Electrochemical regulation on the metabolism of anode biofilms under persistent exogenous bacteria interference

Abstract

The microbial electrochemical systems (MESs) demonstrate advantages in wastewater treatment for enhanced organic contaminants removal by electron flow. Comprehensive investigation of anode metabolism for fermentable substrate, represented by glucose, under electrochemical regulation was essential to understand the operation mechanism of MESs. The anodic COD (chemical oxygen demand) degradation reaction w simulated as a superposition of first-order (background COD remove) and zero-order reaction (anode-respiring COD remove) to COD concentration. Even though the background COD degradation wasn’t directly related with anodic respiration to form electron flow, it was accelerated by increasing current rather than the changed electrode potentials. Statistically, the kinetic constant of background COD degradation generally exhibited a positive linear correlation (R2 = 0.7822) with current. In overall COD removal increment enhanced by electron flow, the improvement of background COD degradation accounted for a relatively stable proportion of 33%. The anode-respiring and background metabolism successively exhibited competition (100–500 mg L−1) and synergy (500–1500 mg L−1) with increasing COD concentration, before being restricted by excessive COD loading (above 1500 mg L−1). The stratification and function differentiation were observed in anode biofilm. The dark-red dense inner layer close to anode surface was directionally enriched anode-respiring bacteria (ARB) like Geobacter (16.23%) and Pseudomonas (13.04%), while the white incompact outer layer separated inner layer from exogenous bacteria interference as a transition layer and assisted for the degradation of fermentable substrate. The anode biofilm helped for the progressive degradation of glucose and the formation of stable electrochemical active inner layer under persistent exogenous bacteria interference.