Factors Affecting Methane Production Research Articles

Impact of Hydrothermal Pretreatment Parameters on Mesophilic and Thermophilic Fermentation and Anaerobic Digestion of Municipal Sludge

Four parameters affecting hydrothermal pretreatment (HTP) of municipal sludge prior to anaerobic digestion and fermentation were investigated. Partial factorial design including several key HTP parameters at two distinct levels, including temperature (170 and 190 °C), retention time (RT) (10 and 30 min), pH (4 and 10), and solid content (SC) (4% and 16%), were studied. Further, the impact of HTP parameters on mesophilic and thermophilic fermentation was explored and compared. Results revealed a significant effect of all HTP parameters on COD solubilization, VFA, and methane yield. There were correlations between HTP parameters and process responses such as VFA yield and methane yield. HTP was found to increase COD solubilization and VFA production between 15 and 20% during thermophilic fermentation in relation to mesophilic treatment. All parameters, including SC, temperature, pH, and RT, were important contributing factors affecting methane production during anaerobic digestion. The highest methane production yield of 269 mL CH4/g TCOD added was observed at the highest SC (16%) and pH (10) and at the lower temperature (170 °C) and RT (10). HTP is expected to be combined with other intensification routes to treat waste with high solid contents improving the fermentation and anaerobic digestion processes.

Rumen microbial system, methanogenesis, and methane mitigation strategies in ruminants

Much of the biomass in this world is rich in fibre which is utilised by the ruminants with the help of rumen microbes to produce a good quality protein for human consumption. However, this conversion of fibre to high-quality protein is paralleled by the production of methane which represents the wastage of feed energy and is a powerful greenhouse gas harmful to the global climate. The microbial community in the rumen has co-evolved with their host animal in a symbiotic relationship over millions of years and methanogenesis has emerged as a result of the refinement of the fermentation process in the rumen. The one-to-one relationship between the methanogen population and the methanogenesis has not been established yet, which indicates the role of associated rumen microbiota, substrate availability, and other functional parameters of the rumen. This review has focused on the total rumen microbial structure, methanogen structure, rumen fermentation process, methanogenesis, factors affecting methane production, and methane mitigation strategies. The balance between the H2 producers and H2 consumers in the rumen determines the level of methane production in the rumen. Therefore, decreasing the availability of H2 in the rumen by fostering alternative H2 sinks, such as propionate production, is very instrumental in reducing the rumen methane emissions. Any strategy of methane abatement should concurrently consider the enhancement of propionate production to prevent the inhibition of rumen functions. Although a great deal of information regarding the rumen microbial community structure, rumen physiology, and methane mitigation strategies is currently available, more research is still needed. The majority of the in vivo experiments pertaining to methane abatement strategies discussed in this review are the short term experiments in which long term unwanted effects could not be precisely predicted. Therefore, there is a need for long-term experiments to draw valid and logical conclusions on the methane abatement strategies.

Factors affecting co-degradation of coal and straw to enhance biogenic coalbed methane

The formation of biogenic coalbed methane is stoichiometrically limited by relative deficiency of hydrogen in coal. As straw is rich in hydrogen and can be easily degraded by microorganisms, it is suggested that the co-degradation of coal and straw to produce biogenic methane can overcome these limitations. However, the factors affecting methane production in co-degradation of coal and straw were unclear. Here, the type and part of straw and the particle size of coal and straw were evaluated with respect to methane production from Qinshui Basin coal. The results showed that the biomethane yields in co-degradations of coal and different types of straw were all higher than that in degradation of only coal or only straw with the yield from rice and coal 25.36 times greater, the yield from sweet sorghum and coal 22.70 times greater, the yield from wheat and coal 19.90 times greater, and the yield from corn and coal 1.74 times greater. The co-degradation of coal and stems also showed a better enhancing effect than that of coal and roots and coal and leaves based on biogenic methane production. With respect to particle size, the coal had a greater influence on biomethane production than the straw. The highest methane production was obtained in the co-degradation with 0.125–0.150 mm of coal and 5 mm of rice straw. The affects were also shown to not correlate well with the additional of hydrogen. Therefore, it is more likely that the enhanced methane production is a result of stimulating the microbial biodegradation of coal. Further efforts would be made to find the specific compounds in straw which interact with coal directly, in order to better understand the mechanism of co-degradation between coal and straw, and make it simpler to improve biomethane production.

Methane Production from the Co-digestion of Algal Biomass with Crude Glycerol by Anaerobic Mixed Cultures

The optimization of factors affecting methane production from the co-digestion of algal biomass with crude glycerol was investigated using response surface methodology with a central composite design. The investigated parameters included algal biomass, crude glycerol and inoculum concentration. The inoculum and algal biomass concentration had a significant individual effect on the methane production (p ≤ 0.05). The interactive effect on methane production was found to be between algal biomass and crude glycerol (p ≤ 0.05). The optimal conditions were 20.02 g-VS/L of crude glycerol, 9.76 g-VS/L of inoculum concentration and 5.50 g-VS/L of algal biomass. Under optimum conditions, the maximum methane production of 58.88 mL-CH4/L was obtained. The difference between the observed methane production (58.88 mL-CH4/L) and the predicted methane (68.94 mL-CH4/L) was 14.59%. Under the optimum conditions, the energy production of 92.47 J/g-VSadded was obtained. The polymerase chain reaction-denaturing gradient gel electrophoresis analysis indicated that the methane producers present in the fermentation broth were Methanosarcina sp., Methanoregula sp., Methanospirillum sp. and Methanoculleus sp.

1436 Factors affecting methane production from ruminal fermentation of fiber isolated from dried distillers' grains and solubles

1436 Factors affecting methane production from ruminal fermentation of fiber isolated from dried distillers' grains and solubles

Optimization of Key Factors Affecting Methane Production from Acidic Effluent Coming from the Sugarcane Juice Hydrogen Fermentation Process

Response surface methodology with a central composite design was applied to optimize the key factors affecting methane production from the acidic effluent coming from the sugarcane juice hydrogen fermentation process. The parameters studied were substrate concentration, ratio of NaHCO3 to substrate concentration and initial pH. The experimental results showed that substrate concentration and initial pH had significant individual (p < 0.05) effect on methane yield (MY). However, there was no interactive effect between these variables (p > 0.05). The maximum MY of 367 mL CH4/g-volatile solid (VS)added was obtained at the optimum conditions of 13,823 mg-COD/L, an NaHCO3 to substrate concentration ratio of 3.09 and an initial pH of 7.07. Under the optimum conditions, MY was enhanced 4.4-fold in comparison to raw effluent.

Factors affecting methane production and mitigation in ruminants

Methane (CH(4)) is the second most important greenhouse gas (GHG) and that emitted from enteric fermentation in livestock is the single largest source of emissions in Japan. Many factors influence ruminant CH(4) production, including level of intake, type and quality of feeds and environmental temperature. The objectives of this review are to identify the factors affecting CH(4) production in ruminants, to examine technologies for the mitigation of CH(4) emissions from ruminants, and to identify areas requiring further research. The following equation for CH(4) prediction was formulated using only dry matter intake (DMI) and has been adopted in Japan to estimate emissions from ruminant livestock for the National GHG Inventory Report: Y = -17.766 + 42.793X - 0.849X(2), where Y is CH(4) production (L/day) and X is DMI (kg/day). Technologies for the mitigation of CH(4) emissions from ruminants include increasing productivity by improving nutritional management, the manipulation of ruminal fermentation by changing feed composition, the addition of CH(4) inhibitors, and defaunation. Considering the importance of ruminant livestock, it is essential to establish economically feasible ways of reducing ruminant CH(4) production while improving productivity; it is therefore critical to conduct a full system analysis to select the best combination of approaches or new technologies to be applied under long-term field conditions.

Analysis of environmental factors affecting methane production from high-solids organic waste

A simple model developed from the Gompertz equation was used to describe the cumulative methane production curve in the batch culture. By using this model, three key parameters, namely methane production rate, potential and lagphase time, in a cumulative methane production curve were exactly estimated based on the experimental data. The results indicate that each gram of dry organic waste of a sludge cake, meat, carrot, rice, potato and cabbage had a methane production potential of 450, 424, 269, 214, 203 and 96 mL, respectively. The methanogenic activity of these digesters decreased with a decrease in the moisture content. The moisture content threshold limit, at which the methanogenic activity dropped to zero, was found to be 56.6% for the sludge cake, but greater than 80% for meat, carrot and cabbage. In the high-solids sludge digestion, the relative methanogenic activity dropped from 100% to 53% when the moisture content decreased from 96% to 90%. The rate of methane production at moisture contents of 90% to 96% functioned in a pH range between 6.6 and 7.8, but optimally at pH 6.8, and the process may fail if the pH was lower than 6.1 or higher than 8.3. On the other hand, the methanogenic activity was dependent on the level of ammonium, NH4+, but not free ammonia, NH3, indicating that the NH4+ was the more significant factor rather than the NH3 in affecting the methanogenic activity of a well-acclimatized bacterial system. In the wide pH range of 6.5 to 8.5, the methanogenic activity decreased with the increase in the NH4+; dropped 10% at the NH4+-N concentration of 1670-3720 mg·L−1, 50% at 4090-5550 mg·L−1 and dropped to zero at 5880-6600 mg·L−1. However, the lagphase time was dependent on the NH3 level, but not on NH4+, and when NH3-N was higher than 500 mg·L−1, a notable shock was observed. This suggests that the NH3 level was the more sensitive factor than the NH4+ level for an unacclimatized bacterial system.

Analysis of environmental factors affecting methane production from high-solids organic waste

Asimple model developed from the Gompertz equation was used to describe the cumulative methane production curve in the batch culture. By using this model, three key parameters, namely methane production rate, potential and lagphase time, in a cumulative methane production curve were exactly estimated based on the experimental data. The results indicate that each gram of dry organic waste of a sludge cake, meat, carrot, rice, potato and cabbage had a methane production potential of 450,424,269,214,203 and 96 mL, respectively. The methanogenic activity of these digesters decreased with a decrease in the moisture content. The moisture content threshold limit, at which the methanogenic activity dropped to zero, was found to be 56.6% for the sludge cake, but greater than 80% for meat, carrot and cabbage. In the high-solids sludge digestion, the relative methanogenic activity dropped from 100% to 53% when the moisture content decreased from 96% to 90%. The rate of methane production at moisture contents of 90% to 96% functioned in a pH range between 6.6 and 7.8, but optimally at pH 6.8, and the process may fail if the pH was lower than 6.1 or higher than 8.3. On the other hand, the methanogenic activity was dependent on the level of ammonium, NH4+, but not free ammonia, NH3 , indicating that the NH4+ was the more significant factor rather than the NH3 in affecting the methanogenic activity of a well-acclimatized bacterial system. In the wide pH range of 6.5 to 8.5, the methanogenic activity decreased with the increase in the NH4+; dropped 10% at the NH4+-N concentration of 1670–3720 mg·L−1, 50% at 4090–5550 mg·L−1 and dropped to zero at 5880–6600 mg·L−1. However, the lagphase time was dependent on the NH3 1evel, but not on NH4+, and when NH3-N was higher than 500 mg°L−1, a notable shock was observed. This suggests that the NH3 level was the more sensitive factor than the NH4+ level for an unacclimatized bacterial system.

Factors affecting methane production under rice

To understand why atmospheric methane is increasing worldwide, accurate estimates are needed of the global input from rice fields. We report greenhouse and laboratory studies over three growing seasons to isolate and control factors that might affect methane emission from rice paddies, including soil texture, added exogenous organic matter (OM), nitrogen and sulfate ion, and water management. Without added OM, methane production was relatively low, increasing during the growing season, and continuing after harvest, provided the soil remained water‐logged. If ground rice straw was added to the soil prior to planting, methane production began shortly after flooding, with an initial burst of the gas after 3 to 5 weeks, and then a gradual increase to a second peak later in the season (and after harvest), with rates considerably higher than in treatments without added OM.