Research On Production Of Electricity Microbial Fuel Cells Using Surplus Sludge And Surplus Sludge Reduction

Microbial fuel cell (MFC) can transform the chemical energy of the organic matter to electrical energy during microorganism in the anode electrode surface metabolic reaction. MFC has become one of the important research directions in environment science and engineering because it can treat wastewater and generate electricity synchronously. The surplus sludge is made of the suspended floc that includes the microbial cell, extracellular polymeric substances (EPS), cation and other fine particles. The content of organic mater in sludge is above60%and it can be used as potential fuel of MFC. MFC using surplus sludge, which achieves the sludge disposal of anaerobic digestion and the recycling of electrical power, would become a new technique of sludge disposal. Most of the organic matters in sludge are microbial cell, and the microbial cell walls must be hydrolyzed before those organics can be used by exoelectrogenic bacteria. However, so far there is no study reported in MFC on the relationship between sludge hydrolysis and produce electricity. Moreover, the relationship between sludge strengthening hydrolysis and electrical characteristics is not clear. Therefore, in this paper, the surplus sludge from the urban sewage treatment plants was selected as the studied material. The electrogenesis property and the decrement of sludge were investigated based on the MFC techniques and different sludge hydrolysis methods (Anaerobic hydrolysis, microwave strengthening hydrolysis and enzyme strengthening hydrolysis).MFC using surplus sludge (SMFC) was successfully started up. In SMFC, the maximum power density, internal resistance and coulombic efficiency (CE) were294.5mW/m2,247.85Ω,4.7%, respectively. The TCOD, TSS and VSS in the sludge were removed by26.2%,24.7%and32.5%, respectively.(Here should provide the full names for TCOD, TSS and VSS.) With the increasing NaCl addition, the internal resistance decreased and the maximum power density increased. When the sludge dilution ratio increased, the internal resistance decreased. But the maximum power density firstly arose and then dropped with the increasing sludge dilution ratio. The decrease of the power density may be attributed to the lack of nutrients in MFCs, which affected the anode microbial growth when the sludge dilution ratio is too high. The churning increased the power output because it improved the material transmission in SMFC. The influence of temperature on the produce electrical characteristics of SMFC was generally obvious. However, the power output did not change significantly in the certain temperature interval (such as20℃～25℃,30℃～40℃, and45℃～50℃). This indicates that exoelectrogenic bacteria have appropriate temperature range. It may be attributed to the production of different exoelectrogenic bacteria at different temperatures. The microbial competition in the sludge was the major factor in MFC electric efficiency. In SMFC, the transmission of cathodic oxgen had no obvious influences on the power output, which is due to the consumption of inelectrogenic bacteria and the protection of anode attachments. This study suggests that the hydrolyzing stage is dominating in sludge anaerobic digestion of SMFC. The internal resistance of SMFC consists of anode resistance, cathode resistance and electrolyte resistance.In MFC using surplus sludge with microwave treatment (MSMFC), the voltage output firstly arose, then dropped slowly. And the cycle was666h. The maximum power density and internal resistance of MSMFC were343.41mW/m2and146.80Ω, respectively. With the increasing microwave power and treatment time, SCOD (provide the full name) of sludge increased. The maximum power density of MSMFC increased with the microwave treatment time. But it firstly arose and then dropped with the microwave power. CE decreased with the increasing microwave treatment time or power. When the microwave time and power were300s and720W, respectively, the cracking capacity of sludge was strongest by microwave (SCOD was1194mg/L), the power density of MSMFC was biggest (163.33mW/m2), and CE was better (76.7%). The dominant microorganism of anode surface and electrolyte were the globular bacteria in MSMFC. The anode resistance in MSMFC was the main part, the cathode resistance was second, and the electrolyte resistance was lowest. This study suggests that the trace dissolved oxygen is conducive to decompose the organic matter (fermentation and aerobic oxidation), restrain methanogenesis process, and improve the power density and CE.Production of electricity in MFC using surplus sludge by enzymes (ESMFC) was investigated. With the addition of enzymes (protease and amylase), the sludge hydrolysis was promoted and MFC electrogenesis characteristics were improved. The energy density with addition of protease and amylase was increased by52%and8%, respectively. When the enzyme addition was10mg/g, the maximum power density increased maximally. The power density with addition of protease and amylase was increased by174%and36%, respectively. Temperature has significant effects on the electrogenesis characteristics. The effect of addition of protease and amylase at40℃ was the most significant to improve power density if only considering the enzyme action. The power density with addition of protease and amylase was increased by174%and66%, respectively. The hydrolyzing effect of sludge with addition of enzyme was obvious. TCOD and VSS removal efficiencies were above60%and70%, respectively. VSS/TSS in sludge was reduced significantly. When the mixture ratio of protease and amylase was2:3, the largest maximum power density and CE were obtained (775.21mW/m2and10.58%).Production of electricity in MFC using surplus sludge by three different treatments was investigated. The longest electricity cycle (41d) and the largest power density (775.21mW/m2) were achieved by ESMFC. The largest CE (84.6%) was obtained by MSMFC. TCOD and VSS removal efficiencies by SMFC were26.2%and32.5%, respectively. The sludge reduction can be promoted by using sludge pretreatment method. TCOD and VSS removal efficiencies by MSMFC were increased to58.5%and73.9%, respectively. TCOD and VSS removal efficiencies by ESMFC were increased to63.2%and77.1%, respectively. The energy efficiency of ESMFC was the biggest, MSMFC was the second, and SMFC was the lowest.