Dry Composting Toilets

A dry toilet is a toilet that operates without flush water, unlike a flush toilet. The dry toilet may be a raised pedestal on which the user can sit, or a squat pan over which the user squats in the case of a squat toilet. In both cases, the excreta (both urine and feces) falls through a drop hole. The urine and feces can either become mixed at the point of dropping or stay separated, which is called urine diversion.

(From Wikipedia)

A composting toilet is a type of dry toilet that uses a predominantly aerobic processing system to treat human excreta, by composting or managed aerobic decomposition. These toilets generally use little to no water.

The human excreta is usually mixed with sawdust, coconut coir or peat moss to facilitate aerobic processing, liquid absorption, and odor mitigation. Most composting toilets use slow, cold composting conditions, sometimes connected to a secondary external composting step.

Composting toilets produce a compost that may be used for horticultural or agricultural soil enrichment as long as the local regulations allow this. A curing stage is often needed to mitigate the toxicity of moderate-temperature (mesophilic) microorganism to plants.

Urine hampers composting process, since urine contains a large amounts of ammonia that inhibits microbiological activity.

A composting toilet consists of two elements: a place to sit or squat and a collection/composting unit. The composting unit consists of four main parts:

Humanure

As public health advocates will be quick to point out, the switch to sewers helps protects us from sewage borne diseases. But it also breaks the nutrient cycle: instead of returning nutrients to the land from where they came, we now reclassify excrement as waste and use chemical fertilizers to replace it. From an agricultural standpoint, the crazy thing isn't the idea of using our crap as fertilizer. It's how far we've strayed.

With this in mind, the idea behind our current system would seem to make sense: more than half of America's sewage sludge is applied to land. But there's a crucial difference between humanure and modern sludge, known in the sewage industry as biosolids. Humanure is made from pure human excrement. It can still contain residues from pharmaceuticals that pass through our bodies, but it lacks the industrial chemicals or other contaminants that make sludge so controversial.

Biosolids, on the other hand, can count as ingredients everything that's dumped into our sewer system, including a mixture of domestic and industrial waste that can include heavy metals, toxic chemicals, and thousands of other pollutants—and its long-term effects on soil are impossible to predict. The main ingredient of biosolids and humanure—feces—might be the same, but when it comes to their potential to contaminate soil, the two materials are fundamentally different.

It's difficult to judge what will ultimately have worse consequences for agriculture and human health: spreading the contaminants in modern sewage sludge on soil or diverting sewage's nutrients away from land. (Both are bad in different ways.) But one thing is certain: creating pure humanure with our current wastewater treatment system would require segregating our waste streams at their sources, which, thanks to the way our sewers are piped, is impossible to do.

To help jumpstart the revolution, Jenkins self-published a guide in 2005 called The Humanure Handbook that features chapters with titles like Crap Happens and an illustrated character named Tommy the Turd. For his first run, Jenkins could only afford to print 600 copies; he's now sold more than 33,000, and portions of the handbook have been translated into Spanish, Norweigan, Korean, Hebrew, Mongolian and Chinese.

The challenge these simple systems face, however, is that most Americans don't like the idea of homemade toilets. We don't like thinking about our shit, period. So a middle ground has emerged: commercially designed toilets that look what you're used to, but have composting systems built in.

Bio-Sun, Aquatron, Equaris, Phoenix—like "biosolids," they all manage to sound vaguely green while avoiding any allusions to the substance they're meant to treat. Talk to people who have owned them, though, and there's no getting around that what you're dealing with is shit. With a typical toilet, all you need to do is flush; with a composting toilet, everything you produce stays right where you left it—and some of these commercial designs, while tempting, aren't big enough to handle daily use. (Horror stories abound.)

Successful composting, while not rocket science, requires attention, devotion and considerable knowledge of the process; far from being an informational brochure, The Humanure Handbook, is 255 pages long. The environmentalist in me wanted to embrace the idea behind Allen's toilet—really, I did—but when it came to dealing with my own excrement, I was like most Americans: the only time I wanted to look back in the bathroom was to flush.

But there are plenty of places in the world not yet hooked up to sewer systems—in fact, an estimated 2.6 billion people don't even have access to toilets. Just as many developing countries adopted cell phones without ever having built the infrastructure for landline phones, poor communities could skip sewer systems and develop an integrated system of composting toilets instead.

How the Composting of Human Faeces Works

Four main factors affect the decomposition process:

  • Sufficient oxygen is necessary for aerobic composting
  • Moisture content from 45 to 70 percent (heuristically, the compost should feel damp to the touch, with only a drop or two of water expelled when tightly squeezed in the hand.)
  • Temperature between 40 and 50 °C (achieved through proper chamber dimensioning and possibly active mixing)
  • Carbon-to-nitrogen ratio (C:N) of 25:1

(From Wikipedia)

From Toilet to Garden

Once the container is full, the contents may be emptied into an outdoor compost pile. A classic three-bin composting system is ideal. Spread six to eight inches of leaves, straw, or other composting materials on the bottom before adding your first batch of humanure to ensure good drainage. Each time you add a batch of humanure, cover the contents with several inches of composting materials. Scrub the bucket with warm soapy water (a long-handled toilet brush is ideal for this), disinfect with diluted bleach, and let it dry before returning it to use.

As the pile grows, use a shovel to create a depression in the center and deposit the fresh humanure there each time. This positions the fresh material in the part of the pile with the greatest biological activity to quickly break down the humanure—and always cover fresh additions with several inches of composting material.

Placing fresh material in the center also promotes aeration, eliminating the need to turn the pile with a pitchfork, as is often suggested in composting books and classes; unlike compost piles for kitchen waste, you should never turn a humanure compost pile since this risks bringing fresh human waste to the outside of the pile where people or pets could come into contact with it.

Once the compost bin is full, let it sit for at least one year for the final stages of decomposition to take place, and start a new pile. After the first pile has matured, use it in your garden beds as you would any compost product.

Is it Safe?

Compost piles made in this fashion reach temperatures of over 160 degrees Fahrenheit, which is high enough to kill any harmful pathogens that are present in the humanure. Letting the compost sit for a year is extra insurance against pathogens, as they cannot survive for an indefinite period without a human host. Jenkins has summarized much of the scientific research on the subject here.

There are several common sense precautions to keep in mind, however. Don't touch the humanure as you transfer it from the collection bin to the compost pile; you can always wear gloves for this part as a safeguard. Have a dedicated shovel for the humanure compost pile and store it in a way that young children, or anyone who may not realize that it's been used for human waste, will not come into contact with the dirty end of it.

Also, don't build the compost pile on boggy ground or in an area prone to flooding. A well-drained site is essential to prevent water contamination, and for maintaining anaerobic conditions in the pile.

While properly composted humanure is completely safe, as a final precaution you may wish to apply it only around fruit trees, berry bushes, and ornamental plants where there is no chance of it coming to contact with something you're going to eat.

Pathogen Removal in Composting of Human Faeces

Excreta-derived compost recycles fecal nutrients, but it can carry and spread pathogens if the process of reuse of excreta is not done properly.

Internal pathogen destruction rates are usually low, particularly helminth eggs, such as Ascaris eggs. This carries the risk of spreading disease if a proper system management is not in place. Compost from human excreta processed under only mesophilic conditions or taken directly from the compost chamber is not safe for food production. High temperatures or long composting times are required to kill helminth eggs, the hardiest of all pathogens. Helminth infections are common in many developing countries.

In thermophilic composting bacteria that thrive at temperatures of 40–60 °C (104–140 °F) oxidize (break down) waste into its components, some of which are consumed in the process, reducing volume and eliminating potential pathogens. To destroy pathogens thermophilic composting must heat the compost pile sufficiently, or enough time (1–2 years) must elapse since fresh material was added that biological activity has had the same pathogen removal effect.

One guideline claims that pathogen levels are reduced to a safe level by thermophilic composting at temperatures of 55 °C for at least two weeks or at 60 °C for one week. An alternate guideline claims that complete pathogen destruction may be achieved already if the entire compost heap reaches a temperature of 62 °C (144 °F) for one hour, 50 °C (122 °F) for one day, 46 °C (115 °F) for one week or 43 °C (109 °F) for one month, although others regard this as overly optimistic.

(From Wikipedia)

Benefits of Dry Composting Toilets

Some people strongly believe that dry toilets (and dry sanitation) are the more sustainable way for sanitation. Dry toilets - or dry sanitation systems - can lead to reduced water consumption, the recovery of valuable resources from domestic wastewater, reduced eutrophication, and reduced toxicity of agricultural soils. They therefore offer potential benefits in areas with low water availability, limited access to synthetic fertilizers, surface water bodies impacted by eutrophication, and agricultural lands affected by heavy metals.