**14.2 Effect of anolyte pH**

## *14.2.1 MFC operation without pH buffer*

Anolyte system using a 10 mM concentration phosphate buffer (pH 6.9) reduces the initial anolyte concentration to 7.2 showing a gradual reduction of pH to 6.9 in 8 days. Utilizing orthophosphoric acid, the pH was set to 7 when the device was run in the absence of buffer. The pH variations were found to be crucial in the absence of buffer. In the absence of a buffer system, the MFC pH gradually increased to 7.51 on the 3rd day, and then fell to 7.03 on the 6th day. Though the efficiency of treatment and OCV was the same, a clear difference was observed in system polarization. The MFC's average power density without buffer was 85.97 mW/m<sup>2</sup> which was almost half the system output using a buffer configuration for 161 mW/ m2 of pH maintenance. The requirement of 8-day batch time for both reactors for 90% COD reduction demonstrated that the pH buffer removal did not affect the bacterial activity. In MFC, the citrate and phosphates remain as proton carriers. While for these carriers the diffusion coefficient is smaller, the concentration gradient is higher across the membrane. In cathode chamber, the concentration gradient is higher due to the deficiency of citrate and phosphates. Due to improved

proton transfer, the internal resistance was typically reduced due to polarization of the concentration of protons, thereby increasing the output of power in the system using pH buffer. Phosphate buffer system has a wonderful impact on the electricity generation by altering the electrochemical reactions although it has not affected MFC's microbial growth and efficiency in COD removal. The higher anolyte power density may be attained at pH 7 [8].
