Enhanced Performance Of Surplus Sludge Microbial Fuel Cells By Additional Mixed Enzymes

Microbial fuel cell (MFC) that can directly convert the chemical energy in the fuel intoelectrical energy, is a high efficient and cleaning technology in recent years. Compared to thetraditional oxy-hydrogen fuel cell (RFC) and solid oxide fuel cell (SCOFCA), the MFC notonly has a wide range of fuel source, but also can achieve double effects of producingelectricity and the degradation of pollutants. Some researches proved that although themaximum output power density produced by MFC with mixture organics was lowercompared with pure organics as the fuel, it possesses the value of practical application. Atpresent, some researchers have applied MFC to the treatment of pollutants, such as sewage,sludge, landfill leachate and so on. The pollutants can not only be efficiently treated, but alsoobtain clean energy.Surplus sludge is the production of active sludge process, which has a great quantity oforganics, such as protein, carbohydrate, and lipid, thus it is a potential fuel. However, themaximum output power density and the hydrolysis efficiency of surplus sludge are low whendirectly use surplus sludge as substrate. The reason may be that the slow hydrolysis rate oforganic substance limits the degradation of organics by microorganism, and thus has a greatimpact on the efficiency of producing electricty and the reduction of excess sludge. How toimprove the hydrolysis rate is the key to enhance the power produced by MFC and thereduction of surplus sludge. The hydrolysis enhanced by additional enzyme can not onlyimprove sludge digestibility, but also reduce disposal costs, and its products are harmless toenvironment.In order to improve electricity production and sludge reduction in MFC using surplussludge as substrate (SMFC), enhanced effect of enzyme on membrane-free single-chamberSMFC was investigated at different temperatures (40℃,45℃and50℃). The resultsshowed that the power density of SMFC increased with the increase of temperature for bothneutral protease and α-amylase addition. The most significant enhanced effect of enzymeswas obtained at the temperature of40℃. Compared with the control group (addedinactivated enzyme), the power density increased198%and130%, respectively. Moreover,the effect of different ratio of enzymes (protease/amylase) on electricity production and sludge reduction in SMFC was analyzed at40℃.The maximum power density of MFC was776mW/m~2when the ratio of enzyme was2/3. The higher the proportion of amylase, thebigger the battery coulomb efficiency was obtained, which could reach18.3%when the ratioof enzyme was4/1. Correspondingly, the removal rates of TCOD, TSS and VSS were70.3%,66.7%and80.4%, respectively. According to the above mentioned, the enhanced effect ofenzyme was more obvious when the temperature was relatively low. Compared with thesingle enzyme, the mix enzyme could strengthen the electrical production and the reduction ofsludge in single chamber SMFC.In order to further analyze the combined effect of temperature and enzyme onelectrogenesis characteristics and sludge reduction in SMFC, a series of mixed enzyme(protease/amylase) experiments were set up, and controlled at40℃,45℃,50℃. Theexperimental results showed that the power density of devices were all increased when thetemperature was increased from40℃to45℃, the increase of power density was the largestwhen the ratio of enzyme was3/1, and it reached1023mW/m~2and increased639%comparedwith the control. The efficiency of sludge reduction enhanced after mix enzyme treatment,and the efficiency of sludge reduction declined with the increase of amylase dosage. Thevariation trend of SMFC was not obvious when the temperature increased from40℃to45℃.The coulomb efficiency increased with the increases of temperature, the maximum coulombefficiency was23%at the enzyme ratio of1/4(protease/amylase) when the temperature is50℃. The efficiency of sludge reduction was increased with the increase of temperature atthe enzyme ratio of2/3. The removal rate of TCOD, TSS and VSS were respectively95%,85%and98%when the temperature was50℃, the reduction effect of which was the best inthe whole experiment.