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Highlights: [•] The two-phase anaerobic co-digestion of CD with PM was evaluated using 4 SBRs and a CSTR. [•] Co-acidification of PM and CD promoted the production and accumulation of VFAs, SCOD and NH4–N. [•] Methanogenic fermentation of the acidification products was efficient and steady. [•] Co-digestion of PM and CD supported higher quantity and diversity of methanogens. [ABSTRACT FROM AUTHOR]

Abstract: The microbial consortium WSD-5 is composed of bacteria and fungi, and the cooperation and symbiosis of the contained microbes enhance the degradation ability of WSD-5. Experiment results showed that the highest cellulase and hemicellulase were obtained when ventilation volume was 4L/min, stirring rate was 0rpm, and substrate loading rate was 3%. After 6days of cultivation, a 67.60% loss in wheat straw dry weight was observed. The crude enzyme secreted from WSD-5 after optimization was evaluated by experiments of saccharification and acidification. The maximum concentration of reducing sugars was 3254mg/L after 48h saccharification. The concentration of sCOD peaked on day 2 with a value of 4345mg/L during acidification, and the biogas yield and methane yield were 22.3% and 32.3% higher than un-acidified samples. This study is the first attempt to explore both the saccharification and the acidification ability of crude enzymes secreted by microbial consortium. [Copyright &y& Elsevier]

The methane yield and microbial community resulting from co-digestion of dairy manure and switchgrass at different mixing ratios [4:0, 3:1, 2:2, 1:3, and 0:4 based on total solids (TS) content] were evaluated. The results indicated that switchgrass is an excellent feedstock for biogas production when co-digested with dairy manure. Mono-digestion of a high dose (>4% TS) of switchgrass led to volatile fatty acid accumulation and process failure, whereas co-digestion of switchgrass and dairy manure could increase the buffering capacity and improve the fermentation efficiency. The optimal mixture ratio of dairy manure and switchgrass was 2:2, with a methane yield that was 39% higher than that obtained by digestion of the individual substrates. The added amount of 8% TS at the 2:2 ratio achieved the highest methane yield of 158.6 mL/g VS, which corresponded to a 1.3-fold increase in the volumetric productivity of methane compared to mono-digestion of 4% TS switchgrass. Quantitative polymerase chain reaction and clone library analyses showed significant differences in the bacterial community resulting from the different co-substrate ratios. Planctomycetes (28%), Chloroflexi (24%), and Bacteroidetes (24%) were the dominant phyla in digesters with a co-substrate ratio of 2:2. [ABSTRACT FROM AUTHOR]

Methane production from lignocellulosic feedstock through high solid anaerobic digestion is a huge potential technology. However, the shortage of an efficient reactor has become a major bottleneck in developing the technology. The continuous feeding and discharge of lignocellulosic feedstock with high solids is difficult to complete. Methane production from the feedstock is low in practice. Thus, it is important to develop a new reactor with efficient feeding and discharge feedstock equipments and improve methane production by an optimized operation process. Based on synthesizing the merits of a number of techniques home and abroad, a novel anaerobic reactor was designed in this study. The reactor had two spiral equipments to implement continuous feeding and discharge feedstock with high solid content and had a high bearing capability of organic loading rate (OLR) to improve methane production. In order to provide a technology and some reliable operating parameters to efficiently produce methane from lignocellulosic feedstock, the continuous anaerobic co-digestion tests were conducted at three total solid contents of 10%, 15% and 20% using corn stalk and dairy manure as feedstock. An integrated two-phase division digestion system was constructed by controlling stirring intensity (h/d) and feeding intensity (d). The methane volumetric production rate (MVPR) of different OLRs was compared. Effects of the total solid (TS) of feedstock, stirring, feeding intensity on height, pH of function divisions, and MVPR were discussed in detail. The results showed that function divisions, including the acidification division of upside and methanogenic division of underpart in the vertical reactor, were obviously formed when TS were 10% and 15%, MVPR gradually increased, and methane content stabilized around 52% with OLR increasing. The highest MVPR reached 1.62 and 1.66 m3/(m3·d) respectively when OLR was 13.44 kg/(m3·d) at 10% TS and 20.17 kg/(m3·d) at 15% TS. MVPR significantly decreased when OLR was 20.17 kg/(m3·d) and 30.0 kg/(m3·d), respectively, which might be caused by the accumulation of volatile fatty acids. MVPR stabilized around 0.98 m3/(m3·d) with OLR increasing, then it dramatically decreased and anaerobic digestion failed when OLR reached 30.0 kg/(m3·d) at 20% TS. The results of two factors interacting declared the highest MVPR at 1.63-1.69 m3/(m3·d) The efficient acidification division and methanogenic division were formed, and the height ratio of both was 1.1-1.6:1 when stirring intensity, feeding intensity, and TS were 6-12 h/d, 6.5-10 d, and 10%-15%, respectively. In summary, the process of continuous feeding and discharge at 10%-20% TS of lignocellulosic feedstock was feasible in the anaerobic digestion reactor. The reactor was more efficient and stable to produce methane at 10% and 15% TS compared to 20% TS, and MVPR could be improved by adjusting stirring intensity and feeding intensity. Therefore, this technology has a promising prospect for industrial scale application. [ABSTRACT FROM AUTHOR]

In China, about 7.0×108 t of crop straws may be collected annually, and the amount suitable for converting to feed was approximately accounted for 85.67%. However, low digestibility and protein content prevent its use in feedlots, much of these materials were disposed by burning, which resulted in environmental pollution. A matrix formed by lignin and hemicellulose surrounds the orderly cellulose microfibrils and reduces their digestibility. The breakdown of the bonds between lignin and cellulose is the key to transform the lignocellulosic substrate into a high quality feed for ruminants. Studies have provided various results that removal of lignin enhanced the digestibility of straws. Although hemicellulose has higher potential digestibility than the other cell wall components, its degradation was not maximized because it concentrated in the primary wall, and no research results has been provided that the removal of hemicelluloses enhanced the digestibility. In order to improve the digestibility and nutrition value of air-dried corn stalk, and to develop a convenient and practical straw feed processing technology, experiments were carried out as follows: 1) Corn stalk was fermented at 60℃ in a feed fermentation machine for 5 days, after the moisture content of which was adjusted to 60%, and hemicellulose-degrading microflora WDC2 was inoculated in them; 2) Lactic acid bacteria community S FC-2 was cultivated in a fermentation tank, the working volume of which was 30 L; 3) Culture broth of SFC-2 was sprayed evenly on the corn stalk being partially degraded, at the rate of 1:1 (m/v) to produce fermented straw feed. In this study, the feasibility of bioconversion of straw as forage by dividing the fermentation into lignocellulose decomposition of corn stalk and malolactic fermentation of lactic acid bacteria, was discussed from the nutriology and the molecular ecology. The results indicated that after 5 days high-temperature fermentation, the degradation rates of cellulose, hemicelluloses and lignin were 5.36%, 18.83% and 3.29%, respectively, and in vitro digestibility of dry matter, neutral detergent fiber and acid detergent fiber improved by 13.94%, 22.56% and 21.12%, respectively. In addition, dry matter, crude protein and water soluble carbohydrate content, as well as in vitro degradation rate showed that the quality of products was stable during the continuous fermentation. The results of PCR-DGGE indicated that the diversity of microorganisms in the decomposed straw was very abundant, however, no pathogenic bacteria was detected. Meanwhile, during the continuous fermentation of lactic acid bacteria, the microbial composition of the lactic acid bacteria community, OD600 and pH value of the culture broth were all stable. However, lactic acid and ethanol content were decreased and acetic acid was increased as the cultivate time. Which indicated that the period of continuous fermentation should be controlled in 10 days for more lactic acid and less acetic acid. Compared with the untreated stalk, the crude protein content of the partially decomposed stalk mixed with the culture broth of SFC-2 increased by 36.17%. Twelve Nanyang cattles were used as experimental animal to determinate their feed intake on the treated straw, the results showed that the dry matter intake increased by 21.71%, compared to the untreated treatment. In conclusion, by coupling lignocellulose decomposition of corn stalk and malolactic fermentation of lactic acid bacteria, both digestibility and nutritive value of corn stalk and dry matter intake of beef cattle on it were improved. [ABSTRACT FROM AUTHOR]