| 1. |
- Bohn, Irene, et al.
(författare)
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Effect of temperature decrease on the microbial population and process performance of a mesophilic anaerobic bioreactor
- 2007
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Ingår i: Environmental Technology. - 1479-487X. ; 28:8, s. 943-952
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Tidskriftsartikel (refereegranskat)abstract
- The effect of a temperature decrease from 33 degrees C to 12 degrees C was investigated for anaerobic digestion of crop residues. A laboratory-scale reactor (R,) was inoculated with mesophilic sludge and operated as continuously stirred fed-batch system at temperatures of 12 degrees C, 18 degrees C and 33 degrees C. Changes in the microbial populations of the sludge were followed by means of fluorescence in situ hybridization analysis. Methane was produced in R, at all temperatures. Stable long-term operation at 18 degrees C was achieved yielding 151 mlCH(4) gVS(added)(-1) at a rate of 108 mlCH(4) l(R)(-1)d(-1) once the microbial populations of the sludge had adapted to this temperature. After operation at 18 degrees C, the contents of R-0, was mixed and distributed into three smaller reactors, which were operated at 18 degrees C (R-18), 25 degrees C (R-25) and 37 degrees C (R-37) respectively. Methane production rates for R-37 and R-25 were 366 and 310 mlCH(4) l(R)(-1)d(-1), respectively, which were higher than the 215 mlCH(4) l(R)(-1)d(-1) obtained in R-0 when this was operated at 33 degrees C. Hydrolysis was found to decrease when temperature was decreased and especially below 25 degrees C. At temperatures below 16 degrees C, acidogenesis and methanogenesis were the rate-limiting steps. Adaptation of the mesophilic sludge to 18 degrees C was indicated by an increase in the ratio of Bacteria to total prokaryotes (sum of Archaea and Bacteria). This was thought to be caused by enrichment of Bacteria in the sludge, which appeared to be an important adaptation mechanism. During the adaptation, the Methanomicrobiales and Methanosarcinaceae populations increased relative to the total Archaea population whereas the Methanosaeta population decreased. The population changes were reflected by reactor performance.
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| 2. |
- Bohn, Irene, et al.
(författare)
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The energy balance in farm scale anaerobic digestion of crop residues at 11-37 degrees C
- 2007
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Ingår i: Process Biochemistry. - : Elsevier BV. - 1873-3298 .- 1359-5113. ; 42:1, s. 57-64
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Tidskriftsartikel (refereegranskat)abstract
- Crop residues can be used for biogas production in farm scale reactors. Use of a process temperature below mesophilic conditions reduces the need for heating as well as investment and operating costs, although it may also reduce the methane yield. In the present study the effect of temperature on net energy output was studied using sugar beet tops and straw as substrates for two pilot-scale reactors. Digestion was found to be stable down to 11 degrees C and optimal methane yield was obtained at 30 degrees C. The methane yield and process performance was studied at 15 degrees C and 30 'C as organic loading rates were increased. It was found that the highest net energy production would be achieved at 30 degrees C with a loading rate of 3.3 kg VS m(-3) day(-1). Running a low-cost process at ambient temperatures would give a net energy output of 60% of that obtained at 30 degrees C. (c) 2006 Elsevier Ltd. All rights reserved.
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| 3. |
- Cirne, Dores, et al.
(författare)
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Anaerobic digestion of lipid-rich waste - Effects of lipid concentration
- 2007
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481. ; 32:6, s. 965-975
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Tidskriftsartikel (refereegranskat)abstract
- The influence of lipid concentration on hydrolysis and biomethanation of a lipid-rich (triolein) model waste was evaluated in batch. The effect of increasing the concentration of lipid from 5% to 47% (w/w), based on chemical oxygen demand (COD), was investigated. The methane recovery observed was above 93% for all tests. An initial lag phase of approximately 6-10 days was observed for all tests. The methane production rate observed was similar for tests with 5%, 10% and 18% lipid (w/w, COD basis). For higher amounts of lipid (31%, 40% and 47%), a stronger inhibition was observed. However, the process was able to recover from the inhibition. When the effect of addition of lipase on enzymatic hydrolysis of lipids was studied, the results showed that the higher the enzyme concentration, the more accentuated was the inhibition of methane production. The enzyme appears to enhance the hydrolysis but the intermediates produced caused inhibition of the later steps in the,degradation process. Since the volatile fatty acid (VFA) profiles presented similar trends for the different concentrations of lipid tested, the major obstacle to methane production was the long-chain fatty acids (LCFA) formation. (c) 2006 Elsevier Ltd. All rights reserved.
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| 4. |
- Cirne, Dores, et al.
(författare)
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Hydrolysis and microbial community analyses in two-stage anaerobic digestion of energy crops
- 2007
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Ingår i: Journal of Applied Microbiology. - : Oxford University Press (OUP). - 1364-5072 .- 1365-2672. ; 103:3, s. 516-527
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Tidskriftsartikel (refereegranskat)abstract
- Aims: The roles of the diverse populations of micro-organisms responsible for biodegradation of organic matter to form methane and carbon dioxide are rudimentarily understood. To expand the knowledge on links between microbial communities and the rate limiting, hydrolytic stage of two-stage biogas production from energy crops, this study was performed. Methods and Results: The process performance. and microbial communities (as determined by fluorescence in situ hybridization) in two separate two-stage batch digestions of sugar beets and grass/clover were studied. The microbial populations developed in the hydrolytic stage of anaerobic digestion of beets and grass/clover showed very few similarities, despite that the hydrolysis dynamics were similar. In both substrates, the solubilization of organic material was rapid for the first 10 days and accompanied by a build-up of volatile fatty acids (VFAs) and lactate. Between days 10 and 15, VFA and lactate concentrations decreased, as did the solubilization rates. For both substrates, Archaea started to appear in the hydrolytic stage between days 10 and 15, and the fraction of Bacteria decreased. The major bacterial group detected in the leachate fraction for beets was Alphaproteobacteria, whereas for grass/clover it was Firmicutes. The number of cells that bound to probes specifically targeting bacteria with cellulolytic activity was higher in the digestion of grass than in the digestion of beet. Conclusions: This study allowed the identification of the general bacterial groups involved, and the identification of a clear shift in the microbial population when hydrolysis rate became limiting for each of the substrates investigated. Significance and Impact of the Study: The findings from this study could be considered as a first step towards the development of strategies to stimulate hydrolysis further and ultimately increasing the methane production rates and yields from reactor-based digestion of these substrates.
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| 5. |
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| 6. |
- Lantz, Mikael, et al.
(författare)
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The prospects for an expansion of biogas systems in Sweden - Incentives, barriers and potentials
- 2007
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Ingår i: Energy Policy. - : Elsevier BV. - 1873-6777 .- 0301-4215. ; 35:3, s. 1830-1843
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Forskningsöversikt (refereegranskat)abstract
- Biogas is a renewable, high-quality fuel, currently produced at more than 200 locations in Sweden. The present production is some 5 PJ/year but the potential is approximately 10 times higher. Biogas can be produced from a wide range of raw materials, from organic waste to dedicated energy crops, and can be utilised for various energy services such as heat, combined heat and power or as a vehicle fuel. Biogas systems are therefore affected by a number of different incentives and barriers, including energy-, waste treatment- and agricultural policies. In this paper, different policies and policy instruments, as well as other factors, which influence a potential expansion of Swedish biogas systems, are identified and evaluated. Existing incentives and barriers can be divided into those affecting the production of biogas, and those affecting the utilisation of the biogas. Only a few types of biogas systems are competitive in Sweden today, while the majority needs increased incentives of different kinds to reach profitability. Such incentives are often motivated from an energy and environmental point of view. Due to the complexity of the biogas systems and the many actors involved, all with different interests, the process of implementing adequate policy instruments will require concerted efforts. (c) 2006 Elsevier Ltd. All rights reserved.
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| 7. |
- Svensson, Mattias, et al.
(författare)
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Enhancing performance in anaerobic high-solids stratified bed digesters by straw bed implementation
- 2007
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Ingår i: Bioresource Technology. - : Elsevier BV. - 1873-2976 .- 0960-8524. ; 98:1, s. 46-52
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Tidskriftsartikel (refereegranskat)abstract
- Anaerobic high-solids single-stage stratified bed digesters have been found to be simple and flexible design candidates for small-scale reactors located in medium- to low-technology environments. In the present study, wheat straw was used as the starter material for the stratified bed. Upon green mass feeding, the anaerobically stabilised straw bed functioned both as a biofilm support and as a particulate filter. It enabled a direct onset of 7 kg VS m(-3) batch loads, added twice a week, and permitted a low but consistent bed permeability during feeding at an average superficial flow velocity of 1 m d(-1) to be achieved. Fed-batch tests with sugar beet tops in pilot- and laboratory-scale setups at an average loading rate of 2 kg VS m(-3) d(-1) resulted in average biogas production rates of 1.2-1.4 m(3) m(-3) d(-1) and methane yields of 0.31-0.36 m(3) kg(-1) VSadded. At the end of the laboratory-scale feeding trial, the 200 day old straw bed had compacted to 50% of its initial volume, without any negative effects on performance being detectable. (c) 2005 Elsevier Ltd. All rights reserved.
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