Other Biological Toilets

(Updated 1/22/2007)

The two systems described on this page are intended to encourage folks to think outside the box. It should be noted that both of them push the envelope of accepted design and I doubt that a permit would be approved for them anywhere in the United States, even on an experimental basis. None-the-less, the following descriptions may serve to stimulate thinking about other designs. These are warm climate systems, not suitable in areas where hard freezes occur regularly.

 

Redworm Sewage Processing System

This low-cost biological sewage treatment system relies on redworms (Eisenia foetida) to convert human feces and toilet paper into worm castings which in turn fertilize edible plants. The system was designed and built at Casa Juliana (in south Texas) in 1994. It has been in continuous use since, producing large quantities of figs and papayas.

 

 

The sewage sources are two conventional bathrooms each containing a flush toilet, shower and lavatory sink. The sewage from each source is routed through a 3" sewer pipe that empties into the worm container which is a partially buried box built of concrete blocks. The bottom of the container is native soil through which effluent leaches to irrigate edible plants surrounding the worm container. The top of the container is a wood and metal lid with two inspection hatches each 2' x 2' square. Two 1 1/2" diameter screened ventilation holes are located in each end of the lid. The dimensions of the container are approximately 4' wide, 8' long and 2' 6" deep. 18" of the container is buried below grade and about 12" is above grade, to prevent flood water from entering. At one end of the container is a bed of coarse gravel about 4" deep. It covers about 2' x 4' of the bottom of the container. The drain pipe from the bathrooms enters the container from the same end several inches above the top of the gravel. The gravel serves as habitat for the worms, allowing them to live above the water level in the bottom of the container, which is typically 1" or less. About 3 pounds of red worms were initially used to seed the gravel. Fruit-bearing trees are planted around the perimeter of the container. The vent pipes for the household sewer system are capped with screen to keep insects from entering the container through the sewer system. 

 

Worm container with lid propped open

Interior of worm container showing soil floor before gravel was placed under drain pipe

 

In use, effluent from the bathrooms flows into the container via the sewage pipe, then flows through the gravel bed and spreads out across the bottom of the floor, where it leaches into the soil to be partially taken up by plant roots. Solids present in the effluent land on the gravel bed and are quickly consumed by the worms. Fecal matter and toilet paper typically disappear overnight as worms convert it to worm manure (castings), which are then flushed through the gravel bed and across the floor of the box with the next surge from toilet or shower use.

This system has worked well for many years in spite of the small 4' x 8' leaching area and fairly heavy soil with a percolation rate of around 30-45 minutes per inch. The reason for its success is that a concerted effort is made to minimize water use in the bathrooms feeding into the system. This is accomplished by using conventional water conservation measures such as 1.6 gal. low flush toilets, water-saving shower heads and lavatory sink aerators. In addition, all regular bathroom users understand the need to minimize water going into the system. The old adage is used in regard to toilet flushing, "If it's yellow it's mellow; if it's brown flush it down," showers are short but adequate and water is turned off during lathering.

About the only maintenance required is to remove excess worm castings about once every year or two. This is accomplished by opening the lid and shoveling out the castings until native soil is reached, then putting the castings into long-term compost, where it composts for at least a year. The resulting composted castings can then be buried around edible shrubs or trees. The wooden lid eventually began to rot and a cast concrete lid would be better.

 

Soil Toilet

If composting toilets were adopted on a broad scale in aridlands, a large supply of organic cover material would be needed in an environment not conducive to the production of such quantities. Although this is at best a distant dilemma, considering it prompted me to explore a "soil toilet" concept, requiring no off-site inputs. In this system, a bucket toilet is used (see Composting Toilets), but soil rather than organic matter is used as the cover material. When the bucket is full, the contents are deposited into a trench about a foot wide and deep, which is dug into topsoil. Edible plants, preferably perennials in which the edible portion is well above the ground, are grown near the trenches and the feces and toilet paper serve to provide fertility for the plants. This treatment method relies on decomposition agents in topsoil to destroy pathogens and to convert feces, urine and toilet paper into available plant nutrients. Although I've experimented with this concept using a bucket toilet, it could also be done with some type of lightweight, portable toilet stand directly above the trench.

In limited experiments, I have made the following observations:

--In our desert climate and in silty soil, feces and toilet paper are broken down into humus within a year.

--Given the weight of soil, the bucket is easier to dump when only about half full.

--Soil used to cover should be very slightly damp. Dry soil tends to be unpleasantly dusty.

--Trenches should be located in well-drained areas, not prone to flooding.

--Trenches should be inaccessible to children and pets.

The trench area per person per year can be roughly calculated based on the following assumptions:

--Each person using the system will produce about 5 gallons of soil covered feces and urine per week.

--Trench size is one foot deep and one foot wide.

--Each bucket dumped requires one foot of trench length for burial, so the trench size is about 50 feet long x 1 foot wide per person per year.

I would imagine using a two trench system. One trench would be used during the first year and the second trench during the second year. The third year, the first trench would be re-dug. This would allow one year of aging before a trench is re-dug.

 

Insect Toilets

Various types of biological toilets have been successfully used, including those that utilize larvae of various insects such as scarab beetles, soldier flies, etc. This type of experimentation can work well, although it should be noted that unlike bacteria, in which population densities can quickly rise and fall in response to available food (fecal matter), more complex life forms such as insects and worms have a longer lag time, so sudden large inputs can overwhelm them, especially following periods of low use such as when a family is on vacation, etc. This also applies to the worm toilet described above.

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