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Combining high-rate aerobic wastewater treatment with anaerobic digestion of waste activated sludge at a pulp and paper mill
Scandinavian Biogas, Stockholm, Sweden.
Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.ORCID iD: 0000-0001-5260-1826
Scandinavian Biogas, Stockholm, Sweden.
Linköping University, Department of Thematic Studies, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences. Scandinavian Biogas, Stockholm, Sweden. (Tema Miljöförändring, Tema Environmental Change)
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.

Place, publisher, year, edition, pages
2018. Vol. 77, no 8, p. 2068-2076
Keywords [en]
Activated sludge, sludge age, anaerobic digestion, biochemical methane potential, CSTR, pulp and paper
National Category
Bioprocess Technology
Identifiers
URN: urn:nbn:se:liu:diva-146089DOI: 10.2166/wst.2018.120ISI: 000435663800011PubMedID: 29722692OAI: oai:DiVA.org:liu-146089DiVA, id: diva2:1204195
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
In thesis
1. Anaerobic digestion in the kraft pulp and paper industry: Challenges and possibilities for implementation
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)
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Supervisors
Available from: 2019-05-07 Created: 2019-05-07 Last updated: 2019-05-13Bibliographically approved

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Ekstrand, Eva-MariaEjlertsson, Jörgen

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