| 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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Effects of bioaugmentation by an anaerobic lipolytic bacterium on anaerobic digestion of lipid-rich waste
- 2006
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Ingår i: Journal of Chemical Technology and Biotechnology. - : Wiley. - 0268-2575 .- 1097-4660. ; 81:11, s. 1745-1752
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Tidskriftsartikel (refereegranskat)abstract
- The effect of bioaugmentation with an anaerobic lipolytic bacterial strain on the anaerobic digestion of restaurant lipid-rich waste was studied in batch experiments with a model waste containing 10% lipids (triolein) under two sets of experimental conditions: (A) methanogenic conditions, and (B) initially acidogenic conditions in the presence of only the lipolytic strain biomass (4 days), followed by methanogenic conditions. The bioaugmenting lipolytic strain, Clostridium lundense (DSM 17049(T)), was isolated from bovine rumen. The highest lipolytic activity was detected at the beginning of the experiments. A higher methane production rate, 27.7 cm(3) CH4(STP) g(-1) VSadded day(-1) (VS, volatile solids) was observed in experiment A with the presence of the bioaugmenting lipolytic strain under methanogenic conditions. The highest initial oleate concentration, 99% of the total oleate contained in the substrate, was observed in the experiments with the bioaugmenting lipolytic strain under treatment A conditions; the levels of palmitate and stearate were also higher until day 15, indicating that the bioaugmentation strategy improved the hydrolysis of the lipid fraction. In general, the results indicated that degradation of the long chain fatty acids (LCFAs) controlled the digestion process. (c) 2006 Society of Chemical Industry.
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| 5. |
- Cirne, Dores, et al.
(författare)
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Enhanced solubilisation of the residual fraction of municipal solid waste.
- 2008
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 57:7, s. 995-1000
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Tidskriftsartikel (refereegranskat)abstract
- The Swedish ordinance banning the landfilling of organic material after 2005 has led to rapid developments towards waste incineration, while biological alternatives have been less studied. In this study, biological alternatives for enhanced methane production from residual municipal waste (the remaining waste fraction after source separation) are investigated. The strategies investigated were recirculation of leachate, recirculation of leachate with aeration, flooding of the solid bed, and enzyme addition after initial leaching in an anaerobic, batch, two-stage digestion process with recirculation of digested leachate. The degree of solubilisation of organic compounds achieved was higher for initial digestion in a two-stage anaerobic digestion system followed by the addition of cellulolytic enzymes than in the other strategies investigated. The overall net solubilisation achieved was 0.48 g COD/g VS(added) corresponding to an increase of 34%. In addition, the digestion time was considerably reduced using this strategy. For the other strategies investigated the solubilisation yields obtained were similar, 0.31 g COD/g VS(added).
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| 6. |
- 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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| 7. |
- Crocetti, Greg, et al.
(författare)
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An update and optimisation of oligonucleotide probes targeting methanogenic Archaea for use in fluorescence in situ hybridisation (FISH)
- 2006
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Ingår i: Journal of Microbiological Methods. - : Elsevier BV. - 1872-8359 .- 0167-7012. ; 65:1, s. 194-201
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Tidskriftsartikel (refereegranskat)abstract
- Fluorescence in situ hybridisation (FISH) is a common and popular method used to investigate microbial populations in natural and engineered environments. DNA oligonucleoticle probes require accurate determination of the optimal experimental conditions for their use in FISH Oligonucleotides targeting the rRNA of methanogenic Archaea at various taxonomic levels have previously been published, although when applied in FISH, no optimisation data has been presented In this study, 3000 Euryarchaeota 16S rRNA gene sequences were phylogenetically analysed and previously published oligonucleoticles were evaluated for target group accuracy. Where necessary, modifications were introduced or new probes were designed. The updated set of probes was optimised for use in FISH for a more accurate detection of methanogenic Archaea. (c) 2005 Elsevier B.V. All rights reserved.
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| 8. |
- Lehtomäki, Anni, et al.
(författare)
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Two-stage anaerobic digestion of energy crops: Methane production, nitrogen mineralisation and heavy metal mobilisation
- 2006
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Ingår i: Environmental Technology. - 1479-487X. ; 27:2, s. 209-218
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Tidskriftsartikel (refereegranskat)abstract
- Energy crops (willow, sugar beet and grass silage) were digested ill pilot scale two-stage anaerobic digesters. The specific methane yields obtained were 0.16, 0.38 and 0.39 m(3) kg(-1) added volatile solids (VSadded) for willow, sugar beet and grass, respectively, corresponding to yearly gross energy yields of 15, 53 and 26 megawatt-hours (MWh) per hectare. With grass and sugar beets as substrate, 84-85% of the harvestable methane was obtained within 30 days. In pilot scale two-stage digestion of willow and sugar beet, 56 and 85,, of the laboratory scale methane yields were obtained, but digestion of grass in two-stage reactors yielded 5% more methane than digestion in laboratory scale completely mixed low solids systems, possibly due to the pH conditions favourable to hydrolysis in the two-stage system. In digestion of grass and sugar beet the liquid at the end of digestion was rich in ammonium nitrogen, and the nitrogen in the substrate was efficiently mineralised. The results show that heavy metal concentrations are not likely to limit the utilisation of residues from digestion of nonmetal accumulating crops. Efficient mobilisation of heavy metals during the acidic phase of digestion revealed the possibility of removing metals from leachate generated in two-stage anaerobic digestion of phytoextracting crops.
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| 9. |
- Mshandete, Anthony, et al.
(författare)
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Effect of aerobic pre-treatment on production of hydrolases and volatile fatty acids during anaerobic digestion of solid sisal leaf decortications residues
- 2008
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Ingår i: African Journal of Biochemistry Research. - 1996-0778. ; 2:5, s. 111-119
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Tidskriftsartikel (refereegranskat)abstract
- The effect of aerobic pretreatment on the production of hydrolases and volatile fatty acids during anaerobic digestion of solid sisal decortications leaf residue (SLDR) was investigated. Batch solid waste bioreactors with working volume of 2 litres were used in this study. Batch loads of aerobically treated or untreated sisal leaf residue inoculated with activated sludge mixed culture were packed into the bioreactors and operated anaerobically for 400 h. The fermentation products were mainly (mg/g total volatile fatty acids, VFAs): acetic acid (287), n-butyric acid (201), n-valeric acid (96) and caproic acid (62) as well as with low amounts of propionic acid and iso-butyric acid for aerobic pre-treated sisal leaf waste solids. Contrarily, for the untreated system, the fermentation products were chiefly (mg/g total volatile fatty acids): propionic acid (317), iso-butyric acid (276), n-butyric acid (96), acetic acid (84) and insignificant amounts of n-valeric acid, iso-valeric acid and caproic acid. Although the activities of hydrolytic enzymes found were similar for both treated and untreated SLDR, proportions of VFAs obtained with the former residues appeared to be better substrates for biomethanantion than those obtained from the latter substrates. These results indicated the potential of aerobic pre-treatment for enhanced bioconversion of SLDR. The present study, reports for the first time the types and levels of VFAs and hydrolases produced during anaerobic digestion of aerobic pre-treated SLDR and could be used as a basis for designing a pilot scale process.
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| 10. |
- Mshandete, Anthony, et al.
(författare)
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Effect of particle size on biogas yield from sisal fibre waste
- 2006
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Ingår i: Renewable Energy. - : Elsevier BV. - 0960-1481. ; 31:14, s. 2385-2392
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Tidskriftsartikel (refereegranskat)abstract
- The degradation and biogas production potential of sisal fibre waste could be significantly increased by pre-treatment for reduction of particle size. Batch-wise anaerobic digestion of sisal fibre waste was carried out in 1-l digesters with fibre sizes ranging from 2 to 100 mm, at an ambient temperature of 33 °C. Sediment from a stabilisation pond at a sisal production plant was used as starter seed. Total fibre degradation increased from 31% to 70% for the 2 mm fibres, compared to untreated sisal fibres. Furthermore, the results confirmed that methane yield was inversely proportional to particle size. Methane yield increased by 23% when the fibres were cut to 2 mm size and was 0.22 m3 CH4/kg volatile solids, compared to 0.18 m3 CH4/kg volatile solids for untreated fibres. By anaerobic digestion and biogas production, the 148,000 tonne of waste sisal fibres generated annually in Tanzania could yield 22 million m3 of methane, and an additional 5 million m3 of methane if pre-treatment by size reduction to 2 mm was applied.
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