Use of faecal pollution indicators to estimate pathogen die off conditions in source separated faeces in Kathmandu Valley, Nepal

As the introduction and promotion of dehydrating toilets progresses, the safety of handling and reuse of their biosolids remains a question. A detailed study to understand the storage conditions and the fate of selected faecal indicators was conducted on four urine diverting dehydrating toilet units, using ash as a major additive, in Kathmandu Valley, Nepal. Presumptive Escherichia coli, total coliforms, enterococci and different fractions of Clostridium perfringens were investigated under field storage conditions. In addition, chemo-physical and chemical (carbon, nitrogen, phosphorous content) parameters were investigated. Observed temperature was low in all the four toilets with a median of 24.0°C, which was in the same range as the ambient temperature. pH was below the desired range of >9 and moisture level was very high (>60%). No single factor of the studied chemo-physical and chemical parameters could be found by statistical analysis to have accounted for the reduction of the indicators in any of the toilets. By time series analysis of the investigated strata in the faecal heaps (n = 96), the determined reduction rate showed increasing persistence characteristics for E. coli, coliforms and enterococci with respective average log₁₀ reduction of -0.4, -0.3 and -0.2 per month ( p < 0.001). No significant reduction was observed for the different fractions of C. perfringens determined for the non-pasteurised and pasteurised fraction at 60°C and 85°C. 72% of randomly selected and analysed samples (n = 36) were found to contain helminthes eggs. The used 6 months storage time did not prove sufficient to reach appropriate safety levels for handling and reuse of the biosolids.