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

Bio-hydrogen production by fermentation is limited to a low hydrogen conversion by 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 and each was 480mL for viable dimension.Carbonaceous fabric of 80mm×80mm in anode chamber and carbonaceous paper in cathode chamber were adopted.The device was run when connected with 1000? external load in ambient temperature (30±2℃).Two reactors(reactor 1# and 2#) were started up simultaneously by different ways.Reactor 1# was run without power supply in early days and then was joined power supply for hydrogen(applied voltage 0.5~0.6V).Hydrogen was obtained in reactror 1# after two months'startup . Total hydrogen conversion of acetate was 3.0 % and a maximum yield was 0.1molH2/molNaAc . Reactor 2# was directly power-supplied startup for hydrogen(applied voltage 0.5~0.6V) . Hydrogen was obtained one month later.Hydrogen recovery of electron was 21 %;total hydrogen conversion of acetate was 11.6% ; the yield of hydrogen from acetate was 0.4molH2/molNaAc . Reactor 2# was higer than reactor 1# in production rate.But the bio-film was not easy to form because of pH rapid dropping in anode chamber. The study analysed the effect of crucial factors for reactor running.Adjustment of pH in anode chamber was very important and activeness of the bio-film in anode was influenced by pH.Excessively low pH caused in losing activeness even reactor not available.Results showed that the suitable pH for functional bacteria in anode chamber ranging from 6.8 to 7.2.The whole efficiency was visible below pH 7.0 in cathode chamber and was improved further with pH decreasing.The low efficiency of PEM was considered to cause the unbalance of pH in two chambers.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 domestication course and steady hydrogen production period.After condition impact,some other bacteria became obvious,such as Desulfomicrobium,Clostridiales and Actinobacillus and so on,which all were mentioned in the study on microbial fuel cells . Proteobacterium sp. and Clostridiales sp were found simultaneously in anode chamber,which was the microbial reason for pH falling.