What started out as a request by my wife to build a "guest latrine" turned into a study of world sanitation methods. While I don't claim to be an expert, I have learned a lot and have found a lot of on-line resources. I also now understand that while the initial focus of most of the projects was to clean up (pun intended) third world sanitation, it it very clear that there are good reasons to make some serious changes in how human waste is dealt with in the first world as well. I suggested this in a previous post. Here I want to fill in the blanks.

Thus, I intend to cover three topics:

• Why changes need to be made
• Low-tech solutions suitable for the third world
• What can be done (and is being done) in the first world

Problems with Current Human Waste Handling

The changes that are needed can be divided into two categories: waste of resources and dangers of mis-management. While somewhat different in nature, these problems exist in both the first world and in the third world.

In the first world we tend to think all is well. Unfortunately, we think that mostly because we tend to not think about much beyond pushing the flush lever. I remember the complaints of people in the U.S. when low-flush toilets were mandated. They were always along the lines of "you can't get a good flush with so little water". While what are called "low-flush toilets" have improved, most people have still missed the point.

That point is that first-world toilets went from using about five gallons of drinking-quality water to 1.6 gallons of drinking-quality water for each flush. Assuming you flush after urination, that means you use about ten times as much drinking water to dispose of the urine even in a low-flush toilet. That is not efficient and not sustainable.

To complicate matters even more, this large volume of fouled water must then be processed before it can be returned to the eco-system. Thus, we have the processing to create drinking-quality water which usually involves the addition of chlorine and then we must once again process it, again before it can be disposed of.

That is but one of the inefficiencies. Another is that human urine, and to a lesser extent, feces, contain nutrients that are needed in agriculture. Primarily we are talking Nitrogen, Potassium and Phosphorous. One study I read suggested that the volume of these chemicals escreted by one person in a year is sufficient to fertilize a grain crop of about 450 lbs. If we don't use these chemicals from human urine it means we must find another source. This typically means manufactured fertilizers.

In much of the third world, particularly in Asia and Africa, human waste is recognized for the resource it is. Problems tend to be more along the lines of unsafe use. For example, spreading raw human waste on food crops. Thus, in the third world, more often than not the biggest danger is one of mis-management.

If you happen to live in the first world, don't be to smug. There has been (and still is) a lot of dumping of raw sewage back into the environment. By converting relatively small volumes of waste into much larger volumes because of the volumes of water used to transport the waste, the first world has actually created a bigger problem to solve.

Low-tech Solutions

;For those of you reading this, you are most likely to think of a typical pit latrine as the most common solution. While I don't have numbers, it will be in some parts of the world, not in others. But, more important, it is not necessarily a good solution. Why?

• In many cases it wastes resources
• It has the potential of polluting ground water

There have been some creative ways of addressing these problems. Just as an example, one solution brought to Africa was the arboloo. This is a shallow pit latrine with a future design. The idea is that the latrine is used for a while and then the building moved to a new pit. A tree is then planted in the old pit. At virtually zero cost, both the concerns are somewhat addressed. That is, less of the resources are wasted and the shallow pit is less likely to pollute ground water.

While I had expected to see composting toilets such as the Clivus-Multrum appear in low-tech solutions, it doesn't seem to be the case. While the Clivus is low-tech in design, misuse can be a serious health hazard. In particular, it is easy to contaminate clean compost with new excreta.

Thus, I have found drying systems to usually be the approach rather than composting systems. The difference is that rather than trying to create an environment where feces are converted directly into a compost suitable for use as fertilizer, they are just dried to reduce volume, odor and the likelihood of attracting flies. After they are dried then can then be composted and used as a fertilizer.

In a low-tech environment, drying typically means just allowing liquid to evaporate, possibly aided by solar heating. This is where urine diversion becomes a serious consideration. Besides aiding in the drying process, urine can be used as fertilizer with minimal waiting times.

There are two approaches to urine diversion, each with advantages and disadvantages. The first is to create an environment where, as much as possible, the person is putting urine in one container and feces in a different one. The other method is to separate the mixed stream.

Much like the idea of using gallons of water to transport human waste and then try to separate this mixed stream and process it, separating a mixed stream of urine and feces is less desirable. Once mixed, the urine could have picked up some contaminants from the feces making it less desirable to directly use as a fertilizer without a substantial time to kill pathogens.

On the other hand, getting the toilet user to do the right thing is a problem. While this appears to be less of a problem with squat toilets which are common in Asia, someone used to using a sit-type toilet is going to have more problems. Providing a separate urinal is a step in the right direction but that tends to not solve the separation issue for females. (Note, however, in doing the research, I found that it is apparently common for many females in the world to pee standing up, particularly in China. So, a urinal could be more of a solution than I had thought but culturally, much like using squat toilets, this is not going to be a quick solution in the western world.)

The typical low-tech solution is then a toilet stand where the bowl is divided into two parts. The front part is for urine, the back part is for feces. Does this work? Somewhat. While there are companies that have patented "solutions", the bottom line is that people and in particular, women and children, are going to need "training" in order to properly use a urine-diverting dry toilet (UDDT). Thus, such a system may work very well for a family but it likely to encounter problems if used as a public or guest facility.

;While a system could be designed that would have sufficient evaporation capacity to deal with some urine appearing in the solid waste stream, that is not the only problem. The research I read suggested that children contaminating the urine stream with feces was a common issue. While some toilets have been designed with a separate children's seat this has proved to be less than perfect.

Thus, for public use, it likely makes more sense to accept that a mixed stream is the best you can do and deal with it. (Note that there are high-tech answers which will be discussed in the First World Changes section below.)

One common type of dry toilet is a vault system. Here, you have two vaults that are used sequentially. That is, one is used until full. The contents are then covered with dry material such as leaves and sealed. The other vault is then used until full. With a six-month to one-year cycle, the waste will have dried out sufficiently to be removed and transported safely.

These systems are typically designed for use with urine diversion. If you want to use this type of system without urine diversion, you can create a false floor. Solid waste remains in the part above the false floor and urine drips through and is the diverted to a drying area or area such as a flow bed where it is absorbed and used.

First World Changes

The good news is that there are some reasonable systems on the market today. Some are more suitable for new construction, others can be easily used in retrofit situations. Most seem to be products of Scandinavia or Germany. Their use appears to be expanding to Australia and New Zealand. In the U.S., unfortunately, there seems to be little acceptance. As the U.S. clearly needs to make changes in this area, I will credit the just push the lever and walk away attitude with the lack of acceptance or concern. I am not sure how more awareness appeared in Scandinavia but it is clear that awareness needs to spread to North America.

On the toilet end, there are water closets that offer a dual-bowl like a dry toilet but are designed to use a traditional water seal and water flush for solid waste. The front bowl is designed for just urine and is flushed with a very small amount of water, generally just a couple of ounces. Even if used in traditional single-sewer environment, there could be significant water saving. If a separate graywater system is available, you get the additional advantage of not having to re-separate graywater and blackwater.

On-site processing systems for both graywater and blackwater have also been developed that are suitable for use in apartment and office buildings. Systems vary in design and capacity but all could be used in new construction. Some systems could also easily be used for retrofits. For example, one system is designed to work with regular mixed streams and uses a passive device called an aquatron attached to the composting system to separate liquids from solids. The liquids are then sterilized using ultraviolet light and added to the graywater stream.

For home use, dry toilets that just sit on the floor and do not require plumbing are available. Some are totally passive while others require electricity to run a heating element to dehydrate the waste. There are no shortage of brands and styles but, once again, most come from Scandinavia.

Resources

I read many books, papers, reports and marketing blurbs before writing this blog entry. Much of what I read duplicated what is presented in the resources listed below or just documented specific implementions—both commercial and non-commercial—of non-traditional disposal and use of human waste. These three books, the last being in Spanish, should paint the whole picture for you and show you how you can build your own UDDT.

Ecological Sanitation, published by Stockholm Environmental Institute. ISBN 91 88714 98 5. The document may be repproduced as long as it is not for profit. It is available here as an attachment.

Ecological Toilets: Start Simple and Upgrade from Arborloo to VIP by Peter Morgan. Published by Stockholm Environmental Institute. (2009 pre-production draft at this point). The document may be reproduced as long as it is not for profit.

Sanitario Ecolólogico Seco, Manual de dise?o, construcción, uso y manteinamiento by Lourdes Castillo Castillo. Available on-line at http://www.zoomzap.org/manuals/SES/download-esp.php