Stability of a percolating anaerobic downflow fixed film reactor under overloading conditions

Summary An anaerobic downflow fixed film (DSFF) reactor was used to treat cheese whey. The reactor was initially operated flooded (DSFF mode) and then the liquid level reduced by 67% (ATF mode); thus, the packing support was completely submerged and one third submerged respectively. The partly submerged anaerobic culture had higher gas production, and was more resistant to general and localized high VFA levels; methanogenic bacteria were acclimated to VFA levels as high as 3000 mg/l of propionate and 1600 mg/l of acetate (pH near neutrality) whilst the reactor remained stable.     

Pattern of non-methanogenic and methanogenic degradation of cellulose in anoxic rice field soil

Rice field soils turn anoxic upon flooding. The complete mineralization of organic matter, e.g. cellulose, to gaseous products is then accomplished by the sequential reduction of nitrate, ferric iron, sulfate and finally by methanogenesis. Therefore, the anaerobic turnover of [U-(14)C]cellulose was investigated in fresh, non-methanogenic and in preincubated, methanogenic slurries of Italian rice field soil. In anoxic soil slurries freshly prepared from air-dried soil [U-(14)C]cellulose was converted to (14)CO(2) and (14)CH(4) in a ratio of 3:1. In methanogenic soil slurries, on the other hand, which had been preincubated for 45 days under anaerobic conditions, [U-(14)C]cellulose was converted to (14)CO(2) and (14)CH(4) in the ratio of 1:1. The turnover times (7-14 days) of cellulose degradation were not significantly different (P0.05) in fresh and methanogenic soil. Chloroform addition abolished CH(4) production, but only slightly (30%) inhibited cellulose degradation in both fresh and methanogenic soil. Under both soil conditions, [(14)C]acetate was the only labeled intermediate detected. A maximum of 24% of the applied radioactivity was transiently accumulated as [(14)C]acetate in both fresh and methanogenic soil slurries. However, when methanogenesis was inhibited by chloroform, 46% and 66% of the applied radioactivity were recovered as [(14)C]acetate in fresh and methanogenic soil, respectively. Only non-radioactive propionate accumulated during the incubation with [U-(14)C]cellulose, especially in the presence of chloroform, indicating that propionate was produced from substrates other than cellulose.     

Changes in in vitro gas and methane production from rumen fluid from dairy cows during adaptation to feed additives in vivo

The adaptation of dairy cows to methane (CH₄)-mitigating feed additives was evaluated using the in vitro gas production (GP) technique. Nine rumen-fistulated lactating Holstein cows were grouped into three blocks and within blocks randomly assigned to one of three experimental diets: Control (CON; no feed additive), Agolin Ruminant^R (AR; 0.05 g/kg dry matter (DM)) or lauric acid (LA; 30 g/kg DM). Total mixed rations composed of maize silage, grass silage and concentrate were fed in a 40 : 30 : 30 ratio on DM basis. Rumen fluid was collected from each cow at days −4, 1, 4, 8, 15 and 22 relative to the introduction of the additives in the diets. On each of these days, a 48-h GP experiment was performed in which rumen fluid from each individual donor cow was incubated with each of the three substrates that reflected the treatment diets offered to the cows. DM intake was on average 19.8, 20.1 and 16.2 kg/day with an average fat- and protein-corrected milk production of 30.7, 31.7 and 26.2 kg/day with diet CON, AR and LA, respectively. In general, feed additives in the donor cow diet had a larger effect on gas and CH₄ production than the same additives in the incubation substrate. Incubation substrate affected asymptotic GP, half-time of asymptotic CH₄ production, total volatile fatty acid (VFA) concentration, molar proportions of propionate and butyrate and degradation of organic matter (OMD), but did not affect CH₄ production. No substrate×day interactions were observed. A significant diet×day interaction was observed for in vitro gas and CH₄ production, total VFA concentration, molar proportions of VFA and OMD. From day 4 onwards, the LA diet persistently reduced gas and CH₄ production, total VFA concentration, acetate molar proportion and OMD, and increased propionate molar proportion. In vitro CH₄ production was reduced by the AR diet on day 8, but not on days 15 and 22. In line with these findings, the molar proportion of propionate in fermentation fluid was greater, and that of acetate smaller, for the AR diet than for the CON diet on day 8, but not on days 15 and 22. Overall, the data indicate a short-term effect of AR on CH₄ production, whereas the CH₄-mitigating effect of LA persisted.     

Betaine increases net portal absorption of volatile fatty acids in Iberian pigs

Betaine is an osmolyte with the potential to increase volatile fatty acids (VFAs) production and hence improve intestinal health.The present study investigated how betaine affects portal and arterial concentrations and net portal absorption (NPA) of VFA in growing Iberian pigs. Eight 30 kg BW Iberian growing barrows with indwelling catheters in portal vein, ileal vein and carotid artery were randomly assigned to a control diet or a diet supplemented with 0.5% betaine. Para-aminohippuric acid was infused into the ileal vein as a marker to determine portal blood flow using the dilution method. Blood samples were simultaneously taken from the carotid artery and portal vein at −60, 60, 120, 180, 240, 300 and 360 min after feeding 1 200 g of the diet. The NPA of VFA (acetate, propionate, butyrate, valerate, isobutyrate and caproate) was determined by multiplying the porto-arterial plasma concentration differences by portal plasma flow. Betaine increased NPA of acetate (1.44 fold; P < 0.001) and total VFA (0.55 fold; P < 0.001) while decreased NPA of propionate (−0.38 fold; P < 0.05) and valerate (−1.46 fold; P < 0.05) compared with control pigs. Estimated heat production potentially derived from NPA of VFA accounted for 0.20–0.27 of metabolizable energy for maintenance. Acetate and propionate accounted for most of the total VFA estimated heat production (0.83–0.89). Regarding bacterial communities, betaine apparently did not change the DNA abundance of fecal total bacteria, Lactobacillus, Bifidobacterium, Enterobacteriaceae, Bacteroides and the Clostridium clusters I, IV and XIV. In conclusion, betaine increased portal appearance and NPA of VFA, contributing to cover maintenance energy requirements.     

Long-term competition between sulfate reducing and methanogenic bacteria in UASB reactors treating volatile fatty acids

The competition between acetate utilizing methane-producing bacteria (MB) and sulfate-reducing bacteria (SRB) was studied in mesophilic (30 degrees C) upflow anaerobic sludge bed (UASB) reactors (upward velocity 1 m h-1; pH 8) treating volatile fatty acids and sulfate. The UASB reactors treated a VFA mixture (with an acetate:propionate:butyrate ratio of 5:3:2 on COD basis) or acetate as the sole substrate at different COD:sulfate ratios. The outcome of the competition was evaluated in terms of conversion rates and specific methanogenic and sulfidogenic activities. The COD:sulfate ratio was a key factor in the partitioning of acetate utilization between MB and SRB. In excess of sulfate (COD:sulfate ratio lower than 0.67), SRB became predominant over MB after prolonged reactor operation: 250 and 400 days were required to increase the amount of acetate used by SRB from 50 to 90% in the reactor treating, respectively, the VFA mixture or acetate as the sole substrate. The competition for acetate was further studied by dynamic simulations using a mathematical model based on the Monod kinetic parameters of acetate utilizing SRB and MB. The simulations confirmed the long term nature of the competition between these acetotrophs. A high reactor pH (+/-8), a short solid retention time (<150 days), and the presence of a substantial SRB population in the inoculum may considerably reduce the time required for acetate-utilising SRB to outcompete MB.     

Decreased activity of a propionate degrading community in a UASB reactor fed with synthetic medium without molybdenum,tungsten and selenium

The composition and dynamics of the propionate degrading community in a propionate-fed upflow anaerobic sludge bed (UASB) reactor with sludge originating from an alcohol distillery wastewater treating UASB reactor was studied. The rather stable propionate degrading microbial community comprised relatives of propionate degrading Syntrophobacter spp., the hydrogen and formate consuming Methanospirillum hungatei and the acetate consuming Methanosaeta concilii. The effect of the long-term absence of molybdenum, tungsten and selenium from the feed to the UASB reactor on microbial community dynamics and activity was examined. Measurements for metal concentrations of the sludge and specific methanogenic activity tests with supplied molybdenum, tungsten and selenium were found to be unsuitable to detect the potential limitation of the microbial activity of the UASB sludge by these trace metals. During a long-term absence of molybdenum, tungsten and selenium from the feed to the UASB reactor, the methanogenic activity decreased while relatives of Smithella propionica and Pelotomaculum spp. competed with Syntrophobacter spp. for propionate consumption.     

A kinetic model for methanogenesis from whey permeate in a packed bed immobilized cell bioreactor

The fermentation kinetics of methane production from whey permeate in a packed bed immobilized cell bioreactor at mesophilic temperatures and pHs around neutral was studied. Propionate and acetate were the only two major organic intermediates found in the methanogenic fermentation of lactose. Based on this finding, a three-step reaction mechanism was proposed: lactose was first degraded to propionate, acetate, CO(2), and H(2) by fermentative bacteria; propionate was then converted to acetate by propionate-degrading bacteria; and finally, CH(4) and CO(2) were produced from acetate, H(2), and CO(2) by methanogenic bacteria. The second reaction step was found to be the rate-limiting step in the overall methanogenic fermentation of lactose. Monod-type mathematical equations were used to model these three step reactions. The kinetic constants in the models were sequentially determined by fitting the mathematical equations with the experimental data on acetate, propionate, and lactose concentrations. A mixed-culture fermentation model was also developed. This model simulates the methanogenic fermentation of whey permeate very well.     

Fermentation pattern of methanogenic degradation of rice straw in anoxic paddy soil

The anaerobic degradation of different fractions of rice straw in anoxic paddy soil was investigated. Rice straw was divided up into stem, leaf sheath and leaf blade. The different straw fractions were mixed with paddy soil and incubated under anoxic conditions. Fermentation of straw components started immediately and resulted in transient accumulation of acetate, propionate, butyrate, isobutyrate, valerate, isovalerate and caproate with much higher concentrations in the presence than in the absence of straw. Also some unidentified compounds with UV absorption could be detected. The maximum concentrations of these compounds were different when using different straw fractions, suggesting differences in the degradation pathway of these straw fractions during the early phase of incubation, i.e. with Fe(III) and sulfate serving as oxidants. When concentrations of the intermediates decreased to background values, CH(4) production started. Rates of CH(4)unamended soil. During the methanogenic phase, the percentage contribution of fermentation products to CH(4) production was determined by inhibition with 2-bromoethanesulfonate (BES). Acetate (48-83%) and propionate (18-28%) were found to be the main intermediates of the carbon flow to CH(4), irrespective of the fraction of the rice straw or its absence. Mass balance calculations showed that 84-89% of CH(4) was formed via acetate in the various incubations. Radiotracer experiments showed that 11-27% of CH(4) was formed from H(2)/CO(2), thus confirming that acetate contributed 73-89% to methanogenesis. Our results show that the addition of rice straw and the fraction of the straw affected the fermentation pattern only in the early phase of degradation, but had no effect on the degradation pathway during the later methanogenic phase.     

Influence of waste water composition on biofilm development in laboratory methanogenic fluidized bed reactors

Summary The influence of the volatile fatty acid composition of waste waters on biofilm development and on the time course of reactor start-up was investigated in laboratory scale fluidized bed reactors. It was found that biofilm development proceeded in a similar way with either acetate, butyrate, propionate or a mixture of these compounds as carbon source in the waste water. Startup was retarded, however, with propionate as sole carbon source. Scanning electron microscopic examination revealed that immobilization of bacteria on the sand used as adhesive support initially occurred in crevices and that thereupon the surface of the sand particles became colonized. The composition of the newly developed biomass was determined when reactors reached steady state. Significant differences in the relative substrate spectra and in the amounts of hydrogenotrophic and acetotrophic methanogenic bacteria were measured. The differences reflected the differences in the composition of the waste waters. The results obtained emphasize the role of the structure of the carrier surface in start-up of methanogenic fluidized bed reactors.Abbreviations used Aw ash weight - COD chemical oxygen demand - EB fluidized bed - hbi vitamin B₁₂-HBI - spt sarcinapterin - UASB upflow anaerobic sludge blanket - VFA volatile fatty acid - VSS volatile suspended solids - Ww wet weight     

High-rate anaerobic treatment of wastewater at low temperatures

Anaerobic treatment of a volatile fatty acid (VFA) mixture was investigated under psychrophilic (3 to 8 degrees C) conditions in two laboratory-scale expanded granular sludge bed reactor stages in series. The reactor system was seeded with mesophilic methanogenic granular sludge and fed with a mixture of VFAs. Good removal of fatty acids was achieved in the two-stage system. Relative high levels of propionate were present in the effluent of the first stage, but propionate was efficiently removed in the second stage, where a low hydrogen partial pressure and a low acetate concentration were advantageous for propionate oxidation. The specific VFA-degrading activities of the sludge in each of the modules doubled during system operation for 150 days, indicating a good enrichment of methanogens and proton-reducing acetogenic bacteria at such low temperatures. The specific degradation rates of butyrate, propionate, and the VFA mixture amounted to 0.139, 0.110, and 0.214 g of chemical oxygen demand g of volatile suspended solids-1 day-1, respectively. The biomass which was obtained after 1.5 years still had a temperature optimum of between 30 and 40 degrees C.     

Methanogenesis at low temperatures by microflora of tundra wetland soil

Active methanogenesis from organic matter contained in soil samples from tundra wetland occurred even at 6 °C. Methane was the only end product in balanced microbial community with H₂/CO₂ as a substrate, besides acetate was produced as an intermediate at temperatures below 10°C. The activity of different microbial groups of methanogenic community in the temperature range of 6–28 °C was investigated using 5% of tundra soil as inoculum. Anaerobic microflora of tundra wetland fermented different organic compounds with formation of hydrogen, volatile fatty acids (VFA) and alcohols. Methane was produced at the second step. Homoacetogenic and methanogenic bacteria competed for such substrates as hydrogen, formate, carbon monoxide and methanol. Acetogens out competed methanogens in an excess of substrate and low density of microbial population. Kinetic analysis of the results confirmed the prevalence of hydrogen acetogenesis on methanogenesis. Pure culture of acetogenic bacteria was isolated at 6 °C. Dilution of tundra soil and supply with the excess of substrate disbalanced the methanoigenic microbial community. It resulted in accumulation of acetate and other VFA. In balanced microbial community obviously autotrophic methanogens keep hydrogen concentration below a threshold for syntrophic degradation of VFA. Accumulation of acetate- and H₂/CO₂-utilising methanogens should be very important in methanogenic microbial community operating at low temperatures.     

Effects of nitrate adaptation by rumen inocula donors and substrate fiber proportion on in vitro nitrate disappearance,methanogenesis, and rumen fermentation acid

A study was conducted to evaluate the main effects of dietary nitrate adaptation by cattle and alfalfa cell wall to starch ratio in in vitro substrates on nitrate disappearance and nitrite and volatile fatty acid (VFA) concentrations, as well as hydrogen (H₂) and methane (CH₄) accumulations. Rumen fluid from steers fed diets containing urea or nitrate was added into in vitro incubations containing sodium nitrate as the sole nitrogen source and 20 cell wall : 80 starch or 80 cell wall : 20 starch as the carbohydrate source. The results showed that during 24 h incubation, rumen fluid inoculums from steers adapted to dietary nitrate resulted in more rapid nitrate disappearance by 6 h of incubation (P < 0.01), no significant effect on nitrite concentration and diminished CH₄ accumulation (P < 0.05). Cell wall to starch ratio did not affect nitrate disappearance, CH₄ accumulation and total VFA concentration. The higher cell wall ratio had the lower total gas production and H₂ concentration (P < 0.05). Ammonia-N (NH₃-N) concentration increased because of adaptation of donors to nitrate feeding (P < 0.05). Nitrate adaptation did not alter total VFA concentration, but increased acetate, and decreased propionate and butyrate molar proportions (P < 0.01).     

Competitive oxidation of volatile fatty acids by sulfate- and nitrate-reducing bacteria from an oil field in Argentina

Acetate, propionate, and butyrate, collectively referred to as volatile fatty acids (VFA), are considered among the most important electron donors for sulfate-reducing bacteria (SRB) and heterotrophic nitrate-reducing bacteria (hNRB) in oil fields. Samples obtained from a field in the Neuquén Basin, western Argentina, had significant activity of mesophilic SRB, hNRB, and nitrate-reducing, sulfide-oxidizing bacteria (NR-SOB). In microcosms, containing VFA (3 mM each) and excess sulfate, SRB first used propionate and butyrate for the production of acetate, which reached concentrations of up to 12 mM prior to being used as an electron donor for sulfate reduction. In contrast, hNRB used all three organic acids with similar kinetics, while reducing nitrate to nitrite and nitrogen. Transient inhibition of VFA-utilizing SRB was observed with 0.5 mM nitrite and permanent inhibition with concentrations of 1 mM or more. The addition of nitrate to medium flowing into an upflow, packed-bed bioreactor with an established VFA-oxidizing SRB consortium led to a spike of nitrite up to 3 mM. The nitrite-mediated inhibition of SRB led, in turn, to the transient accumulation of up to 13 mM of acetate. The complete utilization of nitrate and the incomplete utilization of VFA, especially propionate, and sulfate indicated that SRB remained partially inhibited. Hence, in addition to lower sulfide concentrations, an increase in the concentration of acetate in the presence of sulfate in waters produced from an oil field subjected to nitrate injection may indicate whether the treatment is successful. The microbial community composition in the bioreactor, as determined by culturing and culture-independent techniques, indicated shifts with an increasing fraction of nitrate. With VFA and sulfate, the SRB genera Desulfobotulus, Desulfotignum, and Desulfobacter as well as the sulfur-reducing Desulfuromonas and the NR-SOB Arcobacter were detected. With VFA and nitrate, Pseudomonas spp. were present. hNRB/NR-SOB from the genus Sulfurospirillum were found under all conditions.     

Design of acidogenic reactors for the anaerobic treatment of the organic fraction of solid food waste

Volatile Fatty Acids (VFA) production by anaerobic fermentation of organic solid wastes was studied at laboratory scale. The influence of initial substrate concentration was evaluated on VFA production. Completely mixed reactors (0.9?l) were used at mesophilic temperature (35?°C). Food wastes had 43.8% Total Solids content. Three dilutions of substrate (1/25, 1/10 and 1/5) corresponding to 1.75%, 4.38% and 8.76% of Total Solids and five values of Organic Loading Rates: 2, 5, 10, 12.5 and 25?kg COD/m³?d were studied. It was found that substrate 1/10 led to 14?g VFA/l at a loading rate of 12.5?kg COD/m³?d and an hydraulic retention time of 3.7 d. The main VFA produced were especially acetate and butyrate. Substrate diluted 1/5 led to 26.1?g VFA/l at a loading of 5?kg COD/m³?d and an hydraulic retention time of 15.1 d, but biomass production was not optimal. In a second study, a cascade of three reactors was used. An effluent with 42?g VFA/l was obtained at steady-state conditions at a loading of 12.5?kg of COD/m³?d and an hydraulic retention time of 12.5?d. The distribution of VFA was the following: 36% of propionate, 34% of acetate and 22.5% of butyrate.     

Alcohol and acid formation during the anaerobic decomposition of propylene glycol under methanogenic conditions

Intermediates formed during the anaerobic decomposition of propylene glycol under methanogenic conditions were studied using a serum bottle technique. The pathway is similar to the anaerobic decomposition of ethylene glycol as previously reported. For both compounds, the decomposition is believed to proceed via an initial disproportionation of the glycol to form equal molar amounts of the volatile fatty acid and normal alcohol of the same chain length. In the case of ethylene glycol, disproportionation results in the formation of acetate and ethanol, while disproportionation of propylene glycol produces propionate and n-propanol. Following disproportionation, the alcohols produced from glycol fermentation are oxidized to their corresponding volatile fatty acid with the reduction of protons to form hydrogen. Ethanol and propionate oxidation to acetate proceeds via a well-established syntrophic pathway that is favorable only under low hydrogen partial pressures. Subsequent degradation of acetate proceeds via acetoclastic methanogenesis with the production of carbon dioxide and methane. Despite the production of hydrogen in the initial steps of glycol degradation, both compounds are completely degradable under the methanogenic conditions tested in this study.     

Dynamic Transition of a Methanogenic Population in Response to the Concentration of Volatile Fatty Acids in a Thermophilic Anaerobic Digester

In this study, the microbial community succession in a thermophilic methanogenic bioreactor under deteriorative and stable conditions that were induced by acidification and neutralization, respectively, was investigated using PCR-mediated single-strand conformation polymorphism (SSCP) based on the 16S rRNA gene, quantitative PCR, and fluorescence in situ hybridization (FISH). The SSCP analysis indicated that the archaeal community structure was closely correlated with the volatile fatty acid (VFA) concentration, while the bacterial population was impacted by pH. The archaeal community consisted mainly of two species of hydrogenotrophic methanogen (i.e., a Methanoculleus sp. and a Methanothermobacter sp.) and one species of aceticlastic methanogen (i.e., a Methanosarcina sp.). The quantitative PCR of the 16S rRNA gene from each methanogen revealed that the Methanoculleus sp. predominated among the methanogens during operation under stable conditions in the absence of VFAs. Accumulation of VFAs induced a dynamic transition of hydrogenotrophic methanogens, and in particular, a drastic change (i.e., an approximately 10,000-fold increase) in the amount of the 16S rRNA gene from the Methanothermobacter sp. The predominance of the one species of hydrogenotrophic methanogen was replaced by that of the other in response to the VFA concentration, suggesting that the dissolved hydrogen concentration played a decisive role in the predominance. The hydrogenotrophic methanogens existed close to bacteria in aggregates, and a transition of the associated bacteria was also observed by FISH analyses. The degradation of acetate accumulated during operation under deteriorative conditions was concomitant with the selective proliferation of the Methanosarcina sp., indicating effective acetate degradation by the aceticlastic methanogen. The simple methanogenic population in the thermophilic anaerobic digester significantly responded to the environmental conditions, especially to the concentration of VFAs.     

典型煤层水微生物产甲烷潜力及其群落结构研究

内蒙古自治区二连盆地、海拉尔盆地是我国重要的煤层气产区,其中生物成因煤层气是煤层气的重要来源,但复杂物质转化产甲烷相关微生物群落结构及功能尚不清楚。【目的】研究煤层水中的微生物代谢挥发性脂肪酸产甲烷的生理特征及群落特征。【方法】以内蒙古自治区二连盆地和海拉尔盆地的四口煤层气井水作为接种物,分别添加乙酸钠、丙酸钠和丁酸钠厌氧培养;定期监测挥发性脂肪酸降解过程中甲烷和底物的变化趋势,应用高通量测序技术,分析原始煤层气井水及稳定期产甲烷菌液的微生物群落结构。【结果】除海拉尔盆地H303煤层气井微生物不能代谢丙酸外,其他样品均具备代谢乙酸、丙酸和丁酸产生甲烷的能力,其生理生态参数存在显著差异,产甲烷延滞期依次是乙酸丁酸丙酸;最大比产甲烷速率和底物转化效率依次是丙酸乙酸丁酸。富集培养后,古菌群落结构与煤层气井水的来源显著相关,二连盆地优势古菌为氢营养型产甲烷古菌Methanocalculus (相对丰度13.5%–63.4%)和复合营养型产甲烷古菌Methanosarcina (7.9%–51.3%),海拉尔盆地的优势古菌为氢营养型产甲烷古菌Methanobacterium(24.3%–57.4%)和复合营养型产甲烷古菌Methanosarcina(29.6%–66.5%);细菌群落则与底物类型显著相关,硫酸盐还原菌Desulfovibrio(12.0%–41.0%)、互营丙酸氧化菌Syntrophobacter(39.6%–75.5%)和互营丁酸菌Syntrophomonas(8.5%–21.9%)分别在乙酸钠、丙酸钠和丁酸钠处理组显著富集。【结论】煤层气井水微生物可降解挥发性脂肪酸(乙酸、丙酸和丁酸)并具有产甲烷潜力;乙酸可能被古菌直接代谢产甲烷,而丙酸和丁酸通过互营细菌和产甲烷古菌代谢产甲烷。Desulfovibrio、Syntrophobacter和Syntrophomonas分别在乙酸、丙酸和丁酸代谢过程中发挥了重要作用。这些结果为煤层气生物强化开采提供了一定的微生物资源基础。     

High-Rate Anaerobic Treatment of Wastewater at Low Temperatures

Anaerobic treatment of a volatile fatty acid (VFA) mixture was investigated under psychrophilic (3 to 8°C) conditions in two laboratory-scale expanded granular sludge bed reactor stages in series. The reactor system was seeded with mesophilic methanogenic granular sludge and fed with a mixture of VFAs. Good removal of fatty acids was achieved in the two-stage system. Relative high levels of propionate were present in the effluent of the first stage, but propionate was efficiently removed in the second stage, where a low hydrogen partial pressure and a low acetate concentration were advantageous for propionate oxidation. The specific VFA-degrading activities of the sludge in each of the modules doubled during system operation for 150 days, indicating a good enrichment of methanogens and proton-reducing acetogenic bacteria at such low temperatures. The specific degradation rates of butyrate, propionate, and the VFA mixture amounted to 0.139, 0.110, and 0.214 g of chemical oxygen demand g of volatile suspended solids⁻¹ day⁻¹, respectively. The biomass which was obtained after 1.5 years still had a temperature optimum of between 30 and 40°C.     

Predicting In Vitro Rumen VFA Production Using CNCPS Carbohydrate Fractions with Multiple Linear Models and Artificial Neural Networks

The objectives of this trial were to develop multiple linear regression (MLR) models and three-layer Levenberg-Marquardt back propagation (BP3) neural network models using the Cornell Net Carbohydrate and Protein System (CNCPS) carbohydrate fractions as dietary variables for predicting in vitro rumen volatile fatty acid (VFA) production and further compare MLR and BP3 models. Two datasets were established for the trial, of which the first dataset containing 45 feed mixtures with concentrate/roughage ratios of 10∶90, 20∶80, 30∶70, 40∶60, and 50∶50 were used for establishing the models and the second dataset containing 10 feed mixtures with the same concentrate/roughage ratios with the first dataset were used for testing the models. The VFA production of feed samples was determined using an in vitro incubation technique. The CNCPS carbohydrate fractions (g), i.e. CA (sugars), CB₁ (starch and pectin), CB₂ (available cell wall) of feed samples were calculated based on chemical analysis. The performance of MLR models and BP3 models were compared using a paired t-test, the determination coefficient (R²) and the root mean square prediction error (RMSPE) between observed and predicted values. Statistical analysis indicated that VFA production (mmol) was significantly correlated with CNCPS carbohydrate fractions (g) CA, CB₁, and CB₂ in a multiple linear pattern. Compared with MLR models, BP3 models were more accurate in predicting acetate, propionate, and total VFA production while similar in predicting butyrate production. The trial indicated that both MLR and BP3 models were suitable for predicting in vitro rumen VFA production of feed mixtures using CNCPS carbohydrate fractions CA, CB₁, and CB₂ as input dietary variables while BP3 models showed greater accuracy for prediction.     

Effects of type of ionophore and carrier on in vitro ruminal dry matter disappearance,gas production,and fermentation end products of a concentrate substrate

Effects of ionophore type and carrier on in vitro ruminal digestion and fermentation patterns of a concentrate substrate were evaluated at various incubation times. Treatments were: control (no ionophore); lasalocid sodium commercial premix (Bov); lasalocid sodium mycelium cake (LasBio); laidlomycin sodium salt (LaidNa); laidlomycin propionate commercial premix (LaidPro); monensin sodium salt (Mon); and monensin sodium commercial premix (Rum). The Bov, LasBio, Mon, and Rum treatments supplied 4 μg of ionophore/mL of culture volume, whereas the LaidNa and LaidPro treatments supplied 1.33 μg of ionophore/mL. Total gas and methane production did not differ among treatments at any of the incubation times (P>0.09). Similarly, in vitro dry matter disappearance (IVDMD) was not affected by treatment (P>0.28) at 6, 18, and 24 h of incubation; however, IVDMD (P=0.03) was greater for ionophores than for the control at 12 h of incubation. Molar proportions of acetate (P<0.01), acetate:propionate (P<0.01), and total volatile fatty acid (VFA) concentrations (P<0.01) were decreased and propionate was increased (P<0.001) for the average of all ionophore-containing substrates compared with the control. Total VFA were decreased by Bov, LaidNa, and Rum, contrasted with their specific counterparts (LasBio, LaidPro, and Mon, respectively; P<0.05). Differences were detected among ionophore types for acetate (lasalocid vs. laidlomycin; P<0.05), propionate (lasalocid vs. monensin; P<0.05), and butyrate (monensin vs. lasalocid or laidlomycin; P<0.05). Capture of metabolic hydrogen in end products of fermentation was greater for ionophore-containing treatments (P<0.01) than for the control. These data suggest limited unique effects of ionophore type or carrier on IVDMD, total gas production, and methane; however, VFA proportions varied among ionophore types and carriers, which deserves further study.