Study On Gas Production By Anaerobic Fermentation

Macrocystis pyrifera is a kind of ideal biomass resources due to their increased productivity rates, negligible lignin content and higher CO2 fixation ability compared to terrestrial biomass. In addition, they can be cultivated on vast tracts of sea by sunlight without compete for food with people. Therefore, research on fermentative bio-hydrogen production using M. pyrifera as a feedstock has been attracted great interest in recent years. M. pyrifera biomass residues is the main byproducts of seaweed chemical process, If they can be converted to hydrogen and volatile fatty acid(VFA), it’s have great significance to improve the utilization and economic of M. pyrifera biomass. In the same time, they can reduce waste emissions of seaweed industry.Firstly, effects of different pretreatment condition, substrate concentration and initial pH on hydrogen and VFA production during the anaerobic fermentation of M. pyrifera biomass residues were evaluated. The results indicated that the yield of TVFA is positively correlated with hydrogen production, and the M. pyrifera biomass residues can produce hydrogen and TVFA synchronization. In addition, thermo-alkaline pretreatment was the best method for hydrogen and VFA production. The optimum pretreatment condition, substrate concentration, initial pH were determined to be thermal-alkaline pretreatment at 100 ℃with 0.1 mol/L NaOH, 40 g/L and 7, respectively. Under these conditions, the maximum hydrogen production was 11.38 mL/g-vs, which was approximately twenty-three-fold higher than the yield from untreated M. pyrifera biomass residues. Furthermore, the maximum TVFA yield was fould to be 0.55 g/g-vs. In the process of fermentation, the VFA mainly consisted of acetate and butyrate.Secondly, M. pyrifera were conducted to analyze the effects of pretreatment conditions, inoculum-substrate ratio(ISR) and initial pH on the hydrogen and production VFA from anaerobic digestion of M. pyrifera biomass. The results indicate that M. pyrifera can produce hydrogen and VFA simultaneously. In addition, thermo-alkaline pretreatment was proved as the best method for hydrogen and VFA production. The optimum pretreatment conditions, ISR, initial pH value were determined as thermal-alkaline pretreatment at 100 ℃ with 4 g/L NaOH, 0.3 and 6, respectively. Under these conditions, the maximum hydrogen production was 36.21 mL/g-vs, which resulted in 77.82% improvement compared with the yield from untreated M. pyrifera. Furthermore, the TVFA yield under the optimum conditions was found to be 0.15 g/g-vs and the VFA mainly consisted of acetate and butyrate.Finally, in order to develop the best technology route to product methane, the one-stage process and two-stage process to produce methane from M. pyrifera were compared. The results indicate that one-stage process was suitable for improving methane yield. Under these conditions, the semi-continuous fermentation reactor was used to study the effect of organic load on the yield of methane. When the organic load was 5.14 kg-vs/m3/d, the maximum yield of gas and methane were 32.03 L and 228.24±5.37 mL/g-vs, respectively. When the organic load increased continuously to 8.56kg-vs/m3/d, the increasing of organic acid and salinity leading to the decline of the gas production.