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Building Compost Toilets in Fiji

 

I served with Peace Corps Fiji Sept 2003 thru Oct 2005, surely one of the great experiences of my life. For more on that...

One of the big environmental problems there was pollution of waterways by flush toilets. The government had encouraged villages to adopt flush toilets as a healthier alternative to pit toilets; however there was very little consideration given to what happened to 'the flush'. Without sewer or septic tank, nitrates from village flush toilets were blamed for eutrophication (and death) of the coral reefs.

It was suggested that a Compost Toilet (CT) would be an environmental improvement over flush. Prior to Peace Corps, i'd a degree in Conservation, and home building experience, but i (and my Peace Corps compatriots) had no significant training or experience with CTs. We read books from the Peace Corps library, and researched on the internet. The rest we discovered or made up as we went along.

I was involved in the construction of 3 CTs, and we trained villagers to build more. It's something that might help thruout the tropical and semi-tropical world, if for no other reason than they’re cheaper than flush toilets. Folks continue to ask me about it. Hence, this article.

Below are Design Notes I wrote while there. Also I have photos from the three projects:

 

I express my heartfelt appreciation to my fellow Peace Corps volunteers and staff, and the wonderful people of Fiji.

 

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Composting Toilet Design Notes

maikeli mcmillan m@greatempty.us - 17nov04, amended 19nov04, 2nov09

 

See The Composting Toilet System Book by David Porto & Carol Steinfeld. Actual CT examples in Fiji:

·         Fiji School of Medicine

·         Vunisinu Village, Rewa

·         Komave and Tagaqe Villages, Nadroga

 

Advantages, relative to flush toilet:

·         Cheaper to build.

·         Uses no water.

·         Doesn’t pollute groundwater or surface water.

·         Fertilizes plants.

 

Parts of a CT

 

·         “User interface” – the seat.

·         Storage – where the waste goes and composts. Bug-proof. Actually there are at least 2 Storage units, and use alternates among them. As one is in-use, the other(s) are composting.

·         Liquid separation – a means of letting the liquid component drain off, leaving the solids behind. This reduces odor and promotes composting.

·         Wetland – where the separated liquid drains to.

·         Ventilation – move lots of air thru the Storage area, to promote decomposition and remove odors.

·         Solids removal – a way to remove the solids after they’ve completed the compost process.

 

Conceptual schematic:

How to use it:

·         User waste + toilet paper deposits to Storage. After each use, add dry leaves, ash, veggie waste, grass clippings, or other fine organic matter to promote composting.

·         Liquid component drains off to Wetland. The nutrients are taken up by plants. The water evaporates or transpires.

·         When the Storage is sufficiently full, it is closed off and left to sit & compost for 6 months. Meanwhile a second Storage unit is used.

·         When the 6-mo compost period ends, the solid waste has become dry soil which can be placed in gardens, buried, or distributed over the ground.

 


Design Details

 

User Interface

·         Ideally the opening is somehow sealed to exclude flies & odors.

 

Storage

·         There are 2 basic schemes for the 2+ compartments required:

o        “Wheely-bin” (WB). Portable plastic waste bins or metal drums serve as storage. There is 1 user interface. When one storage unit is full, it is set aside for 6mos and replaced by another. Example: Vunisinu, Tagaqe.

o        “Vault”. 2 side-by-side concrete compartments are the storage. There’s a user interface into each. Use alternates between them per 6mos. Example: Komave.

·         Storage should be dry, water-tight, and bug-and-odor proof.

·         Sizing: The reference cited above says “One person will fill one 55-gallon drum with a grate/leachate-drain in about 200 days at 65 degrees compost temperature, more days at higher temperature.” Of course it’s warmer than that in Fiji, so composting proceeds faster, so the volume reduces itself faster as decomposition proceeds, so it’ll suffice longer than 200 days. (If we’re only talking 1 user, anything over 180 days is fine since that fits with the 6-month exchange cycle.)

·         Sizing gets much more complicated with multiple users, especially a Fijian “family” where it’s not clear who lives where/when/for-how-long. And how many users use a communal toilet? A distinct advantage of the WB system over vault is that if the bins are filling faster than you’d anticipated, just buy more WBs.

·         Sizing: “Rural Water/Sanitation Projects – Water for the World” (Peace Corps Information Collection & Exchange WS052) p.263: “Each person produces about 0.2 cu.meters of waste per year, taking into account volume reduction to excreta and grass clippings by bacterial action.” It says a double vault system, each vault 1.2m x 1.5m x 1.1m high, using each side for a year (rather than 6mos), will therefore accommodate 7 users.

 

Liquid Separation

·         This is some kind of grid that catches solids but lets liquid through. Vunisinu uses a plastic grill. Komave simply uses natural materials.

·         In case of pipe blockage, there should be an easy way to relieve the block without having to get inside the storage compartment (e.g., make the pipe accessible & removable).

·         Each person excretes about 438 liters urine a year. (It’s interesting that most of the fertilizer value of waste is in urine (one reference claims 90%), not the feces.) It is combination of urine and feces which causes most of the disgusting odor associated with human waste. Urine also interferes with composting organisms. Ideally, urine would never contact feces in the first place. The various reference books in the Peace Corps library show clever ways of keeping them separate.

 

Wetland

·         Lined (with cement or plastic sheet) to prevent infiltration of pollutants into the ground.

·         Size?

·         There should be an easy way to relieve pipe blockage.

·         Grey water from shower, sink, etc can go here too.

 

Solids Removal

·         The compartment door should need opening only once per 6 months, so “security” (i.e., how well it seals, prevents undesirable human entry, etc) takes precedence over easy opening.

·         In a coastal environment, any lock opened that infrequently will (1) be rusted shut, and (2) you won’t be able to find the key anyway.

·         Wheely-bin:

o        Adequate clearances, so that removal of the bin is not a big hassle.

o        Where will the WB be stored for its 6-mo compost period?

o        The WB needs continuing ventilation during the 6-mo compost period.

·         Vault:

o        All corners of storage should be easily accessible to a shovel.

o        Adequate outside clearances for wheelbarrow.

 

Ventilation

·         The more ventilation the better.

·         Intakes to windward if possible.

·         A vertical black pipe outlet, exposed to the sun, will promote ventilation. The outlet should be up high to keep odors away from people.

·         Screen to keep bugs out.

 

 

Architectural Considerations

·         The overall height of a toilet and its output-management system may be similar for flush vs composting, but whereas a flush system’s plumbing and septic tank or cess pit is always hidden underground, a CT’s storage will normally be above-ground (to keep it dry, for ease of solids removal, and for urine drainage to wetland); hence the ‘user interface’ needs to be relatively high above ground level.

·         2-story valelailais (outhouses) in a village of 1-story vales (homes) will look really odd.

·         On the other hand, peaked roofs on houses increase their height and therefore make it easier for high CTs to blend in.

·         Likewise, sloping hillside can make the height of a CT less conspicuous:

 

·         Like the flush toilet rooms one finds in koros, depending on what folks’re used to, the residents may prefer a detached outhouse, an attached ‘wing’, or fully integrated facilities.

 

Acceptance Factors

·         Composting toilets seem very much like the pit toilets Fijians have been told to eschew.

·         There is concern of flies, odor, and disgusting internal appearance, just as with pit toilets.

·         Flush toilets are seen as clean & modern (just as in USA). CTs are viewed with suspicion (just as in USA), and no villager wants to look foolish if it doesn’t work out.

·         People generally seem quite happy with things the way they are.

·         It’s the foreigner’s project, not their own.

·         They have many other priorities (church, gatherings, celebrations, other village projects).

·         There is not the environmental consciousness here which in the US gives CTs a chance. Few people are worried about water pollution, and few make a connection between toilet and fish population.

·         But environmental education can change attitudes.

·         Cost (relative to flush systems) is important to people, as is water usage in water-short areas.

·         People seem to like WBs, maybe because they look neat/clean/self-contained. Or maybe the word just sounds fun: “wheely-bin”.

 

Wheely-Bin Metrics

Small WB

Large WB

Drum

Front-to-back (inches)

22

29

23

Side-to-side (inches)

19

23

23

Height (inches)

36

41

34.5

Cost (F$)

?

<140

Cheap

Volume (gal)

65

118

62

 

 

Use of the Compost

 

Per Sanitation Without Water, p.117, and The Composting Toilet System Book, p.22-25: Temperature in a CT doesn’t get high enough for long enough to kill pathogens; fortunately, the CT disrupts the life-style of the bad bugs in other ways (time, pH, inter-microbe competition, etc), sufficient to kill them off. Both books advocate use of the compost and urine for crop fertilizer, though the first one contradicts itself and uses weasel-words. The second reference says to dig a trench, place the compost, cover with 0.1m soil, and “grow vegetables on top”. Unfortunately, growing root crops on fertilizer derived from human or pig waste is often mentioned as a bad idea.

 

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