Study On The Electricity Generation And Reduction Of Sludge By Microbial Fuel Cell

An increasing number of activated sludge is produced from the traditional wastewater treatment process and its treatment and disposal is becoming a much serious environmental problem. At the same time, activated sludge is a kind of resource for its high organic content which contains abundant energy. In this study, the technology of microbial fuel cell was applied to translate the organic matter in the sludge directly into electricity which simultaneously achieve the sludge resourcization and reduction,. Researches were mainly made on the electricity production performance, mechanism and optimization of the sludge MFCs.The test which put the concentrated return sludge taken from the sewage treatment plant into the two chambers of the MFC as well as a certain amount of inoculum sludge to the anodic chamber was made to research the sludge resourcization and reduction. The results showed that the sludge was available for electricity production. When reaching the stability, the maximum voltage of the MFC was0.467V with the maximum power density of39.20mW/m2while some amount of the sludge reduction can be achieved (TSS and VSS of the anodic sludge were reduced by38.07%and38.72%. and that of the cathodic sludge were42.02%and38.90%). In order to improve the electricity production efficiency of the sludge, further study was made to obtain the sludge pretreatment impact on the sludge MFC. The methods of Thermal and alkaline pretreatment were adopted to optimize the electricity generation. The results showed that alkaline treatment could enhance electricity production significantly with its power density of65.99mW/m2, which was higher than that of the untreated sludge with the value of46.47mW/m2. The internal resistance of the alkaline treatment MFC was lower than that of the untreated sludge. On account of the sludge acidification which led to system abnormal operation, the impact of the thermal pretreatment was less than that of the alkaline pretreatment. Moreover, TSS reduction results of alkali and thermal sludge with the values of30.47%and21.70%respectively was higher than that of untreated sludge. As a comparison, the TSS reduction effect of MFC-tested sludge was greater than the sludge in the contolled experiment which illustrated that the sludge usage of electricity generation had positive influence in sludge reduction.In order to investigate the mechanism of the electricity generation and sludge reduction of the pretreated sludge MFC, the organic compound type and content, microbial population, and bacteria distribution of four different kinds of sludge were studied through the methods of molecular biology.. The results showed that the VFA content of the thermal and the alkaline treatment sludge were much higher than that of untreated sludge. The degradation of more organic macromolecules into small organic molecules led to the solution ionic strength increase and the electric production performance enhance for the internal resistance of the sludge MFC decrease. Moreover, the VFA content of the sludge for the electricity generation was higher than that of the traditonal anaerobic digestion. The MFC-test sludge and the pretreated MFC-test sludge with more organic matters degradation promoted the reduction of sludge. The Three-dimensional fluorescence spectra results indicated that the differences in concentration and compounds of the pretreated sludge, raw sludge and controlled sludge were the reasons of the electricity production promotion by sludge pretreatment. The results of the experiment of fluorescence in situ hybridization (FISH) and scanning electron microscopy (SEM) on the anode showed that the microorganisms mainly existed on the surface of the electrode sheet, and electricity generation formed their distribution by layers in the electrode. The organic macromolecules in the sludge was hydrolyzed and fermented by the other bacteria and then the products were utilized by the exoelectrogens which was the electricity generation mechanism of the sludge MFC.The results of optimization of sludge MFC electricity production indicated that the start-up conditons of the anoxic anode chamber and high pH values could improve the effects of electricity production and sludge reduction of the MFCs. And increment of the ionic strength in sludge could reduce the MFC internal resistance, but the effect of sludge reduction and electricity productivity could not be improved. The electricity production capacity of MFC with double-chamber configuration, PEM membrane, carbon felt electrode and cathode platinum catalyst was higher than that of the single room configuration, CEM membrane, carbon paper, coated electrodes and the cathode catalyst without platinum.