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Improving the biogas potential of pulp and paper mills while decreasing the electricity demand for wastewater treatment
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences. (Energi och hållbar utveckling)
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences. (Energi och hållbar utveckling)ORCID iD: 0000-0002-0380-3533
2013 (English)Conference paper, Presentation (Refereed)
Abstract [en]

Sludge formed during the necessary wastewater treatment in forest industry is currently considered to be a waste stream; rich in organic substances and poor in macronutrients, especially phosphorus and nitrogen. Previous work has shown that excessive use of electricity for aeration in wastewater treatment counteracts the potential for energy recovery in the subsequent sludge handling system, as prolonged aeration is used to degrade organic matter. This work shows that chemical oxygen demand of wastewater was not reduced further when the solids retention time was increased in aerated wastewater treatment from 2 days to 10 and 20 days respectively. The results presented here strengthen the previous conclusion that energy should only be used for sufficient effluent treatment, not for sludge reduction. A decreased need for aeration can be achieved by shortening the sludge retention time both by a decreased oxygen requirement and increased aeration efficiency. Shortened sludge retention time was shown here to increase production of biosludge as well as to increase the specific methane potential of biosludge. The results show that sludge with shorter solids retention time in the aerated treatment step gives more production of methane gas compared to sludge with longer solids retention time.

Place, publisher, year, edition, pages
2013.
Keyword [en]
anaerobic digestion, biosludge, efficient aeration, pulp and paper mill
National Category
Energy Engineering
Research subject
Environmental and Energy Systems
Identifiers
URN: urn:nbn:se:kau:diva-26117OAI: oai:DiVA.org:kau-26117DiVA: diva2:602439
Conference
IWA Conference on Holistic Sludge Management, Västerås, 6-8 May 2013
Available from: 2013-02-28 Created: 2013-02-01 Last updated: 2014-10-29Bibliographically approved
In thesis
1. Sludge from pulp and paper mills for biogas production: Strategies to improve energy performance in wastewater treatment and sludge management
Open this publication in new window or tab >>Sludge from pulp and paper mills for biogas production: Strategies to improve energy performance in wastewater treatment and sludge management
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2013. 46 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2013:9
Keyword
anaerobic digestion, pulp and paper mill sludge, methane production, energy efficient sludge management
National Category
Energy Engineering
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-26171 (URN)978-91-7063-484-0 (ISBN)
Public defence
2013-03-15, Nyquistsalen, 9C 203, Karlstads universitet, Universitetsgatan 2, Karlstad, 09:15 (Swedish)
Opponent
Supervisors
Available from: 2013-02-28 Created: 2013-02-04 Last updated: 2016-06-30Bibliographically approved

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