**14.3 Substrate concentration**

The concentration of the substrate in the anode chamber has a significant effect on microbial development. The MFCs were run using an anaerobic metabolism buffer system with an initial pH of 7 anolytes. The substrate concentration varied as a function of COD concentration (800, 1600, and 2800 mg/L). A remarkable variation in the overall OCV obtained by the MFC could be observed. MFC having COD concentration of 1600 mg/L reported a maximum OCV of 760 mV. Operating system with 800 and 2800 mg/L COD concentration achieved maximum OCV of 656 and 612 mV. MFC working with COD concentration of 800, 1600, and 2800 mg/L had a batch time requirement of 6, 7, and 11 days. The peak power density (161 mW/m2 ) was reported at 1600 mg/L COD concentration and is 2.5 and 1.8 fold lower for 800 and 2800 mg/L COD operating MFCs. The columbic efficiency was 2.6 and 1.7 folds lower for MFC with 800 and 2800 mg/L, respectively, compared to MFC at 1600 mg/L COD concentration having 17.16%. The use of wastewater with higher COD results in a reduction in electricity generation, which may be due to microbial growth inhibition mediated by substrates. A dramatic decrease in power output occurred when 800 mg/L of initial COD concentration was used. Power generation decreased with a decline in the initial concentration of the substrate [99]. The initial COD variance did not influence the effluent quality of the MFC, although the duration of treatment improved with an increased substrate concentration.
