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1.
  • Björnsson, Lovisa, et al. (författare)
  • Evaluation of new methods for the monitoring of alkalinity dissolved hydrogen and the microbial community in anaerobic digestion
  • 2001
  • Ingår i: Water Research. - Elsevier. - 0043-1354 (print). ; 35:12, s. 2833-2840
  • Tidskriftsartikel (refereegranskat)abstract
    • New methods for spectrophotometric alkalinity measurement, dissolved hydrogen monitoring and for obtaining a fingerprint of the microbial community were evaluated as tools for process monitoring in anaerobic digestion. The anaerobic digestion process was operated at organic loading rates of 1.5, 3.0 and 4.5g volatile solids l-1d-1 and subjected to pulse loads of carbohydrate, lipid, protein and a mixed sludge substrate. The spectrophotometric alkalinity monitoring method showed good agreement with traditional titrimetric alkalinity monitoring and has the advantage of being easy to modify to on-line monitoring applications. The on-line monitoring of dissolved hydrogen gave valuable information about approaching process overload and can be a good complement to the conventional monitoring of volatile fatty acids. Changing process conditions were also reflected in the microbial fingerprint that could be achieved by partitioning in two-phase systems. The investigated methods showed potential for application in increasing our understanding of the anaerobic digestion process as well as for being applicable for monitoring in the complex environment of full-scale anaerobic digestion processes.
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2.
  • Björnsson, Lovisa, et al. (författare)
  • Evaluation of parameters for monitoring an anaerobic co-digestion process
  • 2000
  • Ingår i: Applied Microbiology and Biotechnology. - Springer. - 1432-0614 (Online) .- 0175-7598 (Print). ; 54:6, s. 844-849
  • Tidskriftsartikel (refereegranskat)abstract
    • The system investigated in this study is an anaerobic digester at a municipal wastewater treatment plant operating on sludge from the wastewater treatment, co-digested with carbohydrate-rich food-processing waste. The digester is run below maximum capacity to prevent overload. Process monitoring at present is not extensive, even for the measurement of on-line gas production rate and off-line pH. Much could be gained if a better program for monitoring and control was developed, so that the full capacity of the system could be utilised without the risk of overload. The only limit presently set for correct process operation is that the pH should be above 6.8. In the present investigation, the pH was compared with alkalinity, gas production rate, gas composition and the concentration of volatile fatty acids (VFA). Changes in organic load were monitored in the full-scale anaerobic digester and in laboratory-scale models of the plant. Gas-phase parameters showed a slow response to changes in load. The VFA concentrations were superior for indicating overload of the microbial system, but alkalinity and pH also proved to be good monitoring parameters. The possibility of using pH as a process indicator is, however, strongly dependent on the buffering capacity. In this study, a minor change in the amount of carbohydrates in the substrate had drastic effects on the buffering effect of the system.
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3.
  • Mshandete, Anthony, et al. (författare)
  • Influence of recirculation flow rate on the performance of anaerobic packed-bed bioreactors treating potato-waste leachate
  • 2004
  • Ingår i: Environmental Technology. - Selper Ltd. - 0959-3330. ; 25:8, s. 929-936
  • Tidskriftsartikel (refereegranskat)abstract
    • The performance of anaerobic, packed-bed bioreactors treating leachate from potato waste was evaluated in terms of organic loading rate (OLR) as well as the recirculation flow rate. Two 1 litre bioreactors, filled with porous glass beads as biofilm carriers and with continuous recirculation flow rates of 10 ml min(-1) and 20 ml min(-1) respectively, were used in the experiment. The OLR applied to each bioreactor was increased stepwise from 4 to 12 kg chemical oxygen demand (COD) m(-3)d(-1) by increasing feed flow rate. The methane yields decreased with increasing OLR in both bioreactors. The methane yield for the bioreactor with the lower recirculation flow rate ranged between 0.10 and 0.14 m(3) CH4 kg COD-1 removed, while for the other bioreactor it was 0.14-0.20 m(3) CH4 kg COD-1 removed. Both bioreactors demonstrated stable COD removal which was around 95% for the bioreactor with lower flow of recirculation while for the other it was 92%, over a range of OLRs of 4-8 kg COD m(-3)d(-1). The bioreactor with the lower recirculation flow rate showed operational stability when a high OLR, namely 12 kg COD m(-3)d(-1), was applied, while the other one became overloaded. There was an accumulation of volatile fatty acids which gave a corresponding drop in pH because the system had a low buffering capacity and this thus ultimately led to process failure. This study demonstrated the suitability of a packed bed bioreactor operated at lower recirculation flow rate for treating leachate from potato waste.
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4.
  • Murto, Marika (författare)
  • Anaerobic Digestion – Microbial Ecology, Improved Operational Design and Process Monitoring
  • 2003
  • Doktorsavhandling (övrigt vetenskapligt)abstract
    • The implementation of anaerobic digestion is important in the concept of sustainable development, especially regarding the environmental benefits. Biogas is produced when organic matter is degraded by microorganisms under oxygen-free (anaerobic) conditions. Biogas production occurs in nature where oxygen is absent; in rice fields, landfills, sediments, the intestinal tract of animals, etc. The advantage of degrading organic matter and at the same time producing renewable energy in the form of energy-rich methane, as well as other environmental benefits, has made anaerobic digestion interesting in industrial applications. Anaerobic digestion has been exploited as an effective biotechnological method for organic waste and wastewater treatment. Current national environmental regulations and other policies governing land use and waste disposal have increased interest in anaerobic digestion. However, the anaerobic degradation of organic matter is a complex process involving microorganisms in an advanced interaction. Our knowledge about the anaerobic digestion process is increasing, but to increase the efficiency of the process and to make it more economically beneficial there is a need for improvements in the technology in many areas. Studying the microbial ecology is important for in-depth understanding of the anaerobic degradation process. Fluorescence in situ hybridisation (FISH) was employed to identify microorganisms in the anaerobic process with the focus on methanogens. Probes commonly used in FISH for detecting methanogens were re-evaluated and redesigned, giving better coverage of the methanogens, and the experimental conditions were optimised for use of the probes in FISH. Using FISH, changes in microbial composition could be detected when changing feed composition in anaerobic reactors, which could be correlated to changes in process conditions. A new application for partitioning in aqueous two-phase systems was developed. The mixed culture from an anaerobic digestion process was multi-step partitioned in an aqueous two-phase system in order to obtain a “fingerprint” of the culture. Differences in operational conditions could be reflected in the distribution profiles obtained. Process control and monitoring are of great importance in improving the efficiency of the anaerobic degradation process. Traditional and new methods were evaluated for the monitoring of anaerobic digestion processes. Since the anaerobic process is so complex, one parameter is seldom sufficient to monitor the conditions in a reactor, and a combination of parameters should be used for reliable process monitoring and control. With a good monitoring and control strategy it is possible to run the digesters closer to their maximum capacity thereby improving the treatment capacity and the process economy. The development of process designs and configurations has improved treatment rates making the process more cost-efficient. The successful co-digestion of agricultural waste with sewage sludge and pig manure was reported. Mixing of waste must be done with care as unsuitable mixtures can lead to unstable process conditions resulting in failure of the anaerobic digestion process. The development of new high-rate reactor designs has increased the efficiency and stability of the biogas process compared with the conventional reactor configuration. Three different high-rate reactor designs were evaluated and successfully applied to the treatment of solid agricultural waste.
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5.
  • Murto, Marika, et al. (författare)
  • Characterisation of anaerobic mixed cultures by partition in an aqueous two-phase system
  • 2002
  • Ingår i: Biotechnology Letters. - Springer. - 0141-5492. ; 24:5, s. 335-341
  • Tidskriftsartikel (refereegranskat)abstract
    • A method to characterise a dynamic microbial consortium is described. By exploiting differences in surface properties between different cells and between cells of different physiological status, it was possible to develop a partition pattern for a mixed culture under different conditions. The separation method used was partition in aqueous two-phase systems and when using a counter current extraction process one could clearly differentiate the partition profile between resting, active and overloaded biomethanation cultures.
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6.
  • Murto, Marika, et al. (författare)
  • Impact of food industrial waste on anaerobic co-digestion of sewage sludge and pig manure
  • 2004
  • Ingår i: Journal of Environmental Management. - Elsevier Ltd. - 0301-4797. ; 70:2, s. 101-107
  • Tidskriftsartikel (refereegranskat)abstract
    • The performance of an anaerobic digestion process is much dependent on the type and the composition of the material to be digested. The effects on the degradation process of co-digesting different types of waste were examined in two laboratory-scale studies. In the first investigation, sewage sludge was co-digested with industrial waste from potato processing. The co-digestion resulted in a low buffered system and when the fraction of starch-rich waste was increased, the result was a more sensitive process, with process overload occurring at a lower organic loading rate (OLR). In the second investigation, pig manure, slaughterhouse waste, vegetable waste and various kinds of industrial waste were digested. This resulted in a highly buffered system as the manure contributed to high amounts of ammonia. However, it is important to note that ammonia might be toxic to the micro-organisms. Although the conversion of volatile fatty acids was incomplete the processes worked well with high gas yields, 0.8-1.0 m(3) kg(-1) VS. (C) 2004 Elsevier Ltd. All rights reserved.
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7.
  • Parawira, Wilson, et al. (författare)
  • Anaerobic batch digestion of solid potato waste alone and in combination with sugar beet leaves
  • 2004
  • Ingår i: Renewable Energy. - Elsevier Ltd. - 0960-1481. ; 29:11, s. 1811-1823
  • Tidskriftsartikel (refereegranskat)abstract
    • The objective of this study was to characterise anaerobic batch biodegradation of potato waste alone and when co-digested with sugar beet leaves. The effects of increasing concentration of potato waste expressed as percentage of total solids (TS) and the initial inoculum-to-substrate ratio (ISR) on methane yield and productivity were investigated. The ISRs studied were in the range 9.0-0.25 and increasing proportions of potato waste from 10% to 80% of TS. A maximum methane yield of 0.32 1 CH4/g VSdegraded was obtained at 40% of TS and an ISR of 1.5. A methane content of up to 84% was obtained at this proportion of potato waste and ISR. Higher ISRs led to faster onset of biogas production and higher methane productivity. Furthermore, co-digestion of potato waste and sugar beet leaves in varying proportions was investigated at constant TS. Co-digestion improved the accumulated methane production and improved the methane yield by 31-62% compared with digestion of potato waste alone. (C) 2003 Elsevier Ltd. All rights reserved.
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8.
  • Parawira, Wilson, et al. (författare)
  • Volatile fatty acid production during anaerobic mesophilic digestion of solid potato waste
  • 2004
  • Ingår i: Journal of Chemical Technology & Biotechnology. - Society of Chemical Industry. - 0268-2575. ; 79:7, s. 673-677
  • Tidskriftsartikel (refereegranskat)abstract
    • The production of volatile fatty acids by anaerobic digestion of solid potato waste was investigated using a batch solid waste reactor with a working capacity of 2 dm(-3) at 37degreesC. Solid potato waste was packed into the digester and the organic content of the waste was released by microbial activity by circulating water over the bed, using batch loads of 500g or 1000 g potato waste. The sequence of appearance of the volatile fatty acids was (acetic, propionic); (n-butyric); (n-valeric, iso-valeric, caproic); (iso-butyric). After 300 h digestion of potato waste on a small scale, the fermentation products were chiefly (mg g(-1) total VFAs): acetic acid (420), butyric acid (310), propionic acid (140) and caproic acid (90), with insignificant amounts of iso-butyric acid, n-valeric and iso-valeric acids. When the load of potato solids was increased, the volatile fatty acid content was similar, but butyric acid constituted 110 mg g(-1) and lactic acid 400 mg g(-1) of the total volatile fatty acids. The maximum soluble chemical oxygen demand (COD) achieved under the experimental conditions used was 27 and 37 g COD dm(-3) at low and high loadings of potato solids, respectively. The total volatile fatty acids reached 19 g dm(-3) of leachate at both loads of potato solid waste. Gas production was negligible, indicating that methanogenic activity was effectively inhibited. (C) 2004 Society of Chemical Industry.
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