Combined modifications of CaO and liquid fraction of digestate for augmenting volatile fatty acids production from rice straw: Microbial and proteomics insights.

The modification sequence of chemical (CaO) and biological (liquid fraction of digestate, LFD) for augmenting volatile fatty acids (VFAs) production from rice straw was investigated in this study. The coupling order of the modifiers influenced acidification performance, and simultaneous modification (CaO-LFD) was superior to other modes. The highest VFAs production was obtained in CaO-LFD, 51% higher than that in the LFD-first additional modification. The CaO-LFD demonstrated the highest selectivity of acetate production, accounting for 79% of the total VFAs. In addition, CaO-LFD modification changed the direction of the domestication of fermentative bacteria and increased populations of the key anaerobes (Atopostipes sp.) responsible for acidification. The synergistic effect of CaO and LFD was revealed, namely, the effective function of CaO in degrading recalcitrant rice straw, the promotion of transport/metabolism of carbohydrates and acetogenesis by LFD.

Current development and perspectives of anaerobic bioconversion of crop stalks to Biogas: A review.

As one of the most abundant biomass resources, crop stalks are great potential feedstock available for anaerobic digestion (AD) to produce biogas. However, the specific physical properties and complex chemical structures of crop stalks form strong barriers to efficient AD bioconversion. To overcome these problems, many efforts have been made over the past few years. This paper reviewed recent research in the evolving field of anaerobic bioconversion of crop stalks and was focused on three critical aspects affecting AD performance: various pretreatment methods and their effects on the improvement of crop stalk biodegradability, determination of specific AD operation parameters for crop stalks, and development of AD technologies. Finally, recommendations on the future development of crop stalk AD were proposed.

Effect of low severity hydrothermal pretreatment on anaerobic digestion performance of corn stover.

The anaerobic digestion (AD) performance of corn stover was investigated under low hydrothermal pretreatment (HP) severity. Pretreated corn stover, with and without ammonia was examined at the three temperatures (50, 70, and 90 °C) coupled with different pretreatment time (24-72 h). The results showed that the pH value decreased with increasing pretreatment time for the same temperature. The highest volatile fatty acids (VFAs) concentration (4616.23 mg/L) was achieved at a HP severity of 4.56. The highest removal rate of cellulose, hemicellulose, and lignin were 19.62%, 25.53%, and 32.91% for HP with ammonia (HPA) severities of 3.34, 3.34, and HP severity of 4.35, respectively. The maximum methane yield of corn stover was 148.19 mL/g∙VS under 50 °C held for 24 h (HPA severity of 2.59), which was 31.35% higher than that of the untreated corn stover. The research results suggest that properly pretreatment severity can play an important role in promoting methane production.

Enhancing methane production of excess sludge and dewatered sludge with combined low frequency CaO-ultrasonic pretreatment.

Methane production of excess sludge (ES) and dewatered sludge (DS) were investigated with low frequency CaO-ultrasonic pretreatment. The results showed that the concentrations of SCOD and VFAs in pretreated ES (P-ES) and DS (P-DS) were 212.11% and 75.26%, 270.30% and 159.52% higher than those of untreated ES and DS, respectively. The contents of acetic acid and ethanol comprised 83.87%-92.88% of the total VFAs. The cumulative methane production (CMP) of P-ES and P-DS were 167.08 and 162.96 mL/g·VS, respectively, which resulted in 40.45% and 36.94% higher than those of untreated ones. The biodegradability of P-ES was 87.65%, which was close to theoretical value. Low frequency CaO-ultrasonic pretreatment could not only improve the performance of anaerobic digestion (AD), but also accelerate the decomposition rate of two kinds of sludge. Therefore, this study provided meaningful insight for exploring efficient pretreatment strategy to stabilize and enhance AD performance for practical application.

Enhancing anaerobic digestion performance and degradation of lignocellulosic components of rice straw by combined biological and chemical pretreatment.

In order to determine eco-friendly pretreatment method, the combination of different pretreatment reagents such as: CaO, ammonia solution (AS), liquid fraction of digestate (LFD), CaO-AS and CaO-LFD were used in this study. The features of physico-chemical structures and anaerobic digestion (AD) performance of rice straw were investigated using different combined biological and chemical pretreatment methods. The results showed that CaO-LFD bio-chemical pretreatment achieved the best effect among different pretreatment conditions. The removal rate of lignocellulosic components from CaO-LFD pretreated rice straw was 20.73% higher than that of the control sample. The ether and ester bonds between lignin and hemicellulose were ruptured during pretreatment. Moreover, the methane yield from CaO-LFD pretreated rice straw was 274.65 mL gVS-1, which was 57.56% more than the control. Compared with the untreated rice straw, T80 decreased by 42.86%. CaO-LFD combined pretreatment has advantages as both biological and chemical pretreatment, which complement each other to improve the degradation of the rice straw. Meantime, AD performance was improved and excellent economic viability was achieved. Therefore, this study provides sustainable insight for exploring efficient pretreatment strategy to stabilize and enhance AD performance for further application.