Magnetite nanoparticles facilitate methane production from ethanol via acting as electron acceptors.

Potential for interspecies hydrogen transfer within paddy soil enrichments obtained via addition of magnetite nanoparticles and ethanol (named as PEM) was investigated. To do this, PEM derived from rice field of Hangzhou (named as PEM-HZ) was employed, because it offered the best methane production performance. Methane production and Fe (III) reduction proceeded in parallel in the presence of magnetite. Inhibition experiments with 2-bromoethane sulfonate (BES) or phosphate showed that interspecies hydrogen transfer and Fe (III) reduction also occurred in methane production from ethanol. 16S rRNA-based Illumina sequencing results showed that Dechloromonas, Thauera, Desulfovibrio and Clostridium were the dominant putative Fe (III) -reducers, and that hydrogenotrophic Methanobacterium accounted for about 88% of the total archaeal community. These results indicated that magnetite nanoparticles that acted as electron acceptor could facilitate rapid oxidation of ethanol by members of the Fe (III) -reducers in PEM-HZ and establishment of the syntrophic relationship of Fe (III) -reducers with Methanobacterium via interspecies hydrogen transfer. Our results could offer a model to understand the microbial interaction with magnetite from a novel angle during methanogenesis.

Secondary thermophilic microaerobic treatment in the anaerobic digestion of corn straw.

Thermophilic microaerobic pretreatment (TMP) has been proved to be an alternative pretreatment method during anaerobic digestion (AD) of corn straw. In this study, in order to improve the fermentation efficiency during late AD stage, improve the methane yield and volatile solid (VS) removal efficiency, a secondary thermophilic microaerobic treatment (STMT) was applied in the late AD stage of corn straw. Results showed STMT obviously improved the fermentation efficiency, methane yield and VS removal efficiency. The maximum methane yield and maximum VS removal efficiency were simultaneously obtained when the oxygen loads during STMT was 10 ml/g VS (VS of residual substrate). The maximum methane yield was 380.6 ml/g VS(substrate), which was 28.45% and 10.61% higher than those of untreated and once thermophilic microaerobic pretreated samples, respectively. The maximum VS removal efficiency was 81.85%, which was 29.43% and 17.23% higher than those of untreated and once thermophilic microaerobic pretreated samples, respectively.

Bioaugmentation with an acetate-type fermentation bacterium Acetobacteroides hydrogenigenes improves methane production from corn straw.

The effect of bioaugmentation with an acetate-type fermentation bacterium in the phylum Bacteroidetes on the anaerobic digestion of corn straw was evaluated by batch experiments. Acetobacteroides hydrogenigenes is a promising strain for bioaugmentation with relatively high growth rate, hydrogen yields and acetate tolerance, which ferments a broad spectrum of pentoses, hexoses and polyoses mainly into acetate and hydrogen. During corn straw digestion, bioaugmentation with A. hydrogenigenes led to 19-23% increase of the methane yield, with maximum of 258.1 mL/g-corn straw achieved by 10% inoculation (control, 209.3 mL/g-corn straw). Analysis of lignocellulosic composition indicated that A. hydrogenigenes could increase removal rates of cellulose and hemicelluloses in corn straw residue by 12% and 5%, respectively. Further experiment verified that the addition of A. hydrogenigenes could improve the methane yields of methyl cellulose and xylan (models for cellulose and hemicelluloses, respectively) by 16.8% and 7.0%.

The thermophilic (55°C) microaerobic pretreatment of corn straw for anaerobic digestion.

Microaerobic process has been proven to be an alternative pretreatment for the anaerobic digestion (AD) process in several studies. In this study, the effect of thermophilic microaerobic pretreatment (TMP) on the AD of corn straw was investigated. Results indicated that TMP process obviously improved the methane yield. The maximum methane yield was obtained at the oxygen loads of 5ml/g VSsubstrate, which was 16.24% higher than that of untreated group. The modified first order equation analysis showed the TMP process not only accelerated the hydrolysis rates but also reduced the lag-phase time of AD process. The structural characterization analysis showed cellulosic structures of corn straw were partly disrupted during TMP process. The crystallinity indexes were also decreased. In addition, large or destroyed pores and substantial structural disruption were observed after pretreatment. The results showed that TMP is an efficient pretreatment method for the AD of corn straw.