Composting of sewage sludge with mole cricket: stability, maturity and sanitation aspects

Abstract

The composting of sewage sludge is constrained by structural insufficiencies such as high water retention, reduced free air space and limited compaction. To overcome these hindrances, this study investigates application of bioconversion method to compost sewage sludge. The bioconversion method uses insect mole cricket that provides benefits such as improved aeration by 32%, enhanced organic matter transformation, stability and maturity of the end product. Bioconversion method was compared with vermicomposting and conventional aerated composting methods. Comparison of the results among the three methods showed that the end product was mature with germination index (GI) > 80%, humification index (E4/E6) < 8, dissolved organic carbon < 10 mg kg(-1) and C/N < 15. However, the end product of the bioconversion method had the highest GI of 140, cation exchange capacity of 91.7 and the lowest C/N ratio of 14 indicating that this compost was relatively more stable than the composts produced by the other two methods. The number of faecal coliforms in mature compost samples was 210, 230 and 750 CFU g(-1) for the bioconversion, vermicomposting and conventional composting methods, respectively. The results highlight that bioconversion method produces a non-phytotoxic and microbiologically safe compost that can be considered as a reliable alternative for composting of sewage sludge.