Showing papers on "Biogas published in 1975"

Thermophilic Anaerobic Digestion of Solid Waste for Fuel Gas Production

Abstract: Anaerobic digestion offers a potential means of converting organic solid waste into fuel gas and thereby provide a supplemental and readily utilizable source of energy. We are particularly interested in the use of thermophilic digestion over a mesophilic operation for it can achieve higher rates of digestion, greater conversion of waste organics to gas, faster solid-liquid separation, and minimization of bacterial and viral pathogen accumulation. Our results comparing mesophilic (37 degree C) and thermophilic (65 degree C) anaerobic digestion of domestic solid waste confirm the increased rate and conversion of waste to methane. In addition, utilizing radioactive labeling of glucose and acetic acid, we have measured the volumetric rates of volatile acid production and disappearance under both mesophilic and thermophilic conditions.

Effect of leaking natural gas on soil and vegetation in urban areas

Abstract: Leakage of natural gas from the gas distribution system affects the physical, chemical and biological processes in the soil. Particularly the microbial oxidation of methane is then of predominant importance for the composition of the soil gas phase. The rate of methane oxidation was measured under varying conditions of gas phase composition, temperature and nutrient supply. Computation models were evolved with which it is possible to calculate the effect of these and other factors on the distribution of methane, oxygen and carbon dioxide around a leak. Experiments with actual and artificial leaks as well as the calculations showed that the extent of the gas zone largely depends on the leakage rate, the depth of the groundwater table, the soil moisture content and the extent of the pavement. The soil temperature also proved to have a significant influence by its effect on the microbial methane oxidation. At low temperatures this microbial process is limited and consequently the anaerobic zone, which is invariably present in summer, may then disappear completely, thus making the probability of injury to vegetation negligible in winter. After repair of the leak the poor aeration conditions in the soil may persist for quite a long time. This is caused by the high consumption rate of oxygen required for the oxidation of organic substances and reduced anorganic compounds accumulated in the soil during gas leakage. The oxygen overdemand and the oxidation rate were determined for various gassed soils. Measures can be taken to accellerate soil recovery processes and to improve conditions for regeneration of injured trees and before planting new trees. Both experiments and calculations with computation models proved that installation of open ventilation channels is very effective, even if the leak cannot be immediately repaired. So ventilation channels can also be installed as preventive measure.

Thermophilic anaerobic digestion of cellulosic waste

Abstract: The anaerobic digestion of domestic solid waste offers an alternative source for supplemental amounts of fuel gas. Using shredded newsprint and primary sewage sludge, we have examined the use of anaerobic digestion at a thermophilic temperature (55°C) for methane production. The maximum productivity occurred at a nominal retention time of 5 days using a total solids feed of 50g/l. The rate of gas production also correlates with the ratio of propionic plus butyric acids to acetic acid in the cell-free broth; this correlation is hypothesized to be the result of higher yields of methane from anaerobic utilization of the longer-chain fatty acids. The methane content of the gas depends on the liquid flow rate; carbon dioxide is much more soluble in water than methane and, as the liquid flow rate is increased, more CO2 is removed in the liquid phase, thus enriching the methane in the gas phase.

Feedlot Wastes to Useful Energy — Fact or Fiction—

Abstract: The large quantities of wastes generated in commercial feedlots have been receiving attention as to their possible energy value. Research has indicated however that on the typical open lot much of the potential energy source is reduced by the natural degradation of the organic matter during the up to 150 days that the material may remain on the lot. Anaerobic digestion was studied as the system for energy recovery. Three case studies for a 35,000-head feedlot were looked at: a dirt lot, a concrete lot, and a total confinement system with fresh manure removal. Anaerobic digestion of dirt lot waste will produce no net gas. Anaerobic digestion of freshly collected wastes may produce excess gas at a cost nearly that of existing natural gas prices. Even at this price it must be approached with caution since other considerations such as cost and energy requirements of confined feeding and sludge disposal must still be considered for each installation.