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System studies of Anaerobic Co-digestion Processes
Mälardalen University, School of Business, Society and Engineering, Future Energy Center.ORCID iD: 0000-0002-3131-0285
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Production of biogas through anaerobic digestion is one pathway to achieving the European Union (EU) goals of reducing greenhouse gas emissions, increasing the share of renewable energy, and improving energy efficiency. In this thesis, two different models (Anaerobic Digestion Model No. 1 and an artificial neural network) are used to simulate a full-scale co-digester in order to evaluate the feasibility of such models. This thesis also includes models of two systems to study the inclusion of microalgae in biogas plants and wastewater treatment plants. One of the studies is a life-cycle assessment in which replacement of the ley crop with microalgae is evaluated. The other study concerns the inclusion of microalgae in case studies of biological treatment in three wastewater treatment plants. Finally, the co-digestion between microalgae and sewage sludge has been simulated to evaluate the effect on biogas and methane yield. The results showed that Anaerobic Digestion Model No.1 and the artificial neural network are suitable for replicating the dynamics of a full-scale co-digestion plant. For the tested period, the artificial neural network showed a better fit for biogas and methane content than the Anaerobic Digestion Model No. 1. Simulations showed that co-digestion with microalgae tended to reduce biomethane production. However, this depended on the species and biodegradability of the microalgae. The results also showed that inclusion of microalgae could decrease carbon dioxide emissions in both types of plants and decrease the energy demand of the studied wastewater treatment plants. The extent of the decrease in the wastewater treatment plants depended on surface volume. In the biogas plant, the inclusion of microalgae led to a lower net energy ratio for the methane compared to when using ley crop silage. Both studies show that microalgae cultivation is best suited for use in summer in the northern climate.

Place, publisher, year, edition, pages
Västerås: Mälardalen University Press , 2017.
Series
Mälardalen University Press Dissertations, ISSN 1651-4238 ; 237
National Category
Bioenergy
Research subject
Energy- and Environmental Engineering
Identifiers
URN: urn:nbn:se:mdh:diva-36515ISBN: 978-91-7485-347-6 (print)OAI: oai:DiVA.org:mdh-36515DiVA: diva2:1144541
Public defence
2017-11-08, Case, Västerås, 09:15 (English)
Opponent
Supervisors
Available from: 2017-09-27 Created: 2017-09-26 Last updated: 2017-09-27Bibliographically approved
List of papers
1. Investigating the possibility of applying an ADM1 based model to a full-scale co-digestion plant
Open this publication in new window or tab >>Investigating the possibility of applying an ADM1 based model to a full-scale co-digestion plant
2017 (English)In: Biochemical engineering journal, ISSN 1369-703X, E-ISSN 1873-295X, Vol. 120, 73-83 p.Article in journal (Refereed) Published
Abstract [en]

This study investigated the possibility of using a model based on the anaerobic digestion model no. 1 (ADM1) on a full-scale 4000 m3 digester in order to understand how such theoretical models can be applied to a real industrial process. The industrial scale digester co-digests the organic fraction of municipal solid waste, grease trap sludge, and ley crop silage with varying feed rates and amounts of volatile solids. A year of process data was collected. Biogas flow, methane content/flow, and ammonia nitrogen were the variables that the model was best at predicting (index of agreement at 0.78, 0.61/0.77, and 0.68, respectively). The model was also used to investigate the effect of increasing the volatile solids (VS) concentration entering the digester. According to simulation results, increasing the influent VS concentration will increase biogas and methane outflow (from 1.5 million Nm3 methane to more than 2 million Nm3 methane), but decrease the amounts of biogas/methane per unit of volatile solids (from about 264 Nm3methane per tonne VS to below 215 Nm3 methane per tonne VS).

Place, publisher, year, edition, pages
Elsevier, 2017
National Category
Bioenergy
Identifiers
urn:nbn:se:mdh:diva-34634 (URN)10.1016/j.bej.2016.12.014 (DOI)000395603900009 ()2-s2.0-85009230307 (Scopus ID)
Available from: 2017-01-16 Created: 2017-01-16 Last updated: 2017-09-26Bibliographically approved
2. Modeling of a full-scale biogas plant using a dynamic neural network
Open this publication in new window or tab >>Modeling of a full-scale biogas plant using a dynamic neural network
2013 (English)Conference paper, Oral presentation with published abstract (Refereed)
Keyword
neural network, anaerobic digestion, biogas, model
National Category
Bioprocess Technology Bioenergy Energy Systems
Research subject
Energy- and Environmental Engineering; Biotechnology/Chemical Engineering
Identifiers
urn:nbn:se:mdh:diva-21600 (URN)
Conference
Sardinia 2013, S. Margherita di Pula, September 30 - October 4
Available from: 2013-09-18 Created: 2013-09-18 Last updated: 2017-09-26Bibliographically approved
3. Simulation of energy balance and carbon dioxide emission for microalgae introduction in wastewater treatment plants
Open this publication in new window or tab >>Simulation of energy balance and carbon dioxide emission for microalgae introduction in wastewater treatment plants
2017 (English)In: Algal Research, ISSN 2211-9264, Vol. 24, 251-260 p.Article in journal (Refereed) Published
Abstract [en]

A case study is described in which the activated sludge process is replaced with a microalgae-activated sludge process. The effects on the heat and electricity consumption and carbon dioxide emissions were evaluated in a system model, based on mass and energy balances of biological treatment and sludge handling process steps. Data for use in the model was gathered from three wastewater treatment plants in Sweden. The evaluation showed that the introduction of microalgae could reduce electricity and heat consumption as well as CO2 emissions but would require large land areas. The study concludes that a 12-fold increase in the basin surface area would result in reductions of 26–35% in electricity consumption, 7–32% in heat consumption and 22–54% in carbon dioxide emissions. This process may be suitable for wastewater treatment plants in Nordic countries, where there is a higher organic load in summer than at other times of the year. During the summer period (May to August) electricity consumption was reduced by 50–68%, heat consumption was reduced by 13–63% and carbon dioxide emissions were reduced by 43–103%.

Place, publisher, year, edition, pages
Elsevier B.V., 2017
National Category
Energy Systems Water Engineering
Identifiers
urn:nbn:se:mdh:diva-35277 (URN)10.1016/j.algal.2017.03.026 (DOI)000404864600025 ()2-s2.0-85017531839 (Scopus ID)
Available from: 2017-05-03 Created: 2017-05-03 Last updated: 2017-09-26Bibliographically approved
4. Microalgal biomethane production integrated with an existing biogas plant: A case study in Sweden
Open this publication in new window or tab >>Microalgal biomethane production integrated with an existing biogas plant: A case study in Sweden
2013 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 112, 478-484 p.Article in journal (Refereed) Published
Abstract [en]

Microalgae are considered as potential sources for biodiesel production due to the higher growth rate than terrestrial plants. However, the large-scale application of algal biodiesel would be limited by the downstream cost of lipid extraction and the availability of water, CO2 and nutrients. A possible solution is to integrate algae cultivation with existing biogas plant, where algae can be cultivated using the discharges of CO2 and digestate as nutrient input, and then the attained biomass can be converted directly to biomethane by existing infrastructures. This integrated system is investigated and evaluated in this study. Algae are cultivated in a photobioreactor in a greenhouse, and two cultivation options (greenhouse with and without heating) are included. Life cycle assessment of the system was conducted, showing that algal biomethane production without greenhouse heating would have a net energy ratio of 1.54, which is slightly lower than that (1.78) of biomethane from ley crop. However, land requirement of the latter is approximately 68 times that of the former, because the area productivity of algae could reach at about 400 t/ha (dry basis) in half a year, while the annual productivity of ley crop is only about 5.8 t/ha. For the case of Växtkraft biogas plant in Västerås, Sweden, the integrated system has the potential to increase the annual biomethane output by 9.4%. This new process is very simple, which might have potential for scale-up and commercial application of algal bioenergy. © 2013 Elsevier Ltd. All rights reserved.

Keyword
Biogas plant, Cold region, Energy balance, Life cycle assessment, Microalgal biomethane
National Category
Engineering and Technology
Identifiers
urn:nbn:se:mdh:diva-19152 (URN)10.1016/j.apenergy.2013.04.087 (DOI)000329377800049 ()2-s2.0-84884283197 (Scopus ID)
Available from: 2013-06-10 Created: 2013-06-10 Last updated: 2017-09-26Bibliographically approved

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