Characterization of activated sludge from domestic sewage treatment plants and their management using composting and co-composting in aerobic silos

In this work,the physico-chemical characteristics of activated sludge from domestic sewage treatment plants were first determined. the composting of waste activated sludge alone (100% w/w) and in presence of sawdust (25% w/w) during nine months was then investigated. aerobic fermentation was monitored during the first month in reactors. after that,samples were transferred in perforated bags for eight months to reach maturation. two aerobic composting reactors (silos) were used simultaneously and under the same conditions (air-flow 20 l/h and external ambient temperature 25±2°c). in order to control biotransformation processes,composting was monitored by determining physico-chemical and microbiological parameters. the evolution of the parameters analyzed (temperature,moisture,ph,organic matter,c/n ratio,nitrogen and carbon) during the nine months of composting process demonstrate the stability and maturity of obtained compost. in the system without sawdust material,the maximum temperature was 40°c. however,the mixture sludge/sawdust 75:25 reaches thermophilic conditions with a maximum temperature of about 58°c,thus providing a best degradation. according to germination index,waste activated sludge mixed with the aforementioned carpentry waste provided compost with visibly positive properties for agricultural use. the addition of sawdust to sludge decreases considerably the number of coliforms in compost; this is mainly due to the effect of dilution and to the level of temperature reached.