Integrated composting–vermicomposting process for stabilization of human faecal slurry

In the present study, feasibility of an integrated composting–vermicomposting process is assessed for stabilization of human faecal slurry using matured vermicompost as bulking material and Eisenia fetida as earthworm species. A preliminary study showed the dominant role of relative humidity over temperature on the water loss from the slurry–vermicompost mixture. The composting stage, spanning 5 months, produced sufficient enrichment of bulking material with organic matter after 20 cycles of recycling and mixing with faecal slurry, and produced materials acceptable for vermicomposting under ambient conditions. Vermicomposting of composted material was conducted for a duration of six months with a stocking density of 3.0 kg/m2. Vermicomposting resulted in significant reduction in volatile solids (from 527 to 340 mg/g dry weight), oxygen uptake rate (from 29.40 to 0.82 mg-O2/g/h), total carbon (43%), total organic carbon (41%), and significant increase in total phosphorus (from 14.0 to 20.5 mg/g dry weight) and potassium (24.8–54.3 mg/g dry weight). No total coliforms, faecal coliforms, Salmonella and viable helminth ova were detected in the processed vermicompost. The results of the study indicated the potential of the integrated composting–vermicomposting system for converting human faecal slurry into organic manure.