Monday, December 12, 2011

What to do with humanure?

Lets face it, humans are mammals, and human excrement is very similar to that of other mammals. Lets begin by calling it humanure.

What to do with humanure?  We used to simply leave it where it came out – as most other mammals do. Because of our propensity for living close together, and the knowledge gained from science that humanure can transmit disease, a sanitation regime has developed. At least where it can be afforded - approximately 30% of humanity still leaves their their feces lying on open ground.

However, the sanitation regime of the industrialized world is problematic in terms of its environmental impact. What follows is a description of what we currently do in America (or what is done on your behalf after you push the flush button), and how we might substantially improve upon it.

First we use a large amount of potable drinking water (approximately 100 times the volume of the feces) to flush it out of our toilets and into our sanitary sewers. There it is further diluted with household gray water. And then we often mix  in industrial waste (often adding toxic heavy metals, e.g., mercury, adding real injury to what so far could be described as merely environmental insult). 

This witch's brew goes to the regional Waste Water Treatment Plant (WWTP), often requiring considerable utilization of energy in pumping. There solids are settled out, and suspended organic matter digested by bacteria to the extent necessary for most of it to also settle out. The remaining liquid is treated with chlorine to render it sterile, and then released into our waterways, still bearing substantial organic matter, heavy metals from industrial waste, and copious quantities of non- metabolized pharmaceutical agents and their biologically active metabolites! Approximately 60% of the anti-depressants and their metabolites pass straight through current WWTPs. If your drinking water comes from waterways with upstream WWTP discharge (and most does), and you are taking anti-depressants, your doctor may soon be able to reduce your prescribed dosage because of what is already in your drinking water! If you don’t want to take anti-depressants … too bad - unless you are willing to pay for distilled water (or water treated by reverse osmosis), an option not available to fish and other wild life.

And what do we do with the WWTP sludge (or biosolids) that settle out. We dump most of it on agricultural fields. A green solution you might think? Wrong, it also carries with it heavy metals from industrial waste, contaminating not only the produce grown there but also the soil. There is also concern about pathogens in the sludge. Regulation prohibits direct human consumption of produce thus grown. In the 1990s, hundreds of dairy cows that ate grass produced from sewage sludge from Augusta, GA died of thallium poisoning.

In summary, our so called civilized treatment of humanure is a process that consumes large amounts of drinking water, uses substantial amounts of electrical energy, pollutes surface waters with WWTP effluent, and contaminates soil (with heavy metal laden biosolids).

In addition, we are wasting potentially valuable bi-products! If manure digestion happens in an anaerobic environment, it yields methane-rich biogas which can be used as fuel for producing electric power and/or heat. Also the resulting biosolids (if they were free of contaminants) would be valuable fertilizer for agriculture.

For these reasons, reform is strongly indicated. I’d like to be involved in the development of a   green humanure paradigm that is congruent with American sensibilities. The crucial question is “to what extent can the technology evolve to reach congruence versus the extent to which American sensibilities can or should evolve toward congruence?” An essential first step is to treat residential waste water separately from that of industry. Also, I expect that village scale (or possibly neighborhood) treatment will be more efficient and effective.

An approach of interest for me is the anaerobic digestion of waste materials for the production of bio-methane for cooking and other domestic uses. Such a digester could be feed with controlled combinations of agricultural animal manure, humanure, kitchen waste. and agricultural plant wastes. 

Small scale biogas plants are widely used in China. It would be appropriate to study the Chinese models (there are several, for different climates), and design a system appropriate for local climate and social values.

It would be crucial to develop a process so that the residue left after anaerobic digestion can be used for agriculture locally without substantial health risk, and in compliance with county and state health codes, possibly through Pasteurization followed by aerobic composting.
Separation of humanure from gray water eases the difficulty of  treating both. Gray water could be treated with  a biological system that includes both microbes and plants, possibly yielding effluent water of sufficient quality to be safely used in agriculture, at least for fuel or fiber crops, and possibly also for closed fruits that grow above ground, e.g., blue berries and apples. The system would ideally be passive in that it would be designed to operate without any pumping of water during treatment. 

Findings should be publicized with the hope that such systems will find broad future acceptance in American culture. This technology could provide a major step toward sustainability for the world, as it eliminates the harmful aspects of "modern" sanitation practice mentioned above, and hopefully creates a cost effective sanitation regime that can more rapidly be adopted in developing regions.The proposed technology could also allow us to eliminate our current practices in rural parts of America where septic systems inject effluent water bearing heavy metals and other poisons into the soil where it often finds its way into the ground water.

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