Estimating qualities and quantities of faecal sludge to determine resource recovery potential : A case study in Phnom Penh, Cambodia

Abstract: A paradigm shift to convert faecal sludge into resources could minimise environmental pollution and public health risks in cities in low- and middle-income countries (LMIC). To support faecal sludge management planning at city scale, this thesis investigated resource recovery potential from faecal sludge, using Phnom Penh as a case and focusing on waterborne systems. Methods used were faecal sludge sampling and analysis, stakeholder interviews, observations and multi-criteria assessment.  Resource recovery potential from faecal sludge in Phnom Penh was found to be limited. Many quality parameters in faecal sludge were low compared with previously reported values, owing to dilution effects of high prevalence of waterborne toilets, addition of water during emptying events, mixed wastewater capture by containment units and connection of containment units to the urban drainage network. Concentrations of two heavy metals (mercury and zinc) exceeded the limits in the Cambodia standard for organic fertiliser and Swedish standard for compost. The highly diluted nutrient content and relatively high heavy metal contamination in faecal sludge limit its reuse potential. However, reuse of sludge could capture around 65 tons of total nitrogen and 13 tons of total phosphorus annually instead of allowing these nutrients to enter natural wetlands.  Three options to tackle the current challenges in faecal sludge management in Phnom Penh were identified: (i) short-term: use of treated faecal sludge as soil conditioner for public green space; (ii) medium-term: upstream source control to prevent contamination of sludge; (iii) long-term: source separation. Solar drying and vermicomposting are appropriate technologies for short-term solutions and co-composting, larval composting and vermicomposting for medium-term solutions, after implementing upstream source controls. For long-term solutions, extensive research on appropriate technologies is needed. Overall, the best option will depend on relative weighs of sustainability criteria and trade-offs for sector stakeholders. These findings can assist sector stakeholders in Phnom Penh and other LMIC cities with similar sanitation systems in improving faecal sludge management.

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