Methods for estimating quantities and qualities (Q&Q) of faecal sludge: field evaluation in Sircilla, India

Estimates of accumulated quantities and qualities (Q&Q) of faecal sludge are essential for developing city-wide management plans. However, standardized approaches are lacking, and examples in scientific literature make use of diverse methodologies and parameters, making their comparability and transferability difficult. This study field-tested an approach for estimating Q&Q in Sircilla, India, and compared three methods for measuring accumulated sludge: (1) faecal sludge accumulation rate from in situ measurement with a core sampler; (2) faecal sludge accumulation rate with volume emptied by desludging truck; and (3) sludge blanket accumulation rate in situ with a core sampler. Measurements were taken at households and commercial establishments, samples were analysed for characteristics, and demographic, environmental, and technical data were collected with a questionnaire. The median total solids (TS), volatile solids (VS), and chemical oxygen demand (COD) concentrations for all containments were 26.8, 17.8, and 32.0 g/L, respectively. The median faecal sludge accumulation rate estimated with the core sampler and truck were 53 and 96 L/cap·year, respectively. The median sludge blanket accumulation rate was 17 L/cap·year. Continued data collection in this fashion will lead to a better understanding of what is accumulating in onsite containments at regional levels. HIGHLIGHTS Comparison of methodologies to estimate the total faecal sludge and sludge blanket accumulation rate.; The selection of Q&Q measurement methods should be based on defined objectives and available resources.; Q&Q studies conducted in this fashion will lead to more locally relevant accumulation rates than standard values.