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.

Effect of supplementation of allicin on methanogenesis and ruminal microbial flora in Dorper crossbred ewes

Background： Garlic extracts have been reported to be effective in reducing methanogenesis. Related mechanisms are not well illustrated, however, and most studies have been conducted in vitro. This study investigates the effects of supplementary allicin（AL） in sheep diet on in vivo digestibility, rumen fermentation, and shifts of microbial flora.Methods： Two experiments were conducted using Dorper × thin-tailed Han crossbred ewes. In experiment 1,eighteen ewes（60.0 ± 1.73 kg BW） were randomly assigned for 29 days to either of two dietary treatments： a basal diet or the basal diet supplemented with 2.0 g AL/head？day to investigate supplementary AL on nutrient digestibility and methane emissions. In experiment 2, six ewes（65.2 ± 2.0 kg BW） with ruminal canulas were assigned to the same two dietary treatments as in experiment 1 for 42 days to investigate supplementary AL on ruminal fermentation and microbial flora. The methane emissions were determined using an open-circuit respirometry system and microbial assessment was done by q PCR of 16 S r RNA genes.Results： Supplementary AL increased the apparent digestibility of organic matter（P 〈 0.001）, nitrogen（P = 0.006）,neutral detergent fiber（P 〈 0.001）, and acid detergent fiber（P = 0.002）. Fecal nitrogen output was reduced（P = 0.001）but urinary nitrogen output was unaffected（P = 0.691）, while nitrogen retention（P = 0.077） and nitrogen retention/nitrogen intake（P = 0.077） tended to increase. Supplementary AL decreased methane emissions scaled to metabolic bodyweight by 5.95 %（P = 0.007） and to digestible organic matter intake by 8.36 %（P = 0.009）. Ruminal p H was unaffected（P = 0.601） while ammonia decreased（P = 0.024） and total volatile fatty acids increased（P = 0.024） in response to supplementary AL. Supplementary AL decreased the population of methanogens（P = 0.001） and tended to decrease that of protozoans（P = 0.097）, but increased the populations of F. succinogenes（P 〈 0.001）, R. flavefaciens（P = 0.001）, and B. fibrisolvens（P = 0.001）.Conclusions： Supplementation of AL at 2.0 g/head？day effectively enhanced OM, N, NDF, and ADF digestibility and reduced daily methane emissions（L/kg BW0.75） in ewes, probably by decreasing the population of ruminal protozoans and methanogens.

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.

Comparative study on microbial community in intermittently aerated sequencing batch reactors （SBR） and a traditional SBR treating digested piggery wastewater

A traditional sequencing batch reactor （SBR） and two intermittently aerated sequencing batch reactors （IASBRs） were parallelly operated for treating digested piggery wastewater. Their microbial communities were analyzed, and the nitrogen removal performance was compared during the long term run. IASBRs demonstrated higher removal rates of total nitrogen （TN） and ammonium nitrogen （NH4＋ -N） than the SBR, and also demonstrated higher resistance against TN shock load. It was found that the more switch times between aerobic/anoxic in an IASBR, the higher the removal rates of TN and NH4＋ N. All the reactors were predominated by Thauera, Nitrosomonas and Nitrobacter, which were considered to be species of denitrifiers, ammonium oxidizing bacteria （AOB） and nitrite oxidizing bacteria （NOB）, respectively. However, the abundance and diversity was of great difference. Compared with SBR, IASBRs achieved higher abundance of denitrification related bacteria. IASBR 1# with four aerobic/anoxic switch times was detected with 25.63% of Thauera, higher than that in IASBR 2# with two aerobic/anoxic switch times （l 1.57% of Thauera）, and much higher than that in the SBR （only 6.19% of Thauera）. IASBR 2# had the highest percentage of AOB, while 1ASBR 1# had the lowest percentage. The denitrifiers abundance was significantly positive correlated with the TN removal rate. However, the NH4＋ N removal rate showed no significant correlation with the AOB abundance, but might relate to the AOB activity which was influenced by the average free ammonium （FA） concentration. Nitrobacter was the only NOB genus detectable in all reactors, and were less than 0.03%.

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.