Renewable Energy – Recycling human waste

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Biogas_pipes-300As the Chinese population moved from the countryside to towns in search of prosperity a lot of things happened. The demand for energy increased and so too did the amount of human waste. Enter Heinz Peter Mang, a German engineer who connected these two events and came up with biogas.

In 2013, China’s urban population had overtaken its rural population when the former breached the 731 million mark, resulting in urban headcount higher by 100 million, Bloomberg reports.

In Beijing alone, city residents’ excrement treated every day is about 6,800 tons, which is enough to fill three Olympic-size swimming pools. Many of the people coming in from the countryside are unused to lavatories and there has been a big cultural push to have urban dwellers use them correctly. The fecal matter is collected and treated using methods familiar to many farmers who use animal manure to created biogas.

Human waste is collected in trucks, which drive to a depot and channel the human waste through a pipe into a machine, where unrecyclable solid material like tissue paper is separated out.

The rest then goes for separation: the solid waste is propelled into a compost wing to ferment at 140° for 10 days. The process kills harmful bacteria and roundworm eggs and turns the excrement into rich fertilizers for trees and vegetables. The liquid material is routed into tanks to generate biogas, and eventually pumped to bigger water-treatment plants.

Human waste recycling is moving from the Third World into developed economies. The UK operates a smaller version of this scheme, which also operates in African countries and Cuba. It seems that where there’s muck there’s money and Credit Suisse estimates this market will grow 200%-400% over the next five years.

Handling your own biowaste

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Composting toilet at Activism Festival 2010 in the mountains outside Jerusalem

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 and may be used as an alternative to flush toilets. They have found use in situations where no suitable water supply or sewer system and sewage treatment plant is available to capture the nutrients in human excreta. They are in use in many roadside facilities and national parks.

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 if the local regulations allow this. A curing stage is often needed to allow mesophilic composting to reduce potential phytotoxins.

Trail-head toilet. The building is by Restroom Solutions, Inc. (RSI), with a Clivus Multrum direct burial compost digester.
Trail-head toilet. The building is by Restroom Solutions, Inc. (RSI), with a Clivus Multrum direct burial compost digester.

Rules on Sewage Treatment 
Disposal of composted material depends on location and local, regional, or National unit policy, as well as State requirements. The compost must be treated as domestic septage for further treatment, unless it is documented to meet 40 CFR 503 requirements as a Class A or Class B sludge. Some States require a permit or permit waiver for surface application. The material may be burned, buried, removed from the site for further treatment, or (with a permit or permit waiver) used as a fertilizer or soil amendment.

Composted material is not as unpleasant to remove as vault waste. It is shoveled into triple heavy-duty plastic or heavy rubber bags for transport by pack animal or maintenance personnel, or into barrels for transport by helicopter.

Composted material can achieve a Class A sludge rating, depending on level of maintenance, level of use, and climate. A permit or permit waiver may be needed from the governing U.S. Environmental Protection Agency office to incorporate the material into the soil as a soil amendment or for reclamation projects. Compost may be used to reclaim rock quarries, slide areas, or mine sites. Maintenance records may be required. Contact the appropriate State office for permit requirements.

A liquid waste disposal method should be incorporated into the system. This may be a subsurface leach line, holding tank, or evaporation trays. The amount of liquid waste depends on type of use (day or overnight use), humidity, and temperature.