| 1. |
- Hagelqvist, Alina
(författare)
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Sludge from pulp and paper mills for biogas production : Strategies to improve energy performance in wastewater treatment and sludge management
- 2013
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The production of pulp and paper is associated with the generation of large quantities of wastewater that has to be purified to avoid severe pollution of the environment. Wastewater purification in pulp and paper mills combines sedimentation, biological treatment, chemical precipitation, flotation and anaerobic treatment, and the specific combination of techniques is determined by the local conditions. Wastewater treatment generates large volumes of sludge that after dewatering can be incinerated and thus used for bio-energy production. Sludge is currently viewed as biofuel of poor quality due to its high water content, and some mills treat it solely as a disposal problem.Two strategies have been identified as feasible options to improve the energy efficiency of sludge management. One is drying using multi-effect evaporation followed by incineration. The other is anaerobic digestion of the wet sludge to produce methane.This thesis explores the energy balances of sludge management strategies in pulp and paper mills with special focus on anaerobic digestion. The first part consists of a system analysis, used to evaluate some wastewater treatment processes and sludge management, and the second part of empirical studies of anaerobic digestion of pulp and paper mill sludge. It was shown that the use of energy for aeration in aerobic biological treatment should be kept to the minimum required for acceptable quality of the processed water. Additional aeration for reduction of the generated sludge will only result in reduced energy generation in a subsequent methane generation stage. In the second part of the thesis, it is shown that anaerobic digestion is a feasible option for sludge management as it leads to production of high value biogas. Co-digestion with grass silage, cow/pig manure or municipal sewage sludge should then be used to counteract the low nitrogen content of pulp and paper mill sludge.
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| 2. |
- Piculell, Maria, et al.
(författare)
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Evaluating the Effect of Biofilm Thickness on Nitrification in Moving Bed Biofilm Reactors.
- 2015
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Ingår i: Environmental Technology. - : Informa UK Limited. - 1479-487X .- 0959-3330. ; :Online 21 August 2015, s. 1-28
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Tidskriftsartikel (refereegranskat)abstract
- This study evaluates the effect of biofilm thickness on the nitrifying activity in moving bed biofilm reactors (MBBRs) in a controlled environment. In-depth understanding of biofilm properties in MBBRs and their effect on the overall treatment efficiency compose the key to optimizing process stability and efficiency. However, evaluating biofilm properties in continuously operated MBBRs can be extremely challenging. This study uses a carrier design which enables comparison of four different biofilm thicknesses, in otherwise equally operated lab-scale MBBRs. The results show that, within the studied range (200-500 µm) and specific operation conditions, biofilm thickness alone had no significant effect on the overall ammonium removal. The nitrate production, however, decreased with a decreasing biofilm thickness, and the ratio between nitrite and ammonia oxidizing activity decreased both with increasing load and decreasing oxygen concentration for all thicknesses. The suggestion that nitratation is disfavored in thin biofilms is an interesting contribution to current research being performed on NOB inhibition for deammonification applications. By indicating that different groups of bacteria respond differently to biofilm thickness, this study accentuates the importance of further evaluation of these complex systems.
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| 5. |
- Bengtsson, Simon, et al.
(författare)
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Acidogenic fermentation of industrial wastewaters: Effects of chemostat retention time and pH on volatile fatty acids production
- 2008
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Ingår i: Biochemical Engineering Journal. - : Elsevier BV. - 1369-703X. ; 40:3, s. 492-499
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Tidskriftsartikel (refereegranskat)abstract
- Acidogenic fermentation of wastewater can serve as a first step in a process for mixed culture production of polyhydroxyalkanoates (PHA) since the produced volatile fatty acids (VFA) are preferred substrates for PHA production. Acidogenic fermentation of industrial wastewaters (cheese whey permeate and three pulp and paper mill effluents) was evaluated in batch and continuous experiments. From the batch experiments, it was found that for whey and one of the paper mill effluents nearly 100% of the soluble COD was readily fermentable. In continuous chemostat experiments with these two effluents, varying the retention time (RT) and pH of the reactors exhibited significant impact on the amount and composition of VFA produced. Increasing RT resulted in increased degrees of acidification up to a maximum of 0.93 g COD of VFA per g influent SCOD at RT 95 h for whey and 0.75 gCOD/gCOD at RT 24 h for the paper mill effluent. Main fermentation products were acetate, propionate and butyrate. Acetate production was rather insensitive to RT while above RT 10 h a shift from butyrate production to propionate production with increasing RT occurred for both effluents. Increasing pH from 5 to 6 resulted in increased amount of propionate. Based on these findings the possibility of regulating PHA monomer composition and associated polymer properties by controlling RT and pH during acidogenic pretreatment was discussed. (c) 2008 Elsevier B.V. All rights reserved.
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| 6. |
- Bengtsson, Simon, et al.
(författare)
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Production of polyhydroxyalkanoates by activated sludge treating a paper mill wastewater
- 2008
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Ingår i: Bioresource Technology. - : Elsevier BV. - 1873-2976 .- 0960-8524. ; 99:3, s. 509-516
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Tidskriftsartikel (refereegranskat)abstract
- Production of polyhydroxyalkanoates (PHAs) in activated sludge treating wastewater represents an economical and environmental promising alternative to pure culture fermentations. A process for production of PHA from a paper mill wastewater was examined at laboratory scale. The three stage process examined consisted of acidogenic fermentation to convert wastewater organic matter to volatile fatty acids (VFAs), an activated sludge system operating under feast/famine conditions to enrich for PHA producing organisms and accumulation of PHA in batch experiments. After fermentation of the wastewater, 74% of the soluble COD was present as VFA (acetate, propionate, butyrate and valerate) and the resulting PHA after batch accumulation consisted of 31-47 mol% hydroxybutyrate and 5369 mol% hydroxyvalerate. The maximum PHA content achieved was 48% of the sludge dry weight and the three stage process exhibited a potential to produce 0.11 kg of PHA per kg of influent COD treated. (c) 2007 Elsevier Ltd. All rights reserved.
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| 7. |
- Bengtsson, Simon, et al.
(författare)
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Production of polyhydroxyalkanoates by glycogen accumulating organisms treating a paper mill wastewater.
- 2008
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Ingår i: Water Science and Technology. - : IWA Publishing. - 0273-1223 .- 1996-9732. ; 58:2, s. 323-330
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Tidskriftsartikel (refereegranskat)abstract
- A process for production of polyhydroxyalkanoates (PHA) by activated sludge treating a paper mill wastewater was investigated. The applied strategy was to select for glycogen accumulating organisms (GAOs) by alternating anaerobic/aerobic conditions. Acidogenic fermentation was used as pretreatment to convert various organic compounds to volatile fatty acids which are preferable substrates for PHA production. Enrichment resulted in a culture dominated by GAOs related to Defluviicoccus vanus (56%) and Candidatus Competibacter phosphatis (22%). Optimization of PHA accumulation by the enriched GAO culture was performed through batch experiments. Accumulation of PHA under anaerobic conditions was limited by the intracellular glycogen stored. Under aerobic conditions significant glycogen production (to 25% of sludge dry weight) was observed alongside PHA accumulation (to 22% of sludge dry weight). By applying a subsequent anaerobic period after an initial aerobic, the produced glycogen could be utilized for further PHA accumulation and by this strategy PHA content was increased to 42% of sludge dry weight. The PHA yield over the entire process was 0.10 kg per kg of influent COD treated which is similar to what has been achieved with a process applying feast/famine enrichment strategy with the same wastewater.
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| 8. |
- Björnsson, Lovisa, et al.
(författare)
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Supports made from recycled glass as biofilm carriers in anaerobic packed bed treatment of high-strength wastewaters
- 1997
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Ingår i: Resource and Environmental Biotechnology. - 1358-2283. ; 1, s. 243-256
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Tidskriftsartikel (refereegranskat)abstract
- The possibility of using carriers made of recycled glass in anaerobic packed bed reactors has been studied in laboratory-scale experiments. Two types of carrier were studied: a porous bead of glass foam and an open ring of a smoother, sintered glass. The performance of processes with these carriers was compared with a conventional upflow anaerobic sludge blanket (UASB) process. The treatment of wastewater from a pulp and paper mill, and from a pharmaceutical plant was studied. Both carrier types were found to be suitable for supporting biofilm growth. With the porous beads, however, suspended sludge accumulated between the carriers, which caused clogging of the process. This, together with the low mechanical strength of the material, makes this carrier less suitable for full-scale processes. The sintered rings showed no signs of clogging and had better mechanical qualities and the maximum loading rate for pulp and paper processing wastewater was 10 kg COD m-3 d-1. This is similar to processes with commercially available plastic carriers, but with the UASB process, the maximum load with this wastewater was around 20 kg COD m-3 d-1, which makes the sintered ring process non-competitive. An anaerobic packed bed process with glass carriers could, however, find applications where the UASB process is not applicable. For example, the wastewater from the pharmaceutical plant could not be treated with conventional suspended sludge methods due to the toxicity of the effluent. Instead, treatment in a packed bed with porous glass beads was tested with good results.
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| 9. |
- Clement, R. Carter, et al.
(författare)
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A proposed set of metrics for standardized outcome reporting in the management of low back pain
- 2015
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Ingår i: Acta Orthopaedica. - : Medical Journals Sweden AB. - 1745-3682 .- 1745-3674. ; 86:5, s. 523-533
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Tidskriftsartikel (refereegranskat)abstract
- Background and purpose - Outcome measurement has been shown to improve performance in several fields of healthcare. This understanding has driven a growing interest in value-based healthcare, where value is defined as outcomes achieved per money spent. While low back pain (LBP) constitutes an enormous burden of disease, no universal set of metrics has yet been accepted to measure and compare outcomes. Here, we aim to define such a set. Patients and methods - An international group of 22 specialists in several disciplines of spine care was assembled to review literature and select LBP outcome metrics through a 6-round modified Delphi process. The scope of the outcome set was degenerative lumbar conditions. Results - Patient-reported metrics include numerical pain scales, lumbar-related function using the Oswestry disability index, health-related quality of life using the EQ-5D-3L questionnaire, and questions assessing work status and analgesic use. Specific common and serious complications are included. Recommended follow-up intervals include 6, 12, and 24 months after initiating treatment, with optional follow-up at 3 months and 5 years. Metrics for risk stratification are selected based on preexisting tools. Interpretation - The outcome measures recommended here are structured around specific etiologies of LBP, span a patient's entire cycle of care, and allow for risk adjustment. Thus, when implemented, this set can be expected to facilitate meaningful comparisons and ultimately provide a continuous feedback loop, enabling ongoing improvements in quality of care. Much work lies ahead in implementation, revision, and validation of this set, but it is an essential first step toward establishing a community of LBP providers focused on maximizing the value of the care we deliver.
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