人工湿地-微生物燃料电池耦合系统缓解生物堵塞试验研究

STUDY ON RELIEVING BIO-CLOGGING WITH THE HYBRID SYSTEM OF CONSTRUCTED WETLAND AND MICROBIAL FUEL CELL

微生物燃料电池(Microbial Fuel Cell,MFC)利用电极表面富集的电化学活性菌(Electrochemically Active Bacteria,EAB)对生物堵塞的胞外聚合物(Extracellular Polymeric Substances,EPS)进行降解,并通过产电过程中形成的微弱电场来抑制微生物胞外多糖大量分泌,可在一定程度上控制人工湿地(Constructed Wetland,CW)的生物堵塞。为此,研究将阴极和阳极电极分别嵌入垂直流人工湿地的不同深度位置处,构建了人工湿地-微生物燃料电池(CW-MFC)耦合系统。通过比较开路和闭路耦合系统的孔隙率、过水速率以及净化效果,评价CW-MFC系统的堵塞延缓能力。结果表明:相较开路系统,闭路系统的过滤速率增幅较大,孔隙率的降幅较小,在一定程度上缓解了堵塞。闭路系统对TN和NH4+-N的去除率显著高于开路系统。嵌入电极形成的CWMFC系统可原位缓解堵塞,有较好的应用潜力。

Extracellular polymeric substances(EPSs) are biosynthetic polymers from prokaryotic(bacteria, archaea)and eukaryotic(algae, fungi) microorganisms, which either form(loose or tight) slimes around the microbial cells or are excreted as discrete gels to the surrounding environment. In biofilm systems, EPSs are mainly responsible for binding cells and other particulate materials together. A large secretion of EPS will continuously form a cohesive dense layer on the surface of the matrix. Therefore, the gradual accumulation of EPSs easily causes the severe bio-clogging of constructed wetlands(CWs) running for a long time. Microbial fuel cells(MFCs) could degrade the macromolecular organics EPS by the electrochemically active bacteria(EAB) colonizing on the surface of the electrodes and inhibit the large secretion of exopolysaccharides from microorganisms by the weak electric field formed during the electro-genesis process. Hence MFCs are supposed to be able to control the bio-clogging. In order to relieve the bio-clogging of CW system, this study constructed a CW-MFC hybrid system by embedding the anode and cathode electrodes into different depths of vertical direction of CWs. Two experiment groups with three parallels were set up in the closed circuit mode and the open circuit mode, respectively. The whole experiment consists of two stages. The first is bio-clogging simulation, and the second is bio-clogging mitigation. In the first stage, the excessive sludge from the sewage treatment plant was added to reactors to simulate the bio-clogging of constructed wetlands. When the obvious banked-up phenomenon happened and inconspicuous change of water filtration velocity were observed, the experiment system was regarded as clogging. In the second stage, the experiment lasted 70 days with two different influent concentrations. From the 1st to 35th day, the influent concentrations of TN, TP and COD were approximately 30, 2.5 and 500 mg/L, respectively. From the 36th day to the end, the TN and TP concentrations in the influent remained the same, while the COD concentration increased to 1000 mg/L. The porosity and the filtration velocity were used as the clogging index, the output voltage, the polarization curves and power density curves were used to evaluate the electro-genesis performance, and the removal rates of COD, TN and NH4+-N were used to assess the purification effect. The results showed that in CW-MFC circuit system, the change of filtration velocity(porosity) is bigger than that in open system. This gap was bigger in higher influent COD, which proves the relieved clogging in CW-MFC circuit system. The high removal rate of TN and NH4+-N indicated a good enrichment of denitrifies in circuit system. On the one hand, the higher the COD influent, the lower the COD effluent. On the other hand, the amount of output voltage or the converted electrical energy did not increase. This implied that more COD was utilized to sustain the growth of the heterotrophic denitrifies. In conclusion, the CW-MFC system can achieve a certain degree of the bio-clogging. Further research will have good application potential as in situ mode.