Performance of Alternating-Current-Enhanced Anaerobic Membrane Bioreactor: Membrane Fouling, Wastewater Treatment, and CH4 Production

An alternating current (ac)-enhanced (+1.0 V/-1.2 V) anaerobic membrane bioreactor system was constructed (AC-AnMBR) with conductive carbon nanotubes hollow-fiber membranes (CHFMs) as the basic separation unit and electrode, simultaneously. Compared with the other two anaerobic membrane bioreactors polarized by anodic direct current (dc) (+1.0 V, AAnMBR) and cathodic dc (-1.2 V, C-AnMBR), the membrane fouling was obviously mitigated based on the always lower transmembrane pressure. Meanwhile, the cake layer on CHFM from AC-AnMBR (similar to 15.7 mu m) was thinner than those from C-AnMBR (similar to 22.8 mu m) and A-AnMBR (similar to 35.7 mu m) after 40 days of operation. In AC-AnMBR, a barrier of electrostatic repulsion force around membranes with -1.2 V hindered the negatively charged pollutants (mainly extracellular polymeric substances) deposited on the membranes' surface. Then, the electrochemical oxidation provided by positively charged membranes would play a role in oxidizing or mineralizing pollutants for deep fouling removal. Two alternating effects reduced the adhesion of living bacteria, eventually causing a bacterial detachment from membrane surface at the same time. Additionally, AC-AnMBR showed a more than 90% effluent COD removal rate. The CH4 production could stabilize at 210 mL/L.day (COD similar to 1500 mg/L) in AC-AnMBR and CAnMBR, about higher 10 mL/L.day than that in A-AnMBR.

Automated summary

The AC-enhanced anaerobic membrane bioreactor system showed better membrane fouling mitigation compared to DC-polarized systems, with thinner cake layers and the ability to remove deep fouling through electrochemical oxidation. It also effectively reduced bacterial adhesion and improved effluent COD removal rate.