96
A. A. S. Al-Gheethi et al.
might occur as a result of decrease in the internal resistance. Moreover, the power
output was reduced by 9% due to the decrease in the temperature from 32 to 20 °C.
The studies conducted on the production of bioenergy as a response to different
pH values in the MFCs indicated that the optimal initial pH is between 8 and 10. In
MFCs, the microbial process in the anodic preferred a neutral pH and decreases at
acidic or alkaline pH. Meanwhile, in the cathode, the biological reaction is high at
alkaline pH (He et al. 2008).
6.4 Optimization of Microbial Fuel Cells
Optimization is one of the most important steps that must be taken to obtain a maximum and high-quality bioenergy production by MFCs. Besides that, optimization
of MFCs is also conducted to reduce the cost of operating process. Many software
programs have been used for the optimization process. However, response surface
methodology (RSM) based on central composite design (CCD) is the most common
method used due to the ability of this method to provide the best operating parameters required for high production of bioenergy with minimum experimental runs. The
optimization process is dependent on the selection of independent factors such as
pH, temperature, microbial concentrations, and incubation period which have direct
and indirect effects on the performance of MFCs and show interaction that can guide
in increasing the overall performance of MFCs. For instance, Madani et al. (2015)
found the best operating parameters for MFC’s performance from the interaction
between pH and buffer concentration. The maximum power generated was 461 mW
m
−2 (at pH of 6.3 and buffer concentration of 82 mM).
Hosseinpour et al. (2014) used RSM to optimize the power generation by MFCs
as a response for three independent factors including buffer concentration, pH, and
ionic strength. The study revealed that the highest power density was increased by
17% at 0.11 M buffer concentration, pH 6.75, and 4.69 mM ionic strength of cathode
chamber. The maximum Coulombic efficiency (3%) in MFCs with power density of
1097 mW/m
3 was reported in the study by Fang et al. (2013). This was observed at
102 mM ionic concentration, pH 7.75, and with 48.4 mg/L of nitrogen at 30.6 °C.
6.5 Conclusion
Based on this review, it can be concluded that MFC is one of the best alternative
methods to getting a green energy. However, many factors should be considered,
in which among them the microbial strains, environmental conditions, cathode and
anode types, and substrates. Moreover, the optimization of these independent factors
might contribute effectively in the high production of bioenergy at lower operating
cost.
A. A. S. Al-Gheethi et al.
might occur as a result of decrease in the internal resistance. Moreover, the power
output was reduced by 9% due to the decrease in the temperature from 32 to 20 °C.
The studies conducted on the production of bioenergy as a response to different
pH values in the MFCs indicated that the optimal initial pH is between 8 and 10. In
MFCs, the microbial process in the anodic preferred a neutral pH and decreases at
acidic or alkaline pH. Meanwhile, in the cathode, the biological reaction is high at
alkaline pH (He et al. 2008).
6.4 Optimization of Microbial Fuel Cells
Optimization is one of the most important steps that must be taken to obtain a maximum and high-quality bioenergy production by MFCs. Besides that, optimization
of MFCs is also conducted to reduce the cost of operating process. Many software
programs have been used for the optimization process. However, response surface
methodology (RSM) based on central composite design (CCD) is the most common
method used due to the ability of this method to provide the best operating parameters required for high production of bioenergy with minimum experimental runs. The
optimization process is dependent on the selection of independent factors such as
pH, temperature, microbial concentrations, and incubation period which have direct
and indirect effects on the performance of MFCs and show interaction that can guide
in increasing the overall performance of MFCs. For instance, Madani et al. (2015)
found the best operating parameters for MFC’s performance from the interaction
between pH and buffer concentration. The maximum power generated was 461 mW
m
−2 (at pH of 6.3 and buffer concentration of 82 mM).
Hosseinpour et al. (2014) used RSM to optimize the power generation by MFCs
as a response for three independent factors including buffer concentration, pH, and
ionic strength. The study revealed that the highest power density was increased by
17% at 0.11 M buffer concentration, pH 6.75, and 4.69 mM ionic strength of cathode
chamber. The maximum Coulombic efficiency (3%) in MFCs with power density of
1097 mW/m
3 was reported in the study by Fang et al. (2013). This was observed at
102 mM ionic concentration, pH 7.75, and with 48.4 mg/L of nitrogen at 30.6 °C.
6.5 Conclusion
Based on this review, it can be concluded that MFC is one of the best alternative
methods to getting a green energy. However, many factors should be considered,
in which among them the microbial strains, environmental conditions, cathode and
anode types, and substrates. Moreover, the optimization of these independent factors
might contribute effectively in the high production of bioenergy at lower operating
cost.