Enhancement of volatile fatty acids production from rice straw via anaerobic digestion with chemical pretreatment.

Rice straw is one of the most abundant renewable biomass sources and was selected as the feedstock for the production of volatile fatty acids (VFAs) from which microbial biodiesel can be produced. Two kinds of chemical pretreatments involving nitric acid and sodium hydroxide were investigated at 150 °C with 20 min of reaction time. The nitric acid pretreatment generated the most hemicellulose hydrolyzate, while significant reduction of the lignin occurred with sodium hydroxide pretreatment. Anaerobic digestion of 20 g/L rice straw yielded 6.00 and 7.09 g VFAs/L with 0.5% HNO3 and 2% NaOH, respectively. The VFAs yield with 2% NaOH was 0.35 g/g.

A comprehensive study on volatile fatty acids production from rice straw coupled with microbial community analysis.

Rice straw is one of the most abundant renewable energy sources available. Through anaerobic acidogenesis, the substance of rice straw can be converted to volatile fatty acids (VFAs). VFAs itself is of value and is a precursor to biofuels. Hence, it can be converted to mixed alcohols by addition of hydrogen, and biodiesel can be produced as a carbon source for oleaginous microorganism. To maximize VFAs production during anaerobic digestion (AD), response surface analysis (RSM) was carried out with respect to temperature, substrate concentration, and pH variables. Optimization results showed maximal VFAs concentration of 12.37 g/L at 39.23 °C, 52.85 g/L of rice straw, and pH 10. In quantification of microbial community by quantitative polymerase chain reaction, the bacterial profile showed that the growth of methanogens was effectively inhibited by methanogenic inhibitors. Furthermore, 454 pyrosequencing showed that members of the Ruminococcaceae family, capable of hydrolyzing lignocellulosic biomass, were the most dominant species in many RSM trials. This study provided a useful insight on the biological improvement of AD performance through the combinational linkage between process parameters and microbial information.

Optimization of volatile fatty acids and hydrogen production from Saccharina japonica: acidogenesis and molecular analysis of the resulting microbial communities.

Response surface methodology (RSM) was used to optimize the production of volatile fatty acids (VFAs) and hydrogen from mixed anaerobic cultures of Saccharina japonica with respect to two independent variables: methanogenic inhibitor concentration and temperature. The effects of four methanogenic inhibitors on acidogenic processes were tested, and qualitative microbial analyses were carried out. Escherichia, Acinetobacter, and Clostridium were the most predominant genera in samples treated with chloroform (CHCl3), iodoform (CHI3), 2-bromoethanesulfonate (BES), or ß-cyclodextrin (ß-CD), respectively. RSM showed that the production of VFAs reached a peak of 12.5 g/L at 38.6 °C in the presence of 7.4 g/L ß-CD; these were the conditions under which hydrogen production was also nearly maximal. The quantitative polymerase chain reaction (qPCR) showed that shifts in the bacterial community population correlated with the concentrations of ß-CD indicating that this compound effectively inhibited methanogens.

Improved volatile fatty acid and biomethane production from lipid removed microalgal residue (LRµAR) through pretreatment.

Renewable energy from lipid removed microalgal residues (LRµARs) serves as a promising tool for sustainable development of the microalgal biodiesel industry. Hence, in this study, LRµAR from Ettlia sp. was characterized for its physico-biochemical parameters, and applied to various pretreatment to increase the biodegradability and used in batch experiments for the production of volatile fatty acids (VFA) and biomethane. After various pretreatments, the soluble organic matters were increased at a maximum of 82% in total organic matters in alkali-autoclaved sample. In addition, VFA and methane production was enhanced by 30% and 40% in alkali-sonicated and alkali-autoclaved samples, respectively. Methane heating value was recovered at maximum of 6.6 MJ kg(-1)VS in alkali-autoclaved conditions with comparison to non-pretreated samples. The pretreatment remarkably improved LRµAR solubilization and enhanced VFA and biomethane production, which holds immense potential to eventually reduce the cost of algal biodiesel.