Showing papers on "Biogas published in 1999"

A comprehensive model of anaerobic bioconversion of complex substrates to biogas

Abstract: A dynamic model describing the anaerobic degradation of complex material, and codigestion of different types of wastes, was developed based on a model previously described (Angelidaki et al., 1993). In the model, the substrate is described by its composition of basic organic components, i.e., carbohydrates, lipids, and proteins, the concentration of intermediates such as volatile fatty acids and long-chain fatty acids, and important inorganic components, i.e., ammonia, phosphate, cations, and anions. This allows dynamic changes of the process during a shift of substrate composition to be simulated by changing the input substrate data. The model includes 2 enzymatic hydrolytic steps, 8 bacterial steps and involves 19 chemical compounds. The model also includes a detailed description of pH and temperature characteristics. Free ammonia, acetate, volatile fatty acids, (VFA) and long-chain fatty acids (LCFA) constitute the primary modulating factors in the model. The model was tested with success in lab-scale reactors codigesting manure with glycerol trioleate or manure with gelatin. Finally, the model was validated using results from a full-scale biogas plant codigesting manure together with a proteinous wastewater and with bentonite-bound oil, which is a waste with high content of lipids. Copyright 1999 John Wiley & Sons, Inc.

Hydrogen production during the anaerobic acidogenic conversion of glucose

Abstract: Experiments on hydrogen production using chemostat-type anaerobic digesters were conducted. The results indicate that the anaerobic acidogenic conversion of glucose can produce hydrogen. The hydrogenic activity of acclimated anaerobic sewage sludge is high at a short solids retention time (SRT) and low pH. At pH 5.7, SRT 0.25 days and an organic loading rate of 416 mmol-glucose dm−3 day−1, each mole of glucose in the mesophilic acidogenic reactor can produce 1.7 mol of hydrogen; each gram of biomass produces 0.456 mole of hydrogen per day. Moreover, the hydrogen productivity of the sludge is comparable to that of an enrichment culture. © 1999 Society of Chemical Industry

Determination of Siloxanes and VOC in Landfill Gas and Sewage Gas by Canister Sampling and GC-MS/AES Analysis

Abstract: Biogases such as landfill gas and sewage gas undergo a combustion process which is generating electric energy. Since several trace compounds such as siloxanes (also halogenated and sulfur compounds) are known to cause severe problems to these gas combustion engines, they are of particular interest. In this work, a new technique for sampling, identification, and quantification of siloxanes and volatile organic carbon (VOC) in landfill gas and sewage gas is presented. After sample collection using evacuated stainless steel canisters biogas was analyzed by gas chromatography-mass spectrometry/atomic emission spectroscopy (GC-MS/AES). Using gas canisters, the sampling process was simplified (no vacuum pump needed), and multiple analysis was possible. The simultaneous application of MSD and AED allowed a rapid screening of silicon compounds in the complex biogases. Individual substances were identified independently both by MSD analysis and by determination of their elemental constitution. Quantification of tr...

Anaerobic digestion of the vegetable fraction of municipal refuses: mesophilic versus thermophilic conditions

Abstract: The phenomena limiting the anaerobic digestion of vegetable refuses are studied through batch tests carried out using anaerobic sludge previously selected under either mesophilic (37 °C) or thermophilic (55 °C) conditions The compositions of the hydrolysed cellulosic and hemicellulosic fractions of these materials are simulated by starch and hemicellulose hydrolysates, respectively Non-hydrolysed mixtures of vegetable waste with sewage sludge are used to ascertain whether the hydrolysis of these polymeric materials is the limiting step of the digestion process or not The experimental data of methane production are then worked out by a first-order equation derived from the Monod's model to estimate the kinetic rate constant and methane production yield for each material Comparison of these results shows that passing from mesophilic to thermophilic conditions is responsible for a slight deceleration of methane production but remarkably enhances both methanation yield and methane content of biogas The final part of the study deals with the fed-batch digestion of the same residues in static digester Working under thermophilic conditions at a loading rate threshold of 60 gCOD/l · d, the hemicellulose hydrolysate ensures the highest methane productivity (60 mmolCH4/l · d) and methane content of biogas (60%), while unbalance towards the acidogenic phase takes place under the same conditions for the starch hydrolysate The intermediate behaviour of the non-hydrolysed mixture of vegetable waste with sewage sludge demonstrates that hemicellulose hydrolysis is the limiting step of digestion and suggests the occurrence of ligninic by products inhibition on methane productivity

Performance of thermophilic semi-dry anaerobic digestion process changing the feed biodegradability.

Abstract: The study concerns the application of the semi-dry single phase thermophilic anaerobic digestion process to the organic fraction of municipal solid waste. The xperiments were carried out using 3 m3 and 1 m3 CSTR pilot scale reactors. The process performance in terms of biogas yields, digester stability and kinetic spects was studied, considering a progressive increase in the feed biodegradability, in order to evaluate the process behaviour changing from an undifferentiated collection of waste to a separate collection. This was carried out using blends of two different kinds of substrates: mechanically sorted organic fraction of municipal solid wastes (MS-OFMSW) and source sorted organic fraction of municipal solid wastes (SS-OFMSW). The study shows that OLR up to 6 kgTVS/m3d can be applicable for the medium selected fraction (TVS/TS≤0.7), while for the MS-OFMSW alone this limit can be doubled. The results obtained with SS-OFMSW alone suggest the use of the double phase process to give more stable conditions.

Hydrolysis and thermophilic anaerobic digestion of sewage sludge and organic fraction of municipal solid waste

Abstract: An attempt is presented and discussed to adapt a well-known process successfully employed in the U.S.A. for the simultaneous treatment of the organic fraction of municipal solid waste (MSWOF) and sewage sludge to the particular situation of water works in Italy. It consists of preliminary domestic grinding of MSWOF, its discharge into the sewer, screening, and final digestion of the resulting residue together with sewage sludge. In order to avoid extension work of the present activated sludge sections necessary to face the organic load increase, a fine screening is necessary, while the efficiency of anaerobic digestion can be improved by shifting the system from mesophilic (37 °C) to thermophilic (55 °C) conditions. The effects of thermal, chemical, and biological pretreatments of both MSWOF and sewage sludge on methane, carbon dioxide, and biogas productions are investigated either separately or jointly. During these pretreatments, volatile suspended solid (VSS) concentration remarkably decreased while soluble chemical oxygen demand (COD) increased as the result of the progressive hydrolysis of the polymeric materials present in the feed. Finally, the kinetic parameters of the hydrolysis of these materials are estimated and compared in order to provide useful information on the factors limiting the anaerobic digestion as well as to suggest the best way to carry out the process on a large scale.

Effects of total solids concentrations of poultry, cattle, and piggery waste slurries on biogas yield.

Abstract: The effects of total solids concentrations of poultry, cattle and piggery waste slurries on biogas yield was investigated. Twelve laboratory-size anaerobic batch digesters with 25 L volume were constructed and used for the experiments. Three replicates of 5%, 10%, 15%, and 20% TS concentrations of poultry, cattle, and piggery waste slurries were anaerobically digested for a 30-day detention period and gas yield was measured by the method of water displacement. Temperature variation within the digesters was measured with a maximum and minimum thermometer. Anaerobic digestion of the slurries was undertaken in the mesophilic temperature range (20-40°C). The carbon: nitrogen ratio of each of the slurries digested was determined. The carbon content was determined using the wackley-Black method, and nitrogen content was determined by the regular kjeldhal method. The pH was measured weekly during the period of digestion from a digital pH meter. Gas quality (% methane fraction) was also measured weekly from an analyser. Coefficient of variation was computed to ascertain the status of the digestion process. Analysis of variance was used to determine the significant difference in gas yield at p < 0.05. Duncan’s New Multiple Range Test at p < 0.05 was used to analyze the difference in gas yield among the various TS concentrations of the slurries investigated. The results indicate that biogas yield is of the order: 5% TS > 10% TS > 15% TS > 20% TS. This result shows that gas yield increases with decreasing TS concentration of the slurries. The ANOVA showed that the gas yield from the various TS % was significantly different (p < 0.05). DNMRT showed that there was significant difference in gas yield from the slurries and wastetypes investigated. Poultry waste slurries had the greatest gas yield (L CH4/kg TS) as the gas yield from the waste types was of the order: Poultry > Piggery > Cattle. The pH of the slurries was of the range 5.5 to 6.8 (weakly acidic). The C:N of the slurries varied between 6:1 and 9:1. The Coefficient of Variation (CV) for 10 consecutive days of digestion was less than 10% indicating a steady state in all the digesters.

The economy of alternative fuels when including the cost of air pollution

Abstract: In this study, the costs involved in the use of petrol, diesel, natural gas, biogas, and methanol (produced from natural gas and biomass) in cars and heavy trucks are compared. The cost includes fuel cost, extra capital cost for vehicles using alternative fuels, and the environmental cost of VOC, NOx, particulate and CO2 emission based on actual 1996 and estimated 2015 emission factors. The costs have been calculated separately for rural, urban and city-centre traffic. A complete macroeconomic assessment of the effect of introducing alternative fuels is not, however, included in the study. The study shows that no alternative fuel can compete with petrol and diesel in rural traffic when the economic valuation of CO2 emission is taken as current Swedish CO2 taxes ($200/tonne C). In cities with a natural gas network, natural gas is the fuel with the lowest cost for both cars and heavy trucks, based on 1996 emission factors. Methanol from natural gas and biogas from waste products can also compete with diesel in urban traffic. With predicted improvements in technology and subsequent emission reductions, no alternative fuel can compete with petrol in any of the traffic situations studied by 2015, and only in city-centre traffic will alternative fuels be less costly than diesel in heavy vehicles. Of the biomass-based fuels studied, low-cost biogas from waste products is the most competitive one and is, already at current CO2 taxes, the fuel with lowest cost for heavy trucks in urban traffic in areas where natural gas networks do not exist. To enable the more widespread use of biomass-based fuels, i.e. using feedstocks such as energy crops or logging residues that are available in larger amounts, the economic valuation of CO2 emission has to be 2–2.5 times higher than current Swedish CO2 tax level.