In this installment, I am going to discuss the composting of human manure as a small scale operation and present information on the composting process.

While I believe it will someday be possible to perform large or industrial scale humanure composting, it is not very practical considering current infrastructures and social constraints. In order to ensure that the compost is free of heavy metals and other potentially hazardous compounds, people have to watch what they put down the drain. For a family of five people this is not hard.  It will more difficult for a small group of people (say 30-50 individuals), but still feasible and realistic. But for a community of 5,000, this is nearly impossible, and since chemicals and products containing metals and other contaminants are very common, it is too hard to account for what goes down the 5,000 community members’ drains and toilets.

An additional consideration is the volume and types of  drugs (prescription, over the counter, and recreational) consumed by community members.  The presence of pharmaceuticals and personal care products (PPCPs) in wastewater is a very real concern. PPCPs consist of pharmaceutical, veterinary and recreational drugs as well as ingredients in fragrances, cosmetics, soaps, sunscreen, cleaners, vitamins and other personal care products (Daughton and Ternes 1999).  They can be present ubiquitously in the global environment since pharmaceuticals are present wherever humans exist.  Classes of pharmaceuticals include hormones, analgesics, sedatives, antibiotics, antidepressants, chemotherapeutics, blood pressure medicines, antidiabetics, etc.  These drugs and their metabolites are biologically active (bioactive), usually mobile due to high water solubility relative to molecular weight and are not easily biodegraded (Kümmerer 2004). 

The main path of pharmaceutical removal from the body is excretion via the kidneys, so it is common for compounds and their metabolites to end up in our waste. At this time, I am not aware of any studies that have been performed that investigate the fate of pharmaceutical residues under thermophilic conditions, but I would hazard to guess that a combination of heat, microbial action, and the UV rays in sunlight would cause the decomposition of many of these residues. However, until more is known, it would be prudent to avoid the application of composted humanure to food crops if it contains wastes from individuals who are on numerous medications that are not readily degraded in the environment. (If you are curious to know more about this, contact me.) With that said, we move on to the composting processes.
   
There are two ways that human manure can be composted:  slowly at a relatively low temperature over an extended period of time or thermophilically composted.  Composting toilets, such as ones produce by Clivus Multrum, are systems into which one does their business and over time microbes digest the material and turn it into compost. The compost temperature does not usually climb above 32° C (90° F) so it is likely that pathogens still remain in the compost; for this reason, compost from composting toilets is recommended for ornamental garden use only or burial under one foot of soil (Jenkins 1999). This method saves a lot of water and electricity compared to conventional toilets and human excrement is kept out of water supplies altogether.  It is said that one person using a Clivus Multrum “will produce 40 kg (88 lbs) of compost per year while refraining from polluting 25,000 liters (6604 gallons) of water annually (Jenkins 1999).”

The second method is thermophilic composting, which uses microorganisms that can tolerate high temperatures (above 45° C) to digest human excrement.  Human excrement is placed on a compost heap along with kitchen and other organic wastes, covered with a layer of cover material (such as hay, sawdust, or peat moss) which traps air and balances out the carbon/nitrogen (C/N) ratio needed for proper composting.  A good compost pile’s C/N ratio range is 20 C/1 N to 35/1. Too much carbon is bad because there is not enough nitrogen for microorganisms to use to synthesize proteins, whereas too much nitrogen is bad since there is not enough carbon present for them to metabolize. A pile containing too much nitrogen will release it in the form of ammonia, which is rather smelly. (Think of a chicken farm on a hot humid day.)  

A thermophilic compost pile can heat up to 70° C, but more realistic temperatures range from 47-55° C.  A temperature of 50° C maintained for 24 hours is sufficient to kill all pathogens.  A temperature between 47-55° C maintained for three days will kill all pathogens, while temperatures between 55-60° C can sufficiently kill pathogens in 30 minutes to an hour.  After the thermophilic stage, the compost cools down until eventually mesophilic bacteria and critters such as earthworms work their way into the pile and decompose things even more.  The next step is for the pile to age, usually for a year (if it came from a healthy population) to three years (for a diseased population).  The average recommended aging time is two years, after which the compost can be added to soil intended for food crops or anything else one wants to do with it (Jenkins 1999).  The resulting compost is “rich in nutrients” and “composted human manure is a valuable soil amendment that helps to maintain fertility and crop yields (Agroecological Research Group 2001).” 

If you are really interested in humanure and want to learn more about how to do it, I recommend you get yourself a copy of The Humanure Handbook by Joseph Jenkins. It is an invaluable resource and a pleasurable read.

Part 1  Part 3

Works Consulted

Agroecology Research Group. 2001. Case Studies: Thermophilic Composting of Human Manure in Pennsylvania, USA. Online. Available http://www.agroecology.org/Case%20Studies/humanmanure.html

Daughton, C. G., and T. A. Ternes.  1999.  Pharmaceuticals and personal care products in the environment: agents of subtle change? Environmental Health Perspectives Supplements 107(Supplement 6):907-938.

Jenkins, Joseph. 1999. The Humanure Handbook; A Guide To Composting Human Manure.  Chelsea Green Publishing, VT.

Kümmerer, K.  2004.  Pharmaceuticals in the environment: sources, fate, effects and risks. Springer-Verlag, Berlin.

Last update: April 28, 2008
08:09 am

Published in : Eco Blogs, Eco Culture

Keywords : human manure, humanure, compost, permaculture, sustainability, poop, shit, fecal, excrement sustainable poop, re-using waste, waste reprocessing, waste disposal, sustainable waste disposal, PPCs

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