Influencing Factors Of Hydrogen Production By Anaerobic Fermentation From Waste Activated Sludg

The process of biohydrogen production from anaerobic fermentation has become the first choice in the biohydrogen production due to its advantage of high hydrogen yield, stability and waste utilization. Waste activated sludge from wastewater treatment plant contains high levels of organic matters such as proteins and polysaccharides, and thus is regarded as a potential substrate for producing hydrogen. The purpose of this study is to resolve the difficulties of realizing high and stable hydrogen production from excess activated sludge by anaerobic fermentation. In this paper waste activated sludge was used as substrate to produce hydrogen, and then the influences of sludge characteristics on bio-hydrogen production were researched. Two approaches of changing the substrate characteristics to improve bio-hydrogen yield were investigated. Besides, a new type of biology sludge pretreated method was applied to break sludge, and then to complete the process of biohydrogen production from anaerobic fermentation.Batch tests were carried out to analyze influence of using sludge filtrate for the substrates for anaerobic fermentation. The sludge would release lots of organic matters after sterilization pretreatment, and then the filtrate was obtained from vacuum filtering the pretreated sludge through a filter. Both the pretreated sludge and their pretreated filtrate were used as the substrates for hydrogen production by Pseudomonas sp.GZ1 respectively. The hydrogen yield and the change of soluble COD,protein,carbohydrate and pH value during of the fermentation processes were compared and monitored. The results showed that using filtrate would produce more hydrogen than using the biosolids. Using filtrate as substrate could produce a hydrogen yield of 4.44 mgH2·gCOD-1, approximately 3.3 times to the pretreated sludge. It was demonstrated that the solids phase in waste sludge could release more nutrients during fermentation, but it was disadvantage for hydrogen production, and the possible reasons for the phenomenon were analyzed.A new-style of heavy metals sorbent (CHAP) was utilized to remove the dissolved heavy metals from microwave pretreated waste sludge. Then the pretreated sludge in which different dosages of CHAP were added was used as the substrates for comparing the effect of anaerobic fermentive hydrogen production by Enterococcus sp. LG1. The results showed when the dosage of CHAP in the substrate was 5 g·L-1 (sludge), the hydrogen yield reached to 10.01mgH2·gCOD-1and improved nearly 30%. However, when the dosage of CHAP in the substrate was more than 10g·L-1 (sludge), the anaerobic fermentation was obviously inhibited by the substrates and even have a little hydrogen was detected. In this study, the hydrogen yield and the change of the character of substrates during the fermentation processes were measured, the possible reasons for the phenomenon were analyzed. It was demonstrated the hydrogen yield could be effectively improved though removing the appropriate heavy metals.Compared to common sludge pretreatments, biological pretreatment is lower energy and investment cost, much cleaner and securer. Batch tests were carried out to analyze the effects of anaerobic fermentative hydrogen production using excess sludge pretreated by S-TE (solubilization by thermophilic enzyme) with and without inoculation of hydrogen-producing bacteria, Enterococcus sp.LG1. The performance of biohydrogen production of the S-TE pretreated sludge and the 65℃thermally pretreated sludge was also compared in batch fermentation tests. The results showed that sludge pretreated by S-TE without inoculation could make good bio-hydrogen production. The maximal hydrogen yield (H2/VS) was 16.3mL H2/g, 26.4% higher than sludge pretreated by 65℃heat with inoculation and 15.6% than 65℃heat without inoculation. Hydrogen and carbon dioxide were only produced and methane was not observed during the process. The lay time for hydrogen production was only 3~4 hours ,and after reaching its maximum, the bio-hydrogen was able to maintain stable for above 10 hours with little consuming. The bio-hydrogen yield of the S-TE pretreated sludge inoculated Enterococcus sp.LG1 was very low, only 10.7 mL/g.