Leveraging Anaerobic Digestion Solids Retention Time to Mitigate Recalcitrant Dissolved Organic Compounds Formed during the Maillard Reaction at Various Thermal Hydrolysis Temperatures

Abstract

Recalcitrant dissolved organic compounds formed during thermal hydrolysis pretreatment (THP) of municipal wastewater sludge pose a challenge to water resource recovery facilities (WRRFs) that seek to achieve stringent discharge standards. This study investigated the effects of anaerobic digester solids retention time (SRT) at 15 and 23 days on the aerobic recalcitrance of Maillard reaction-derived dissolved organic compounds formed during THP operated at temperatures of 135, 150, and 165 °C. Over 460 days of continuous THP and anaerobic digester operation, results revealed that digester SRT strongly influenced the biodegradability of these THP-derived recalcitrant dissolved organic compounds. In particular, extending the digester SRT from 15 to 23 days enhanced the degradation of these compounds that can be resistant to aerobic degradation but biodegradable under anaerobic conditions. Furthermore, using a digester SRT of 23 days to treat sludge produced from lower upstream THP temperatures (e.g., 135 °C) resulted in more effective aerobic degradation of such dissolved organic compounds. This study highlights the previously overlooked but pivotal role of digester SRT in managing THP-derived recalcitrant compounds in WRRF effluent, providing an additional operational lever beyond the THP temperature for mitigating sidestream impacts under different treatment priorities.