**14.6 The effect of external resistance**

*Environmental Issues and Sustainable Development*

density may be attained at pH 7 [8].

**14.3 Substrate concentration**

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

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

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

The operating time was longer at low temperatures than that at high temperatures, but the voltage generation at high temperatures (30 and 35°C) was higher [100, 101]. The peak current and voltage intensity was measured at 35°C. Decreasing voltage, output and current intensity may occur for a variety of reasons. As temperature rises, the biochemical reactions, bacterial metabolism, and bacterial growth rate increases, leading to rapid bacterial growth and better voltage efficiency. Nonetheless, during long processing periods while bacteria are at high temperatures, essential cell's compounds like nucleic acid and other temperaturesensitive material can be irreversibly impaired, resulting in extreme cell function degradation or death. The voltage and current strength decrease drastically in this case. The slow bacterial growth rate at low temperatures often leads to a reduction

in the bacterial population and activity and voltage output decreases [102].

A number of studies on the generation of electricity by MFCs have also shown that amount of current generated in both closed and continuous MFC depends upon organic loadings. The MFC research analyzed various organic loadings and measured their effects on current and power during service. During the 30 days of operation, the maximal current and power density was achieved in OLR equal to 53.21 kg COD/

d. This is because the MFC requires more time at low OLR to achieve the optimum current and power density. But in greater OLR, maximal current and power density

improved with an increased substrate concentration.

**14.5 The effect of organic loading rate (OLR)**

**14.4 The effect of temperature**

) was

**118**

m3

Higher external resistance results in diminished power density. Therefore, MFC has to be constructed with lower external resistance for better performance. In other words, the voltage rises as the resistance increases, and the current decreases. The voltage produced decreases from 0.855 to 0.319 V when the external resistance increases from 1 to 25 KΩ. The decrease in voltage indicates that processes other than cathodic reactions used some electrons [1]. Low voltage may be due to a reduced rate of usage of electrons in the cathode with high electrical resistance relative to the rate of transfer from the external circuit. It is acceptable that the ejection of electrons via the circuit reduces as the resistance of a circuit increases. Electrons in the cathode have been used to eliminate other electron receptors from the cathode, like sulfate, permeable oxygen, or nitrate. Electrons quickly pass through the external circuit at lower external resistance and oxidize the electron carriers in the anodic chamber on the external membrane of the microorganism. Maximum power density is also obtained in MFC systems where internal and external resistances are equivalent. Differences in MFC output with varied external resistances can be due to differences in activation losses at the anode, which is a result of the electrochemical behavior of the microorganism-reducing anode [103].
