| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 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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