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Composting Toilets, Pasteurization and Permits

This paper is intended as an introduction to composting toilets. Be forewarned of the commitment needed to maintain a healthy composting toilet. Remember that you are dealing with and responsible for a living system. It needs care to survive just like a house plant or a garden. An unhappy composting toilet will let you know of problems in potentially unpleasant ways. Hopefully this paper will help you prepare for, and help you deal with some problems that are typically encountered.

Compost Toilet Justification

Americans are gradually confronting environmental realities and looking into alternatives for processing our excreta. Traditional sewer treatment facilities are expensive to build and often create many environmental problems. Small communities do not have the population base to make centralized treatment facilities economically feasible. Some community areas are geologically and environmentally unfit for the traditional septic tank technology. Regulatory agencies are beginning to refuse to issue permits, thus creating a de facto building moratorium.


The United States has had a small but real interest in composting toilets in their current form since about 1970. During the late 1960s the country was becoming aware of environmental side effects of industrialization. Interest in composting toilets emerged from the growing concern for technologies which were "earth-wise." Some manufacturers have been pushing their composters into a more broad acceptance since that time.

Still, most regulatory agencies are hesitant to issue permits for composting toilet systems due to their questionable design, do-it-yourself nature, and the lack of accepted scientific data on the systems. Furthermore, getting health authorities to approve is difficult because a total home system needs to also treat household greywater in an appropriate manner. These greywater systems are usually completely separate from most composting toilet installations. They may present a health problem if the greywater has been contaminated by sick people and is used for surface watering.

Meanwhile, backyard inventors, government, and academic interests were enthusiastically proclaiming the virtues of these water-saving devices. Most of the literature from that era reflects common sense applications of the technology. Three works comprise the bulk of the available literature specifically dealing with composting toilets from the 1960s to the early 1990s: The Toilet Papers by Sim Van der Ryn (1978), Goodbye to the Flush Toilet by Carol Stoner (1977), Composting Toilets: A Guide for Owner-Builders by Robin Adams (1979), and The Composting Toilet System Book by David Del Porto and Carol Steinfeld (1999).

General Composting Parameters

There are four general composting parameters to be concerned with in the composting chamber(s): carbon/nitrogen ratio, aeration, moisture, and heat.

Carbon/nitrogen ratio. For general maintenance a good rule of thumb is to add about one half to one coffee can, +/- one quart volume, of carbonaceous matter for each poop. Varying this ratio can be an effective means of controlling odors. When more carbon is added more nitrogen is absorbed, and unavailable for offgassing (odor). However, too much carbon results in very slow compost digestion and lower temperatures. A carbon/nitrogen ratio (c/n ratio) of 30:1 is recommended. Urine has high nitrogen content and feces have a somewhat lower nitrogen content; both need additional carbon to make a happy compost pile.

Aeration is necessary to achieve aerobic digestion. Lack of air or enough air movement through the compost will result in anaerobic digestion and methane offgassing. This type of offgassing is the offensive type usually associated with pit privies and will create an obnoxious toilet room environment. Increase airflow by turning on the toilet fan, if there is one, or open auxiliary vents. However, small amounts of air flowing through the compost allow it to stay hotter, which is a good thing. Therefore, only increase airflow when anaerobic smells are evident.

When the compost has been digesting for a while, air will have a hard time naturally filtering through the compost piles. At this point the pile(s) need to be turned to re-aerate them and to mix up the contents a little. When this time arrives the compost will let you know by stubbornly producing obnoxious odors.

Moisture content of the compost is usually the most neglected composting parameter. The moisture content needs to be at about 50% all the time. Add a spray of water, and additional pee does not count! A moisture meter such as those available from gardening catalogs needs to be exclusively dedicated to use in the toilet's chambers. Use the moisture meter in the chambers as the final say in any questions regarding moisture content.

Heat is generated by the compost microbes' metabolism the same way we humans generate heat when working or exercising. This heat of metabolism cannot be expected to heat the compost to thermophilic temperatures in most composting toilets because of the lack of sufficient volume and because of the multi-aged nature of the batches. Other heat sources should be considered. A solar pasteurization toilet has been developed by Dr. John Cobb of Corrales, N.M. This SOLatrine uses a bread box style solar cooker to pasteurize the batch. Similar bread box solar cookers could be made to treat the finished product of non-pasteurizing composting toilets (i.e. most commercial and homemade units).


Odors tend to be inherent in most composting toilets. This is a main reason that the general public is wary about the technology. Most often offensive odors are associated with "outhouses" and are perceived as a sign of backwardness and lack of social sophistication. Thus odor mitigation becomes a major skill in compost toilet operation and maintenance, especially in a public setting. Two sources of odors in a dry composting toilet are ammonia from urine and methane from anaerobic digestion. The ammonia odors will generally be due to urine splashing on the poop chute. Rinse often! Methane due to anaerobic digestion will have a very different odor than ammonia. Learn to tell the difference! Each odor has a different type of most effective mitigation measure.

Sanitation and Health Precautions

One of the most effective ways to lessen your risks is to know who uses the toilet. People who live together have high biological communication anyway. If only the residents use the toilet then only the residents' microbes will be in the toilet. I strongly suggest limiting the toilet's use to residents and occasional guests. Do you want to deal with all the other people's shit? Does the occasional user ever show up when it's time to turn the piles?

Daily Use

There are no special precautions to be taken with composting toilets that aren't also good practices for general hygiene. Be sure to wash your hands after pooping! This one habit alone can do more to protect public health than any other single thing.

Safe Handling Practices

If the compost is dry and dusty be sure to moisturize it first so you will not breathe the dust. Use gloves while handling tools, probes and gauges. All tools, probes and gauges are exclusively designated for the toilets! Don't be tempted to use the nifty moisture meter elsewhere. Any accidental contact of the compost to your skin isn't a cause for immediate disinfecting procedures. Plan to take a shower after you are done and use soap. Be aware not to wipe your nose or otherwise touch your face until after your shower.

Vector Problems

The biggest possible problem, as I see it, is the potential for composting toilets to become a habitat to vectors. These can be any critter that can carry a pathogen to a more common human living environment. These include flies, moths, mosquitoes, other flying insects, mice, rats, voles, etc. They can gain access to the piles in the most ingenious ways.

Creative ways to deal with vectors that do not involve chemical inoculation include:
·  Increase maintenance to daily if need be (this could knock out the breeding cycle of the vector, if it has established a colony, by destroying the larvae)
·  Shut off access to the piles by the vector. (e.g. fix a screen or locate a mouse chew hole)
·  Make the compost piles unfit for the vector's home (add blood meal, cool the piles down or heat the piles up)

Other Potential Problems

There is always the chance for things to go wrong and the operator/maintainer will be the one to deal with it. The major default sequence can always be used to insure that there will be minimal risks to public health. Possible problems which could be cause for concern are:
·  Too much moisture
·  Lack of use
·  Bad carbon/nitrogen mix
·  Sabotage
·  Refusal of users to follow instructions
·  Non-compostable trash in chambers

Major Problem Default Sequence

If you determine that the compost batch presents a threat to your health and the health of the community that cannot be adequately addressed, then the "major problem default sequence" alternative should save the integrity of the future soil amendment and insure a health-risk free environment. You will need one or two 55 gallon steel drums with removable lids. Place all of the offending chamber's contents in the drums and seal tight. Place the drums in the greenhouse or another sunny, warm area. Leave there for one year. Be sure to bury the resulting product around ornamental growth only. The batch thus entombed will go anaerobic, but as pressure builds up in the drums the anaerobic microbes will stop metabolizing also. After a year the stuff will not be any more digested than when you put it in, but the year retention time coupled with burying the product around ornamentals will allow for minimum public health risks.


Pasteurization is an event whereby the operator(s) can be assured of a health risk-free end product. This event takes place when the compost in a chamber is uniformly heated to a certain temperature for long enough to destroy all of the potential pathogenic microbes present in the compost.

It has been shown that thermophillic temperatures as created by microorganism metabolism in composting toilets is not sufficient to guarantee pasteurization. Furthermore, the notion that the long isolation time of the compost batch will effectively pasteurize it, is not substantiated in scientific literature. A true pasteurizing toilet will provide a way to uniformly heat the material to the pasteurization temperature threshold separate from the heat of metabolism.

Understanding the Permitting Agencies

The present system of segregating humans from their excreta via waterborne sewage took hold upon western civilization during the middle 19th century. Between 1830 and 1870, several cholera epidemics occurred in and around London, England, resulting in several thousand deaths. The cause of these epidemics was directly attributed to the worsening sanitary conditions existing in the urban areas. In response to these concerns, two urban systems were developed, one using earth, and the other using water to isolate human excrement. The portable water closet became the throne of choice and the predecessor to the modern flush toilet. Sewage engineers mark their firm establishment from this time.

During the first half of the 20th century there was a steady proliferation of the waterborne sewer treatment technology. In America today whole generations have come and gone which have used water flush toilets all of their lives. To speak of defecating into any receptacle except one containing water is social blasphemy at worst and likened to primitive conditions or going backwards in time at best.

In the present are the social taboos and bureaucratic inertia which impose the 'flush toilet, waterborne sewage' technology upon the vast majority of human excreta processing situations irrespective of the appropriateness of the application. We have generations of professional engineers who have made a livelihood from designing sewer treatment facilities. There is a whole industrial complex dependent upon selling the waterborne sewage technologies, and almost all government regulatory agencies know of no other way of doing business.

There is an unwritten mandate within regulatory agencies that the general population cannot be left to deal with their own shit; somehow, grave public health disasters would be perpetuated upon society. It is my belief that corporate profit has a vested interest in maintaining the status quo, and thus corporate/bureaucratic inertia becomes formidable.


There are more public health concerns with greywater effluent from a household than with composting toilets. Permitting agencies tend to be aware of this and will most always refuse alternative systems based upon insufficient greywater treatment. Therefore owners/permittees need to deal with this issue primarily in order to acquire a permit. There are many effective and innovative systems being used and developed to deal with greywater. Unfortunately almost all of these systems are being subjected to the same permitting agency paradigms as the composting toilet.

Ron Sutcliffe is a former director of Humboldt State University's Center for Appropriate Technology where he was head of the greywater and composting toilet research committee. Ron received his bachelor degree in Environmental Engineering from Humboldt State. This is a condensed version of a generic 'operation and maintenance manual' which is currently being developed. This manual will soon be available from the author.

Ron Sutcliffe
PO Box 511
Reserve NM 87829


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