Fouling dynamics varied by filtration cycles in high-solid anaerobic membrane bioreactors for sewage sludge treatment

Anaerobic membrane bioreactors (AnMBRs) are highly effective in treating sewage sludge (SewS) by promoting the rate-limiting hydrolysis process through biosolids concentration. The treatment of SewS in this study by the high-solid AnMBR achieved an exceptional COD removal efficiency of 99.1 % and a substantial bioenergy yield of 157.8 mL-CH₄/g-COD_add. However, membrane fouling remains a critical challenge, restricting the long-term stable operation of high-solid AnMBRs for SewS treatment. To address this challenge, membrane filtration performance was evaluated under various combinations of instantaneous flux and filtration/relaxation ratios (F/R). The optimal F/R was identified as 3:1 (min/min), effectively mitigating membrane fouling and maintaining a total resistance of at least 7.20 × 10¹² m^-1, where the flux maintenance efficiency of this filtration cycle peaked at 94.7 % for 4 h. An empirical model describing the relationship between filtrate volume and ΔTMP was established as ln(ΔTMP) = k ⋅ ln(v) + b, exhibiting high coefficients of determination. The influence of filtration cycles on membrane fouling rates was analyzed through the power-law model. Furthermore, real-time transmembrane pressure (TMP) curves were utilized to identify fouling types based on the constant-flux filtration models (dp/dv = k'pⁿ^'). Filtration cycles with high instantaneous flux (16.68-23.60 LMH) and extended relaxation periods (2-3 min) predominantly exhibited cake layer formation, whereas cycles with lower instantaneous flux (7.40-11.79 LMH) and shorter relaxation periods (1 min) were more prone to intermediate pore blocking. This study provides mechanistic insights into the optimization of filtration process in engineering applications, paving the way for the long-term sustainable operation of high-solid AnMBR systems.