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The route towards stable and efficient anaerobic digestion of fibrous wastewater from pulp and paper mills in high-rate CSTRs with sludge recirculation
Linköping University, The Tema Institute, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.ORCID iD: 0000-0001-5260-1826
Linköping University, The Tema Institute, Department of Water and Environmental Studies. Linköping University, Faculty of Arts and Sciences.
Scandinavian Biogas.
Linköping University, The Tema Institute, Tema Environmental Change. Linköping University, Faculty of Arts and Sciences.
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2015 (English)Conference paper, Poster (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 Once a day, reactor sludge was withdrawn and centrifuged.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.

Place, publisher, year, edition, pages
Keyword [en]
Anaerobic digestion, fibre sludge, nutrient deficiency, pulp and paper mill, sludge recirculation
National Category
Other Chemical Engineering
URN: urn:nbn:se:liu:diva-127023OAI: diva2:918874
14th World Congress in Anarobic Digestion (AD14), ,15-18 November 2015, Vina del Mar, Chile
Swedish Energy Agency, 32802-1
Available from: 2016-04-12 Created: 2016-04-12 Last updated: 2016-04-27

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Ekstrand, Eva-MariaKarlsson, MarielleBjörn, AnnikaSvensson, Bo H.
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Tema Environmental ChangeFaculty of Arts and SciencesDepartment of Water and Environmental Studies
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ReferencesLink to record
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