TUESDAY, JAN 17, 2023: NOTE TO FILE
Module 2-4
Composting toilets
IN WESTERN SOCIETIES human feces are disposed of through a water-carrier system, through flush toilets that send excrement into sewers where it is mixed with other domestic wastewater and rainwater. This is a highly inefficient system, from the perspective of water use, as well as the waste of a precious resource that should be returned to the soil. Treating human waste through anaerobic digestion destroys pathogens and removes potential pollutants from the environment.
Waterborne diseases transmitted through human excrement are a leading cause of death worldwide, especially in the so-called developing world. Some diseases caused by untreated human sewage are Cholera, Typhoid fever, Paratyphoid fever, Salmonella, Dysentery, Gastroenteritis, Leptospirosis, Meningitis, Hepatitis, and various parasitic diseases. Nonetheless, humanure contains nutrients and when treated in a biodigester or through (hot) composting and returned to the land as fertilizer, we can see that this is ‘closing the loop’. Watch this short and amusing film about humanure from a permaculture farm in New Zealand:
Composting toilets are excellent options for individual houses and if there are only a small number of villagers in a settlement. In villages with centralised facilities, many such toilets can be built in a block. However, there can be cultural taboos against dry toilets, and the community should be consulted before adopting this technology.
Humanure can also be used in a biogas digester to produce gas for cooking.
Source: BPBO (2006)
Many small decentralized (household) biogas systems have been effectively installed all over the world.
Here is a video for a biogas digester construction that explains the step-by-step process.
The amount of biogas that can be yielded from human waste is limited in comparison to livestock manure and other feedstocks. Our stomachs are just too efficient! David House states in his excellent book that 1000 lbs of human waste produces about 0.6 cubic meters of biogas (enough cooking fuel for about 1 to 2 persons). But that amount quickly adds up. Biogas digesters have a great deal of potential to dispose safely of otherwise untreated sewage in developing countries, and can have a major role to play in the developed world as well. You can find below a short documentary (7mins) called “A Tale of Two Villages.” It shows the difference the installation of a biogas digester made to a village in China.
There are also hybrid systems that use normal flushing toilets followed by solids separation by centrifuge. The solids are then composted in a separate digester, while the liquids are disinfected (where necessary) and discharged with the grey water system.
The Aquatron uses a normal flushing toilet which combines public acceptability and convenience with some of the benefits of composting toilets, particularly no sludge and the creation of humus.
When the toilet (1) is flushed, the contents of the bowl are transported to the Aquatron Separator (2) where approx. 98 % of the liquid fraction is separated by using the momentum of the flushing water, centrifugal force and gravity. The Aquatron Separator needs no moving parts. The solid waste (paper and feces) falls down into the Bio Chamber (3) where it is composted by bacteria and, if desired, by worms. If using worms, the volume of the solid waste will be reduced by approx. 95 %. The need for emptying and handling the waste is therefore reduced to a minimum. Optionally, after installing an Aquatron System, some 250-300 worms are placed into the Bio Chamber. The number of worms needed to maintain the composting process will be adjusted automatically by nature. Optimal temperature for the composting is 12-25 degrees Celsius, a temperature level recommended for year-round inhabited homes. Freezing will kill the worms. The composting process is free from odour and flies because the Bio Chamber is ventilated and the small amount of liquid following the paper down into the Bio Chamber is removed by a drain at the base of the Bio Chamber. When the Aquatron 90 and 400 models are emptied, the refuse must be composted to soil in the garden together with the normal garden and kitchen waste. The liquid proceeds to the UV unit (4) where it is exposed to Ultraviolet light, which kills bacteria and viruses. The liquid may then be treated as Grey Water (bath, dish washing and laundry water), which means that the toilet wastewater may be infiltrated into the ground or into a suitable receptacle. Since the liquid fraction is separated from the solid waste, Aquatron Systems are not sensitive to peak load usage.
Module 2, lesson 5
