Safe resource recovery from faecal sludge: evidence from an innovative treatment system in rural Tanzania

Abstract

Globally, innovative treatment systems are needed to incentivise safe faecal sludge management practices and resource recovery. In rural Tanzania 83% of the population do not have access to basic sanitation. Communities rely on on-site sanitation (pit latrines) that are not safely managed and allow for faecal sludge to contaminate groundwater used for drinking. This study reports on the design and evaluation of a novel treatment system; dewatering of faecal sludge in solar drying beds, followed by capturing of faecal sludge leachate and leachate heat sterilisation using a rocket stove fired with agricultural waste. Faecal sludge was manually extracted from 25 pit-latrines in rural Tanzania and analyzed at 0.5 m depth profiles. For aged latrine sludge (1.5 m deep) the ratio of total volatile solids to total solids halved, indicating stabilization. However, densities of Escherichia coli remained elevated (5.6 × 10⁴ cfu g⁻¹). Extracted sludge was loaded (∼0.9–1.35 m³) into drying beds for 21 days and final E. coli densities were highly variable. The leachate was captured from drying beds in 150 L batches and took 40 min to heat to 98 °C in the rocket-stove with a rice husk fuel feeding rate of 48 kg h⁻¹. Heat treatment of leachate completely inactivated 3.1 × 10⁵ cfu/100 ml of E. coli (5.5 log₁₀ reduction) and reduced total coliforms by 99.9% (3.1 log₁₀); reaching safe guideline values for unrestricted agricultural reuse. Thus, the stove is an innovative low-cost technology for treatment of faecal sludge for rural communities in developing countries that produces faecal products that can be safely used in agriculture.