Valuing Human Waste as an Energy Resource. A Research Brief Assessing the Global Wealth in Waste

Reducing by half the proportion of untreated wastewater has been established as a target in the UN’s recently released Agenda 2030 for sustainable development (Goal 6.3). Staggering volumes of wastewater are discharged into receiving waters each year, and as much as 90% of the wastewater is discharged untreated (Corcoran et al., 2010). Meanwhile, almost 1 billion people defecate in the open, and approximately 2.4 billion people do not have access to proper sanitation (UNICEF and WHO, 2015). Failing or inadequate septic, collection, and treatment systems further exacerbate poor water quality conditions worldwide. Three main problems plague sanitation and the operation and maintenance of wastewater treatment systems: 1. Large up-front capital costs associated with infrastructure; 2. Financing the operation, maintenance, rehabilitation, and expansion; and, 3. Providing incentives for use. Given a global mindset that sees this waste as an expensive liability, it is all too common to neglect its potential value as a resource. As the saying goes, necessity is the mother of invention, and water scarce regions are driving the interest in wastewater reuse, particularly to expand marginal agricultural lands (Sato et al., 2013). However, pilot projects reveal a missed opportunity to utilize faecal sludge, particularly for rural areas and small towns. Human waste, as with all organic matter, contains nutrients, as well as thermal heat value, since it is combustible when dry. Nutrient values in human excreta vary with age and diet. Ek et al. (2006) suggest a normalised nutrient breakdown in urine of 3600 g of nitrogen per m3, 310 g of phosphorous per m3, 900 g of potassium per m3, and 300 g of sulphur per m3, based on a Swedish population. The nutrients in the urine from one person in a year are sufficient to provide 50-100 kg N/ha for a crop area of up to 400 m2 (Richert et al., 2010). Faecal sludge contains fewer nutrients than urine, estimated at 548 g of nitrogen, 183 g of phosphorus, and 460 g of potassium per person, per year (Vinnerås and Jönsson, 2002). Taken together, “black water” or urine plus faeces has a general nutrient value of 4550 g of nitrogen and 548 g of phosphorus per person, per year (Richert et al., 2010). The nutrient value in human waste for food production has been well-documented, both in terms of the benefits to crop productivity (for example, a 2-6 fold increase in relative yield, depending on the crop type) and cost benefit analysis (Richert et al., 2010). Human waste is utilised for food production in various forms around the world, with guidelines for ensuring its safe use (WHO, 2006). The potential energy value of human waste has been given less attention to date and its benefits are less likely to be appreciated. There are two potential sources of energy from human waste. “Biogas” is generated through anaerobic (oxygen free) digestion through bacteria breakdown of faecal matter and any other organic material. Biogas is approximately 60% methane by volume and has an average thermal value of 25MJ per m3 (Cao and Powlowski, 2012). Dried and charred faecal sludge has been found to have similar energy content to coal and charcoal, with a heating value of approximately 25 MJ/kg, depending on the temperature at which charring occurs (Ward et al., 2014). This is an extremely important observation. While biogas has been harnessed in many large municipal wastewater treatment plants, and some countries have undertaken concerted (and successful) efforts to develop household biogas systems using either animal or human faeces, there has been little uptake of processed faecal sludge as an alternative to coal and charcoal. Given that the global production of fuelwood reached 1.9 billion cubic metres in 2013 (World Bioenergy Association, 2015) and that deforestation is contributing to soil and land degradation, as well as declining water quality, the use of dried sludge as an alternative energy source is a significant social, environmental, and economic opportunity. In this context, a “Waste to Wealth”1 national framework for Uganda was developed by UNU-INWEH with a seed grant from federally-funded Grand Challenges Canada and in partnership with the Ugandan Ministry of Water and Environment, its agencies, and other NGO and academic partners. Waste to Wealth modern bioenergy technologies to convert human and other organic wastes into resources that provide economic benefits, as well as protecting the environment and human health. It is founded in the application of anaerobic digestion technologies linked to sanitation systems. With a focus on rural growth centers and small towns in Uganda, as well as high population density institutions such as schools and prisons, the biogas and residual material left from energy conversion will be used as a resource with economic value to provide the return on investment necessary to improve sanitation. The ultimate goal of Waste to Wealth is self-financing and sustaining decentralised (on site) faecal waste management in Uganda. By identifying the value in waste for energy and/or fertilizer, Waste to Wealth provides an incentive to use toilets and a mechanism to finance the capital costs as well as operation, maintenance, and expansion of sanitation infrastructure. In addition to the economic opportunities, sanitation interventions have known benefits to individual, household, and community health and wellbeing (Hutton, 2015).

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