Anaerobic Transformations of Wastewater Organic Matter in Sewer Systems

Anaerobic transformations of wastewater organic matter in the bulk water phase of sewer networks were investigated in laboratory scale experiments. The wastewater was collected from 3 locations, providing wastewater samples with different characteristics, ranging from fresh to mature. Hydrolysis, fermentation and sulfate reduction were identified as the main processes. Significant quantities of readily biodegradable substrate were produced by hydrolysis and fermentation, although fermentation was found to be generally limited by hydrolysis. The readily biodegradable substrate generated was almost entirely composed of the VFAs acetic acid and propionic acid. A production of sulfide was observed in all experiments, demonstrating that part of the readily biodegradable substrate was consumed by sulfate respiration. The sulfide production was most pronounced in mature wastewater that had previously undergone anaerobic transport. These processes that occur in the bulk water phase can significantly affect the quality of the wastewater which may impact the subsequent wastewater treatment.