Gas production during refuse decomposition

Decomposition of domestic wastes in an anaerobic environment results in the production of landfill gas. Public concern about landfill disposal and particularly the production of landfill gas has been heightened over the past decade. This has been due in large to the increased quantities of gas being generated as a result of modern disposal techniques, and also to their increasing effect on modern urban developments. In order to avert diasters, effective means of preventing gas migration are required. This, in turn requires accurate detection and monitoring of gas in the subsurface. Point sampling techniques have many drawbacks, and accurate measurement of gas is difficult. Some of the disadvantages of these techniques could be overcome by assessing the impact of gas on biological systems. This research explores the effects of landfill gas on plants, and hence on the spectral response of vegetation canopies. Examination of the landfill gas/vegetation relationship is covered, both by review of the literature and statistical analysis of field data. The work showed that, although vegetation health was related to landfill gas, it was not possible to define a simple correlation. In the landfill environment, contribution from other variables, such as soil characteristics, frequently confused the relationship. Two sites are investigated in detail, the sites contrasting in terms of the data available, site conditions, and the degree of damage to vegetation. Gas migration at the Panshanger site was dominantly upwards, affecting crops being grown on the landfill cap. The injury was expressed as an overall decline in plant health. Discriminant analysis was used to account for the variations in plant health, and hence the differences in spectral response of the crop canopy, using a combination of soil and gas variables. Damage to both woodland and crops at the Ware site was severe, and could be easily related to the presence of gas. Air photographs, aerial video, and airborne thematic mapper data were used to identify damage to vegetation, and relate this to soil type. The utility of different sensors for this type of application is assessed, and possible improvements that could lead to more widespread use are identified. The situations in which remote sensing data could be combined with ground survey are identified. In addition, a possible methodology for integrating the two approaches is suggested.

Determining optimum well locations is a crucial step in field development. Often, broad possibilities and constrains on computational resources limit the scenarios that can be considered. When dealing with heterogeneities, the intuitive engineering judgment may not be sufficient, and use of optimization algorithms becomes necessary in finding a favorable production plan. Although there have been extensive publications on optimization algorithms for oil reservoirs, there is little research aimed at gas or gas condensate reservoirs. In this work, we studied optimization of horizontal well placement in gas condensate reservoirs. One of the current challenges in development of gas condensate fields is condensate blockage. As pressure decreases condensate accumulates around the wellbore, leading to significant reduction in gas production. Horizontal wells can effectively solve this problem. However, due to their high cost, and complex phase behavior determining optimum locations cannot be based only on intuitive judgments. Here we present a horizontal well-placement optimization method for gas condensate reservoirs based on a modified genetic algorithm. Unlike oil reservoirs, the cumulative production in gas reservoirs does not vary significantly (although the variation is not economically negligible) and there are possibly more local optimums. Therefore the possibility of finding better production scenarios in subsequent optimization steps is not much higher than the worse case scenarios, which delays finding the best production plan. In this work, we use a cumulative distribution function to magnify the difference between production scenarios. As a result of this change we were able to find the best scenario with considerably fewer simulations. We apply the modified algorithm to a section of Qatar's North Field, a gas condensate field with the world's largest gas reserves. Our results show that this method can efficiently find the optimum horizontal well locations and can lead to valuable increase in gas and condensate production.

Under certain conditions, the uncontrolled migration of natural gas in the subsurface can result in an explosion, with the potential for significant property damage and loss of life. In western Pennsylvania, there are numerous possible sources of stray natural gas, including producing and abandoned wells, transportation pipelines, subsurface storage reservoirs, coal mines, and municipal waste landfills. The landfill gases are strictly of microbial origin, whereas the others are largely thermogenic in origin. Baseline geochemical data from gases generated in municipal landfills and those produced from gas wells and coals in western Pennsylvania help to identify sources of stray methane while investigating gas migration incidents. Landfill gases exhibit C1/(C2 + C3) ratios > 3.8 × 103, δ13CO2 values of −19.7 to + 17.4 permil, δDCH4 values of −197 to −353 permil, and δ 13CH4 values of −33.2 to −57.4 permil. Most δ13CO2 values are positive, whereas most methane, carbon, and hydrogen are isotopically light. Exceptions to these generalizations can be traced to isotope fractionation due to methane oxidation in soil environments. 14C activity in the landfill methanes ranges from 125 to 145% modern. Thermogenic methane in the subsurface rocks of the region have δ13C and δD values of approximately −27 to −55 permil and −150 to −303 permil, respectively. Chemical and isotopic analyses, combined with a thorough site investigation, provide a comprehensive approach for differentiating microbial from thermogenic gases and thermogenic gases from different sources. We used such an approach to confirm the offsite migration of landfill methane from a municipal landfill and the migration of stray methane from an abandoned gas pool to the soils adjacent to a commercial office building in western Pennsylvania.

Hydraulic fracturing is the main technical means for the reservoir stimulation of coalbed methane (CBM) vertical wells. The design of fracturing fluid volume (FFV) is mainly through numerical simulation, and the numerical simulation method does not fully consider the water block damage caused by the leakage of fracturing fluid into the reservoir. In this work, the variance analysis method was used to analyze the production data of 1238 CBM vertical wells in the Fanzhuang block and Zhengzhuang block of the Qinshui Basin, to clarify the relationship between the FFV and the peak gas production (PGP) under the different ratios of critical desorption pressure to reservoir pressure (Rc/r), and to reveal the controlling mechanism of fracturing fluid on CBM migration. The results show that both the FFV and Rc/r have a significant impact on gas production. When Rc/r < 0.5, the PGP decreases with the increase of the FFV, and the FFV that is beneficial to gas production is 200–500 m3. When Rc/r > 0.5, the PGP increases first and then decreases with the increase of FFV. Specifically, the FFV that is favorable for gas production is 500–700 m3. Excessive FFV does not significantly increase the length of fractures due to leaks in the coal reservoir. Instead, it is more likely to invade and stay in smaller pores, causing water block damage and reducing gas production. Reservoirs with high Rc/r have larger displacement pressure, which can effectively overcome the resistance of liquid migration in pores, thereby reducing the damage of the water block. Therefore, different reservoir conditions need to match the appropriate fracturing scale. This study can provide guidance for the optimal design of hydraulic fracturing parameters for CBM wells.

Influence of Dietary Supplementation of Ensiled Devil Fish and Staphylococcus saprophyticus on Equine Fecal Greenhouse Gases Production

A completely randomised design was adopted with five treatments urea levels of 0, 2, 4, 6, and 8% of dry matter and five replicates per treatment. The fermentation products were analysed using an in vitro semiautomatic gas production technique. Ammoniation had a significant linear effect on DM, NDF, hemicellulose, acid detergent fiber, and neutral detergent insoluble nitrogen. Ammoniation had a positive linear effect on crude protein (CP) content; increasing urea by 1% caused an increase in CP by 5.19 g kg−1 DM. The gas production based on DM, OM, and NDF decreased linearly with increasing urea for every 1% urea added to the hay, there was a reduction in gas production of 1.40, 3.27, and 4.21 ml/g DM, OM, and NDF, respectively. The concentration of methane decreased linearly with urea dose; for each 1% reduction in urea, there was a 0.15, 0.34, and 0.41 ml/g reduction in methane concentration during the degradation of DM, OM, and NDF, respectively. Ammoniation with 8% urea improved the chemical composition of cassava stem hay and decreased methane production.

Kilic, U. 2010. Nutritive values of whole-crop wheat hay and silage and effect of microbial inoculants on in vitro gas production. J. Appl. Anim. Res., 37: 67–71. The aim of this study was to determine the nutritive value and in vitro gas production kinetics of wheat hay (WH) and wheat silage (WS) by using in vitro gas production technique and to determine the effects of microbial inoculant (Maize-All) on rumen fermentation and gas production parameters. There were no significant differences between WH and WS in terms of in vitro gas production kinetics and estimated parameters such as metabolizable energy (ME), net energy lactation (NE L ) and organic matter digestibility (OMD). WH without Maize-All had higher ME, NEL and OMD values compared to WH with Maize-All. However, this difference was not found between WS without Maize-All and WS with Maize-All. The crude protein degradability of WH was significantly higher than that of WS (P<0.01). No difference in in vitro gas production between WH and WS was found. However, the reduction in gas production by the inclusion of Maize-All might be due to the change of microbial population in a negative way. The relative feed value (RFV) and dry matter intake (DMI) of WS were significantly higher than those of WH (P<0.01). The RFV of WS was significantly higher than that of WH. However, in vivo experiments are required to evaluate how these differences will affect the performance of ruminants.

Previous studies have found that Astragalus Polysaccharide (APS) and Lactobacillus plantarum PS128 (PS128) have potential antidepressant effects, but their effects on the gut microbiota and metabolites of major depressive disorder (MDD) are still unclear. We examined the effect of APS on gut microbiota and metabolites of first-episode and drug naïve MDD patients using in vitro fermentation, and further explored whether PS128 could enhance the utilization ability of APS. Fresh fecal samples from 15 MDD patients were collected, and analyzed for differences in gas production, gut microbiota, and tryptophan (Trp) related metabolites after 48 h of fermentation. APS fermentation increased the abundance of Bifidobacterium and decreased the abundance of Lachnoclostridium (p < 0.05). APS also increased total gas production and levels of indole lactic acid (ILA), Trp, and 5-hydroxytryptophan (5-HTP) (p < 0.05). Compared with APS, APS with PS128 synbiotics fermentation increased the abundance of Lactobacillus (p < 0.05), reduced total gas production and percentages of CO2, H2, and H2S (p < 0.05), and to some extent increased the levels of ILA, Trp, and 5-HTP, although not statistically significant (p > 0.05). Correlation analysis showed Bifidobacterium was positively correlated with ILA, Trp and 5-HTP; On the contrary, Lachnoclostridium was negatively correlated with ILA, Trp, and 5-HTP. All these results suggest that APS could regulate gut microbiota structure and Trp related metabolites in MDD patients; Compared to APS, APS and PS128 synbiotic fermentation could reduce gas production but shows limited ability to modulate gut microbiota structure or Trp related metabolites in MDD patients.

The objective was to evaluate the fermentation profile, in vitro gas production and nutritional quality of pornunça (Manihot spp.) silages containing levels of condensed tannin (CT; 0, 4, 8 and 12% on dry matter (DM) basis), at five opening times (0, 3, 7, 14, 28 and 56 days). A completely randomized design in a 4 × 5 factorial arrangement was adopted, with four replications, totalling 80 experimental silos. The pH and NH3-N analyses were performed at all opening times of the silos. The other analyses were performed only with silages opened at 56 days of storage. There was an interaction effect between CT levels and silo opening times for pH and NH3-N. Tannin levels in pornunça silages after 56 days ensiling increased the pH and DM and reduced crude protein (CP) and neutral detergent fibre (NDF). There was a quadratic effect for NH3-N, acetic acid, butyric acid, gas losses, dry matter recovery (DMR), hemicellulose and acid detergent fibre. Inclusion of 4 and 8% CT in pornunça silage promotes a rapid decline in pH, being within the acceptable limit for adequate fermentation at 3 days of ensiling. Silages with 4% CT establish the pH at 28 days of opening the silos, with reduced NH3-N. Silages with 4% CT present higher concentrations of acetic and butyric acids and greater DMR. Inclusion of CT in pornunça silage after 56 days ensiling increases DM and reduces CP and NDF, directly affecting the in vitro degradability and reducing gas production.

Utilization of agroindustrial waste as feed for ruminant should consider not only biomass availability but also the impact to environment. Methanogenesis has been one of the issues regarding to the utilization of agroindustrial was as feed for ruminant. Lemon grass (Cymbopogon nardus L.) has known for its potential as feed for ruminant, however the information on its methanogenesis activities is very few. Ensiling process of the lemon grass waste may enhance the potential. Lemon grass waste were divided into two group of in vitro digestibility experiment; control (T0) and ensilage (T1) lemon grass waste. Observed parameters were pH, total gas production (mL) and rumen methane concentration (ppm). The Data were applied to T-tes student with 10 replications. The results showed that the pH was not significantly different (p> 0.05), while gas production and rumen methane concentration was significantly different (p <0.05). It can be concluded that the use of lemon grass waste silage can maintain the stability of pH values, reduce gas production, and methane gas concentration in cattle.

Complex inhibitions on anaerobic degradation of monosodium glutamate in wastewater under low COD/sulfate ratios

Surface tension plays a very important role in the stimulation of gas wells. A low surface tension is required to reduce capillary forces that trap the aqueous phase in the formation. Accumulation of the aqueous phase near the wellbore area, known as water blockage, leads to a significant reduction in gas production. An experimental study was conducted to examine the effects of various acids and stimulation additives on surface tension. A Krüss tensiometer (Model K-12) was used to conduct surface tension measurements. Acids examined included: HCl, acetic, citric, formic, and combinations of these acids. Stimulation additives tested included: mutual solvent, short-chain alcohols, corrosion inhibitors, hydrogen sulfide scavengers, iron-control agents, and clay stabilizers. In addition, the effects of three classes of surfactants (nonionic, cationic and anionic) on surface tension of acid solutions were investigated. The surface tension of acid stimulating fluids is a complex function of acid type, concentration, and additive type and concentration. Acetic and formic acids had lower surface tension values than HCl, especially at high acid concentrations. The surface tension of the organic acids examined depended on the pKa value of the acid. Organic acids with high pKa values had low surface tension values. The surface tension of hydrochloric acid can be reduced by mixing with acetic acid. EGMBE lowered the surface tension of acetic, formic and hydrochloric acids up to 10 wt%. Increasing the concentration of EGMBE above 10 wt% had no significant effect on the surface tension of these acids. The effect of organic acid strength on surface tension diminished in the presence of EGMBE. Short-chain alcohols reduced the surface tension of 15 wt% HCl with the greatest reduction obtained with n-butanol. Citric and erythorbic acids, which are usually used as iron control agents significantly reduced the surface tension of 15 wt% HCl. Ionic surfactants reduced the surface tension of hydrochloric acid more than the two nonionic surfactants tested. The three corrosion inhibitors examined reduced surface tension up to a critical concentration beyond which they had no effect on surface tension. An aldehyde-based H2S scavenger lowered the surface tension of 15 wt% acid solutions at very low concentrations. Clay stabilizers (cationic polymers) did not significantly affect the surface tension of 15 wt% HCl. Addition of a hydrogen sulfide scavenger, a nonionic surfactant or a corrosion inhibitor into solutions of 15 wt% HCl and EGMBE had a small effect on the surface tension of the acid.

Results obtained using a new technique for studying cell metabolism are presented. The technique, consisting in CO2 production monitoring, has been applied to Saccharomyces cerevisiae yeast cells. Also the cells were irradiated using the soft X-ray laser-plasma source at Rutherford Appleton Laboratory with the aim of producing a damage of metabolic processes at the wall level, responsible for fermentation, without great interference with respiration, taking place in mitochondria, and DNA activity. The source was calibrated with PIN diodes and X-ray spectrometers and used Teflon stripes as target, emitting X-rays at about 0.9 keV, with a very low penetration in biological material. X-ray doses delivered to the different cell compartments were calculated following a Lambert-Bouguet-Beer law. Immediately after irradiation, the damage to metabolic activity was measured again by monitoring CO2 production. Results showed a general reduction in gas production by irradiated samples, together with non-linear and non-monotone response to dose. There was also evidence of oscillations in cell metabolic activity and of X-ray induced changes in oscillation frequency.

Summary High-precision core analysis has been performed on eight Devonian gas shale samples from the Appalachian basin. Seven of the core samples consist of the Upper Devonian Age Huron member of the Ohio shale, six of which came from wells in the Ohio River valley, and the seventh from a well in east-central Kentucky. The eighth core sample consists of Middle Devonian Age Marcellus shale obtained from a well in Morgantown, WV. The core analysis was originally intended to supply accurate input data for Devonian shale numerical reservoir simulation. Unexpectedly, the work has identified a number of geological factors that influence gas production from organic-rich shales. The presence of petroleum as a mobile liquid phase in the pores of all seven Huron shale samples effectively limits the gas porosity of this formation to less than 0.2%, and gas permeability of the rock matrix is commonly less than 0.1 μd at reservoir stress. The Marcellus shale core, on the other hand, was free of a mobile liquid phase and had a measured gas porosity of approximately 10%, and a surprisingly high permeability of 20 μd. Gas permeability of the Marcellus was highly stress-dependent, however; doubling the net confining stress reduced the permeability by nearly 70%. The conclusion reached from this study is that the gas productivity potential of Devonian shale in the Appalachian basin is influenced by a wide range of geologic factors. Organic content, thermal maturity, natural fracture spacing, and stratigraphic relationships between gray and black shales all affect gas content and mobility. Understanding these factors can improve the exploration and development of Devonian shale gas.

This document consists of the following papers: inorganic geochemistry studies of the Eastern Kentucky Gas Field; lithology studies of upper Devonian well cuttings in the Eastern Kentucky Gas Field; possible effects of plate tectonics on the Appalachian Devonian black shale production in eastern Kentucky; preliminary depositional model for upper Devonian Huron age organic black shale in the Eastern Kentucky Gas Field; the anatomy of a large Devonian black shale gas field; the Cottageville (Mount Alto) Gas Field, Jackson County, West Virginia: a case study of Devonian shale gas production; the Eastern Kentucky Gas Field: a geological study of the relationships of Ohio Shale gas occurrences to structure, stratigraphy, lithology, and inorganic geochemical parameters; and a statistical analysis of geochemical data for the Eastern Kentucky Gas Field.