Microorganism screening for ethanol production using gasification gas from agricultural residue

Abstract: Ethanol is one of the most important alternative biofuels, which provides a net energy gain, has environmental benefits and is economically competitive. Ethanol production from syngas anaerobic fermentation appears to be a potential and promising technology compared to the existing chemical conversion techniques. Currently, syngas fermentation is being developed as one option towards the production of bio-ethanol from biomass. Agricultural residue biomass such as corn stalks and wheat stalks, has been an important part of the biomass resource in the world. Much attention has been attracted on the conversation and utilization of these biomasses with high value. The gasification of the agricultural residue biomass is a mature and industrialized technology up to now. Gasification of agricultural lignocellulosic residue followed by syngas fermentation to produce bio-ethanol is being explored owing to the low cost and availability of agricultural residue feedstock. The process can not only change trash to treasure but also be of benefit to reduce environmental pollution, which will promote the sustainable development of agriculture and improve the rural environment. It has been found that some anaerobic bacteria can be used to convert syngas to ethanol and acetic acid, such as Clostridium ljungdahlii and C. autoethanogenum. But the excellent strains are still very limited and their productivity levels are not high. According to the fact that bio-ethanol production from syngas in anaerobic conditions still can not be industrialized, special emphasis has been given to obtain the efficient microorganism fermenting that transfers syngas to ethanol. In order to obtain strains for high efficient ethanol production by syngas generated from agricultural residue, ethanol fermentations taking syngas as the sole carbon source and energy source were carried out. Ethanol production potentials were compared among the mixed-cultures A-fm4, B-fm4, G-fm4 and LP-fm4 and the reported strains Clostridium carboxidivorans P7, Clostridium sp. P11, C. ljungdahlii and C. autoethanogenum DSM10061. Meanwhile, microbial mixed-cultures A-fm4, B-fm4, G-fm4 and LP-fm4 were isolated from animal faeces samples of alpaca, papion, lesser panda and gibbon respectively under strict anoxic condition in 200 mL bottle. Batch fermentations were done in 300 mL serum bottles each containing 60 mL fermentation medium. 10% (v/v) of inoculum was transferred to fresh media. The 240 mL syngas was injected into the 300 mL serum bottle by syringe. Experiments were conducted for 7 days. The results showed that all of the cultures/mixed-cultures can transform syngas into biofuel ethanol. The net ethanol production and specific cell growth rate were 179.23, 152.92, 115.08 mg/L and 1.46, 1.66, 1.18 d-1, respectively, for culture/mixed-cultures LP-fm4, Clostridium sp. P11 and A-fm4. Their specific ethanol production rate and ethanol production amount per cell were 3.50, 2.05, 0.78 d-1 and 2252.90, 1450.20, 1132.37 mg/g (dry cell weight, DCW), respectively. These parameters were significantly higher than those of other treatments. Duncan analysis and dendrogram of cluster analysis also agreed that mixed-culture/strain LP-fm4 and Clostridium sp. P11 were the ideal microorganisms for ethanol production by syngas generated from agricultural residue, and mixed-culture A-fm4 was a potential candidate. The research results will provide excellent microorganisms for fermentation of syngas generated from agricultural residue in the future.