Human feces: an unexpected material for recycling

February 22, 2019

Human feces: an unexpected material for recycling

Technologies to recycle human feces solve a hygiene problem, can be a source of energy and provide fertilizers for a more sustainable agriculture with lower environmental impact.

Getting rid of manure (including human feces) has become an urgent global health matter. Worldwide, researchers and entrepreneurs are exploring potential solutions to this problem, as reported by the prestigious scientific magazine Nature.

According to the World Health Organization, 2.3 billion people in the world have no access to basic hygiene, and 892 million people are forced to defecate in the open air, with all the risks that his practice implies (cholera and diarrhea in the first instance), with Sub-Saharan Africa, South and South-East Asia leading this sad ranking. There is even a date on the calendar, established by the United Nations General Assembly: 19 November is World Toilet Day. The date was set in 2015 with the ambitious objective of achieving universal toilets within 15 years. Unfortunately this objective is still remote: it is likely that in 2030 there will still be 5 billion people with no basic sanitation. Raising awareness is not enough, we need to act, and do so quickly. 



After ad hoc treatment, human and animal manure can be used as fertilizer and fuel (for example a recent Israeli research has assessed its effectiveness), but some people also use dry excrements as construction material, together with bricks and cement. Several companies are evaluating whether the fat acids found in feces can provide components for bioplastics and industrial chemical products. 

"The entire economic model of sanitation is changing from public service provision to private management, at least in part, as companies find value in excrements" stated Doulaye Kone, Deputy Director of the Water, Sanitation and Hygiene program of the Bill & Melinda Gates Foundation (the same foundation that is sponsoring Reinvent the Toilet Challenge, a call for innovative sanitation projects). 

In Ghana, where less than 5% of the population has access to sanitation, farmers ask for sewage to be sent to their fields as their best option of low cost fertilizer; however, since sewage is not properly treated, it can become a vessel for pathogens, causing gastrointestinal diseases that impact on the physical and cognitive development of young people, if ingested repeatedly. 

While transforming manure into fertilizer is not a technological challenge, making a profit from it is difficult. In Tema, east of the capital Accra, a new plant is treating excrements using considerably less energy compared to the standard composting technique: it qualified for a government subsidy program and has just began selling its first 50 kilo fertilizer bags. According to economist Solomie Gebrezgabher of the International Water Management Institute (IWMI),the business will turn profitable within the next three years. 

From waste to energy source

According to a 2015 United Nations University report, if all human feces produced every year were converted to biogas, they could power over 138 million households. Once exhausted, they could be dried again to make a fuel that is similar to vegetable coal, which could be used by thousands more. A few companies active in the field of manure recycling in Rwanda have realized this, and they have managed to produce a solid fuel in powder or granule form, that yields 20% more energy than other biomass fuels. 

Solutions from the animal world, from South Africa to India

The Black Soldier fly (Hermetia illucens), a tropical insect, plays a key role in reducing the mass and polluting load of waste and sewage, since they feed on it in their larva stage. Hence, Cape Town firm AgriProtein began farming them, and with the support of the city of eThekwini and the Bill & Melinda Gates Foundation, in 2016 it launched a pilot sewage treatment plant in Durban, the third most populous city in South Africa. Further research could lead to the flies directly purifying the city's sewage system. 

"The potential is high", said Teddy Gounden, Sanitation Manager of the Municipality of eThekwini. "Other governments are waiting to see the outcome of our project". 


To help other cities follow this example, the team of Linda Strande, an environmental engineer at the Swiss Federal Institute of Water Science and Technology in Dübendorf, developed a pamphlet and several online courses designed for local engineers who want to set up systems for the commercial exploitation of human manure. 

Tiger Toilets is an Indian startup that developed a new type of toilet with a price tag of 25,000 rupees (about 300 Euro), using a specific worm (Eisenia fetida) in its drainage system. This technology can protect citizens from the epidemics generated by open sky toilets, and is a great help for women and children who are often forced to dangerously stray away from the city center just to use the toilet.