Composting Toilets May Help Save the World

A key discovery of nineteenth century science was that diseases can be transmitted via pathogens in human waste.  In regions of high population density, this can lead to epidemics if adequate sanitation facilities are not available. A milestone in epidemiology was the 1854 cholera outbreak in London. A physician named John Snow analyzed the incidence of the disease and concluded that the Broad Street public water pump was the source of infection. Even though he had no explanation in terms of germ theory at that time, he persuaded the authorities to remove the handle of that pump. This stopped the cholera epidemic. The well from which this pump drew had been dug a few feet away from an infected cesspool. A replica of this pump still stands in London:

The replica Broad Street Pump in Soho

Improved sanitation in the West and in prosperous areas of the rest of the world led to a dramatic decrease in deaths by disease, especially among children. Using water to sluice wastes to a septic tank or to a central treatment plant has proven an effective means to handle these wastes, for single homes and for vast urban population centers.   However, an estimated 2.5 billion people, about a third of the world’s population, still lack access to basic sanitation. Those living in rural settings may cope by relieving themselves in the woods or fields, but many live in crowded urban slums and are too poor to install flush toilets with their requisite water supply and sewage piping and treatment facilities. Microsoft founder Bill Gates has attempted to address this problem. The Bill and Melinda Gates Foundation has initiated the Reinvent the Toilet Challenge, to support the development of a “next-generation” toilet which:

  • Removes germs from human waste and recovers valuable resources such as energy, clean water, and nutrients.
  • Operates “off the grid” without connections to water, sewer, or electrical lines.
  • Promotes sustainable and financially profitable sanitation services and businesses that operate in poor, urban settings.

These are lofty goals for the humble commode. Some of the technologies put forward to meet this challenge involve high cost or high-tech components whose maintenance could be problematic.

My guess is that any viable sanitation solution for the masses will likely involve some much lower-tech approach. To that end, a few years back I examined a suite of small composting toilets. In North America these devices are sold primarily for use in vacation homes or on boats or for emergency preparedness. I evaluated them for these purposes, based on information and comments on the internet. From an engineering point of view, I examined the key materials-handling aspects of these different models, and attempted to predict which features might be most useful in a “global toilet”.

My full article on this subject was: Comparison of Composting Toilets: Towards a Global Commode. Here I will just summarize some key findings.

With leading brands of self-contained composing toilets, liquids and solids drop into the same vessel. This vessel contains some porous, fibrous medium like peat moss or shredded coconut husks. That whole stew is stirred periodically to keep it aerated, and the holding vessel is ventilated to the outside with a fan. The picture below shows the innards of one such toilet.

Innards of Biolet composting toilet

If all goes well, the mix is moist but not too moist, and after say two months of use it has digested down to a manageable soil-like brown mass, which you can spread as compost on your plantings (but not on your vegetable garden). The trouble is, often all does not go well with these types of toilets, and you have a stinking gooey mess on your hands (or on your bathroom floor). But never fear, I came across an alternative type of small commode, which again does not require water plumbing or sewage lines or septic tanks.

This alternative type of toilet is typically termed “urine-diverting”. Right below where you sit down, there is a contoured plate with a smaller hole towards the front and a larger hole toward the back. I realize we may be getting into Too Much Information here. Suffice it to say that handling liquids and solids separately makes the operation of these small units much easier and nearly foolproof.  This holds true for North Americans playing at living off-grid, but this ease of use should carry over to usage in less-developed countries.

You might not think that devices of this nature would garner warm-hearted reviews from users, but they do. For the full story, see the link above to the lavishly illustrated full article.

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