Effect of copper ions on glucose fermentation pathways in bioelectrochemical system

Toxic metal ions were previously found to be effective removed by anodic biofilms under the coexistence of organics in bioelectrochemical system (BES). However, the effect of toxic metal ions on the organics fermentation pathways remains unclear. To investigate the pathway systematically, the glucose fermentation pathways were discussed under different Cu²⁺ concentrations. After introducing Cu²⁺, more acetate and less propionate were observed, implying that the metabolic reaction of glucose fermentation altered from mixed acid type to acetogenesis type. This pattern produced more "food" (acetate or hydrogen) for methanogens, thus, the methane content increased by 19.67%, 39.51%, and 27.71% in the presence of 0.1, 1, and 7 mg L^-1 Cu²⁺ compared to the blank, respectively. Increased Cu²⁺ concentrations resulted in the decrease of current production, which was associated with the decrease of electricigen (Geobacter). Consistent with the change of fermentation type, the fermenters (Klebsiella and norank_f__norank_o__Bacteroidales) that related to the production of acetate increased, while the dominant methanogens (Methaospirillum) didn't decrease until the Cu²⁺ concentration reached 7 mg L^-1.