# Performance of the Dual-Chamber Fungal Fuel Cell in Treating Tannery Wastewater
## 2 Materials and Methods
### FFC Performance  
In two studied FFCs, operations were studied for a treatment time of 165 h. Along with different external resistances ranging from 10 to 20,000 \(\Omega\), the internal resistance decreased in the electrolytic cell reaching 65 \(\Omega\) while the non-electrolyte one was 110 \(\Omega\). For an external resistance 1000 \(\Omega\) and time interval from 15 h to 165 h, the energy output of the electrolytic cell showed an obvious increase compared to the non-electrolyte one. The voltages and power output were gradually decreased along with time according to substrate availability and the level of oxidation/reduction reactions until the power output became stable at 165 h of operation, as shown in Table 4. The rate of decrease in the electrolytic cell was less than that of non-electrolyte cell due to the presence of electrolytes, and in accordance with the change in voltage [46]. The decreasing rate of power activity showed an increase after 90 h for the non-electrolyte cell while it was after 105 h for the electrolytic cell. At 105 h of operation, the electrolyte FFC had a voltage output of 0.613 V, PD of 0.055 mW \(\times\) m\({}^{-2}\), and CD of about 0.089 mA \(\times\) m\({}^{-2}\) while the non-electrolyte FFC \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline _A. niger_ & **Q\({}_{e}\)** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** & **[PERSON]** \\ \hline \multirow{4}{*}{Trained} & 9.7 & 5.2 & 7.2 & 7.2 & 7.3 & 2.6 & 3.1 & 6.3 & 6.1 & 2.8 \\  & 22.7 & 23.4 & 24.2 & 24.2 & 24.2 & 18.2 & 20.7 & 23.8 & 24.0 & 19.6 \\  & 43.6 & 44.8 & 44.4 & 44.4 & 44.3 & 42.1 & 45.5 & 44.9 & 44.4 & 45.2 \\  & 63.6 & 62.9 & 62.4 & 62.4 & 62.3 & 62.1 & 64.6 & 62.9 & 62.3 & 65.2 \\  & 81.8 & 81.8 & 82.1 & 82.1 & 82.1 & 80.1 & 80.7 & 81.3 & 81.9 & 80.6 \\ \hline \multirow{4}{*}{Control} & 8.8 & 8.0 & 9.4 & 5.9 & 9.5 & 8.1 & 5.9 & 7.8 & 9.5 & 5.4 \\  & 20.4 & 21.0 & 21.2 & 19.7 & 21.3 & 20.9 & 19.7 & 20.9 & 21.3 & 18.7 \\ \cline{1-1}  & 38.2 & 38.5 & 37.5 & 39.4 & 37.4 & 38.4 & 39.4 & 38.6 & 37.4 & 39.3 \\ \cline{1-1}  & 54.1 & 53.6 & 52.8 & 54.7 & 52.7 & 53.6 & 54.7 & 53.7 & 52.7 & 55.4 \\ \cline{1-1}  & 67.5 & 67.8 & 68.5 & 66.7 & 68.6 & 67.6 & 66.7 & 67.2 & 68.6 & 66.5 \\ \hline \end{tabular}
\end{table} 
Table 3: Experimental and calculated Q\({}_{e}\) during hexavalent chromium isotherm studies for both the control and trained _A. niger_ strains. Figure 6: Isotherm models for Cr\({}^{6+}\) removal by the control and trained strain. had voltage output 0.482 V, PD of 0.032 mW \(\times\) m\({}^{-2}\), and CD of 0.067 mA \(\times\) m\({}^{-2}\). At 165 h of operation, the electrolyte FFC had a voltage output of 0.106 V, PD of 0.0016 mW \(\times\) m\({}^{-2}\), and CD of about 0.015 mA \(\times\) m\({}^{-2}\), while the non-electrolyte FFC had a voltage output of 0.063 V, PD of 0.0005 mW \(\times\) m\({}^{-2}\), and CD of 0.008 mA \(\times\) m\({}^{-2}\). Therefore, the use of electrolytes increases the fungal fuel cell (FFC) performance in terms of power activity and output cell voltages. After 15 h of operation, the FFC voltage outputs were measured and the internal resistance was determined via applying various external resistances ranging from 10 to 20,000 \(\Omega\). FFCs voltage, current density showed a relationship, and the line slope led to internal resistance [47]. According to our findings, electrolytic FFCs had internal resistances of just 65 \(\Omega\), whereas non-electrolytic FFCs had an internal resistances of 110 \(\Omega\). In addition to the power output, the COD, total nitrogen, and total chromium removal efficiency were examined in both FFCs, as shown in Figure 7. In the anode part, sodium acetate and organic substances present in tannery wastewater were oxidized to CO\({}_{2}\) using fungal strain enzymes.