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5 Variations in Plant MFC
Plant MFC is a promising technology utilizing the correlation between plant and
microbes at rhizosphere of root zone. Root system of aquatic plant exudates acts as
substrate for bacteria in rhizosphere for oxidation. Based on plant-microbe harmony
at the soil interface and plant species used in such coupled biosystem, different
variations in plant MFC design such as constructed wetland MFC (CW-MFC),
microbial carbon capture cells (MCCs), microbial solar cells (MSCs), floating
islands, hydroponics-MFC, and paddy field MFC were used for practical applications as discussed below (Fig. 2). Table 2 compared the performance of different
plant MFCs based on applications for wastewater treatment and power generation.
5.1 Constructed Wetland MFC (CW-MFC)
The integration of conventional constructed wetland (CW) system and microbial
fuel cell (MFC) exerts symbiotic relationship between plant bacteria present in the
rhizosphere of aquatic plants through the formation of root exudates as endogenous
substrates for oxidation (Fig. 3) and a microbial activity [16, 20]. Different wetland
plants such as Phragmites australis were used in CW-MFC under upflow conditions
to maximize the redox potential gradient across the substrate. Similar CW-MFC
was capable to remove nitrate by 86.5%, soluble chemical oxygen demand (sCOD)
by 92%, phosphate removal efficiency of 56.3%, and total suspended solid removal
efficiency of 78.4% along with energy recovery of 33.52 mW/m
3
during treatment
of graywater [21].
During comparison of air cathode CW-MFC and typical CW-MFC, the removal
efficiency of COD and NO 3 -N as well as power density (4.21 mW/m
2
) in
CW-ACMFC was slightly higher than that of CW-MFC, which might be resulted
from the growth and metabolism of microorganisms and plant stimulated by a
higher voltage [22]. In some CW-MFC, additional filtration media (sand filter layer)
were provided to serve as a medium for protons to move in and to facilitate the
simple filtration of sewage during upflow of substrate [23]. Such CW-MFC can
serve as a polishing treatment for sewage treatment plant along with its advantages:
easy operation, inexpensive, wide availability, and recyclability.
5.2 Microbial Carbon Capture Cells (MCCs)
To address the issue of carbon storage and utilization, the modified MFC system
such as microbial carbon capture cell (MCC) has a potential to provide a sustainable
and effective solution by utilizing the concept of carbon capture and conversion to
algal biomass using algal biocathode, treating wastewater simultaneously and facilitating energy recovery in the form of electricity.
D. A. Jadhav et al.
5 Variations in Plant MFC
Plant MFC is a promising technology utilizing the correlation between plant and
microbes at rhizosphere of root zone. Root system of aquatic plant exudates acts as
substrate for bacteria in rhizosphere for oxidation. Based on plant-microbe harmony
at the soil interface and plant species used in such coupled biosystem, different
variations in plant MFC design such as constructed wetland MFC (CW-MFC),
microbial carbon capture cells (MCCs), microbial solar cells (MSCs), floating
islands, hydroponics-MFC, and paddy field MFC were used for practical applications as discussed below (Fig. 2). Table 2 compared the performance of different
plant MFCs based on applications for wastewater treatment and power generation.
5.1 Constructed Wetland MFC (CW-MFC)
The integration of conventional constructed wetland (CW) system and microbial
fuel cell (MFC) exerts symbiotic relationship between plant bacteria present in the
rhizosphere of aquatic plants through the formation of root exudates as endogenous
substrates for oxidation (Fig. 3) and a microbial activity [16, 20]. Different wetland
plants such as Phragmites australis were used in CW-MFC under upflow conditions
to maximize the redox potential gradient across the substrate. Similar CW-MFC
was capable to remove nitrate by 86.5%, soluble chemical oxygen demand (sCOD)
by 92%, phosphate removal efficiency of 56.3%, and total suspended solid removal
efficiency of 78.4% along with energy recovery of 33.52 mW/m
3
during treatment
of graywater [21].
During comparison of air cathode CW-MFC and typical CW-MFC, the removal
efficiency of COD and NO 3 -N as well as power density (4.21 mW/m
2
) in
CW-ACMFC was slightly higher than that of CW-MFC, which might be resulted
from the growth and metabolism of microorganisms and plant stimulated by a
higher voltage [22]. In some CW-MFC, additional filtration media (sand filter layer)
were provided to serve as a medium for protons to move in and to facilitate the
simple filtration of sewage during upflow of substrate [23]. Such CW-MFC can
serve as a polishing treatment for sewage treatment plant along with its advantages:
easy operation, inexpensive, wide availability, and recyclability.
5.2 Microbial Carbon Capture Cells (MCCs)
To address the issue of carbon storage and utilization, the modified MFC system
such as microbial carbon capture cell (MCC) has a potential to provide a sustainable
and effective solution by utilizing the concept of carbon capture and conversion to
algal biomass using algal biocathode, treating wastewater simultaneously and facilitating energy recovery in the form of electricity.
D. A. Jadhav et al.