Solid State Culture Conditions for Composting Sewage Sludge

Composting is applied to treat sewage sludge from treatment plants to enhance its quality and suitability for agricultural use. In this work the optimal conditions for composting sewage sludge from domestic wastewater treatment plants in a horizontal drum bioreactor (HDB) were investigated. This study investigated the physico-chemical conditions affecting the use of filamentous fungi in composting. The average number of faecal coliforms was 2.3 107 bacteria/g waste dry weight at the beginning of the composting process, and decreased considerably to 8.2 103, 8.1 103, 8.5 103, 8.0 103,and 8.4 103 bacteria/g, respectively for experiments T1 to T5. This decrease was presumably the result of raising temperature. The phase of hygienisation was marked by a very significant decrease in the number of E. coli cells (1.8 107, to 3.7 103, 3.8 103, 3.3 103, 3.2 103, and 3.6 103 bacteria/g) for T1 to T5 experiments, respectively: A second aspect was the investigation of a possible reduction of hazardous pollutants. The highest concentration was for Fe and the lowest for Pb, showing that Fe is the most loosely bound to the sewage sludge organic matrix and Pb the most strongly bound, the Cd reduction by composting was more than 50%. Keywords: Sewage sludge, compost, horizontal drum bioreactor, hazardous