Hydrothermal pretreatment of sewage sludge enhanced the anaerobic degradation of cationic polyacrylamide (cPAM)

Cationic polyacrylamide (cPAM) is a widely used flocculant to dewater sewage sludge (SS) for high-solids anaerobic digestion (AD), and its degradation is crucial since it would release toxic acrylamide (AM) once entering environment. Hydrothermal treatment (HTT) is an efficient method to enhance the AD efficiency of SS. However, the effects of cPAM on AD of SS and the degradation of cPAM during HTT-AD process have not be studied. The study showed cPAM at 20 mg/g TS increased methane yield of SS from 127.0 to 138.9 ml CH4/g TS in HTT-AD process, and the biodegradability of cPAM was 76.3%, which was much higher than that (7.4%) without HTT. In HTT-AD process, the enrichment of certain microbes (e.g. Gelria sp.) was observed, which might be related with cPAM degradation. HTT decreased the molecular weight (MW) of cPAM, and resulted in the production of 2-hydroxy-ethyl-trimethylammonium, ammonia, trimethylamine, and ethanol. Methane potential tests of the main HTT products also showed they were easily to be degraded. Overall, HTT-AD integrated process was an efficient method to reduce environmental risk of cPAM as well as increase energy output (biogas), and the study also provided insights into the degradation mechanism of cPAM during HTT. (c) 2020 Elsevier Ltd. All rights reserved.