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  • 1.
    Carlsson, My
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Pre-treatment of substrates for anaerobic digestion: potential and development needs2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Substrate pre-treatment has been gaining interest in anaerobic digestion (AD) as a means to increase biogas yields with nowadays more diversified substrate sources. The objective of this thesis is to identify improvement potentials and development needs within applications of substrate pretreatment in anaerobic digestion (AD) based on literature and specific examples, with special focus on the impact assessment and exemplified by the case of electroporation(EP) pre-treatment.The substrate inherent limitations to conversion of organic material to methane include content of non-biodegradable organic compounds, incorporation of biodegradable matter into recalcitrant structures and large particle size. WAS and lignocellulosic material are specific substrates that express significant substrate inherent limitations, especially WAS from WWTPs with long sludge age and lignocellulosic material with high lignin content.Improved AD performance relies on increasing operational methane yield as to approximate as much as possible the actual potential methane yield of the substrate at the highest possible digestion rate. This could potentially be achieved by the application of a pre-treatment, via the mechanisms of particle size reduction/solubilisation of biodegradable/bioavailable matter and/or conversion/exposure of non-biodegradable/non-bioavailable matter as to make it available or degradable. Pre-treatment mechanisms that could potentially counteract these effects are the removal of organic matter and/or the formation of refractory compounds. Pre-treatment by electroporation has the potential to affect substrates and, in some cases improve AD process performance. However, the effect of a specific pre-treatment may differ depending on the type of substrate upon which it is applied. The assessment of pre-treatment effects may be performed on different levels, representing impacts from micro to macro scale. On a substrate level, COD solubilisation is commonly measured, but the interpretation is aggravated by the application of different measurement approaches. In addition, solubilisation of COD as a result of pre-treatment does not necessarily translate into increased operational methane yield, and vice versa, the increased operational yield is not necessarily caused by increased COD solubilisation. On an AD process performance level, BMP tests have been used to assess both increased biodegradability and increased rate of degradation. Both applications rely on appropriate set-up as well as understanding of the limitations of the test. Substrate pre-treatment affects the quality of the outputs as well as the downstream processes of an AD process. A systematic approach is therefore necessary to understand how the introduction of a pre-treatment process as well as the changes in process performance with respect to qualities and quantities of outputs affect the balances of the system with respect to assessment bases such as energy, CO2 or economics.Several areas that would gain from further development can be identified within the area of substrate pre-treatment. These include improved understanding of substrate characteristics with improved descriptors, such as improved understanding of COD composition, and of BMP applicability and limitations. In addition, improved understanding of the relationship between substrate composition and process performance would be helpful to improve the understanding of different pre-treatment effects.Improved understanding of system effects where case-specific conditions can be considered is necessary for the full-scale implementation of pre-treatments to a larger extent. The application of tools for systems analysis to systems including pre-treatment should be further evaluated and a sensitivity analysis with respect to which specific conditions may render pre-treatments beneficial or non-beneficial should be performed.The practical applicability of electroporation pre-treatment for different substrates needs further development and the energy efficiency of the pre-treatment should be evaluated considering upscaling effects.

  • 2.
    Carlsson, My
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    When and why is pre-treatment of substrates for anaerobic digestion useful?2015Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Anaerobic digestion (AD) plays a key role in the recovery of renewable energy, in the form of biogas, and nutrients from waste materials. Pre-treatment of AD substrates has the potential to improve process performance in terms of increased methane yield and solids reduction, but pretreatments are not yet widely implemented into full-scale AD systems. The aims of this thesis were to identify conditions that determine when pre-treatment has a positive impact on an AD system and ways to improve the practical utility of pre-treatment impact assessment. Key steps towards meeting these aims were to determine and critically analyse effects of pre-treatments on AD, and current evaluation schemes at three levels: AD substrate level – Direct effects on the substrate’s chemical and physical characteristics and its biodegradability/bioavailability; Local AD system level – Effects of pre-treatment on the AD process and its outputs, required inputs and (local) upstream and downstream processes. System boundaries are “at the gate” of the AD plant and the system analysis may consider energy and/or financial parameters; Expanded AD System level – Includes indirect effects of pre-treatment, with system boundaries including external processes. The system analysis may address environmental and/or economic effects. Different substrate traits represent different types and degrees of limitations to optimal AD performance that can be met by different pre-treatment mechanisms. Most importantly, potential mechanical problems must be handled by dilution and/or homogenisation and unwanted components, as generally found in source-sorted food waste from households (FW), must be separated. These traits may hinder the actual operation of AD and the potential for recovery of nutrients, which is often the motivation for biological waste treatment. When these practical barriers are overcome, pre-treatment focus may be directed towards maximizing the conversion of organic material to biogas, which is potentially limited by the rate and/or extent of hydrolysis. Lignocellulosic structures and aerobically stabilised biological sludge represent significant barriers to hydrolysis, which can be overcome by pre-treatment-induced solubilisation. Other particulates are merely hydrolysis-limited by their size, which can be reduced by specific pre-treatments. Finally, substrates may contain non-biodegradable organic compounds, which need to be chemically transformed in order to be converted to biogas. The substrates considered for AD incorporate these traits in varying degrees and even among substrates of the same category, such as plant material and excess sludge from wastewater treatment (WWT), the potential effect of pretreatments may vary considerably. Overcoming the substrate barriers via pre-treatment may potentially improve the AD system by enhancing operational stability, increasing methane yields and solids reduction under similar operating conditions to those without pre-treatment or by increasing methane productivity by allowing reductions in hydraulic retention time without changing the methane yield. However, the required inputs as well as the associated effects on related sub-processes must also be considered. The ultimate usefulness of a pre-treatment in a specific system is determined by the mass- and energy balance and the associated financial or environmental costs/values of inputs and outputs. The accuracy and applicability of pre-treatment impact assessment is challenged by method limitations and lack of transparency. A common measure of the pre-treatment effects is COD solubilisation, but the interpretation is complicated by the application of different measurementapproaches. In addition, solubilisation of COD as a result of pre-treatment does not necessarily translate into increases in operational methane yields. This is due to potential formation of refractory compounds and the fact that hydrolysis is not necessarily rate limiting for all particulates. Pre-treatments’ effects on biodegradability and degradation rates can be better assessed by BMP tests (biochemical methane potential), provided that the test conditions are appropriate and the tests’ limitations are properly considered. However, extrapolation of BMP results to continuous processes is complicated by the batch mode of the tests. On the other hand, results from continuous trials allow assessments of methane yields in practical systems and the digestate’s physico-chemical properties, but are inevitably tied to the specific process conditions tested. Thus, results from multiple experimental conditions, possibly strengthened by computer simulations, are necessary for generalisations of pre-treatment effects on AD process performance. Pre-treatments have the potential to considerably improve AD systems, but their implementation must to be guided by the actual improvement potential of the specific substrate and valued in theirspecific context with respect to process design and framework conditions.

  • 3.
    Carlsson, My
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Holmström, David
    Profu AB, Mölndal.
    Bohn, Irene
    NSR, North Western Scania Waste Management Company, Helsingborg.
    Bisaillon, Mattias
    Profu AB, Mölndal.
    Morgan-Sagastume, Fernando
    AnoxKaldnes AB, Klosterängsvägen 11A, 226 47 Lund.
    Lagerkvist, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Impact of physical pre-treatment of source-sorted organic fraction of municipal solid waste on greenhouse-gas emissions and the economy in a Swedish anaerobic digestion system2015In: Waste Management, ISSN 0956-053X, E-ISSN 1879-2456, Vol. 38, p. 117-125Article in journal (Refereed)
    Abstract [en]

    Several methods for physical pre-treatments of source sorted organic fraction of municipal solid waste (SSOFMSW) before for anaerobic digestion (AD) are available, with the common feature that they generate a homogeneous slurry for AD and a dry refuse fraction for incineration. The selection of efficient methods relies on improved understanding of how the pre-treatment impacts on the separation and on the slurry’s AD. The aim of this study was to evaluate the impact of the performance of physical pre-treatment of SSOFMSW on greenhouse-gas (GHG) emissions and on the economy of an AD system including a biogas plant with supplementary systems for heat and power production in Sweden. Based on the performance of selected Swedish facilities, as well as chemical analyses and BMP tests of slurry and refuse, the computer-based evaluation tool ORWARE was improved as to accurately describe mass flows through the physical pre-treatment and anaerobic degradation. The environmental and economic performance of the evaluated system was influenced by the TS concentration in the slurry, as well as the distribution of incoming solids between slurry and refuse. The focus to improve the efficiency of these systems should primarily be directed towards minimising the water addition in the pre-treatment provided that this slurry can still be efficiently digested. Second, the amount of refuse should be minimised, while keeping a good quality of the slurry. Electricity use/generation has high impact on GHG emissions and the results of the study are sensitive to assumptions of marginal electricity and of electricity use in the pre-treatment.

  • 4. Carlsson, My
    et al.
    Lagerkvist, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Ecke, Holger
    Electroporation for enhanced methane yield from municipal solid waste2008Conference paper (Refereed)
  • 5.
    Carlsson, My
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Veolia Water Technologies AB (AnoxKaldnes), Lund, Sweden.
    Lagerkvist, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Morgan-Sagastume, Fernando
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering. Veolia Water Technologies AB (AnoxKaldnes), Lund, Sweden.
    Energy balance performance of municipal wastewater treatment systems considering sludge anaerobic biodegradability and biogas utilisation routes2016In: Journal of Environmental Chemical Engineering, ISSN 2160-6544, E-ISSN 2213-3437, Vol. 4, no 4, p. 4680-4689Article in journal (Refereed)
    Abstract [en]

    The energy balance of a municipal wastewater treatment (WWT) system was evaluated considering the influence of excess biological sludge anaerobic biodegradability (BDAn) and of biogas utilisation as either fuel for co-generation of heat and power (CHP) or for vehicle transport. Sludge thermal pre-treatment prior to anaerobic digestion and high-rate carbon removal were considered as modifications of a reference municipal WWT system to impact the sludge BDAn. Both thermal pre-treatment and a high-rate process with a short sludge retention time (SRT = 1-3d) led to ∼30% higher sludge BDAn than that of untreated sludge from a low-rate WWT system with long SRT ( > 8d), which enhanced methane yields and energy production correspondingly. An efficient separation (40% of CODin) of primary solids promoted biogas production by capturing a significant part of the incoming COD, and lowered aeration energy demands for carbon oxidation due to lower loads of particulate organics into the biological treatment. Thermal pre-treatment can most effectively increase the biodegradability of sludge originating from a low-rate WWT system with a long SRT. Sludge solubilization alone as an indicator of increase biodegradability by a pre-treatment is inadequate for sludge types with inherently high biodegradability. A WWT system with primary separation, sludge pre-treatment, and CHP from biogas can be a net electricity producer and self-sufficient in thermal energy, provided the thermal energy from CHP is available for the pre-treatment. With other types of energy carriers as inputs and outputs, the WWT performance also needs evaluation with respect to the energy economic and environmental value. 

  • 6.
    Carlsson, My
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Lagerkvist, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Morgan-Sagastume, Fernando
    AnoxKaldnes AB.
    The effects of substrate pre-treatment on anaerobic digestion systems: a review2012In: Waste Management, ISSN 0956-053X, E-ISSN 1879-2456, Vol. 32, no 9, p. 1634-1650Article in journal (Refereed)
    Abstract [en]

    Focus is placed on substrate pre-treatment in anaerobic digestion (AD) as a means of increasing biogas yields using today’s diversified substrate sources. Current pre-treatment methods to improve AD are being examined with regard to their effects on different substrate types, highlighting approaches and associated challenges in evaluating substrate pre-treatment in AD systems and its influence on the overall system of evaluation. WWTP residues represent the substrate type that is most frequently assessed in pre-treatment studies, followed by energy crops/harvesting residues, organic fraction of municipal solid waste, organic waste from food industry and manure. The pre-treatment effects are complex and generally linked to substrate characteristics and pre-treatment mechanisms. Overall, substrates containing lignin or bacterial cells appear to be the most amendable to pre-treatment for enhancing AD. Approaches used to evaluate AD enhancement in different systems is further reviewed and challenges and opportunities for improved evaluations are identified.

  • 7.
    Carlsson, My
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Naroznova, Irina
    Department of Environmental Engineering (DTU Environment), Technical University of Denmark.
    Möller, Jacob Steen
    Department of Environmental Engineering (DTU Environment), Technical University of Denmark.
    Scheutz, Charlotte
    Department of Environmental Science and Engineering, Technical University of Denmark.
    Lagerkvist, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Importance of food waste pre-treatment efficiency for global warming potential in life cycle assessment of anaerobic digestion systems2015In: Resources, Conservation and Recycling, ISSN 0921-3449, E-ISSN 1879-0658, Vol. 102, p. 58-66Article in journal (Refereed)
    Abstract [en]

    A need for improvement of food waste (FW) pre-treatment methods has been recognized, but few life cycle assessments (LCA) of FW management systems have considered the pre-treatment with respect to input energy, loss of organic material and nutrients for anaerobic digestion (AD) and/or further treatment of the refuse. The objective of this study was to investigate how FW pre-treatment efficiency impacts the environmental performance of waste management, with respect to global warming potential (GWP). The modeling tool EASETECH was used to perform consequential LCA focusing on the impact of changes in mass distribution within framework conditions that were varied with respect to biogas utilization and energy system, representing different geographical regions and/or different time-frames. The variations of the GWP due to changes in pre-treatment efficiency were generally small, especially when biogas and refuse were substituting the same energy carriers, when energy conversion efficiencies were high and slurry quality good enough to enable digestate use on land. In these cases other environmental aspects, economy and practicality could be guiding when selecting pre-treatment system without large risk of sub-optimization with regards to GWP. However, the methane potential of the slurry is important for the net LCA results and must be included in the sensitivity analysis. Furthermore, when biogas is used as vehicle fuel the importance of pre-treatment is sensitive to assumptions and approach of modelling marginal energy which must be decided based on the focus and timeframe of the study in question

  • 8.
    Lindmark, Johan
    et al.
    School of Business, Society and Engineering, Mälardalen University, Västerås.
    Lagerkvist, Anders
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Nilsson, Erik
    School of Business, Society and Engineering, Mälardalen University, Västerås.
    Carlsson, My
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Thorin, Eva
    School of Business, Society and Engineering, Mälardalen University, Västerås.
    Dahlquist, Erik
    School of Business, Society and Engineering, Mälardalen University, Västerås.
    Evaluating the Effects of Electroporation Pre-treatment on the Biogas Yield from Ley Crop Silage2014In: Applied Biochemistry and Biotechnology, ISSN 0273-2289, E-ISSN 1559-0291, Vol. 174, no 7, p. 2616-2625Article in journal (Refereed)
    Abstract [en]

    Exploiting the full biogas potential of some types of biomass is challenging. The complex structures of lignocellulosic biomass are difficult to break down and thus require longer retention times for the nutrients to become biologically available. It is possible to increase the digestibility of the substrate by pre-treating the material before digestion. This paper explores a pre-treatment of ley crop silage that uses electrical fields, known as electroporation (EP). Different settings of the EP equipment were tested, and the results were analyzed using a batch digestion setup. The results show that it is possible to increase the biogas yield with 16 % by subjecting the substrates to 65 pulses at a field strength of 96 kV/cm corresponding to a total energy input of 259 Wh/kg volatile solid (VS). However, at 100 pulses, a lower field strength of 48 kV/cm and the same total energy input, no effects of the treatment were observed. The energy balance of the EP treatment suggests that the yield, in the form of methane, can be up to double the electrical energy input of the process.

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