Abstract
Anaerobic membrane bioreactors (AnMBRs) can alleviate the inhibitory effect of sludge calcification on anaerobic process when treating high-calcium wastewater. However, sludge calcification induced by high-calcium wastewater and flocculated sludge formation under reactor aeration shear will inhibit membrane filtration performance. In this study, an intermittently operated AnMBR (A2) was used to treat high-calcium wastewater, and continuously operated AnMBR (A1) was used as the parallel control. When treating 200–1000 mg/L calcium ion wastewater, A2 achieved a stable chemical oxygen demand removal efficiency of 91.8±3.9 %. The methane production of A2 was 188.2±22.5 mL/(gVSS⋅d), which was marginally higher than the continuous AnMBR (A1) methane production of 174.7±11.7 mL/(gVSS⋅d). Analysis of the microbial community demonstrated significant enrichment in hydrolyzing acidifying bacteria and archaea in A2, compared to A1, which played a crucial role in improving the performance of anaerobic process. A1 exhibited a maximum transmembrane pressure (TMP) of 19.6 kPa, and scanning electron microscopy (SEM) analysis revealed the deterioration of membrane fouling due to sludge calcification on the membrane surface. Surprisingly, the maximum TMP of A2 was just 3.6 kPa during the study. When treating 1000 mg/L of high calcium wastewater, the average effluent calcium concentration in A2 was 650 mg/L, which indicated that A2 effectively retained calcium ions. SEM analysis revealed that anaerobic sludge had a tendency to agglomerate, which slowed down membrane fouling in A2. Sludge agglomeration was due to intermittent operation effectively increasing the contact time of sludge with calcium ions, thereby stimulating the protein secretion of extracellular polymers. These results showed that the intermittent operation effectively mitigated membrane fouling. This work provides a new strategy for comprehensively addressing the challenges of high-calcium wastewater and achieving the stable performance of anaerobic reactors.
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