# Towards Bio-Hybrid Energy Harvesting in the Real-World:
## 3 Research Progress in Energy Harvesting from Microorganisms
### Applications of MFCs
#### 3.4.2 Wastewater Treatment  
To date, conjugated power generation and waste-removal has remained as one of the most popular applications of MFCs. One motivation behind this solution is that the combined system produces less sludge than conventional methods of waste treatment while generating additional power [29] that can either partially or completely meet the power requirements of the waste processing mechanism. [PERSON] et al. [125] reported their work on power generation with single chamber MFC with brush anodes and carbon cloth-based cathodes while processing food waste and found that a different order of organic waste loading affects the MFC performance. [PERSON] et al. [126] reported an MFC-adsorption hybrid system with air-cathode and with granulated activated carbon based anodes. For a more detailed review of MFC application on wastewater pro cessing, please see the review study by [PERSON] [215] and for the impact of wastewater substrate composition, please see the works of [PERSON] et al. [216]. To go into more detail of how to integrate wastewater processing with MFC technologies, please see the works of [PERSON] et al. [55]. [PERSON] et al. [29] classified conventional wastewater treatment-MFC power-generation systems into 5 major groups including sediment MFCs, constructed wetland MFCs, membrane bioreactor MFCs (MBR-MFCs), desalination MFCs (DS-MFCs) and others. The authors also performed comparison between the classes in terms of their substrate, power density, and chemical oxygen demand rate. [PERSON] et al. [217] reported their work on simultaneous electricity production real dye textile wastewater processing. Further work on textile waste water processing with different MFC configurations has also been reported. For example, decolorization of azo dye with bioachode configuration [218; 219; 220]. Use of algae in MFC systems has been another promising trend, whether being used as bioachode material [217] or as substrate [10]. Constructed wetland is a man-made wetland used for organic degradation for the wide range of agricultural to industrial wastewater [221]. Various efforts can be found on integrating the organic process of constructed wetland with MFCs. [PERSON] et al. [221] built an up-flow constructed wetland where anaerobic and aerobic regions were naturally developed in the lower and upper bed and the system obtained a 100% chemical oxygen demand removal efficiency. [PERSON] et al. [222] reported the use of another vertical flow constructed wetland system to remove different dye from synthetic wastewater and generate electricity as well. The configuration achieved the maximum value of 93.15% dye removal efficiency following 96 h of treatment from the wastewater with 500 mgl\({}^{-1}\) initial dye concentration. [PERSON] et al. [223] tested the applicability of horizontal subsurface flow constructed wetland for performing simultaneous organic waste processing and power generation. This study offered two major observations: the photosynthetic activity of the macrophytes, _Phragmites australis_ was dependent affected on the light/darkness changes, and this caused voltage fluctuations and affected stable performance of the system. [PERSON] et al. [224] demonstrated that use of _Ipomoae aquatic_ plant in their constructed wetland MFC system provided a higher power density and nitrogen removal in comparison to their contemporary systems. The authors also worked on optimizing the vertical constructed wetland with 3 different electrode materials (stainless steel mesh, carbon cloth, granular activated carbon) and found both stainless steel mesh and granular activated carbon's suitability for such configurations. [PERSON] et al. [219] reported another successful combination of _Ipomoae aquatic_ plantation constructed wetland-MFC system for azo dye decolorization. The planted system achieved the decolorization rate of maximum 91.24% with a voltage output of about 610 mV.