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Sludge from pulp and paper mills for biogas production: Strategies to improve energy performance in wastewater treatment and sludge management
Karlstad University, Faculty of Health, Science and Technology (starting 2013), Department of Engineering and Chemical Sciences.
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 [en]
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: urn:nbn:se:kau:diva-26171ISBN: 978-91-7063-484-0 (print)OAI: oai:DiVA.org:kau-26171DiVA: diva2:603009
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
List of papers
1. Energy Use and Recovery Strategies within Wastewater Treatment and Sludge Handling at Pulp and Paper Mills
Open this publication in new window or tab >>Energy Use and Recovery Strategies within Wastewater Treatment and Sludge Handling at Pulp and Paper Mills
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.

Keyword
Pulp and paper mills; wastewater treatment; sludge handling; bioenergy; sustainability.
National Category
Other Mechanical Engineering
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-3850 (URN)10.1016/j.biortech.2009.02.041 (DOI)
Available from: 2009-03-25 Created: 2009-03-25 Last updated: 2013-02-28Bibliographically approved
2. Improving the biogas potential of pulp and paper mills while decreasing the electricity demand for wastewater treatment
Open this publication in new window or tab >>Improving the biogas potential of pulp and paper mills while decreasing the electricity demand for wastewater treatment
2013 (English)Conference paper, Oral presentation only (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.

Keyword
anaerobic digestion, biosludge, efficient aeration, pulp and paper mill
National Category
Energy Engineering
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-26117 (URN)
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
3. Batchwise mesophilic anaerobic co-digestion of secondary sludge from pulp and paper industry and municipal sewage sludge
Open this publication in new window or tab >>Batchwise mesophilic anaerobic co-digestion of secondary sludge from pulp and paper industry and municipal sewage sludge
2013 (English)In: Waste Management, ISSN 0956-053X, E-ISSN 1879-2456, Vol. 33, no 4, 820-824 p.Article in journal (Refereed) Published
Abstract [en]

Residues from forest-industry wastewater-treatment systems are treated as waste at many pulp and paper mills. These organic substances have previously been shown to have potential for production of large quantities of biogas. There is concern, however, that the process would require expensive equipment because of the slow degradation of these substances. Pure non-fibrous sludge from forest industry showed lower specific methane production during mesophilic digestion for 19 days, 53 ± 26 Nml/g of volatile solids as compared to municipal sewage sludge, 84 ± 24 Nml/g of volatile solids. This paper explores the possibility of using anaerobic co-digestion with municipal sewage sludge to enhance the potential of methane production from secondary sludge from a pulp and paper mill. It was seen in a batch anaerobicdigestion operation of 19 days that the specific methane production remained largely the same for municipal sewage sludge when up to 50% of the volatile solids were replaced with forest-industry secondary sludge. It was also shown that the solid residue from anaerobic digestion of the forest-industry sludge should be of suitable quality to use for improving soil quality on lands that are not used for food production.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Anaerobic digestion
National Category
Energy Engineering
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-26116 (URN)000317798000006 ()23294534 (PubMedID)
Projects
SWX-Biogas
Note

Artikel är publicerad som manuskript i Alina Hagelqvists avhandling och heter där Stoica, A. / Batchwise mesophilic anaerobic co-digestion of secondary sludge from pulp industry and municipal sewage sludge / 2013 /

Available from: 2013-02-28 Created: 2013-02-01 Last updated: 2017-12-06Bibliographically approved
4. Co-digestion of manure with grass silage and pulp and paper mill sludge using nutrient additions
Open this publication in new window or tab >>Co-digestion of manure with grass silage and pulp and paper mill sludge using nutrient additions
2016 (English)In: Environmental technology, ISSN 0959-3330, E-ISSN 1479-487X, Vol. 37, no 16, 2113-2123 p.Article in journal (Refereed) Published
Abstract [en]

The purpose of this research is to evaluate how methane production is affected by the co-digestion of pig and dairy manure with grass silage and pulp and paper mill sludge at mesophilic conditions, and to assess whether methane production is affected by other factors than the now known ones, i.e., nutrient deficiency, low buffering capacity, inadequate dilution, and an insufficient activity and amount of microorganism culture. The season of grass silage and manure collection proved to be an important, previously unreported, factor affecting short-term (20 days) methane production.

Place, publisher, year, edition, pages
Taylor & Francis Group, 2016
Keyword
agricultural waste, anaerobic digestion, biomethane potential, co-digestion
National Category
Energy Engineering
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-26120 (URN)10.1080/09593330.2016.1142000 (DOI)000379772100011 ()
Note

Titel i avhandling:Co-digestion of manure with grass silage and pulp and paper mill sludge using the BMP methodology

Available from: 2013-02-01 Created: 2013-02-01 Last updated: 2017-07-04Bibliographically approved
5. Anaerobic self-degradation of pig and dairy manure using co-digestion with grass silage and pulp and paper mill sludge to shorten the start-up time
Open this publication in new window or tab >>Anaerobic self-degradation of pig and dairy manure using co-digestion with grass silage and pulp and paper mill sludge to shorten the start-up time
2013 (English)In: Waste Management, ISSN 0956-053X, E-ISSN 1879-2456Article in journal (Refereed) Submitted
Abstract [en]

The aim of this study was to find a way to shorten the start-up time of a pig and dairy manure based anaerobic digester without addition of external inoculum. Self-degradation was tested to simulate the setting of many sites where the use of external seed culture is not feasible because of the large distance to a nearest location where appropriate material can be collected. In this case study, co-digestion of pig and dairy manure with grass silage and pulp and paper mill sludge was tested using different compositions. The results showed that one tertiary mixture of 17 per cent of piggery manure, 17 per cent of dairy manure and 66 per cent of pulp and paper mill sludge resulted in a considerably shorter start-up time (about 15 days) as well as in a higher methane yield (120 ml CH4/g VS added after 44 days of batch operation) as compared to other mixtures tested. This mixture composition is recommended to start-up the full-scale process. Concentrations of ammonium of 0.4 g/l combined with slowly degradable material favoured a rapid start and efficient digestion.

Keyword
agricultural waste, anaerobic digestion, reactor start-up, total ammonia
National Category
Energy Engineering
Research subject
Environmental and Energy Systems
Identifiers
urn:nbn:se:kau:diva-26122 (URN)
Available from: 2013-02-01 Created: 2013-02-01 Last updated: 2017-12-06Bibliographically approved

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