Biogas by two-stage microbial anaerobic and semi-continuous digestion of Chinese cabbage waste

Anaerobic digestion of Chinese cabbage waste was investigated through a pilot-scale two-stage digester at a mesophilic temperature of 37 ℃. In the acidification digester, the main product was acetic acid, with the maxi- mum concentration of 4289 mg·L^-1 on the fourth day, accounting for 50.32% of total volatile fatty acids. The oxidation reduction potential （ORP） and NH^＋-N level decreased gradually with hydraulic retention time （HRT） of acidification. In the second digestion phase, the maximum methanogenic bacterial concentration reached 9.6 × 10^10ml^-1 at the organic loading rate （OLR） of 3.5-4 kg VS·m^-3, with corresponding HRT of 12-16 days. Accordingly, the optimal biogas production was 0.62 m^3· （kg VS）^-1, with methane content of 65%-68%;. ORP and NH4^＋-N levels in the methanizer remained between -500 and -560 mV and 2000-4500mg· L^-1, respec- tively. Methanococcus and Methanosarcina served as the main methanogens in the anaerobic digester.

Direct-fed microbial: Animal nutrition and reproduction responses

Manipulating the gastrointestinal microbial ecosystem to enhance animal performance and reproductive responses has been one of the main goals of animal science researchers and veterinarians.Recent restrictions to the use of antimicrobials as growth promoters led researchers to seek alternative practices that can show promise both from the standpoint of efficacy as well as from the practical and economic aspects.One of the alternatives that surfaced as very promising in the last few decades is the use of direct-fed microbials （DFM） as a means to modulate the effects of the gastrointestinal microbiome on the host immune status, health and productivity.

Effects of treatment time and temperature on the DC corona pretreatment performance of waste activated sludge

In order to improve the anaerobic digestion efficiency of waste activated sludge（WAS）,a pretreatment procedure should be carried out so as to disrupt the microbial cell structure,thus releasing intracellular organic matters.In this paper,a corona discharge triggered by a DC voltage was employed to pre-treat WAS for various time periods under different temperatures.The magnitude of the DC voltage was 4 k V at both negative and positive polarities.The changes in the soluble chemical oxygen demand,phosphorus and nitrogen content,and p H value within the WAS were utilized to estimate the pretreatment performance of the DC corona.It was found that with increasing treatment time,the pretreatment efficiency tends to be reduced.With increased temperature,the pretreatment efficiency appears to be better.It is suggested that the oxidative species and the active particles generated in the corona discharge play an important role in disrupting the microbial cell structure,which is dependent upon the treatment time and the temperature.

Determination of the archaeal and bacterial communities in two-phase and single-stage anaerobic systems by 454 pyrosequencing

2-Phase anaerobic digestion（AD）, where the acidogenic phase was operated at 2 day hydraulic retention time（HRT） and the methanogenic phase at 10 days HRT, had been evaluated to determine if it could provide higher organic reduction and methane production than the conventional single-stage AD（also operated at 12 days HRT）. 454 pyrosequencing was performed to determine and compare the microbial communities. The acidogenic reactor of the 2-phase system yielded a unique bacterial community of the lowest richness and diversity, while bacterial profiles of the methanogenic reactor closely followed the single-stage reactor. All reactors were predominated by hydrogenotrophic methanogens, mainly Methanolinea. Unusually, the acidogenic reactor contributed up to 24%of total methane production in the 2-phase system. This could be explained by the presence of Methanosarcina and Methanobrevibacter, and their activities could also help regulate reactor alkalinity during high loading conditions through carbon dioxide production. The enrichment of hydrolytic and acidogenic Porphyromonadaceae, Prevotellaceae, Ruminococcaceae and unclassified Bacteroidetes in the acidogenic reactor would have contributed to the improved sludge volatile solids degradation, and ultimately the overall 2-phase system＇s performance. Syntrophic acetogenic microorganisms were absent in the acidogenic reactor but present in the downstream methanogenic reactor, indicating the retention of various metabolic pathways also found in a single-stage system. The determination of key microorganisms further expands our understanding of the complex biological functions in AD process.

Intramolecular carbon isotope of propane from coal-derived gas reservoirs of sedimentary basins:Implications for source,generation and post-generation of hydrocarbons

An intramolecular isotopic study was conducted on natural gases collected from coal-derived gas reser-voirs in sedimentary basins of China to determine their position-specific isotope distributions.The propane from the Turpan-Hami Basin exhibited negativeΔc-T(δ13Ccentral-δ13Cterminal)values ranging from-3.9‰to-0.3‰,with an average of-2.1‰.Propane from the Ordos Basin,Sichuan Basin,and Tarim Basin showed positiveΔC-T values,with averages of 1.3‰,5.4‰and 7.6‰,respectively.Positionspecific carbon isotope compositions reveal the precursors and the propane generation pathways in the petroliferous basins.Propane formed from the thermal cracking of TypeⅢkerogen has largerδ13Ccentral andδ13Cterminal values than propane from TypeⅠ/Ⅱkerogen.The precursor for natural gases collected in this study is identified to be TypeⅢkerogen.Comparing our data to calculated results for thermal cracking of TypeⅢkerogen,we found that propane from the low-maturity gas reservoir in the Turpan Basin was generated via the i-propyl radical pathway,whereas propane from the Sulige tight gas reservoir in the Ordos Basin was formed via the n-propyl radical pathway.δ13Cterminal values covered a narrow range across basins,in contrast toδ13Ccentral.The terminal carbon position in propane is less impacted by microbial oxidation and more relevant to maturity levels and precursors.Thus,δ13Cterminal has a good potential to infer the origin and maturity level of natural gas.In examining post-generation processes,we proposed an improved identification strategy for microbial oxidation of natural gases,based on the position-specific carbon isotope distributions of propane.Samples from the Liaohe Depression of the Bohai Bay Basin and the Sichuan Basin were detected of post-generation microbial oxidation.Overall,position-specific carbon isotope composition of propane provides new insights into the generation mechanism and post-generation processes of natural gas in the geological period at the atomic level.

Mechanisms of carbon storage and the coupled carbon, nitrogen and sulfur cycles in regional seas in response to global change

1.Great challenges in scientific frontiers of marine carbon storage in the scenario of global change The marine carbon cycle is influenced by anthropogenic activities,affecting global climate change and casting a significant impact on ecosystems.However,the complex spatiotemporal process of the marine carbon cycle results in the uncertainty in the estimation of marine carbon budget。