Mesophilic anaerobic digestion of thermally hydrolyzed sludge in anaerobic membrane bioreactor: Long-term performance, microbial community dynamics and membrane fouling mitigation

Thermal hydrolysis (TH) was integrated into an anaerobic membrane bioreactor (AnMBR) to stimulate sludge bioconversion and methane production. Sludge solubilization degree and methane productivity increased with TH temperature. The optimal performance was observed at 125 °C, with a 2.56-time increase in soluble chemical oxygen demand (1116.2 ± 62 mg/L). Methane production rate approached 73.2 ± 7.5 mL/L_reactor/d, rising by 2.96 times. Integration of TH effectively mediated membrane fouling, inducing a stable membrane flux of 10.8 ± 0.5 L/m²/h and low transmembrane pressure (TMP, ≤4.7 kPa). Cake layer deposited on the membrane surface accounted for 66.1 ± 1.0% of total resistance, with proteins and polysaccharides as the main contributors to membrane fouling (or increased TMP) (protein: R_p = 0.89, p_0.05 = 0.04; polysaccharide: R_p = 0.99, p_0.05 = 0.01). 16s rRNA gene analysis demonstrated that utilization of TH could regulate microbial diversity and enhance the proliferation of organics-degrading bacteria (i.e. Bacteroidetes, Firmicutes, etc.) and methane-producing methanogens (i.e. Methanosaeta, Methanobacterium, etc.), which accelerated the biodegradation of organics while alleviating membrane fouling and upgrading methane production. This study demonstrated the great potential of the combined TH-AnMBR system as a new strategy in promoting sludge solubilization, methane bioconversion and membrane fouling mitigation.