Biogas from toilet waste in Nepal

Blog post by Natalie Boyd Williams

Dr Jen Dickie and her PhD student Natalie Boyd Williams travelled to Nepal in August to interview users of domestic toilet-linked anaerobic digesters.  It is estimated that 2.5 billion people, mostly in Asia, use traditional biomass fuels such as wood, animal dung (dung cakes) and crop residue. Each year, close to 4 million people die prematurely from illness attributable to household air pollution from inefficient cooking practices. Inadequate sanitation is estimated to cause 432,000 diarrhoeal deaths annually and countries where open defaecation is most prevalent, have the highest number of deaths of children aged under 5 years as well as the highest levels of malnutrition and disparities in wealth (WHO Factsheets). Where sanitation is provided it is often without emptying, transport and treatment services which results in a build-up of toxic waste.

Anaerobic digestion (AD) transforms organic waste into biogas, a flammable clean fuel and digestate, a nutrient-rich fertiliser. AD fundamentally realigns flows of nutrients, water, energy and finance helping to achieve more sustainable livelihoods.  Linking a toilet to an anaerobic digester means that households can produce additional biogas and manage a toxic household waste.  The researchers wanted to determine whether users of toilet-linked AD were actually using the connection and therefore the biogas and the digestate, as such products were considered dirty and unacceptable by many.  They found that the key motivation was the actual toilet provision, showing that ADs were not only accepted by households, but highly valued – important information regarding people’s decision making around the ADs and the use of excreta derived products.