Anaerobic degradation of pesticide wastewater: Improving sludge characteristics and reducing membrane fouling with combined tandem UASB+membrane system with high velocity settlers

•Proposing a combined system for the effective treatment of pesticide wastewater.•Biogas production increased by 26.48 %, achieving a higher energy recovery rate.•The membrane fouling was delayed by 19-22 % and the membrane life was extended.•The trends of membrane fouling with EPS content were illustrated. In this pilot study, a combined tandem UASB+membrane reactor (R2) with high velocity settlers was proposed for the treatment of pesticide wastewater at different hydraulic retention times (HRT) and compared with a control reactor (R1). The average COD removal efficiencies of the R2 at HRTs of 96, 72, and 48 h were 83.7 %, 82.8 %, and 74.2 %, which are 14 %, 17 %, and 21 % higher than those of the R1, respectively. Throughout the operation, the biogas production of R2 was 33 %, 19 % and 28 % higher than that of R1 at the same stage, respectively, and the methane yield of R2 (0.19-0.26 L CH4/gCODremoved) was improved by 10-17 % compared to that of R1. Mean α values (VFA/ALK) of 0.13∼0.22 indicated that R2 did not undergo acidification. R2 reduced the extracellular polymers (EPS) content in the attached sludge by 56-62 % compared to R1. It also successfully delayed membrane fouling rate by 19-22 %. The results demonstrate that the R2 has a high treatment capacity, stability, and methane recovery, while also effectively reducing membrane fouling. [Display omitted]