Showing papers on "Biogas published in 2005"

Influence of Environmental Conditions on Methanogenic Compositions in Anaerobic Biogas Reactors

Abstract: The influence of environmental parameters on the diversity of methanogenic communities in 15 full-scale biogas plants operating under different conditions with either manure or sludge as feedstock was studied. Fluorescence in situ hybridization was used to identify dominant methanogenic members of the Archaea in the reactor samples; enriched and pure cultures were used to support the in situ identification. Dominance could be identified by a positive response by more than 90% of the total members of the Archaea to a specific group- or order-level probe. There was a clear dichotomy between the manure digesters and the sludge digesters. The manure digesters contained high levels of ammonia and of volatile fatty acids (VFA) and were dominated by members of the Methanosarcinaceae, while the sludge digesters contained low levels of ammonia and of VFA and were dominated by members of the Methanosaetaceae. The methanogenic diversity was greater in reactors operating under mesophilic temperatures. The impact of the original inoculum used for the reactor start-up was also investigated by assessment of the present population in the reactor. The inoculum population appeared to have no influence on the eventual population.

Utilization of flue gas for cultivation of microalgae Chlorella sp.) in an outdoor open thin-layer photobioreactor

Abstract: Flue gas generated by combustion of natural gas in a boiler was used for outdoor cultivation of Chlorella sp. in a 55 m2 culture area photobioreactor. A 6 mm thick layer of algal suspension continuously running down the inclined lanes of the bioreactor at 50 cm s−1 was exposed to sunlight. Flue gas containing 6–8% by volume of CO2 substituted for more costly pure CO2 as a source of carbon for autotrophic growth of algae. The degree of CO2 mitigation (flue gas decarbonization) in the algal suspension was 10–50% and decreased with increasing flue gas injection rate into the culture. A dissolved CO2 partial pressure (pCO2) higher than 0.1 kPa was maintained in the suspension at the end of the 50 m long culture area in order to prevent limitation of algal growth by CO2. NO X and CO gases (up to 45 mg m−3 NO X and 3 mg m−3 CO in flue gas) had no negative influence on the growth of the alga. On summer days the following daily net productivities of algae [g (dry weight) m−2] were attained in comparative parallel cultures: flue gas = 19.4–22.8; pure CO2 = 19.1–22.6. Net utilization (η) of the photosynthetically active radiant (PAR) energy was: flue gas = 5.58–6.94%; pure CO2 = 5.49–6.88%. The mass balance of CO2 obtained for the flue gas stream and for the algal suspension was included in a mathematical model, which permitted the calculation of optimum flue gas injection rate into the photobioreactor, dependent on the time course of irradiance and culture temperature. It was estimated that about 50% of flue gas decarbonization can be attained in the photobioreactor and 4.4 kg of CO2 is needed for production of 1 kg (dry weight) algal biomass. A scheme of a combined process of farm unit size is proposed; this includes anaerobic digestion of organic agricultural wastes, production and combustion of biogas, and utilization of flue gas for production of microalgal biomass, which could be used in animal feeds. A preliminary quantitative assessment of the microalgae production is presented.

Use of flyash and biogas slurry for improving wheat yield and physical properties of soil

Abstract: This study explores the potential use of by-products of energy production, i.e., (i) flyash from coal-powered electricity generation and (ii) biogas slurry from agricultural waste treatment, as nutrient sources in agriculture. These residues are available in large amounts and their disposal is a major concern for the environment. As both residues contain considerable amounts of plant nutrients, their use as soil amendment may offer a promising win-win opportunity to improve crop production and, at the same time, preventing adverse environmental impacts of waste disposal. Effect of flyash and biogas slurry on soil physical properties and growth and yield of wheat (Triticum aestivum) was studied in a field experiment. Leaf area index, root length density and grain yield of wheat were higher in plots amended with flyash or biogas slurry compared to unamended plots. Both types of amendments reduced bulk density, and increased saturated hydraulic conductivity and moisture retention capacity of soil. The study showed that flyash and biogas slurry should be used as soil amendments for obtaining short-term and long-term benefits in terms of production increments and soil amelioration.

Conversion of food waste into hydrogen by thermophilic acidogenesis.

Abstract: Conversion of food waste into hydrogen by thermophilic acidogenesis was investigated as a function of organic loading rate (OLR), hydraulic retention time (HRT) and pH in a continuous stirred tank reactor. In order to identify hydrogen-producing microorganisms, denaturing gradient gel electrophoresis (DGGE) of the polymerase chain reaction (PCR) – amplified V3 region of 16S rDNA analysis was conducted at each tested pH. The conversion of food waste into hydrogen was strongly influenced by the operational conditions. The hydrogen production was increased as OLR increased up to 8 gVSl-1 d-1, but drastically decreased at 10 gVSl-1 d-1. The yield of hydrogen was decreased from 2.2 to 1.0 mol-H2/mol-hexose consumed as HRT decreased from 5 to 2 days. More carbohydrates in the food waste were decomposed at longer HRT, 76–90%, at HRT of 2–5 days. The hydrogen production peaked at pH 5.5 ± 0.1 and significantly decreased at pH 5.0 ± 0.1. The biogas produced was composed of hydrogen and carbon dioxide, but no methane was detected at all tested conditions. The hydrogen contents in the gas produced were more than 55% (v/v) and not sensitive to all tested conditions. The optimum operational condition for continuous hydrogen production from the food waste was obtained at 8 gVSl-1d-1, 5 days HRT and pH 5.5 ± 0.1 where the hydrogen production rate, content, yield and the efficiency of carbohydrate decomposition were 1.0 l H2/l-d, 60.5% (v/v), 2.2 mol-H2/mol-hexose consumed and 90%, respectively. The hydrogen production was related with the concentration of total organic acids (TOA) which was strongly dependent on that of butyrate indicating that the reaction was mainly butyrate fermentation. The hydrogen-producing microorganism of Thermoanaerobacterium thermosaccharolyticum that involved in acetate/butyrate fermentation, was detected with strong intensity at all tested pHs by denaturing gradient gel electrophoresis (DGGE) of the polymerase chain reaction (PCR) – amplified V3 region of 16S rDNA analysis and sensitive to the tested pHs. The experimental results indicated that effective hydrogen production from the food waste could be obtained continuously by thermophilic acidogenesis at proper operational condition.

Dry anaerobic digestion of differently sorted organic municipal solid waste: a full scale experience.

Abstract: This paper presents a comparison of dry anaerobic digestion reactors fed with differently sorted municipal organic solid wastes. One reactor was fed with source sorted organic wastes and a second reactor was fed with mixed organic wastes consisting of grey wastes, mechanically selected municipal solid wastes and sludge. The two reactors utilised the same process (Valorga) and operational conditions at full scale. The results of the study emphasise the influence of the kind of treated material on the process performances, especially in terms of biogas and methane production, thus, energy reclamation. The reactor treating the source sorted organic waste and the reactor treating the mixed organic wastes generated some 200 m3 and 60 m3 of biogas per ton of waste treated, respectively, while the specific methane production was some 0.40 and 0.13 m3CH4/kgTVS, respectively. The mass balance and the final fate of the digested material from the two reactors were also clearly different. As for the costs, these were some 29 € per ton of treated waste (50% for personnel) and 53 €/ton for disposing of the rejected materials. Incomes were some 100 €/ton (on average) and an other 15 €/ton came from green certificates. The initial investment was 16 million Euros.

Anaerobic codigestion of waste activated sludge and OFMSW: the experiences of Viareggio and Treviso Plants (Italy)

Abstract: The paper presents the results of two full-scale applications of the anaerobic co-digestion process of waste activated sludge together with the organic fraction of municipal solid wastes. The experiences were carried out at Viareggio and Treviso wastewater treatment plants (Italy). In the first plant, 3 tons per day of source sorted OFMSW were co-digested with waste activated sludge, increasing the organic loading rate from 1.0 to 1.2 kgTVS/m 3 d. This determined a 50% increase in biogas production. At Treviso WWTP, which has been working for 2 years, some 10 tons per day of separately collected OFMSW are treated using a low-energy consumption sorting line, which allows the removal of 99% and 90% of metals and plastics respectively. In these conditions, the biogas yield increased from 3,500 up to 17,500 m 3 /month. Industrial costs were evaluated less than 50 € per ton of organic waste, while the payback time was calculated as two years.

Prediction of trace compounds in biogas from anaerobic digestion using the MATLAB Neural Network Toolbox

Abstract: The outlook to apply the highly energetic biogas from anaerobic digestion into fuel cells will result in a significantly higher electrical efficiency and can contribute to an increase of renewable energy production. The practical bottleneck is the fuel cell poisoning caused by several gaseous trace compounds like hydrogen sulfide and ammonia. Hence artificial neural networks were developed to predict these trace compounds. The experiments concluded that ammonia in biogas can indeed be present up to 93 ppm. Hydrogen sulfide and ammonia concentrations in biogas were modelled successfully using the MATLAB Neural Network Toolbox. A script was developed which made it easy to search for the best neural network models' input/output-parameters, settings and architectures. The models were predicting the trace compounds, even under dynamical conditions. The resulted determination coefficients ( R 2 ) were for hydrogen sulfide 0.91 and ammonia 0.83. Several model predictive control tool strategies were introduced which showed the potential to foresee, control, reduce or even avoid the presence of the trace compounds.

Anaerobic co-digestion of potato tuber and its industrial by-products with pig manure

Abstract: The possible use of potato tuber and its industrial by-products (potato stillage and potato peels) on farm-scale co-digestion with pig manure was evaluated in a laboratory study. The methane yields (m 3 kg −1 volatile solids (VS) added waste ) achieved on semi-continuous co-digestion at loading rate of 2 kg VS m −3 day −1 in continuously stirred tank reactors at 35 °C were 0.13–0.15 at 100:0 (VS% pig manure to VS% potato co-substrate), 0.21–0.24 at 85:15 and 0.30–0.33 at 80:20 feed ratio. Increasing the loading rate from 2 to 3 kg VS m −3 day −1 at a feed VS ratio of 80:20 (pig manure to potato waste) produced methane yields of 0.28–0.30 m 3 kg −1 VS added waste . Post-digestion (60 days) of the digested materials in batches produced 0.12–0.15 m 3 kg −1 VS added waste of methane at 35 °C. The results suggest that successful digester operation can be achieved with feed containing potato material up to 15–20% of the feed VS and that under similar feed VS, loading rate, retention time and feed VS ratio, the methane yields and process performance for potato tuber would be similar to that of its industrial residues. Thus, co-digestion of potatoes and/or its industrial by-products with manures on a farm-scale level would generate renewable energy and provide a means of waste treatment for industry.

Short Communication Prediction of trace compounds in biogas from anaerobic digestion using the MATLAB Neural Network Toolbox

Abstract: The outlook to apply the highly energetic biogas from anaerobic digestion into fuel cells will result in a significantly higher electrical efficiency and can contribute to an increase of renewable energy production. The practical bottleneck is the fuel cell poisoning caused by several gaseous trace compounds like hydrogen sulfide and ammonia. Hence artificial neural networks were developed to predict these trace compounds. The experiments concluded that ammonia in biogas can indeed be present up to 93 ppm. Hydrogen sulfide and ammonia concentrations in biogas were modelled successfully using the MATLAB Neural Network Toolbox. A script was developed which made it easy to search for the best neural network models’ input/output-parameters, settings and architectures. The models were predicting the trace compounds, even under dynamical conditions. The resulted determination coefficients (R 2 ) were for hydrogen sulfide 0.91 and ammonia 0.83. Several model predictive control tool strategies were introduced which showed the potential to foresee, control, reduce or even avoid the presence of the trace compounds.

A Rational Procedure for Estimation of Greenhouse-Gas Emissions from Municipal Wastewater Treatment Plants

Abstract: Municipal wastewater treatment may lead to the emission of greenhouse gases. The current Intergovenmental Panel on Climate Change (Geneva, Switzerland) approach attributes only methane emissions to wastewater treatment, but this approach may overestimate greenhouse gas emissions from the highly aerobic processes primarily used in North America. To better estimate greenhouse gas emissions, a procedure is developed that can be used either with plant-specific data or more general regional data. The procedure was evaluated using full-scale data from 16 Canadian wastewater treatment facilities and then applied to all 10 Canadian provinces. The principal greenhouse gas emitted from municipal wastewater treatment plants was estimated to be carbon dioxide (CO2), with very little methane expected. The emission rates ranged from 0.005 kg CO2-equivalent/m3 treated for primary treatment facilities to 0.26 kg CO2-equivalent/m3 for conventional activated sludge, with anaerobic sludge digestion to over 0.8 kg CO2-equivalent/m3 for extended aeration with aerobic digestion. Increasing the effectiveness of biogas generation and use will decrease the greenhouse gas emissions that may be assigned to the wastewater treatment plant.