Effects Of Nitrogenous Heterocyclic Compounds On The Performance Capability Of Microbial Fuel Cells

Refractory organic compound is a class of organics that is difficult to bebiodegraded such as phenols compound and heterocyclic. Their poor biodegradabilitymakes it difficult to effectively treat in natural environment. Most of recalcitrantcontaminants can exist stably in water and soil, they constitute a danger for the humanhealth and the environmental quality due to their toxicity, carcinogenicity andteratogenic nature. Therefore, the research on the effective treatment technology ofhazardous substance is increasingly focused and become a challenge in theenvironmental protection domain. Various types of technologies have been used totreat refractory organic compound and can be divided into five categories: oxidationtechnique, electrolysis technology, bioaugmentation technique, enzyme technology,immobilized cell technique. However, these methods have some shortcomings such asstrict operational way, poor treatment efficiency, long treating time, high cost and soon.Recently the fundamental problems are resolving environmental pollution andexploring new energy needs to achieve the goal of sustainable development. Microbialfuel cell (MFC) is a technology of microbiology and battery, which is a devicecapable of directly transforming microbial metabolic energy into electricity viaelectrochemical reactions involving biochemical pathways. MFC techniquecombining the advantages of the anaerobic and aerobic metabolism can deal withwastewater effectively and at the same time produce electricity energy, which providesome information for treating wastewater. MFCs have gained a lot of attention andinterest in recent years as a new system of energy conversion. It has been reportedthat microbes in the MFC can convert many types of organics, including readilydegradable compounds (organic acid and carbohydrate), biorefractory organics(phenol and lignocellulosic biomass), synthetic and practical wastewater (brewerywastewater and starch processing wastewater). The research and application of MFCtechnology involved the field of microorganisms, electrochemistry, materials andenvironmental engineering.The paper introduced the basic characteristics and the latest investigation ofMFC. Two-chamber MFCs were designed and inoculated with anaerobic sludgeacclimated for several months, which obtained from the anaerobic digested sludge of the Second Wastewater Treatment of Changsha City in China and kept in arefrigerator at4℃before use. The experiments were conducted to test the potentialfor biodegradation of refractory organic matters and electricity generation usingrepresentative N-heterocyclic compounds (pyridine, quinoline and indole), and tocompare the differences between MFC technique and conventional anaerobictreatment method in the biological degradation of toxic and recalcitrant contaminants.Meanwhile, we discussed the metabolic fate and pathway of substrate degradation inthe MFC. We also investigated the power generation and analyzed the variation ofsludge component by using anaerobic sludge as the sole fuel at the beginning. Theexperimental results indicated that anaerobic sludge as inoculum had little impact onthe electricity generation of N-heterocyclic compounds in the DMFCs. When usingpyridine, quinoline and indole as the sole carbon source, power output curvesdisplayed a regular three periods: rising stage, stabilization stage, falling stage.However, electricity generation is different in the tested substrate and power densitiesof indole and quinoline are higher than that of pyridine, which suggested thatelectricity-generating microbes existing in the anode had selectivity to the substrates.A maximum voltage of524mV (indole,120mg/L),494mV (quinoline,120mg/L),413mV (pyridine,60mg/L) based on an external resistance of1000, and thecorresponding maximum power densities of228.8mW/m2,203.4mW/m2,142.1mW/m2were obtained from pyridine, quinoline, and indole, respectively. The maximumoutput voltage gradually increased and electrical cycle and stable operation timeextend with the increasing of the concentration of substrate. But pyridine wasinconsistent with the above regularity. Meanwhile, the maximum degradationefficiency of these substrates and COD (chemical oxygen demand) removal were upto90%and88%, respectively. The molecular structure and charge characteristics offuels had a great impact on the effect of MFC productivity and metabolic degradation.The MFC with closed circuit control enhanced N-heterocyclic compoundbiodegradation by about10％compared to open circuit control, which indicatedMFC could enhance utilization and biodegradation of the substrates, or existed newmetabolic pathway of substrate degradation. The metabolic intermediate productswere detected by GC/MS analyses of the anode solution. The results clearlydemonstrated the feasibility of using the MFC to generate electricity usingN-heterocyclic compound as fuel and simultaneously degrading the substrates. Theseresults indicated MFC offer a new method of enhancing biodegradation of recalcitrantcontaminants in practical applications．It is hoped that MFC technology combining the advantages of power output and biological treatment will be used leading to asustainable and economical bioenergy from almost any renewable materials includingwastes.