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Ekstrand, E.-M. (2019). Anaerobic digestion in the kraft pulp and paper industry: Challenges and possibilities for implementation. (Doctoral dissertation). Linköping: Linköping University Electronic Press
Open this publication in new window or tab >>Anaerobic digestion in the kraft pulp and paper industry: Challenges and possibilities for implementation
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[sv]
Anaerob behandling inom pappers- och massaindustri : Utmaningar och möjligheter för implementering vid sulfabruk
Abstract [en]

The pulp and paper industry is a large producer of wastewater and sludge, putting high pressure on waste treatment. In addition, more rigorous environmental legislation for pollution control and demands to increase the use of renewable energy have put further pressure on the pulp and paper industry’s waste treatment, where anaerobic digestion (AD) and the production of methane could pose a solution. Kraft pulping makes up 80% of the world production of virgin wood pulp, thus, the wastewaters from this sector represent a large unused potential for methane production.

There are three main types of substrates available for AD at pulp and paper mills, the wastewaters, the primary sludge/fibre sludge, and the waste activated sludge. AD treatment of these streams has been associated with several challenges, such as the presence of inhibiting compounds or low degradability during AD. The aim of this thesis was to experimentally address these challenges and potentials, focusing on wastes from kraft mills.

Methane potential batch tests showed that many wastewater streams still posed challenges to AD, but the alkaline elemental chlorine-free bleaching stream and the condensate effluents had good methane potentials. Further, the methane potential of kraft mill fibre sludge was high, and co-digestion of kraft mill fibre sludge and waste activated sludge was feasible in stirred tank reactors with sludge recirculation. By increasing the organic loading in a pilot-scale activated sludge facility and thereby lowering the sludge age, the degradability of the waste activated sludge was improved. The higher wastewater treatment capacity achieved by this method provides an opportunity for the mills to increase their pulp and paper production. Further, by dewatering the digestate after AD and returning the liquid to the activated sludge treatment, costs for nutrient supplementation can be reduced.

In conclusion, the thesis shows that AD of wastes from the kraft pulp and paper industry was feasible and carried many benefits regarding the generation of methane as a renewable energy carrier, improved wastewater treatment and reduced costs. Different strategies on how AD may be implemented in the kraft pulp and paper industry were formulated and discussed.

Abstract [sv]

Produktionen av pappers- och massa genererar stora mängder avloppsvatten, vilket ställer höga krav på en effektiv vattenrening. Därtill har skärpta regler för utsläpp till vatten och luft tillsammans med en ökad efterfrågan på användning av förnyelsebar energi ytterligare ökat trycket på vattenreningen inom pappers-och massaindustrin, där anaerob nedbrytning med metanproduktion som följd skulle kunna utgöra en lösning. Produktionen av sulfatmassa (en kemiskt kokad pappersmassa) utgör 80% av den globala nyproduktionen av massa, vilket innebär att avloppsvatten från denna sektor representerar en stor outnyttjad potential för metanproduktion.

Det finns huvudsakligen tre typer av substrat tillgängliga för rötning vid pappers- och massabruk, avloppsvatten, primärslam/fiberslam, och aktivt slam/överskottsslam. Flera utmaningar är kopplade till anaerob nedbrytning av dess strömmar, såsom förekomst av inhiberande ämnen eller låg nedbrytbarhet. Målet med avhandlingen var att bemöta dessa utmaningar, med ett särskilt fokus på behandling av avloppsströmmar från sulfatbruk.

Metanpotentialtester visade att många av avloppsvattnen fortfarande var svåra att behandla med anaerob nedbrytning, men att alkaliska blekeriströmmar och kondensatströmmar vid sulfatbruk visade lovande metanpotentialer. Massafiber från sulfatoch sulfitbruk uppvisade höga metanpotentialer, och en stabil kontinuerlig samrötning av fiberslam och aktivt slam från sulfatbruk uppnåddes vid hög organisk belastning och låg hydraulisk uppehållstid i omrörda tankreaktorer med slamåterföring. Resultaten visade vidare att den låga nedbrytbarheten hos aktivt slam kunde bemötas genom att sänka slamåldern i den luftade anläggningen, med högre metanpotential i slammet som följd. Via denna metodik erhålles en högre vattenreningskapacitet, vilket innebär att bruken kan öka sin produktion av papper och massa. Dessutom kan rötresten avvattnas och den kvarvarande vätskan återföras till den luftade anläggningen för att minska behovet av näringstillsatser.

Sammanfattningsvis visar avhandlingen att anaerob nedbrytning av avloppsströmmar från sulfatbruk var fullt möjlig och innebar många fördelar, i form av metanproduktion, förbättrad kapacitet för vattenrening och reducerade kostnader jämfört med dagens teknik. Olika möjligheter för implementering av anaerob teknik vid sulfatbruk har också formulerats och diskuterats.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2019. p. 50
Series
Linköping Studies in Arts and Sciences, ISSN 0282-9800 ; 769
Keywords
Pulp and paper, anaerobic digestion, fibre sludge, activated sludge, condensates, bleaching wastewater, wastewater treatment, methane, degradability, nutrient recirculation, Pappers- och massa, anaerob nedbrytning, fiberslam, aktivt slam, kondensat, vattenrening, metan, nedbrytbarhet, näringsåterföring
National Category
Water Treatment Paper, Pulp and Fiber Technology Renewable Bioenergy Research Bioenergy Energy Systems
Identifiers
urn:nbn:se:liu:diva-156667 (URN)10.3384/diss.diva-156667 (DOI)9789176850633 (ISBN)
Public defence
2019-05-24, TEMCAS, Hus T, Campus Valla, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2019-05-07 Created: 2019-05-07 Last updated: 2019-05-13Bibliographically approved
Magnusson, B., Ekstrand, E.-M., Karlsson, A. & Ejlertsson, J. (2018). Combining high-rate aerobic wastewater treatment with anaerobic digestion of waste activated sludge at a pulp and paper mill. Water Science and Technology, 77(8), 2068-2076
Open this publication in new window or tab >>Combining high-rate aerobic wastewater treatment with anaerobic digestion of waste activated sludge at a pulp and paper mill
2018 (English)In: Water Science and Technology, ISSN 0273-1223, E-ISSN 1996-9732, Vol. 77, no 8, p. 2068-2076Article in journal (Refereed) Published
Abstract [en]

The activated sludge process within the pulp and paper industry is generally run to minimize the production of waste activated sludge (WAS), leading to high electricity costs from aeration and relatively large basin volumes. In this study, a pilot-scale activated sludge process was run to evaluate the concept of treating the wastewater at high rate with a low sludge age. Two 150 L containers were used, one for aeration and one for sedimentation and sludge return. The hydraulic retention time was decreased from 24 hours to 7 hours, and the sludge age was lowered from 12 days to 2–4 days. The methane potential of the WAS was evaluated using batch tests, as well as continuous anaerobic digestion (AD) in 4 L reactors in mesophilic and thermophilic conditions. Wastewater treatment capacity was increased almost four-fold at maintained degradation efficiency. The lower sludge age greatly improved the methane potential of the WAS in batch tests, reaching 170 NmL CH4/g VS at a sludge age of 2 days. In addition, the continuous AD showed a higher methane production at thermophilic conditions. Thus, the combination of high-rate wastewater treatment and AD of WAS is a promising option for the pulp and paper industry.

Keywords
Activated sludge, sludge age, anaerobic digestion, biochemical methane potential, CSTR, pulp and paper
National Category
Bioprocess Technology
Identifiers
urn:nbn:se:liu:diva-146089 (URN)10.2166/wst.2018.120 (DOI)000435663800011 ()29722692 (PubMedID)
Note

Funding agencies: Swedish Energy Agency [32802-2]; Scan-dinavian Biogas Fuels AB; Poyry AB; BillerudKorsnas AB; SCA; Fiskeby Board AB; Purac AB

Available from: 2018-05-07 Created: 2018-05-07 Last updated: 2019-05-07Bibliographically approved
Larsson, M., Ekstrand, E.-M., Truong, X.-b., Nilsson, F., Ejlertsson, J., Svensson, B., . . . Björn, A. (2015). The biomethane potential of chemical thermo-mechanical pulp wastewaters in relation to their chemical composition.
Open this publication in new window or tab >>The biomethane potential of chemical thermo-mechanical pulp wastewaters in relation to their chemical composition
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2015 (English)Manuscript (preprint) (Other academic)
Abstract [en]

This study evaluates the biomethane potential of composite pulping and bleaching chemical thermo-mechanical pulp (CTMP) wastewaters in relation to their composition of organic compounds, as well as to their sulphur contents. The biomethane potential was determined in batch experiments and the CTMP wastewaters from production of bleached spruce-, birch- and aspen pulp and unbleached spruce pulp were analysed for dissolved lignin, carbohydrates, wood extractives, acetic acid and total sulphur content. The biomethane potential obtained for the wastewaters ranged from 350 to 670 NmL g TOC-1 with the highest yield for wastewater from the production of bleached birch CTMP followed by bleached aspen-, bleached spruce- and unbleached spruce CTMP. The main differences in wastewater composition were related to the raw material used for the pulp production, i.e. softwood vs. hardwood. The compounds mainly promoting the biomethane production were acetic acid, xylose, wood extractives, triglycerides and steryl esters, whereas dissolved lignin, sulphur, arabinose, mannose, lignans and free fatty-/resin acids lowered the potential. However, the individual contribution of each variable was not possible to evaluate due to covariations among them.

Keywords
CTMP; bleaching; softwood; hardwood; biomethane potential; dissolved lignin; carbohydrates; wood extractives
National Category
Water Engineering
Identifiers
urn:nbn:se:liu:diva-122339 (URN)
Available from: 2015-10-29 Created: 2015-10-29 Last updated: 2016-05-04Bibliographically approved
Ekstrand, E.-M., Karlsson, M., Truong, X.-B., Björn, A., Karlsson, A., Svensson, B. H. & Ejlertsson, J. (2015). The route towards stable and efficient anaerobic digestion of fibrous wastewater from pulp and paper mills in high-rate CSTRs with sludge recirculation. In: : . Paper presented at 14th World Congress in Anarobic Digestion (AD14), ,15-18 November 2015, Vina del Mar, Chile.
Open this publication in new window or tab >>The route towards stable and efficient anaerobic digestion of fibrous wastewater from pulp and paper mills in high-rate CSTRs with sludge recirculation
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2015 (English)Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

The pulp and paper industry carries high costs in wastewater treatment. By combining present techniques with anaerobic digestion (AD), expenses for electricity use and sludge disposal can be reduced. The large wastewater volumes require high-rate systems sensitive to suspended solids, and this has so far excluded treatment of the energy-rich wood fibres. In this study, AD of fibrous wastewater was examined in high-rate CSTRs with sludge recirculation. Two lab-scale reactors (4L) were run for 780 days. Once a day, reactor sludge was withdrawn and centrifuged. The main part of the supernatant was discarded, while the pellet was suspended with the substrate and returned to the reactor. This gave a sludge retention time of 10-16 days and a hydraulic retention time of 4-8 days. One reactor (denoted R1) was fed with fibre sludge, and the second reactor (denoted R2) was co-digesting fibre sludge and activated sludge. Both substrates were taken from a Kraft mill in Sweden. Initially, both reactors experienced frequent drops in pH, and continuous alkali supplements were necessary for process stability. Additions of magnesium and potassium were also needed to obtain stable process performance at an OLR of 3 g VS L-1·day-1. R1 and R2 behaved similarly, but R2 (co-digestion) was more robust with less or no fluctuations in VFA and pH. Addition of activated sludge also to R1 allowed an increase in OLR to 4 g VS L-1·day-1. In summary, stable and efficient operation of a high-rate CSTR with sludge recirculation digesting fibre sludge was achieved at an OLR of 4 g VS L-1·day-1, a HRT of 4 days and a methane production of 260±20 Nml. In addition, co-digestion with activated sludge stabilized the performance at increased OLR and thus gave more methane produced per reactor volume.

Keywords
Anaerobic digestion, fibre sludge, nutrient deficiency, pulp and paper mill, sludge recirculation
National Category
Other Chemical Engineering
Identifiers
urn:nbn:se:liu:diva-127023 (URN)
Conference
14th World Congress in Anarobic Digestion (AD14), ,15-18 November 2015, Vina del Mar, Chile
Funder
Swedish Energy Agency, 32802-1
Available from: 2016-04-12 Created: 2016-04-12 Last updated: 2016-04-27
Björn, A., Ekstrand, E.-M., Larsson, M., Truong, X.-B., Cardell, L., Borgström, Y., . . . Karlsson, A. (2012). The methane potential of Swedish pulp and paper industry - A screening of wastewater effluents. In: International Conference on Applied Energy 2012. Paper presented at International Conference on Applied Energy, July 5-8, 2012, Suzhou, China.
Open this publication in new window or tab >>The methane potential of Swedish pulp and paper industry - A screening of wastewater effluents
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2012 (English)In: International Conference on Applied Energy 2012, 2012Conference paper, Published paper (Other academic)
Keywords
Biogas, anaerobic digestion, kraft pulp, chemica thermo-mechanical pulp, neutral sulfite semi chemical pulp
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-81650 (URN)
Conference
International Conference on Applied Energy, July 5-8, 2012, Suzhou, China
Available from: 2012-09-20 Created: 2012-09-20 Last updated: 2016-05-04
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-5260-1826

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