Biogas upgrading and membrane anti-fouling mechanisms in electrochemical anaerobic membrane bioreactor (EC-AnMBR): Focusing on spatio-temporal distribution of metabolic functionality of microorganisms

Abstract

Electrochemical anaerobic membrane bioreactor (EC-AnMBR) by integrating a composite anodic membrane (CAM), represents an effective method for promoting methanogenic performance and mitigating membrane fouling. However, the development and formation of electroactive biofilm on CAM, and the spatio-temporal distribution of key functional microorganisms, especially the degradation mechanism of organic pollutants in metabolic pathways were not well documented. In this work, two AnMBR systems (EC-AnMBR and traditional AnMBR) were constructed and operated to identify the role of CAM in metabolic pathway on biogas upgrading and mitigation of membrane fouling. The methane yield of EC-AnMBR at HRT of 20 days was 217.1 ± 25.6 mL-CH4/g COD, about 32.1 % higher compared to the traditional AnMBR. The 16S rRNA analysis revealed that the EC-AnMBR significantly promoted the growth of hydrolysis bacteria (Lactobacillus and SJA-15) and methanogenic archaea (Methanosaeta and Methanobacterium). Metagenomic analysis revealed that the EC-AnMBR promotes the upregulation of functional genes involved in carbohydrate metabolism (gap and kor) and methane metabolism (mtr, mcr, and hdr), improving the degradation of soluble microbial products (SMPs)/extracellular polymeric substances (EPS) on the CAM and enhancing the methanogens activity on the cathode. Moreover, CAM biofilm exhibits heterogeneity in the degradation of organic pollutants along its vertical depth. The bacteria with high hydrolyzing ability accumulated in the upper part, driving the feedstock degradation for higher starch, sucrose and galactose metabolism. A three-dimensional mesh-like cake structure with larger pores was formed as a biofilter in the middle and lower part of CAM, where the electroactive Geobacter sulfurreducens had high capabilities to directly store and transfer electrons for the degradation of organic pollutants. This outcome will further contribute to the comprehension of the metabolic mechanisms of CAM module on membrane fouling control and organic solid waste treatment and disposal.