Enhanced Disintegration And Electricity Generation Of Sewage Sludge By Freezing/Thawing-Microbial Fuel Cell

Energy shortage and environmental pollution are the two crises of present world. Microbial fuel cells(MFCs), which can dispose the sewage and generae electricity simultaneously, are an emerging technology with huge potential value. Freezing/thawing in natural condition can be used as sludge pretreatment in winter in cold northern areas. Thus, this study deales with the effects of sewage disposal and electrical energy recovery by MFC associated with freezing/thawing(F/T) pretreatment in cold areas.With freezing/thawing as pretreatment, freezing/thawing-microbial fuel cell(F/T-MFC) treatment was used to dispose the sewage sludge. Degradation and electricity generation of sewage sludge by F/T-ferricyanide MFC, F/T-double chamber biocathode MFC and F/T-three chamber biocathode MFC were studied. The characteristics changes of sludge organic fraction before and after optimized F/T-MFC treatments were analyzed to evaluate the character of sludge organic matter fraction.Study on effect of freezing/thawing treatment on sewage sludge showed that freezing/thawing treatment could promote the solubilization of organics and realize the transformation of organic matter from solid to liquid. Take the sludge frozen at-20 oC for example, soluble chemical oxygen demond(SCOD) increased sharply after 3 h freezing, which indicated that only sludge entered the curing stage, organic dissolution could be apparent. With relatively higher ambient temperature during freezing stage(in this experiment-5oC), lower ambient temperature during curing stage(in this experiment-20oC), and long curing time(in this experiment not exceed 42 h), organics dissolution would be better. Based on the experimental results, the optimized freezing/thawing treatment was as followed: first, freezing at-5oC for 6 h followed by freezing at-20 oC for another 42 h, then the sewage was placed at room temperature(20oC) to thaw for 12 h. The results of the simulated F/T pretreatment showed that SCOD, soluble carbohydrates and soluble protein content increased by 2.14 times, 1.33 times and 2.65 times, respectively. The p H was decreased and alkalinity was increased, accompaning by the release of nitrogen.The results of sewage sludge organic matter degradation after three types of F/T-MFC treatments showed that SCOD concentration peaked at 6 d in the system of F/T-double chamber ferricyanide MFC and the TCOD removal efficiency was 69.2% at 20 d. SCOD of the sewage sludge in F/T-double chamber biocathode MFC peaked at 15 d and the TCOD removal efficiency was 80.6% at 30 d. TCOD removal efficiency of F/T-three chamber biocathode MFC was 85.5% at 40 d. F/T stage of F/T-MFC treatment could increase the concentration of soluble organic matter fed into MFC. High concentration of soluble organic matter could enhance the hydrolysis of sewage organic matter in MFC. At the beginning of F/T-double chamber ferricyanide MFC, the effects of organic matter hydrolyzation and TCOD removal were obvious. However, for the F/T-three chamber biocathode MFC, sewage organic matter could be dissolved and degraded more thoroughly.The results of electricity generation of sewage sludge after three types of F/T-MFC treatments showed that the maximum power density of F/T-double chamber ferricyanide MFC was 10.3 W/m3 at 6 d. The maximum power density of F/T-double chamber biocathode MFC was 13.7 W/m3 at 20 d. The maximum power density of F/T-three chamber biocathode MFC was 12.6 W/m3 at 15 d, respectively. F/T-double chamber ferricyanide MFC treatment started fast and had no stagnation, while F/T-three chambers biocathode MFC treatments had the advantages of no need to periodic replacement of cathode liquid, cathode liquid environment-friendly and achieving higher power density, which were more conducive to electricity generation of sludge.Characters change of sludge organic fractions after F/T-MFC indicated that the concentration of sludge dissolved organic carbon(DOC) in dissolved organic matter and extracellular biological organic matter(EBOM) were increased by freezing/thawing process, the sludge biodegradability was improved, and the hydrolysis of aromatic compounds of HPO-A in the sewage solids to liquid phase was promoted. Weak humic fluorophores were appeared in HPI of EBOM and TPI-A of supernatant, which could promote electricity production of subsequent MFC. Sudies of characters change of sludge organic fractions after F/T-double chamber ferricyanide MFC and F/T-three chamber biocathode MFC showed that simple aromatic proteins and soluble microbial byproduct could be degraded by F/T-three chamber biocathode MFC more thoroughly, and the F/T-three chamber biocathode MFC was more conducive to the degradation of sludge and energy recovery.