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Methane potentials of the Swedish pulp and paper industry - A screening of wastewater effluents
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences. Linköping University, Biogas Research Center.
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences. Linköping University, Biogas Research Center.
Linköping University, Biogas Research Center. Scandinavian Biogas Fuels AB, Sweden .
Linköping University, Biogas Research Center. Scandinavian Biogas Fuels AB, Sweden .
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2013 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 112, 507-517 p.Article in journal (Refereed) Published
Abstract [en]

With the final aim of reducing the energy consumption and increase the methane production at Swedish pulp and paper mills, the methane potential of 62 wastewater effluents from 10 processes at seven pulp and/or paper mills (A-G) was determined in anaerobic batch digestion assays. This mapping is a first step towards an energy efficient and more sustainable utilization of the effluents by anaerobic digestion, and will be followed up by tests in lab-scale and pilot-scale reactors. Five of the mills produce kraft pulp (KP), one thermo-mechanical pulp (TMP), two chemical thermo-mechanical pulp (CTMP) and two neutral sulfite semi-chemical (NSSC) pulp. Both elementary and total chlorine free (ECF and TCF, respectively) bleaching processes were included. The effluents included material from wood rooms, cooking and oxygen delignification, bleaching (often both acid- and alkali effluents), drying and paper/board machinery as well as total effluents before and after sedimentation. The results from the screening showed a large variation in methane yields (percent of theoretical methane potential assuming 940 NmL CH4 per g TOC) among the effluents. For the KP-mills, methane yields above 50% were obtained for the cooking effluents from mills D and F, paper machine wastewater from mill D, condensate streams from mills B, E and F and the composite pre-sedimentation effluent from mill D. The acidic ECF-effluents were shown to be the most toxic to the AD-flora and also seemed to have a negative effect on the yields of composite effluents downstream while three of the alkaline ECF-bleaching effluents gave positive methane yields. ECF bleaching streams gave higher methane yields when hardwood was processed. All TCF-bleaching effluents at the KP mills gave similar degradation patterns with final yields of 10-15% of the theoretical methane potential for four of the five effluents. The composite effluents from the two NSSC-processes gave methane yields of 60% of the theoretical potential. The TMP mill (A) gave the best average yield with all six effluents ranging 40-65% of the theoretical potential. The three samples from the CTMP process at mill B showed potentials around 40% while three of the six effluents at mill G (CTMP) yielded 45-50%.

Place, publisher, year, edition, pages
Elsevier , 2013. Vol. 112, 507-517 p.
Keyword [en]
Biogas; Anaerobic digestion; Kraft pulp; Chemical thermo-mechanical pulp; Neutral sulfite semi-chemical pulp; Bleaching
National Category
Social Sciences
URN: urn:nbn:se:liu:diva-104129DOI: 10.1016/j.apenergy.2012.12.072ISI: 000329377800053OAI: diva2:694663
Available from: 2014-02-07 Created: 2014-02-07 Last updated: 2015-10-29
In thesis
1. Anaerobic Digestion of Wastewaters from Pulp and Paper Mills: A Substantial Source for Biomethane Production in Sweden
Open this publication in new window or tab >>Anaerobic Digestion of Wastewaters from Pulp and Paper Mills: A Substantial Source for Biomethane Production in Sweden
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Swedish pulp and paper industry is the third largest exporter of pulp and paper products worldwide. It is a highly energy-demanding and water-utilising industry, which generates large volumes of wastewater rich in organic material. These organic materials are to different extents suitable for anaerobic digestion (AD) and production of energy-rich biomethane. The implementation of an AD process within the wastewater treatment plant of a mill would increase the treatment capacity and decrease the overall energy consumption due to less aeration and lower sludge production and in addition produce biomethane. Despite the many benefits of AD it is only applied at two mills in Sweden today. The reason for the low implementation over the years may be due to problems encountered linked to the complexity and varying composition of the wastewaters. Due to changes in market demands many mills have broadened their product portfolios and turned towards more refined products. This has increased both the complexity and the variations of the wastewaters´ composition even further, as the above changes can imply an increased pulp bleaching and utilisation of more diverse raw materials within the mills.

The main aim of this thesis was therefore to generate knowledge needed for an expansion of the biomethane production within the pulp and paper industry. As a first step to achieve this an evaluation of the biomethane potential and the suitability for AD of wastewaters within a range of Swedish pulp and paper mills was performed. Thus, around 70 wastewater streams from 11 different processes at eight mills were screened for their biomethane potential. In a second step, the impact of shifts in wood raw material and bleaching on the AD process and the biomethane production was investigated and further evaluated in upflow anaerobic sludge bed (UASB) reactors.

The screening showed that the biomethane potential within the Swedish pulp and paper industry could be estimated to 700 GWh, which corresponds to 40% of the Swedish biomethane production during 2014. However, depending on the conditions at each specific mill the strategy for the establishment of AD needs to differ. For mills producing kraft pulp the potential is mainly found in wastewaters rich in fibres, alkaline kraft bleaching wastewaters and methanol-rich condensates. The biomethane potential within thermo-mechanical pulp- (TMP) and chemical thermo-mechanical pulp (CTMP) mills is mainly present in the total effluents after pre-sedimentation and in the bleaching effluents as these holds high concentrations of dissolved organic material. The screening further showed that the raw material used for pulp production is an important factor for the biomethane potential of a specific wastewater stream, i.e. hardwood (HW) wastewaters have higher potentials than those from softwood (SW) pulp production. This was confirmed in the lab-scale UASB reactor experiments, in which an alkaline kraft bleaching wastewater and a composite pulping and bleaching CTMP wastewater were used as substrates. AD processes were developed and maintained stable throughout shifts in wastewater composition related to changes in the wood raw materials between SW and HW for the kraft wastewater and spruce, aspen and birch for the CTMP wastewater. The lower biomethane production from SW- compared to HW wastewaters was due to a lower degradability together with a higher ratio of sulphuric compounds per TOC for the SW case. The impact of shifts between bleached and unbleached CTMP production could not be fully  evaluated in the continuous process mainly due to technical problems. However, due to the large increase in dissolved organic material when bleaching is applied, the potential biomethane production will increase during the production of bleached pulp compared to unbleached pulp. Based on the biomethane potentials obtained for one of the included CTMP mills, their yearly production of biomethane was estimated to 5-27 GWh with the lowest and the highest value corresponding to the production of unbleached spruce pulp vs. bleached birch pulp.

Thus, the results of the investigations presented in this thesis show that the UASBreactor is suitable for AD of wastewaters within the pulp and paper industry. The results also show that challenges related to variations in the organic material composition of the wastewaters due to variations in wood raw materials could be managed. The outcome of the thesis work also imply that the production of more refined products, which may include the introduction of an increased number of raw materials and extended bleaching protocols, could increase the potential biomethane production, especially if the pulp production will make use of more HW.

Abstract [sv]

Den svenska pappers- och massaindustrin är den tredje största exportören av massa och pappersprodukter och en viktig industriell aktör i Sverige. Det är en industri med hög energi- och vattenanvändning, som genererar stora mängder avloppsvatten rika på organiskt material. Detta organiska material kan via anaerob nedbrytning användas för att producera energirik biometan. Användandet av anaerob behandling, som ett steg i brukens vattenrening, genererar inte bara biometan utan kan också öka reningskapaciteten och minska energiförbrukning och kostnader tack vare minskat behov av luftning och minskad slamproduktion. Trots de många fördelarna med anaerob behandling är den idag bara tillämpad på två bruk i Sverige. En av orsakerna till detta kan vara processproblem som relaterats till avloppsvattnens komplexitet samt varierande sammansättning och flöden. Många pappers- och massabruk har utökat sina produktportföljer med bl a mer förfinade produkter, som en följd av en förändrad marknad. Dessa förändringar har ökat avloppsvattnens komplexitet och variation än mer, då ovan exempelvis kan medföra en ökad produktion av blekt massa samt att fler typer av träråvaror används vid ett och samma bruk.

Huvudsyftet med föreliggande avhandling är att bidra med kunskap för en ökad produktion av biometan inom pappers- och massaindustrin. Som ett första steg genomfördes en övergripande utvärdering av ca 70 avloppsvattenströmmar från totalt 11 olika processer vid åtta svenska pappers- och massabruk med fokus på biometanpotential samt lämplighet för anaerob behandling. I ett andra steg utvärderades hur skiften i träråvara samt blekning påverkar biometanproduktionen samt processtabiliteten för en kontinuerlig anaerob nedbrytningsprocess i en UASBreaktor.

Den initiala utvärderingen visade att den svenska pappers- och massaindustrin skulle kunna bidra med 700 GWh biometan per år, vilket motsvarar 40% av biometanproduktionen i Sverige under 2014. Beroende på utformningen av det enskilda bruket kommer strategier för implementering av anaeroba processer att se olika ut. För bruk som producerar sulfatmassa återfanns huvuddelen av biometanpotentialen i fiberrika avloppsvattenstömmar, alkaliska blekeriavlopp samt metanolrika kondensat. För bruk som producerar termomekanisk- (TMP) eller kemitermomekanisk (CTMP) massa föreligger biometanpotentialen framförallt i avloppsvatten rika på löst organiskt material såsom totalavlopp efter sedimentering och blekeriavlopp. Den initiala utvärderingen visade också att användandet av lövved ger en högre biometanpotential jämfört med barrved. Dessa resultat kunde bekräftas vid kontinuerliga experiment med anaerob nedbrytning i UASB-reaktorer, där ett alkaliskt blekeriavlopp från ett sulfatmassabruk och ett kombinerat massaproduktions- och blekeriavlopp från ett CTMP-bruk användes som substrat. Stabila anaeroba processer etablerades och bibehölls vid förändrad avloppsvattensammansättning på grund av skiften i träråvara (löv- och barrved för sulfatmassabruket samt gran, asp och björk för CTMP bruket). Den lägre produktionen av biometan för barrved jämfört med lövved kunde förklaras med en lägre nedbrytbarhet samt ett ökat svavelinnehåll i relation till mängden organiskt material. Skiften mellan avloppsvatten från blekt- och oblekt CTMP massa kunde inte utvärderas fullständigt i den kontinuerliga processen på grund av tekniska problem. Produktionen av blekt massa ökar dock mängden organiskt material i  avloppsvattnet, vilket medför att mer biometan kan produceras jämfört med då oblekt massa produceras. Baserat på biometanpotentialerna för ett av i studien ingående CTMP bruk uppskattas den årliga produktionen av biometan till 5-27 GWh, där den lägsta produktionen motsvarar oblekt granmassa och den högsta produktionen motsvarar blekt björkmassa.

Sammanfattningsvis visar studien att UASB-reaktorer är lämpliga för anaerob behandling av avloppsvatten inom pappers- och massaindustrin. Vidare visar resultaten från de kontinuerliga försöken att de utmaningar som medförs av den varierande sammansättningen av avloppsvattnens organiska material knutet till träråvaran kan hanteras. Slutligen, breddade produktportföljer samt produktionen av mer förfinade produkter, vilket kan innebära en ökad massablekning och ett ökat användande av olika träråvaror, kan öka brukens potentiella biometanproduktion, särskilt om mer lövved används för massaproduktion.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2015. 66 p.
Linköping Studies in Arts and Science, ISSN 0282-9800 ; 660
Anaerobic digestion; wastewater treatment; biogas; methane; pulp and paper mill wastewater; pulp bleaching; wood raw material, Anaerob nedbrytning, vattenrening; biogas; metan; avloppsvatten från pappers- och massaindustrin; massablekning; träråvara
National Category
Environmental Sciences related to Agriculture and Land-use Environmental Sciences Environmental Biotechnology
urn:nbn:se:liu:diva-122340 (URN)10.3384/diss.diva-122340 (DOI)978-91-7685-925-4 (print) (ISBN)
Public defence
2015-11-24, TEMCAS, Hus T, Campus Valla, Linköping, 10:15 (English)
Available from: 2015-10-29 Created: 2015-10-29 Last updated: 2015-11-27Bibliographically approved

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Larsson, MadeleineBjörn, AnnikaEjlertsson, JörgenSvensson, Bo
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