventilation in the storage room we had to connect two barrels
ventilation tubing, using a “Y connector” that was placed in the sub ceiling the two ventilation
tubing was joined, to create one tube, that would then connect and exit the basement through the
metal vent duct. Connecting the ventilation tubing to the three-inch PVC “Y connector” are zip
ties, which create and air tight seal without damaging the ventilation canvas tubing. The layout
for the ventilation system can be seen in Figure 13.

Figure 13: System Layout

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5.2.4 Step Box

The step box is constructed so that a person can easily step up and sit on the toilet seat. Refer to
Figure 10 in Section 5.2.1 for box design and dimensions. The box is constructed with wood and
screws. The sides of the box are 3/4 inch plywood cut outs. The step and platform are made
from 3/4 inch think particle board with a lament covering the top. A cargo strap is attached to the
back so that the toilet drum can be secured to the box. Rubber pads are placed on the bottom to
prevent unwanted sliding on the ground.

5.3 Cost Analysis
The costs that went into the design and implementation of the composting toilet solution are
versatile. There were many man-hours put into the research and design necessary to select an
appropriate system for the given situation. More person-hours as well as physical resources were
necessary to construct and prepare the system for use by the client. Many of the physical
resources did not require purchase while others did. The real or potential cost of each of these
materials is shown in this section. The maintenance of the system will also require time and
monetary resources over the projected period of its use.

5.3.1 Design Costs

The costs of the design for this system are represented by the input of time by the three team
members involved. This chart, Figure 14, shows the total hours of input as well as the hours
used to fulfill each phase of the design process.

Figure 14: Project Hours Pie Chart

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5.3.2 Construction Cost

The construction of the composting toilet system required numerous materials. A portion of the
materials were made available by the client, some were donated to the team, and the remaining
materials were purchased. The following table shows all the materials used to construct and
implement the system. For purchased items the price paid is shown in the chart. For donated
items an estimated cost is shown so a total estimated cost of the system is shown.

Table 6: Materials Cost

Our Market Cost
Materials Cost($) ($)
70ft. Ventilation Hose 48.30 48.30
3 Cork Screws 20.00 60.00
3 AC Fans 40.00 40.00
3 Plastic Barrel Inserts 24.00 24.00
3 Insulation Jackets 45.00 45.00
Toilet Seat 15.00 15.00
3 55-Gallon Drums 0.00 156.00
Pump 0.00 45.58
15 Casters 0.00 75.00
3 Grates 0.00 59.96
3 Wooden Bases 0.00 30.00
Wire Mesh 0.00 10.00
Wood Frame 0.00 40.00
10ft. 2 1/2" PVC Pipe 0.00 6.49
3" PVC "T" Connector 0.50 0.50
1ft. 4" PVP Pipe 0.00 1.39
52 Screws 8.28 8.28
1 Bag Zip Ties 7.00 7.00
Total: 208.08 672.50

5.3.3 Maintenance Cost

The system is designed for three users to withstand at least five years and contains a few fragile
parts. We predict that the ventilation system will be the most likely to require maintenance, on
account that the material is very fragile plastic canvas. Another frail part of the system would be
the mesh screens that keep the solid mass from the liquids; they are reused and may need to be
replaced. Maintenance costs should not exceed $40.00 a year and only in the event ripping in the
ventilation or corrosion of the mesh screens.

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Table 7: Maintenance Cost

Maintanence tasks Time Projected
Frequency
Cleaning /Emptying Barrels 1 hour per 4 months
Rotating Container Positions 15 minutes per 4 months
Adding Bulking Materials 1 minute per day
Stirring/Pumping 25 minutes per week
Ventilation check 30 minutes per year
Ventilation Maintanence (possible damages only if necessary) 1 hour per year
Screen Maintanence (damages only if necessary) 1 hour per year
TOTAL: 34 hrs. per year

Table 8: Usage Costs

Projected Usage Money ($) Projected Frequency
Bulking Material 0.00 per week
Electricity use NA per month
vetilation replacement 20.00 every 5 years
grate/screen replacement 30.00 every 3 years
plastic insert replacement 8.00 every 3 years
fan replacement 20.00 every 3 years

5.4 Implementation Instructions
5.4.1 Overview

The composting toilet is divided into three stages, refer back to Figure_ in section 5.2.3. The first
stage is receiving fresh waste and is located in the bathroom. The second stage is composting
with no fresh material being added and is located in the storage room. The third stage is
continuing to compost and is also located in the storage room. After four months the barrels will
rotate to the next stage with the third stage barrel being emptied and cleaned, and then put in the
bathroom to receive fresh waste.

5.4.2 Barrel setup

Each 55-gallon drum contains a plastic barrel liner, a barbeque grate covered with a wire mesh,
an insulating cover around the outside of the barrel, a pump sleeve pipe, a stir rod, a barrel lid
which contains a vent fan and vent connection, and the whole barrel is set on a rolling cart.
Insure that all components are present and in correct placement. Refer to Section 5.2.1 for
barrel description and set up.

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5.4.3 Stage One

Stage one is located in the bathroom and is the waste receptacle. The barrel placed in the cut out
of the box and strapped to the box so that the barrel will not move while in use. The lid with the
toilet seat should remain at stage one. Before use of the system the barrel should be filled with
six inches of wood shavings. And after every use more shavings should be added to cover the
feces, about half a liters worth. The contents of the barrel should be stirred with the stirring rod at
least once a week and the pump should be used to suck the liquid from the bottom of the barrel to
the top of the composting pile. After around an estimated four months the barrel will be rotated
to stage two; however, no new raw waste should be added if the barrel is more than three
quarters full.

5.4.4 Stage Two

Stage two is located in the storage room where the waste will be composting. The barrel should
be placed under the vent closest to the wall adjacent to the bathroom. The lid should be put on
the barrel and the vent connected. The fan should be plugged in and running. No new raw waste
should be added. Wood shavings can be added if necessary for the composting process. The
compost pile should be stirred once a week. The pump may also need to be taken from the barrel
in the bathroom, placed in the sleeve pipe, and used to pump the liquids from the bottom of the
barrel. If there is no liquid in the barrel then the pump is not necessary. After approximately four
months the barrel will be rotated to stage three.

5.4.5 Stage Three

Stage three is also located in the storage room. In this stage the compost will continue to break
down. The barrel should be moved over from stage two and placed under the vent closest to the
exterior wall. Follow the same directions as stage two for pumping and stirring.

5.4.6 Emptying and Cleaning

After stage three the material will be ready to be used as compost. The vent should be removed
and the barrel should be rolled outside to the dumping location. Remove the stir rod and dump
the barrel over. Use a shovel to empty the barrel if necessary, but caution should be used so as to
not rip or tear the plastic liner. Remove as much compost as possible. The metal screen and the
inside of the barrel should be hosed off.

5.5 Prototype Performance
The composting toilet was completed on December 9th, 2009 and is in place at the CCAT house
on campus. This system performance cannot be evaluated at this point; however a similar Sun
Frost design is working at the Arcata Educational Farm.

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6. Appendices
Appendix A – Brainstorming Notes

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Brainstorming Notes (Continued)

32


33


34


35


36

Appendix B - References
Anonymous, (2004). Sun Frost “Human Humus Machine” Composting Toilet,
< http://www.sunfrost.com/composting_toilets.html>, (Sep. 28, 2009)

Anonymous, (1993, 2009). Compost Quality: Performance Requirement Characteristics,
http://www.ciwmb.ca.gov/organics/products/Quality/PerfChar.htm, (Sep. 24,2009)

Anonymous, (2005) Humboldt County, California: Climate.
http://co.humboldt.ca.us/portal/about.asp (Oct. 1, 2009)
Beckman, C. (2008). “Category:Composting toilets.” Appropedia,
<http://www.appropedia.org/Category:Composting_toilets> (Sept. 23, 2009).

Haskett, Tobey. Personal Interview. Oct. 7, 2009.

Henry, C., Olsen, E., Fioravanti, M. (2009). “Improving Sanitation with Composting Toilets,”
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