Fate of sterols, polycyclic aromatic hydrocarbons, pharmaceuticals, ammonia and solids in single-stage anaerobic and sequential anaerobic/aerobic/anoxic sludge digestion

Abstract Emerging contaminants (ECs), such as pharmaceuticals, sterols and polycyclic aromatic hydrocarbons (PAHs) are frequently detected in the environment. ECs are refractory, toxic, tend to bioaccumulate and have a potential to disrupt the endocrine system of living organisms. These compounds are only partially eliminated in wastewater treatment plants (WWTPs). Due to their hydrophobic nature, they tend to accumulate in sludge. However, the fate of the majority of ECs in sludge treatment processes is not fully understood. In this study, the effect of a sequential anaerobic/aerobic/anoxic (AN/AERO/ANOX) digestion and a conventional single-stage AN digestion (as control) was investigated on mixed primary and secondary sludge. Digesters were operated at an overall solid retention time (SRT) of 18 days. The steady-state results have shown that sequential AN/AERO/ANOX digestion configurations improved the removal of three classes of ECs (e.g., sterols, PAHs and pharmaceuticals) by either reducing their accumulation or enhancing their removal. Moreover, sequential AN/AERO/ANOX digestion also achieved 45% less ammonia generation, 20% faster digestate dewaterability and 4% enhanced volatile solids removal compared to single-stage AN digestion.