1.5　The possible of combing BER and MFC with constructed wetland

Electrochemical system,especially biolm-electrode reactor(BER),offer a feasible technology for nutrient removal while at the same time acclimating microbial community compositions.In BER systems,production of H2 by water electrolysis could be used as electrons in denitrification; the coexistence autotrophic bacteria and denitrifying bacteria can be immobilized on the surface of the cathode by micro-electric field(Mousavi et al.,2012; Park et al.,2006).Moreover,the inorganic carbon source(CO2)generated by anode electrode material(carbon)could serve as pH buffer in BER(Hao et al.,2013).Notably,organic carbon source is also employed to strengthen the process of denitrication in BER(Feng et al.,2013).Furthermore,the nitrogen removal also significantly affected by the current intensity in the BER system.When current ranged from 0mA to 20mA,the nitrogen removal efficiency had apparently positive correlation with current intensity(Sakakibara et al.,1994).However,when electric current intensity exceeds 0.029mA/cm2,the denitrification efficiency has been inhibited by a plenty of hydrogen production(Sakakibara et al.,1994).Therefore,the hybrid of CW and BER for wastewater treatment should be applied with the current density in a reasonable range.

Under the background of natural resources depletion and increasingly severe water pollution,many scholars are starting to pay attention on the bio-electrochemical technology to harvest bioelectricity in the process of wastewater treatment.It has estimated that 1.5 billion tons of oil equivalent(TOE)of energy will be required and two-thirds of the global individuals will face the aquatic environment problems by 2025(Eliasson,2014).Recently,CW-MFC is a novel way into developing technical platform for recycling bioelectricity production during the wastewater treatment,which has been widely studied on the domestic and industrial wastewater treatment through the combinations of physical,chemical and biological processes under different conditions due to its advantages of low cost,easy operation,and simple maintenance(Yadav et al.,2012).In recent novel power generation technologies,MFC is integrated with constructed wetlands(CW-MFC)and significant progresses have been made(Yadav et al.,2012; Liu et al.,2014; Fang et al.,2015).It was reported that the maximum power density(15.73mW/m2)and current density(69.75mA/m2)were obtained with wastewater containing 1000mg/L dye(Yadav et al.,2012).Similarly,after integrating MFC into a CW with a granular activated carbon and stainless steel mesh(GAC-SSM)bio-cathode,Liu et al.(2014)achieved the maximum power density of 55.05mW/m2.Recently,Fang et al.(2015)developed a CW-MFC to treat Azo dye wastewater and realized the highest power density of 852mW/m2 and the decolorization rate of 95.6%.Fang et al.(2013)implied that the closed circuit in a CW-MFC was conducive to the growth of EAB especially autotrophs such as Geobacter sulfurreducens and Betaproteobacteria (Cha et al.,2010).

Herein,in this book,we described that the use of CW combined with biofilm-electrode reactor and integrating biofilm-electrode with CW with an aim to increase the removal nitrogen from wastewater based on the enhancement of relative abundance of autotrophic bacteria.Secondly,the micro-electric filed coupled with CW system was performed to strengthen the removal of heavy metals during the wastewater treatment.Thirdly,the effects of operational conditions(pH,COD concentrations,anode and cathode electrode materials,substrate material sizes,and plant types)on the bioelectricity generation and wastewater treatment performance was investigated in a hybrid system of integrating MFC into CW.Notably,the high-throughput sequencing analysis was employed to study the diversification and richness of microbial community,which indicated that the evenness,richness and distribution of the microorganisms were apparently changed with the application of these methods into CW.Through the development of these methods,the contaminant removal performance of CW was significantly enhanced for the treatment of wastewater.Thus,this book can serve as an implication and reference for researchers to study the mechanisms of water purification in the coupled systems of CW.