Primary Research On Bio-Hydrogen Production By Eletrochemically Assisted Microbial Process From Acetate

Bio-hydrogen production by fermentation is limited to a low hydrogen conversion on one mole substrate. This paper studies on how to utilize fermentation products, acetic acid mainly for example, to further generate hydrogen by microbial way. Base on microbial fuel cell(MFC), hydrogen is produced successfully by electrochemically assisted microbial process with acetate as the sole carbon source.The seed sludge was sewage sludge collected from the sedimentation tank and sludge thickener in Wen Chang Wastewater Treatment Plant in Harbin. The two-chamber microbial fuel cell reactor was employed to start up in ambient temperature 20²8℃. We found batch way could keep enough biomass to speed startup and we chose two different ways in startup process. One was directly power-supplied startup for hydrogen(1^# reactor, applied voltage 0.5⁰.6V) ; another was electricity-generated startup(2^# and 3^# reactor). Hydrogen was obtained in reactror 1^# after 2 months'startup. Maximum hydrogen percentage came to 70%(v/v) in headspace of cathode chamber; hydrogen recovery of electron was 21.0%; total hydrogen conversion of acetate was 11.6%; a maximum yield was 0.4molH₂/molNaAC. A primary stable bio-film with electrochemical activity bacteria was formed in a short time by electricity-generated way. A primary stable output voltage reached to 400mV with 1000Ωexternal load in reactor 3^# after 1 month's startup and the maximum output voltage was 440mV; startup process in reactor 2^# produced a Coulomic efficiency of 15.0%±0.5% and a maximum output voltage of 500mV. The preliminary results of 3^# showed that the maximum hydrogen level reached to 51.4%(v/v) in cathode chamber headspace, which was much higher than 25%(v/v) in buffering bottle. Total hydrogen conversion of acetate was 2.9% calculated by hydrogen fraction of 30%, and the yield of hydrogen from acetate was 0.1molH₂/molNaAC.The water decomposition experiment analysis demonstrated that the applied voltage 0.5⁰.6V in reactor 1^# was far less than that of water decomposition voltage and cathode potential analysis showed that a smaller voltage could be applied to produce hydrogen. Hydrogen production was the result of electron- transfer bacteria, different from electrolysis process. Under a fixed voltage current changes were related to acetate metabolism. That could be explained for the transferred electrons of functional bacteria. It was indicated that pH affected the efficiency of system obviously. Results showed that the suitable pH for functional bacteria in anode chamber ranging from 6.5 to 7.2. The whole efficiency was visible below 7.0 of cathode chamber and was improved further with pH decreasing. So the low efficiency of proton exchange membrane (PEM) was considered to cause the unbalance of the two chambers and proteobacterium sp. and Clostridiales sp. were the microbial reason for pH falling in anode chamber.SSCP analysis of microbial communities indicated that the electron-transfer bacteria mainly consisted of Pseudomonas sp. and Shewanella sp. They were the dominant species in both the domestication course and steady hydrogen production period. After condition impact, some other bacteria became obvious, including Desulfomicrobium,Clostridiales and Actinobacillus.