Synergistic effect of two bacterial strains promoting anaerobic digestion of rice straw to produce methane

A large amount of agricultural waste causes global environmental pollution. Biogas production by microbial pretreatment is an important way to utilize agricultural waste resources. In this study, Sporocytophaga CG-1 (A, cellulolytic strain) was co-cultured with Bacillus clausii HP-1 (B, non-cellulolytic strain) to analyze the effect of pretreatment of rice straw on methanogenic capacity of anaerobic digestion (AD). The results showed that weight loss rate of filter paper of co-culture combination is 53.38%, which is 29.37% higher than that of A. The synergistic effect of B on A can promote its degradation of cellulose. The cumulative methane production rate of the co-culture combination was the highest (93.04 mL/g VS substrate), which was significantly higher than that of A, B and the control group (82.38, 67.28 and 67.70 mL/g VS substrate). Auxiliary bacteria can improve cellulose degradation rate by promoting secondary product metabolism. These results provide data support for the application of co-culture strategies in the field of anaerobic digestion practices.

An efficient strategy to improve enzymatic hydrolysis of naked oat straw pretreated by Irpex lacteus

The objective of this study was aiming at developing an efficient strategy to promote enzymatic hydrolysis of naked oat straw and deciphering the potential mechanism. Irpex lacteus and Phlebia acerina were employed to inoculated on the naked oat straw for 4 weeks which the changes of fiber components, fermentation losses, lignin-degrading enzymes production pattern were determined weekly. Furthermore, the 72 h enzymatic hydrolysis of ultimately fermented naked oat straw were also evaluated. The acid detergent lignin was degraded at about 25% along with the moderate dry matter and cellulose loss which both showed selective degradation. The lignin-degrading enzymes production patterns of the two fungi were different which lignin peroxidase was not detected in Irpex lacteus treatment. In addition, the activities of cellulolytic enzymes were higher in Phlebia acerina treatment. After 72 h enzymatic hydrolysis, the reducing sugar content and hydrolysis yield pretreated by Irpex lacteus was 12.92 g/L and 69.49%, respectively. It was much higher than that in sterilized substrate and Phlebia acerina treatment. Meanwhile, the hydrolysis yields of glucose, sum of xylose and arabinose were all improved by Irpex lacteus which were 30.96% and 25.62%, respectively, and showed significant enhancements compared to control and Phlebia acerina treatment. Irpex lacteus is one of effective white rot fungi which could promote the enzymatic hydrolysis of naked oat straw obviously.

Bio-pretreatment promote hydrolysis and acidification of oilseed rape straw: Roles of fermentation broth and micro-oxygen

Oilseed rape straw (ORS) is capable of producing renewable energy. However, cellulose, hemicellulose and lignin are intertwined together in ORS, which makes it difficult for anaerobic digestion (AD). Hence, pretreatment is the key factor in reducing the rate-limiting step of AD. This study reports that the pretreatment combined fermentation broth and micro-oxygen could enhance the degradation of ORS. The maximum biodegradation ratios of cellulose, hemicellulose, and lignin (CHL) were 20.6%, 18.1%, and 24.7%, respectively, at 120 mL/gVS/d oxygen load. The maximum volatile fatty acids and soluble chemical oxygen demand of hydrolysis and acidification of the pretreated groups were significantly higher than that of the control groups. Microorganisms in the fermentation broth at micro-aerobic conditions led to the reduction of CHL content, and altered the structure of ORS. The fermentation broth bio-pretreatment could effectively decrease the functional groups related to lignin.

Importance of storage time in mesophilic anaerobic digestion of food waste

Storage was used as a pretreatment to enhance the methanization performance of mesophilic anaerobic digestion of food waste. Food wastes were separately stored for 0, 1, 2, 3, 4, 5, 7, and 12days, and then fed into a methanogenic reactor for a biochemical methane potential (BMP) test lasting up to 60days. Relative to the methane production of food waste stored for 0-1day (285-308mL/g-added volatile solids (VSadded)), that after 2-4days and after 5-12days of storage increased to 418-530 and 618-696mL/g-VSadded, respectively. The efficiency of hydrolysis and acidification of pre-stored food waste in the methanization reactors increased with storage time. The characteristics of stored waste suggest that methane production was not correlated with the total hydrolysis efficiency of organics in pre-stored food waste but was positively correlated with the storage time and acidification level of the waste. From the results, we recommend 5-7days of storage of food waste in anaerobic digestion treatment plants.

Effect of biodegradation on thermogravimetric and chemical characteristics of hardwood and softwood by brown-rot fungus

The thermogravimetric and chemical characterization of hardwood Eucalyptus urophylla (Ep) and softwood Pinus massoniana (Mp) pretreated by brown-rot fungus Gloeophyllum trabeum were investigated. The results indicated that the brown-rot fungus pretreatment can optimize the thermal decomposition and decrease the initiation temperatures (8-11°C lower) of both the Ep and Mp pyrolysis. The mean activation energy values of the bio-treated samples were 29.7kJ/mol (for Ep) and 42.3kJ/mol (for Mp) lower than that of the un-treated samples at the conversion rate from 0.1 to 0.7 based on Flynn-Wall-Ozawa (FWO) method. After the bio-pretreatment, the required temperatures were lower (4-7°C) for the pyrolysis rates of hemicellulose and cellulose in Mp reaching maximum and termination. However, the situation was just the opposite for Ep. The variations in chemical properties of hydrogen bonding, as well as the relative changes in lignin/carbohydrate composition of both wood species were also examined.

Biological pretreatment of corn stover with ligninolytic enzyme for high efficient enzymatic hydrolysis

Aiming at increasing the efficiency of transferring corn stover into sugars, a biological pretreatment was developed and investigated in this study. The protocol was characterized by the pretreatment with crude ligninolytic enzymes from Phanerochete chrysosporium and Coridus versicolor to break the lignin structure in corn stover, followed by a washing procedure to eliminate the inhibition of ligninolytic enzyme on cellulase. By a 2 d-pretreatment, sugar yield from corn stover hydrolysis could be increased by 50.2% (up to 323 mg/g) compared with that of the control. X-ray diffractometry and FT-IR analysis revealed that biological pretreatment could partially remove the lignin of corn stover, and consequently enhance the enzymatic hydrolysis efficiency of cellulose and hemeicellulose. In addition, the amount of microbial inhibitors, such as acetic acid and furfural, were much lower in biological pretreatment than that in acid pretreatment. This study provided a promising pretreatment method for biotransformation of corn stovers.