Effect of temperature and solids retention time on the removal of antibiotic resistance genes during anaerobic digestion of sludge

This study investigated how anaerobic digestion (AD) of sludge under different operating temperatures (35 °C and 55 °C) may respond to changes in solids retention time (SRT = 20, 30, and 40 days) in terms of the removal of antibiotic resistance genes (ARGs) and biogas production. It was observed that at short SRTs (20 days), ARGs in thermophilic AD (TAD) were less abundant than in mesophilic AD (MAD) with a higher removal rate of 75.80 % vs. 45.78 %, respectively. At longer SRTs (30 and 40 days), the removal of ARGs in MAD increased to 51.79 % and 79.63 % while it decreased to 53.95 % and 24.65 % in TAD. These findings indicate that MAD needs longer SRTs to remove more ARGs, while thermophilic reactors are more effective at shorter SRTs. Moreover, 34–42 % more biogas was produced at thermophilic conditions relative to mesophilic conditions at different SRTs, suggesting that shortening the SRT and increasing the temperature are effective strategies for producing biogas.