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Energy Use and Recovery Strategies within Wastewater Treatment and Sludge Handling at Pulp and Paper Mills
Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
Karlstad University, Faculty of Technology and Science, Department of Energy, Environmental and Building Technology.
2009 (English)In: Bioresource Technology, ISSN 0960-8524, E-ISSN 1873-2976, Vol. 100, no 14, 3497-3505 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents an inclusive approach with focus on energy use and recovery in wastewater management, including wastewater treatment (WWT) and sludge handling. Process data from three Swedish mills and a mathematical model were used to evaluate seven sludge handling strategies. The results indicate that excess energy use in WWT processes counters the potential energy recovery in the sludge handling systems. Energy use in WWT processes is recommended to aim for sufficient effluent treatment, not for sludge reduction. Increased secondary sludge production is favourable from an energy point of view provided it is used as a substrate for heat, biogas or electricity production.

Place, publisher, year, edition, pages
2009. Vol. 100, no 14, 3497-3505 p.
Keyword [en]
Pulp and paper mills; wastewater treatment; sludge handling; bioenergy; sustainability.
National Category
Other Mechanical Engineering
Research subject
Environmental and Energy Systems
Identifiers
URN: urn:nbn:se:kau:diva-3850DOI: 10.1016/j.biortech.2009.02.041OAI: oai:DiVA.org:kau-3850DiVA: diva2:209485
Available from: 2009-03-25 Created: 2009-03-25 Last updated: 2013-02-28Bibliographically approved
In thesis
1. Forest industry sludge as a resource for energy recovery
Open this publication in new window or tab >>Forest industry sludge as a resource for energy recovery
2009 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Forest industries produce large amounts of carbon rich sludges as by-products in their processes. Presently sludge is treated as a poor quality biofuel for co-incineration, some mills treat it solely as a disposal problem. This thesis provides an introduction to production, composition and disposal issues of sludge. It also includes a presentation of strategies for sludge handling.

The main concern with energy recovery from sludge is connected to high content of water (50-80%). Mechanical dewatering is an energy efficient method of decreasing the water content. However, there are limitations to how far sludge can be dewatered mechanically. Thermal dewatering is sometimes required to dewater the sludge beyond these limits, in order to obtain a high quality biofuel for incineration and/or thermal gasification. It is often inefficient, from an energy point of view, to incorporate thermal dewatering in the sludge handling strategy.

An interesting alternative to thermal processes is anaerobic digestion, which is a biological process used for energy recovery. Advantages with anaerobic digestion include biogas production, efficient treatment of sludge with high content of water and potential for nutrients recovery. The process and the kinetics of anaerobic digestion are presented.

The aim of this thesis is to present a method for evaluating different sludge handling strategies from an energy perspective, and to further develop anaerobic digestion as a process for energy recovery from sludge. The thesis is based on two papers. Paper I presents an inclusive approach with focus on energy use and energy recovery in wastewater management, including wastewater treatment and sludge handling. Paper II explores the possibility to enhance biogas production by anaerobic co-digestion of pulp mill sludge with municipal sewage sludge.

Place, publisher, year, edition, pages
Karlstad: Karlstad University, 2009. 27 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2009:26
National Category
Energy Engineering
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-3872 (URN)978-91-7063-249-5 (ISBN)
Distributor:
Fakulteten för teknik- och naturvetenskap
Presentation
2009-05-20, Karlstad, 13:15 (Swedish)
Supervisors
Available from: 2009-05-04 Created: 2009-03-25 Last updated: 2016-06-30Bibliographically approved
2. Efficient treatment of forest industrial wastewaters: Energy efficiency and resilience during disturbances
Open this publication in new window or tab >>Efficient treatment of forest industrial wastewaters: Energy efficiency and resilience during disturbances
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This work concerns the efficient treatment of wastewaters from pulp and paper mills by means of aerobic biological processes. For treatment processes there are many aspects of efficiency and the present study investigates both energy efficiency and purification efficiency during disturbances.

Special focus is put on wood extractives, such as resin acids and fatty acids, since they can cause negative effects in fish and other organisms in the receiving waters. They can furthermore be toxic to microorganisms in a biological treatment plant. They also affect oxygen transfer, which is important for energy efficient aeration of aerobic biological treatment processes.

This thesis includes five papers/studies and presents a strategy for efficient treatment of forest industrial wastewaters. The results should help creating resilient wastewater treatment strategies with efficient use of energy. One new strategy proposed here includes separation of extractives before the wastewater is treated biologically, and the use of the extra amount of sludge as an energy source, shifting the energy balance from negative to positive.

Place, publisher, year, edition, pages
Karlstad: Karlstads universitet, 2012. 70 p.
Series
Karlstad University Studies, ISSN 1403-8099 ; 2012:22
Keyword
Forest industry, wastewater, oxygen transfer rate, black liquor, surface active, extractives
National Category
Engineering and Technology
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-13031 (URN)978-91-7063-426-0 (ISBN)
Public defence
2012-06-07, Nyqvistsalen 9C203, Karlstads universitet, Karlstad, 09:15 (Swedish)
Opponent
Supervisors
Available from: 2012-05-24 Created: 2012-04-18 Last updated: 2012-08-27Bibliographically approved
3. 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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Stoica, AlinaSandberg, MariaHolby, Ola

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