| 11. |
- 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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| 12. |
- 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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| 13. |
- 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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| 14. |
- Mshandete, Anthony, et al.
(författare)
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Enhancement of anaerobic batch digestion of sisal pulp waste by mesophilic aerobic pre-treatment
- 2005
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Ingår i: Water Research. - : Elsevier BV. - 1879-2448 .- 0043-1354. ; 39:8, s. 1569-1575
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Tidskriftsartikel (refereegranskat)abstract
- Pre-treatment of sisal pulp prior to its anaerobic digestion was investigated using an activated sludge mixed culture under aerobic conditions in batch bioreactors at 37 degrees C. The progression of aerobic pre-treatment of the residue in relation to the activities of some extracellular hydrolytic enzymes in the slurry was monitored. The highest activity of hydrolytic enzymes was obtained at 9 h of pre-treatment. Filter paper cellulase had a maximum activity of 0.90 IU/ml, while carboxymethyl cellulase, amylase and xylanase were produced to a maximum of about 0.40 IU/ml. The methane yield obtained after anaerobic digestion of the pre-treated pulp ranged between 0.12 and 0.24 m(3) CH4/kg VS added. The highest and lowest values were obtained for 9 and 72 h of pre-treatment, respectively. Nine hours of pre-treatment of sisal pulp prior to anaerobic digestion demonstrated a 26 % higher methane yield when compared to the sisal pulp without pre-treatment. The consortia of microorganisms in activated sludge demonstrated a useful potential in the production of hydrolases acting on major macromolecules of sisal pulp. The fact that a correlation was observed between high enzyme activity and high methane yield at 9h of aerobic pre-treatment suggests that such a short pretreatment period could be an alternative option for increasing solubilization of sisal pulp and promoting methane productivity. (c) 2005 Elsevier Ltd. All rights reserved.
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| 15. |
- Mshandete, Anthony Manoni, et al.
(författare)
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Performance of biofilm carriers in anaerobic digestion of sisal leaf waste leachate
- 2008
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Ingår i: Electronic Journal of Biotechnology. - : Elsevier BV. - 0717-3458. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Three methanogenic biofilm bioreactors were studied to evaluate the performance of three types of carriers. The carrier material were consisted of sisal fibre waste, pumice stone and porous glass beads, and the bioprocess evaluated was the methanogenesis anaerobic digestion of sisal leaf waste leachate. Process performance was investigated by increasing the organic loading rate (OLR) step-wise. The best results were obtained from the bioreactor packed with sisal fibre waste. It had the highest chemical oxygen demand ( COD) removal efficiencies in the range of 80-93% at OLRs in the range of 2.4-25 g COD L(-1)d(-1). The degradation pattern of volatile fatty acids (VFAs) showed that the degradation of propionate was limiting at higher OLRs. The stable pH and higher partial alkalinity (PA) of the outflow illustrated that packed-bed bioreactors have a good ability to withstand the variations in load and volatile fatty acid concentrations that can occur in a two-stage anaerobic process. In conclusion, sisal fibre waste was shown to be a novel promising biofilm carrier and would work very well in methanogenic biofilm bioreactors treating sisal leaf tissue waste leachate. Furthermore both sisal wastes are available in the neighbourhood of sisal industries, which makes anaerobic digestion scale up at sisal factory level feasible and cost-effective.
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| 16. |
- Mshandete, Anthony, et al.
(författare)
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Performance of a sisal fibre fixed-bed anaerobic digester for biogas production from sisal pulp waste
- 2005
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Ingår i: Tanzania Journal of Science. - : African Journals Online (AJOL). - 0856-1761. ; 31:2, s. 41-52
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Tidskriftsartikel (refereegranskat)abstract
- A single stage anaerobic digester employing a sisal fibre waste fixed bed was studied for biogas production from sisal pulp waste. The fibre was colonized by microorganisms involved in biogas production. The sisal pulp waste to be digested was fed from the top and was sprinkled intermittently with recirculating leachate from the material. Organic loading rates of 0.1-10 kg volatile solids (VS) m-3d-1 could be applied and methane yields in the range of 0.13-0.48 m3 CH4 kg-1 VS added were obtained. The average methane content in the biogas produced from sisal pulp waste was 55%, and the biogas production rate was 0.15-0.54 m3m-3d-1. The methane yield obtained and the highest organic loading rate that could be sustained by this simple, fixed-bed digester are indications of an attractive system in terms of performance and reliability. It is concluded that the sisal fibre waste fixed bed is a promising carrier for microbes and can be employed for long-term operation without changing the bed.
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| 17. |
- Mshandete, Anthony, et al.
(författare)
-
Two-stage anaerobic digestion of aerobic pre-treated sisal leaf decortications residues: hydrolases activities and biogas production profile
- 2008
-
Ingår i: African Journal of Biochemistry Research. - 1996-0778. ; 2:11, s. 211-218
-
Tidskriftsartikel (refereegranskat)abstract
- A two-stage system was investigated for anaerobic digestion (AD) of aerobically pre-treated sisal leaf decortication residue (SLDR) with regard to hydrolytic enzymes and biogas production. The system consisted of a solid-bed bioreactor for hydrolysis connected to methanogenic bioreactor packed with sisal fibre decortication residues (SFDR) as biofilm carriers. Some of the enzymes produced by microorganisms to hydrolyse SLDR were found to be pectinase, filter paper cellulase, amylase, beta-glucosidase, carboxylmethyl cellulase, xylanase and protease. Enzyme activities observed in the acidogenic bioreactor were much higher than those in the methanogenic bioreactor. The hydrolysis and the methanogenic stages were well separated, as indicated by the high carbon dioxide production, high volatile fatty acids (VFAs) concentration and low pH in the acidogenic bioreactor compared with high methane production, low VFAs concentration and above neutral pH in the effluent of the methanogenic bioreactor. Digestion of SLDR gave energy yields of 2.45 kWh/kg volatile solids added in the form of methane. The integrity of the methane filter was maintained throughout the period of operation producing biogas with 51-70% methane content. A stable effluent pH showed that the methanogenic bioreactor had good ability to withstand the variations in load and VFAs concentrations that occurred in the two-stage process. In conclusion, the results of this study showed that the two-stage system was suitable for effective stabilization and biomethanation of SLDR.
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| 18. |
- Parawira, Wilson, et al.
(författare)
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Energy production from agricultural residues: high methane yields in pilot scale two-stage anaerobic digestion
- 2008
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Ingår i: Biomass & Bioenergy. - : Elsevier BV. - 1873-2909 .- 0961-9534. ; 32:1, s. 44-50
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Tidskriftsartikel (refereegranskat)abstract
- There is a large, unutilised energy potential in agricultural waste fractions. In this pilotscale study, the efficiency of a simple two-stage anaerobic digestion process was investigated for stabilisation and biomethanation of solid potato waste and sugar beet leaves, both separately and in co-digestion. A good phase separation between hydrolysis/ acidification and methanogenesis was achieved, as indicated by the high carbon dioxide production, high volatile fatty acid concentration and low pH in the acidogenic reactors. Digestion of the individual substrates gave gross energy yields of 2.1–3.4 kWh/kg VS in the form of methane. Co-digestion, however, gave up to 60% higher methane yield, indicating that co-digestion resulted in improved methane production due to the positive synergism established in the digestion liquor. The integrity of the methane filters (MFs) was maintained throughout the period of operation, producing biogas with 60–78% methane content. A stable effluent pH showed that the methanogenic reactors had good ability to withstand the variations in load and volatile fatty acid concentrations that occurred in the two-stage process. The results of this pilot-scale study show that the two-stage anaerobic digestion system is suitable for effective conversion of semi-solid agricultural residues as potato waste and sugar beet leaves.
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| 19. |
- Selling, Robert, et al.
(författare)
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Two-stage anaerobic digestion enables heavy metal removal.
- 2008
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 57:4, s. 553-558
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Tidskriftsartikel (refereegranskat)abstract
- To fully exploit the environmental benefits of the biogas process, the digestate should be recycled as biofertiliser to agriculture. This practice can however be jeopardized by the presence of unwanted compounds such as heavy metals in the digestate. By using two-stage digestion, where the first stage includes hydrolysis/acidification and liquefaction of the substrate, heavy metals can be transferred to the leachate. From the leachate, metals can then be removed by adsorption. In this study, up to 70% of the Ni, 40% of the Zn and 25% of the Cd present in maize was removed when the leachate from hydrolysis was circulated over a macroporous polyacrylamide column for 6 days. For Cu and Pb, the mobilization in the hydrolytic stage was lower which resulted in a low removal. A more efficient two-stage process with improved substrate hydrolysis would give lower pH and/or longer periods with low pH in the hydrolytic stage. This is likely to increase metal mobilisation, and would open up for an excellent opportunity of heavy metal removal.
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| 20. |
- Svensson, L M, et al.
(författare)
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Biogas production from crop residues on a farm-scale level in Sweden: scale, choice of substrate and utilisation rate most important parameters for financial feasibility
- 2006
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Ingår i: Bioprocess and Biosystems Engineering. - : Springer Science and Business Media LLC. - 1615-7605 .- 1615-7591. ; 29:2, s. 137-142
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Tidskriftsartikel (refereegranskat)abstract
- Anaerobic digestion would enable the energy potential of agricultural crop residues such as ley crops and sugar beet tops to be harnessed in Sweden. In the present study, the financial prospects of single-stage fed-batch high-solids digestion on three different scales, 51, 67, and 201 kW, were calculated on the basis of experimental results and observations. In addition to scale, the effects of methane yield and fertiliser recovery (compared to green manuring) was investigated by testing different substrate mixtures. The biogas was disposed as heat, combined heat and power, or as vehicle fuel. Besides the positive effect of scale, the results indicate the importance of choosing substrates with a high methane yield and high nitrogen content, and the necessity of fully utilising both the capacity of the equipment installed and the energy carriers produced. Net unit costs of 5.3 and 8.1 Euroct/kWh were achieved (201 kW), heat and vehicle fuel, respectively.
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