Efficiency of autothermal thermophilic aerobic digestion and thermophilic anaerobic digestion of municipal wastewater sludge in removing Salmonella spp. and indicator bacteria

The study is focused on the comparison of autothermal thermophilic aerobic digestion, thermophilic and mesophilic anaerobic digestion, based on long term monitoring of all processes in full-scale wastewater treatment plants, with an emphasis on the efficiency in destroying pathogens. The hygienisation effect was evaluated as a removal of counts of indicator bacteria, thermotolerant coliforms and enterococci as CFU/g total sludge solids and a frequency of a positive Salmonella spp. detection. Both thermophilic technologies of municipal wastewater sludge stabilisation had the capability of producing sludge A biosolids suitable for agricultural land application when all operational parameters (mainly temperature, mixing and retention time) were stable and maintained at an appropriate level.