| 1. |
- Andersson, Jonatan, et al.
(author)
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Evaluation of straw as a biofilm carrier in the methanogenic stage of two-stage anaerobic digestion of crop residues
- 2002
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In: Bioresource Technology. - 1873-2976. ; 85:1, s. 51-56
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Journal article (peer-reviewed)abstract
- Straw was evaluated as a biofilm carrier in the methanogenic stage of the two-stage anaerobic digestion of crop residues. Three reactor configurations were studied, a straw-packed-bed reactor, a glass packed-bed reactor and a reactor containing suspended plastic carriers. The reactor with the packed straw bed showed the best results. It had the highest methane production, 5.4 11(-1) d(-1), and the chemical oxygen demand (COD) removal ranged from 73-50% at organic loading rates from 2.4-25 g COD 1(-1) d(-1). The degradation pattern of volatile fatty acids showed that the degradation of propionate and longer-chain fatty acids was limiting at higher organic loading rates. A stable effluent pH showed that the packed-bed reactors had good ability to withstand the variations in load and volatile fatty acid concentrations that can occur in the two-stage process. The conclusion is that straw would work very well in the intended application. A further benefit is that straw is a common agricultural waste product and requires only limited resources concerning handling and cost. (C) 2002 Elsevier Science Ltd. All rights reserved.
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| 2. |
- Björnsson, Lovisa, et al.
(author)
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Evaluation of new methods for the monitoring of alkalinity dissolved hydrogen and the microbial community in anaerobic digestion
- 2001
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In: Water Research. - 1879-2448. ; 35:12, s. 2833-2840
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Journal article (peer-reviewed)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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| 3. |
- Björnsson, Lovisa, et al.
(author)
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Evaluation of parameters for monitoring an anaerobic co-digestion process
- 2000
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In: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 54:6, s. 844-849
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Journal article (peer-reviewed)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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| 4. |
- Björnsson, Lovisa
(author)
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Intensification of the biogas process by improved process monitoring and biomass retention
- 2000
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Doctoral thesis (other academic/artistic)abstract
- The utilisation of energy in the form of biogas is one of the environmentally sound alternatives available using renewable energy sources. Biogas is formed by anaerobic degradation of organic material, the main consistuent being energy-rich methane. There is a large unused potential of organic waste that is suitable for biogas production and the anaerobic digestion process has the potential of becoming an important waste treatment and bioenergy generating method in the future. Laws, government grants, taxes and an increasing environmental concern are presently directing developments in a favourable direction for the increased use of the biogas process, but the implementation of anaerobic digestion technology is not straightforward and there is a need for further efforts to develop reliable, economically feasible technology. Anaerobic degradation is performed by a well-organised community of several microbial populations, and is a complex process. Some of the microbial groups involved are slow-growing and sensitive to changes in operating conditions. This can cause instability during both the start-up and operation of the anaerobic process. To make the biogas process more attractive from a commercial point of view, and to facilitate increased integration into our energy supply systems, these instability problems must be overcome in an economically viable way. The purpose of the present work was to investigate different methods of improving the performance and efficiency of the anaerobic digestion process. Based on the knowledge concerning microbial and physical events in the anaerobic digestion process, two main strategies were applied; biomass retention and improved process monitoring. Support materials were utilised to facilitate the retention of slow-growing organisms in biofilms, thereby stabilising the process. It was shown that the protected environment of a biofilm in combination with a long adaptation period made the treatment of toxic wastewater possible. A support material was also successfully used when treating waste containing a high concentration of insoluble particles. No clogging problems occurred, and the retention of important bacteria resulted in a change in metabolic flow and increased process stability. In a two-phase process, a protected environment can be created for the sensitive methanogens. A biosensor that could be used for monitoring of the flow of organic compounds reaching the methanogens was developed. The sensor was able to measure the biochemical oxygen demand (BOD) in a few minutes, making it suitable for on-line monitoring. More efficient operation can be achieved by improving process monitoring, which allows waste treatment at a higher rate. Traditional off-line monitoring methods used in anaerobic digestion were investigated; the results indicating that the present monitoring strategy is not adequate if the process is to be operated at a higher rate. The very rapid response to overload indicates that on-line monitoring is necessary to make suitable process control possible. A new method for utilising a semiconductor sensor for the monitoring of dissolved hydrogen on-line was described. The method was evaluated together with other traditional and new monitoring methods, and proved to be a useful tool in on-line anaerobic digester process monitoring.
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| 5. |
- Björnsson, Lovisa, et al.
(author)
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Utilisation of a Pd-MOS sensor for on-line monitoring of dissolved hydrogen in anaerobic digestion
- 2001
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In: Biotechnology and Bioengineering. - 1097-0290. ; 73:1, s. 35-43
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Journal article (peer-reviewed)abstract
- The use of a hydrogen-sensitive palladium-metal oxide semiconductor (Pd-MOS) sensor in combination with a membrane for liquid-to-gas transfer for the detection of dissolved hydrogen was investigated. The system was evaluated with known concentrations of dissolved hydrogen in water. The lowest concentration detected with this set-up was 160 nM. The method was applied to monitoring of a laboratory-scale anaerobic digestion process employing mixed sludge containing mainly food/industrial waste. Pulse loads of glucose were added to the system at different levels of microbial activity, and the microbial status of the culture was reflected in the dissolved hydrogen response. Simultaneous headspace hydrogen measurements were performed, and at the lower levels of dissolved hydrogen no corresponding headspace hydrogen could be detected. When glucose was added to a resting culture the dissolved hydrogen response was rapid and the first response could be detected 9 min after addition of glucose, whereas headspace hydrogen concentrations increased only after 80 to 110 min. This indicates limitations in the liquid-to-gas hydrogen transfer and illustrates the importance of hydrogen monitoring in the liquid. The sensor system developed is flexible, the membrane is easily replaceable, and the probe for liquid-to-gas hydrogen transfer can be adjusted easily to large-scale applications.
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| 6. |
- Liu, Jing, et al.
(author)
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Immobilised activated sludge based biosensor for biochemical oxygen demand measurement
- 2000
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In: Biosensors & Bioelectronics. - 1873-4235. ; 14:12, s. 883-893
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Journal article (peer-reviewed)abstract
- A biochemical oxygen demand (BOD) sensor, based on an immobilised mixed culture of microorganisms in combination with a dissolved oxygen electrode, has been developed for the purpose of on-line monitoring of the biological treatment process for waste and wastewater. The sensor was designed for easy replacement of the biomembrane, thereby making it suitable for short-term use. The drawbacks of activated sludge based sensor, such as short sensor lifetime, were thereby circumvented. The sensor BOD measurements were carried out in the kinetic mode using a flow injection system, resulting in 25 s for one measurement followed by 4-8 min recovery time. Based on the results of normalised sensor responses, the OECD synthetic wastewater was considered to be a more suitable calibration solution in comparison with the GGA solution. Good agreement was achieved between the results of the sensor BOD measurement and those obtained from BOD5 analysis of a wastewater sample from a food-processing factory. Reproducibility of responses using one sensor was below +/-5.6% standard deviation. Reproducibility of responses using different sensors was within acceptable bias limits, viz. +/-15% standard deviation.
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| 7. |
- Murto, Marika, et al.
(author)
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Impact of food industrial waste on anaerobic co-digestion of sewage sludge and pig manure
- 2004
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In: Journal of Environmental Management. - : Elsevier BV. - 0301-4797. ; 70:2, s. 101-107
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Journal article (peer-reviewed)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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| 8. |
- Svensson, Mattias, et al.
(author)
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Startup of an anaerobic single stage digester with a fixed wheat straw bed
- 2001
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In: 9th World Congress, Anaerobic Digestion 2001, Anaerobic Conversion for Sustainability, Proceedings. - 9076019169 ; , s. 549-551
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Conference paper (other academic/artistic)abstract
- The most common form of technology for energy utilization via anaerobic treatment is slurry digestion with a low solids contents, such as sewage sludge or manure. Process control and maintenance are relatively simple, but costs involved with liquid handling and heating favour large, centralised plants. Raising the solids content of a digester to 30% significantly improves the economy of anaerobic digestion, increasing the methane production per volume unit reactor, and avoiding the handling and heating of large volumes of process water. One simple and potentially cheap method of high-solids reactor implementation is a single stage fixed bed reactor, with a solid substrate as the bed and a recycled leachate stream One potential problem with this design is an initial organic acid production during reactor startup, which originates from the easily degradable substrate. A low initial loading rate gives a safer but prolonged startup, and decreases gas production in this period. The choice of substrate strongly influences the probability of clogging. A more careful choice of carrier material allows quicker startup, and reduces the risk of clogging. The material should degrade slowly, to avoid overload during startup, and have a rigid structure in order to avoid clogging. This bed can then be fed from the top with more easily degradable substrate, e.g. crop residue. In this study, we demonstrate startup of a single stage wheat straw (low biodegradability) reactor in a fixed bed.
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| 9. |
- Svensson, Mattias, et al.
(author)
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The effect of packing density on the startup and operation of an anaerobic single stage fixed wheat straw bed digester
- 2002
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In: Proceedings of 3rd International Symposium for Anaerobic Digestion of Solid Wastes. ; , s. 14-14
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Conference paper (other academic/artistic)abstract
- In Southern Sweden, production of renewable energy from crop residues digestion is viewed as a worthwhile alternative. Also, the process gives valuable mineralised nitrogen as a by-product, which when produced at farm-scale can be recycled for ecological farming. It is difficult to achieve economic utilisation of crop residues in centralised slurry digestion, mainly because of the greater transport costs. Traditional reactor designs have a too low cost efficiency on farm-scale level, and therefore it is essential to introduce technologies and practices leading to economically viable reactor systems on this scale. One very simple reactor design being considered is the vertical column fixed bed digester. This allows relatively high loading rates, combined with a low maintenance requirement. Plant material can be used as a biofilm carrier, and is an inexpensive and highly efficient alternative to traditional support materials, and wheat straw, with its rigid structure and low biodegradability, is a good candidate. In this study, the influence of packing density on startup and single stage semi-batch operation of vertical column fixed bed digesters was examined in one laboratory-scale and three pilot-scale systems.
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