Decentralized faecal sludge management in rural India by integrating drying beds for dewatering and coagulation for leachate treatment: A sustainable, cost-effective, nature-based solution

Abstract

Discharging untreated faecal sludge (FS) from on-site sanitation into the environment poses environmental and public health risks in semi-urban and rural areas of India. Therefore, designing a low-cost, resource-efficient, sustainable, and effective FS treatment system is crucial. This study investigated a hybrid treatment approach combining planted and unplanted drying beds for FS dewatering, followed by leachate treatment using natural coagulants, Moringa oleifera and chitosan. The planted and unplanted drying beds achieved removal efficiencies of 95.84 % and 94.47 % for total solids, 98.09 % and 97.71 % for chemical oxygen demand, 93.46 % and 91.17 % for biochemical oxygen demand, 95.09 % and 86.85 % for total phosphorus, 80.04 % and 71.71 % for total nitrogen, and 99 % and 97.71 % for E. coli, respectively. The macrophyte Nerium oleander, planted in the drying bed, exhibited healthy growth under FS loading conditions, with the plant height increasing from 0.75 m to 1.8 m, indicating its potential for phytoremediation and resilience. The natural coagulants M. oleifera and chitosan achieved 95.77 % and 96.29 % turbidity removal, and 81.67 % and 84.17 % COD removal, respectively. The dried FS exhibited C/N ratios of 8.56 (planted) and 7.16 (unplanted), alongside favourable organic matter and nutrient content, indicating its suitability for organic manure. The calorific value of the dried sludge was 14.76 MJ/ kg (planted) and 15.93 MJ/ kg (unplanted), suggesting potential for use as solid fuel. This treatment system can provide a sustainable FS management solution for rural areas of India, as it achieves overall treatment goals and enables resource recovery.