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Science & Technology

How the Clivus Multrum Works

Composting toilets in building layout
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Since its invention in 1939, Clivus Multrum composting toilet systems have been used in homes, parks and commercial buildings as the sole method of treating toilet waste. The composting process is reliable, convenient and safe. Its results are both conservative and productive; water is saved from use as a carriage medium and the fertilizer content in excreta is made available for reuse.

The Clivus composting toilet uses aerobic decomposition to slowly break down both urine and feces into stable compounds within the polyethylene composting unit. The sloped design (“Clivus Multrum” means inclined chamber) separates urine from feces.

As urine moves by gravity to the lowest point of the composting unit, bacterial action causes a chemical transformation that converts the chemically unstable components of urine (urea and ammonia), into a liquid end-product containing nitrite and nitrate. This liquid end-product is biologically and chemically stable and contains nutrients which are valuable for fertilizer. The liquid end-product is generated at a rate of about one gallon for every 20 uses and, in most cases, is automatically pumped from the compost chamber into a separate storage tank.

The separation of urine from feces ensures that feces remain in an aerobic environment which includes bacteria, fungi, insects and compost worms. The organisms slowly break down feces into a compost material that has chemical, biological and aesthetic characteristics similar to topsoil and reduces its volume by over 90%.

Since the mass of organic matter in the composting unit available to the decomposer organisms is relatively small, temperatures inside the composting unit never exceed 100°F. Carbon dioxide (CO2) and water vapor are the primary vent gases. A continuously operating fan pulls air down the toilet fixture and out through a vent stack creating a completely odorless bathroom at all times.

Potential human pathogens are either killed by predatory organisms or by the long retention time in the system, as demonstrated by National Sanitation Foundation field testing. No compost is removed before a year of use and it is often several years before any is taken out of the compost tank.

All Clivus compost toilet systems are certified under the National Sanitation Foundation’s Standard 41, as required by many state and local governments. Health or environmental codes regulate the use of the liquid or solid compost products from the Clivus system. We encourage the use of these compost products as a fertilizer/soil conditioner wherever codes allow.

Composting Science

Composting system process diagram
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Composting is the bio-chemical decomposition of organic matter by aerobic organisms, i.e., organisms which get oxygen from the atmosphere and give off carbon dioxide. Composting takes place in all soils which support plant and animal life. The compost toilet employs the same process in the controlled environment of the compost chamber.

This process is distinct from anaerobic decomposition, which takes place naturally in water-saturated environments such as swamps, and is typical of septic tanks. Anaerobic, or liquid-saturated, conditions produce methane and the offensive odors associated with septic systems.

Organisms found in the composter include bacteria, actinomycetes, fungi, arthropods, and earthworms and are added manually once the system is operating. Energy, carbon dioxide and water vapor are released by the organic matter in feces through the activity of the composting organisms. A less chemically complex, more chemically stable substance, rich in organic matter, is produced. Feces volume, which is mostly water, is reduced by over 90%.

Temperatures in the compost toilet remain in the middle, or mesophilic, range (65-113°F) and don’t exceed 100°. Potential pathogens in feces are, therefore, not destroyed by heat. Those pathogens that require an aqueous environment die quickly in the non-saturated condition of the compost chamber. Others die because of the intense competition for nutrients; still others are consumed by predators which populate the system. The biological content of the dry end-product is similar to that found in topsoil. As a measure of its stability, the dry end-product from the Clivus Multrum contains less than 200 MPN (Most Probable Number) of fecal coliform per 100 grams. This meets the level required under National Sanitation Foundation Standard 41 for Non-saturated Systems. The dry end-product contains a wide array of plant nutrients and is intended to be used as a fertilizer/soil conditioner. Its use may or may not be regulated by local authorities.

Urine is also transformed by the activity of microorganisms. As compared to feces, urine contains most of the nitrogen from food. The primary form of nitrogen in urine is urea. Left alone, urea will degrade into ammonia and carbon dioxide. Bacteria in the compost unit (specifically Nitrobacter and Nitrosomonas) prevent this degradation and, instead, convert urea into nitrite and nitrate. That these are forms of nitrogen required for plant growth indicates the value of the compost toilet for nutrient recycling. The liquid end-product from the Clivus Multrum contains less than 200 MPN of fecal coliform per 100 ml. This also meets the level required under National Sanitation Foundation Standard 41 for Non-saturated Systems. The nitrogen-rich liquid end-product is intended to be used as a fertilizer. Use of the liquid-end product as a fertilizer may or may not be regulated by local authority.

Greywater Science

Greywater system design diagram
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Greywater is defined as wastewater that originates from clothes washers, bathtubs, showers, dishwashers, and sinks, but does not include blackwater: wastewater from toilets, urinals, or kitchen sinks that are installed with garbage disposal units.

Although greywater contains less than 10% of nitrogen found in blackwater, greywater has a higher level of un-reacted organic material readily available to micro-organisms and therefore decomposes much faster than blackwater. Blackwater, by contrast, contains material already exposed to one of nature's most efficient "treatment plants": the digestive tract of the human body, which means further decomposition will proceed much more slowly. The high decomposition rate of greywater allows it to quickly achieve chemical stability through organic reactions in the soil, but this rapid decomposition rate also requires greywater to be treated within 1-2 days of its production. Greywater should not be stored in holding tanks as it will quickly use up available dissolved oxygen and begin to decompose anaerobically, producing an offensive odor.

The Clivus Multrum system releases greywater into the biologically active, aerobic layer of the soil (the top 8-12") in order to fully stabilize the liquid. In this level of soil greywater is treated by many of the same soil organisms present in the compost toilet: bacteria, actinomycetes, fungi, arthropods, and earthworms. Nutrients in greywater from soaps are used by plants and the greywater not taken up by plants assists in groundwater recharge. Although pathogen levels in greywater are much lower than blackwater content, most potential pathogens will be slowly consumed by naturally occurring predators.

The Environment

Today's widespread waste treatment technologies result in pollution.
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Conventional ‘waste’ treatment systems (both sewer and septic systems) pollute by design. That is, they are not intended to capture nutrients from human excreta in a form that would allow their healthy re-use. Instead, both systems mix excreta with a large amount of water, and both discharge most of the nutrients into water: sewers into oceans, bays, and rivers; septic systems indirectly into groundwater. In oceans, rivers, and bays this causes first, the proliferation of aquatic plant life, then, as the plant life dies and decays, the removal of oxygen from the water and finally, the destruction of habitat.

Sewer and septic systems invite toxic substances from industry and homes to be mixed with excreta. Thousands of chemicals from manufacturing processes are inevitably found in sewage sludge. Toxic household chemicals are dumped into toilets as a matter of course. Once this mixture is made, excreta are ruined for reuse. More importantly, the toxic components make their way back to water and our food supply. In a perversion of the idea of recycling, sewage sludge is applied to farmland as fertilizer or sold at retail stores for use in home gardens under the disingenuous title “biosolids.”

These dangerous practices are new and unprecedented. For nearly all of our agricultural history, humans have practiced sustainable farming, including the use of our excrement for fertilizer. Only in the second half of the 20th century did those of us in North America and Europe begin to abandon the principles of reuse that were once required by our circumstances.

Source Separation

Source Separation requires potential polluters to handle their own waste and eliminates contamination of reusable materials.
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Compost toilets and greywater technologies represent a key concept for rational environmental behavior. By keeping large amounts of water and all commercial, industrial and household toxics separate from excreta, two things become possible:

1. Nutrients in excreta become available for sustainable reuse in agriculture. By returning these nutrients to agriculture we reduce the use of fossil fuel which is a major ingredient in the production of chemical fertilizer. We also broaden the spectrum of available plant nutrients: healthful food requires all the nutrients plants need, not just nitrogen, potassium, and phosphorous which are the only constituents of chemical fertilizers.

2. Keeping toxic substances out of excreta makes it possible to reconsider their role in manufacturing processes. If industry became responsible for the disposal of the toxic substances it uses, it could either use them in a closed-loop system or find less harmful, alternative substances. If alternative substances are not possible, then a decision can be made about whether the use of toxics is to be continued. That decision would be made properly with participation by all those potentially affected by it. At the moment, the decision is made surreptitiously thanks to the mostly unregulated opportunity for industry to use the sewer as a low-cost dump.

Right now, the way our society currently handles human excreta, food production, and industrial waste is neither sustainable nor rational. The broad acceptance of these practices might make source separation seem naïve or impossible, but we at Clivus Multrum believe it is the only rational way forward.

Here are links to a fuller discussion of environmental issues addressed by Clivus Multrum technologies:

Omnivore’s Dilemma, Michael Pollan Discusses the problems factory food production in the US

Enriching the Earth, Vaclav Smil A background on the creation of the world agricultural fertilizer industry

Unquenchable, Robert Glennon The present water crisis in the US

Toxic Sludge is Good for You, John Stauber and Sheldon Rampton How the PR industry promotes the use of sludge

The Big Necessity: The Unmentionable world of human waste and why it matters, Rose George A highly readable look into the practices and politics surrounding human waste.