The objectives of this study are to present a model for biogas production systems to help achieve a more cost-effective system, and to analyse the conditions for connecting combined heat and power (CHP) plants to the biogas system. The European electricity market is assumed to be fully deregulated. The relation between connection of CHP. increased electricity and heat production, electricity prices, and electricity certificate trading is investigated. A cost-minimising linear programming model (MODEST) is used. MODEST has been applied to many energy systems, but this is the first time the model has been used for biogas production. The new model, which is the main result of this work, can be used for operational optimisation and evaluating economic consequences of future changes in the biogas system. The results from the case study and sensitivity analysis show that the model is reliable and can be used for strategic planning. The results show that implementation of a biogas-based CHP plant result in an electricity power production of approximately 39 GW h annually. Reduced system costs provide a profitability of 46 MSEK/year if electricity and heat prices increase by 100% and electricity certificate prices increase by 50%. CO2 emission reductions up to 32,000 ton/year can be achieved if generated electricity displaces coal-fired condensing power.

Sweden has ambitions to phase out fossil fuels and significantly increase the share of biofuels it uses. This articlefocuses on Stockholm County and biogas, with the aim to increase the knowledge about regional preconditions.Biogas-related actors have been interviewed, focusing on the demand side. Biogas solutions play an essentialrole, especially regarding bus transports and taxis. Long-term development has created well-functioning sociotechnicalsystems involving collaboration. However, uncertainties about demand and policy cause hesitation andsigns of stagnating development.Public organizations are key actors regarding renewables. For example, Stockholm Public Transport procuresbiogas matching the production at municipal wastewater treatment plants, the state-owned company Swedaviasteers via a queuing system for taxis, and the municipalities have shifted to “environmental cars”.There is a large interest in electric vehicles, which is expected to increase significantly, partially due tosuggested national policy support. The future role of biogas will be affected by how such an expansion comesabout. There might be a risk of electricity replacing biogas, making it more challenging to reach a fossil-freevehicle fleet. Policy issues strongly influence the development. The environmental car definition is of importance,but its limited focus fails to account for several different types of relevant effects. The dynamic policylandscape with uncertainties about decision makers’ views on biogas seems to be one important reason behindthe decreased pace of development. A national, long-term strategy is missing. Both the European Union andSweden have high ambitions regarding a bio-based and circular economy, which should favor biogas solutions.

Biogas solutions can contribute to more renewable and local energy systems, and also involve other essential aspects such as nutrient recycling. From a theoretical feedstock perspective there is a great biogas potential in Sweden, but the development has been relatively slow as many biogas producers face challenges of different types. Among the many influencing factors, the choice of feedstocks (biomass) is of strategic importance. Within the Biogas Research Center (BRC), hosted by Linköping University in Sweden, a research project focused on feedstock has been ongoing for several years. It has involved researchers, biogas and biofertilizer producers, agricultural organizations and others. The main aim has been to develop a method to assess the suitability of feedstock for biogas and biofertilizer production, and to apply this method on a few selected feedstocks. A multi-criteria method has been developed that covers potential, feasibility and resource efficiency, operationalized via 17 indicators directed towards cost efficiency, technological feasibility, energy and environmental performance, accessibility, competition, policy and other issues. Thus the method it is relatively comprehensive, yet hopefully simple enough to be used by practitioners.

The main ambition, applying the method, has been to collect and structure relevant information to facilitate strategic overviews, communication and informed decision making. This is relevant for development within the biogas and biofertilizer industry, for policymakers, to define and prioritize among essential research projects, etc. This report presents some essential parts of this project, focusing on the multi-criteria method and results regarding ley crops, straw, farmed blue mussels and food waste (and stickleback to some extent). It clarifies how the method can be applied and highlights barriers, drivers and opportunities for each feedstock. Comparisons are also made. The results indicate that biogas production from food waste and ley crops is the most straightforward, and for straw and farmed blue mussels there are more obstacles to overcome. For all of them, the dynamic and very uncertain policy landscape is a barrier. In the final chapter, some conclusions about the method and its application are drawn.

Biogas Research Center (BRC) is a center of excellence in biogas research funded by the Swedish Energy Agency, Linköping University and a number of external organizations with one-third each. BRC has a very broad interdisciplinary approach, bringing together biogas-related skills from several areas to create interaction on many levels:

• between industry, academia and society,
• between different perspectives, and
• between different disciplines and areas of expertise.

BRC’s vision is:

BRC contributes to the vision by advancing knowledge and technical development, as well as by facilitating development, innovation and business. Resource efficiency is central, improving existing processes and systems as well as establishing biogas solutions in new sectors and enabling use of new substrates.

For BRC phase 1, the first two year period from 2012-2014, the research projects were organized in accordance with the table below showing important challenges for biogas producers and other stakeholders, and how these challenges were tackled in eight research projects. Five of the projects had an exploratory nature, meaning that they were broader, more future oriented and, for example, evaluated several different technology paths (EP1-5). Three projects focused more on technology and process development (DP6-8).

This final report briefly presents the background and contains some information about competence centers in general. Thereafter follows more detailed information about BRC, for example, regarding the establishment, relevance, organization, vision, corner stones and development. The participating organizations are presented, both the research groups within Linköping University and the partners and members. Further on, there is a more detailed introduction to and description of the challenges mentioned in the table above and a short presentation from each of the research projects, followed by some sections dealing with fulfillment of objectives and an external assessment of BRC. Detailed, listed information is commonly provided in the appendices.

Briefly, the fulfillment of objectives is good and it is very positive that so many scientific articles have been published (or are to be published) from the research projects and also within the wider center perspective. Clearly, extensive and relevant activities are ongoing within and around BRC. In phase 2 it essential to increase the share of very satisfied partners and members, where now half of them are satisfied and the other half is very satisfied. For this purpose, improved communication, interaction and project management are central. During 2015, at least two PhD theses are expected, to a large extent based on the research from BRC phase 1.

In the beginning of 2014 an external assessment of BRC was carried out, with the main purpose to assess how well the center has been established and to review the conditions for a future, successful competence center. Generally, the outcome was very positive and the assessors concluded that BRC within a short period of time had been able to establish a well-functioning organization engaging a large share of the participants within relevant areas, and that most of the involved actors look upon BRC as a justifiable and well working investment that they plan to continue to support. The assessment also contributed with several relevant tips of improvements and to clarify challenges to address.

This report is written in Swedish, but for each research project there will be reports and/or scientific papers published in English.

The work presented in this report has been financed by the Swedish Energy Agency and the participating organizations.

Proper pretreatment of organic residues prior to anaerobic digestion (AD) can maximize global biogas production from varying sources without increasing the amount of digestate, contributing to global decarbonization goals. However, the efficiency of pretreatments applied on varying organic streams is poorly assessed. Thus, we performed a meta-analysis on AD studies to evaluate the efficiencies of pretreatments with respect to biogas production measured as methane yield. Based on 1374 observations our analysis shows that pretreatment efficiency is dependent on substrate chemical dominance. Grouping substrates by chemical composition e.g., lignocellulosic-, protein- and lipid-rich dominance helps to highlight the appropriate choice of pretreatment that supports maximum substrate degradation and more efficient conversion to biogas. Methane yield can undergo an impactful increase compared to untreated controls if proper pretreatment of substrates of a given chemical dominance is applied. Non-significant or even adverse effects on AD are, however, observed when the substrate chemical dominance is disregarded.

The textile industry is one of the largest environmental polluters in the world. Although waste management via anaerobic digestion (AD) is a sustainable strategy to transform waste into clean energy and water recovery, the efficiency of the AD process is reduced by the presence of recalcitrant materials, chemicals, and toxic contents. This study aims to investigate the performance of several chemical, physical, and biological pretreatments applied to improve the biodegradability of textile waste. We performed a meta-analysis with 117 data extracted from 13 published articles that evaluated the efficiency of pretreatments applied to textile waste prior to AD to increase biogas production measured as methane (CH4) yield. Even though the majority of the studies have focused on the effect of chemical and physical pretreatments, our results showed that the application of biological pretreatments are more efficient and eco-friendlier. Biological pretreatments can increase CH4 yield by up to 360% with lower environmental risk and lower operating costs, while producing clean energy and a cleaner waste stream. Biological pretreatments also avoid the addition of chemicals and favor the reuse of textile wastewater, decreasing the current demand for clean water and increasing resource circularity in the textile industry.

Anaerobic digestion (AD) is a versatile manure management approach that can combine waste treatment, energy generation and nutrient recovery, thus playing a central role in circular economy. The AD process is highly influenced by manure composition which, depending on the source, may contain high loads recalcitrant materials (e.g., lignocellulosic and fibers) or lead to the formation of toxic compounds (e.g., NH₃), decreasing the energetic potential of the waste and requiring specific pretreatments to increase its degradability and biogas production. Although there are distinctions in the chemical composition of manure according to animal diets, different manure sources are usually grouped together, leading to a suboptimal performance of both the pretreatment and the AD process. Here, we performed a meta-analysis of 54 studies to evaluate the effects of different pretreatments on different manure types and their effect on methane (CH₄) yield and we estimated the energy potential if the appropriate pretreatment is applied to largest manure producing countries. The results showed that chemical and/or biological pretreatments were more effective for omnivore manure (e.g., swine, chicken), while physical and a combination of chemical and physical pretreatments negatively affected CH₄ production. Physical and/or chemical pretreatments had a positive effect on CH₄ yield from herbivore manure (e. g., cattle, horses), while biological pretreatments had a negative effect. The application of the adequate pretreatment can more than double the energy recovered from manure, allowing for an important substitution of fossil fuels, while decreasing operational costs and environmental risks and ultimately improving profitability. The development of pretreatment technologies and their application are strongly related to public policies for sustainable manure management and biogas use and production.

The aim of this study was to assess the feasibility of moderate thermal treatment (70 ^◦C for one hour) of digestate in combination with post-digestion targeting residual biomethane potentials from three full-scale biogas plants digesting food waste (FW), agricultural waste (AW) and a mixture of AW and manure (AWM). Dissolved organic carbon (DOC), biomethane production, and digestate quality were investigated. For the study six laboratory-scale continuously stirred tank biogas reactors working as post-digesters, with thermally-treated and non-treated digestate were used. DOC for thermally-treated digestates increased significantly (t-test, p < 0.05); FW-digestate (110–200 %), AW-digestate (24–92 %) and for AWM-digestate (4–73 %). Indexes for corresponding DOC quality showed lower apparent organic molecular weights and decreased aromaticity (with the exception of FW-digestate). Thermal treatment of digestate improved the biomethane production during post-digestion by 21–22 % (FW-digestate) and 9 % (AW-digestate). For AMW-digestate no clear positive effect was observed, most likely due to biogas plant operational process disturbances. 

Non-symbiotic globin class #1 (Glb1) genes are expressed in different plant organs, have a high affinity for oxygen, and are related to nitric oxide (NO) turnover. Previous studies showed that soybean Glb1 genes are upregulated in soybean plants under flooding conditions. Herein, the GmGlb1-1 gene was identified in soybean as being upregulated in the nematode-resistant genotype PI595099 compared to the nematode-susceptible cultivar BRS133 during plant parasitism by Meloidogyne incognita. The Arabidopsis thaliana and Nicotiana tabacum transgenic lines overexpressing the GmGlb1-1 gene showed reduced susceptibility to M. incognita. Consistently, gall morphology data indicated that pJ2 nematodes that infected the transgenic lines showed developmental alterations and delayed parasitism progress. Although no significant changes in biomass and seed yield were detected, the transgenic lines showed an elongated, etiolation-like growth under well-irrigation, and also developed more axillary roots under flooding conditions. In addition, transgenic lines showed upregulation of some important genes involved in plant defense response to oxidative stress. In agreement, higher hydrogen peroxide accumulation and reduced activity of reactive oxygen species (ROS) detoxification enzymes were also observed in these transgenic lines. Thus, based on our data and previous studies, it was hypothesized that constitutive overexpression of the GmGlb1-1 gene can interfere in the dynamics of ROS production and NO scavenging, enhancing the acquired systemic acclimation to biotic and abiotic stresses, and improving the cellular homeostasis. Therefore, these collective data suggest that ectopic or nematode-induced overexpression, or enhanced expression of the GmGlb1-1 gene using CRISPR/dCas9 offers great potential for application in commercial soybean cultivars aiming to reduce plant susceptibility to M. incognita.

Reaching climate goals depends on appropriate and accurate methods to quantify greenhouse gas (GHG) fluxes and to verify that efforts to mitigate GHG emissions are effective. We here highlight critical advantages, limitations, and needs regarding GHG flux measurement methods, identified from an analysis of &gt;13 500 scientific publications regarding three long-lived GHGs, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O). While existing methods are well-suited for assessing atmospheric changes and local fluxes, they are expensive and have limited accessibility. Further, we are typically forced to choose between methods for very local GHG sources and sinks and their regulation (m(2)-scaled measurements), or methods for aggregated net fluxes at &gt;ha or km(2) scales measurements. The results highlight the key need of accessible and affordable GHG flux measurement methods for the many flux types not quantifiable from fossil fuel use, to better verify inventories and mitigation efforts for transparency and accountability under the Paris agreement. The situation also calls for novel methods, capable of quantifying large scale GHG flux patterns while simultaneously distinguishing local source and sink dynamics and reveal flux regulation, representing key knowledge for quantitative GHG flux modeling. Possible strategies to address the identified GHG flux measurement method needs are discussed. The analysis also generated indications of how GHG flux measurements have been distributed geographically and across flux types, which are reported.

Sweden has the ambition to increase its annual biogas production from the current level of 1.9 to 15 TWh by 2030. The unused capacity of existing anaerobic digesters at wastewater treatment plants is among the options to accomplish this goal. This study investigated the feasibility of utilizing the organic fraction of municipal solid waste (OFMSW) as a co-substrate, with primary and waste-activated sewage sludge (PWASS) for production of biogas, corresponding to 3:1 ratio on volatile solid (VS) basis. The results demonstrated that co-digestion of OFMSW with PWASS at an organic loading rate of 5 gVS l−1 day−1 has the potential to increase the biogas production approximately four times. The daily biogas production increased from 1.0 ± 0.1 to 3.8 ± 0.3 l biogasl−1 day−1, corresponding to a specific methane production of 420 ± 30 Nml methane gVS−1 during the laboratory experiment. Co-digestion of OFMSW with PWASS showed a 50:50 distribution of hydrogenotrophic and aceticlastic methanogens in the digester and enhanced the turnover kinetics of intermediate products (acetate, propionate, and oleate). Practical limitations potentially include the need for sludge dewatering to maintain a sufficient hydraulic retention time (17 days in this study), as well as additional energy consumption for mixing due to an increased sludge apparent viscosity (from 1.8 ± 0.1 to 45 ± 4.8 mPa*s in this study) at elevated OFMSW-loading rates.

Digestate processing is a strategy to improve the management of digestate from biogas plants. Solid-liquid separation is usually the primary step and can be followed by advanced treatments of the fractions. The knowledge about the performance of the separators and the quality of the fractions is scattered because of many available techniques and large variability in digestate characteristics. We performed a systematic review and found 175 observations of full-scale solid-liquid separation of digestate. We identified 4 separator groups, 4 digestate classes based on substrate, and distinguished whether chemical conditioners were used. We confirmed the hypothesis that the dominant substrate can affect the efficiency of the digestate separation. Furthermore, the results showed that centrifuges separated significantly more dry matter and total P than screw presses. Use of chemical conditioners in combination with a centrifuge lowered the dry matter concentration in the liquid fraction by 30%. Screw presses consumed 4.5 times less energy than centrifuges and delivered 3.3 tonne ammonium N in the liquid fraction and 0.3 tonne total P in the solid fraction using 1 MWh. The results can provide data for systems analyses of biogas solutions and can support practitioners when choosing among full-scale separator techniques depending on the digestate type. In a broader perspective, this work contributes to the continuous improvement of biogas plants operations and to their role as nutrients recovery sites.

This article is focused on performing a SWOT analysis of agricultural waste management methods. This approach can be applied in the biogas technology strategic planning process in Ukraine, which can solve the issue of implementation of environmental guidelines for the development of biofuels and biofertilizers. The main factors that determine how digestate is used are its quality, local conditions, regulations, and documents. Fertilizing fields with digestate provides many advantages, for example: reduced demand for plant protection products, reduction of unpleasant odor, and destruction of possible pathogens. The strengths and weaknesses of the implementation of biogas plants in Ukraine have been identified, and opportunities and threats have been considered. In general, the introduction of biogas technology is a very promising solution for the agricultural sector. Taking into account that a biogas plant is considered a potentially hazardous object for workers, it is necessary to constantly monitor the parameters of reactor operation in order to ensure the technological and environmental safety of the engineering facilities. For Ukraine, there is a shortage of specialists to set up an effective operation of biogas equipment and bring it to the industrial scale. It is necessary to consult with medium and small farms interested in the feasibility study and implementation of biogas technologies. 

Biogas production via anaerobic digestion is an established and robust technology that produces energy and recycles nutrients. Several biotechnological attempts have been applied to this process to increase biogas production, including adding nanoparticles, but several discrepancies have been reported. To elucidate the contradictory results, we performed a literature review followed by a meta-analysis to evaluate the effect of adding natural nanoparticles to biogas sludge. Our results showed that adding nanoparticles can increase biogas production by up to two orders of magnitude. Considering that, we attribute these results to variability in the nanoparticles applied, leading to less reliable, consistent, and even contradictory results. We observed that the magnetite nanoparticles are the most tested ones with the most promising positive effects. In addition, we observed that concentrations of nanoparticles higher than 100 mg/L can have adverse effects, with an overall decrease in biogas production. The findings in this study highlight the need for a proper characterization of the nanomaterials type and concentration applied to the process to understand the interactions and effects on the microbial communities and dynamics that lead to an overall increase or decrease in biogas yield.

Background: This study examines the destiny of macromolecules in different full-scale biogas processes. From previousstudies it is clear that the residual organic matter in outgoing digestates can have significant biogas potential,but the factors dictating the size and composition of this residual fraction and how they correlate with the residualmethane potential (RMP) are not fully understood. The aim of this study was to generate additional knowledge of thecomposition of residual digestate fractions and to understand how they correlate with various operational and chemicalparameters. The organic composition of both the substrates and digestates from nine biogas plants operating onfood waste, sewage sludge, or agricultural waste was characterized and the residual organic fractions were linked tosubstrate type, trace metal content, ammonia concentration, operational parameters, RMP, and enzyme activity.

Results: Carbohydrates represented the largest fraction of the total VS (32–68%) in most substrates. However, inthe digestates protein was instead the most abundant residual macromolecule in almost all plants (3–21 g/kg). Thedegradation efficiency of proteins generally lower (28–79%) compared to carbohydrates (67–94%) and fats (86–91%).High residual protein content was coupled to recalcitrant protein fractions and microbial biomass, either from thesubstrate or formed in the degradation process. Co-digesting sewage sludge with fat increased the protein degradationefficiency with 18%, possibly through a priming mechanism where addition of easily degradable substrates alsotriggers the degradation of more complex fractions. In this study, high residual methane production (> 140 L CH4/kgVS) was firstly coupled to operation at unstable process conditions caused mainly by ammonia inhibition (0.74 mgNH3-N/kg) and/or trace element deficiency and, secondly, to short hydraulic retention time (HRT) (55 days) relative tothe slow digestion of agricultural waste and manure.

Conclusions: Operation at unstable conditions was one reason for the high residual macromolecule content andhigh RMP. The outgoing protein content was relatively high in all digesters and improving the degradation of proteinsrepresents one important way to increase the VS reduction and methane production in biogas plants. Post-treatment

During the process of pulp- and papermaking, large volumes of fibre-rich primary sludge are generated. Anaerobic digestion of primary sludge offers a substantial potential for methane production as an alternative approach to the inefficient energy recoveries by commonly used incineration techniques. However, a systematic study of the importance of upstream process techniques for the methane potential of pulp fibres is lacking. Therefore, biochemical methane potentials were determined at mesophilic conditions for 20 types of fibres processed by a variety of pulping and bleaching techniques and from different raw materials. This included fibres from kraft, sulphite, semi-chemical, chemical thermo-mechanical (CTMP) and thermo-mechanical pulping plants and milled raw wood. The pulping technique was clearly important for the methane potential, with the highest potential achieved for kraft and sulphite fibres (390–400 Nml CH4 g VS− 1 ). For raw wood and CTMP, hardwood fibres gave substantially more methane than the corresponding softwood fibres (240 compared to 50 Nml CH4 g VS− 1 and 300 compared to 160 Nml CH4 g VS− 1 , respectively). Nuclear magnetic resonance characterization of the organic content demonstrated that the relative lignin content of the fibres was an important factor for methane production, and that an observed positive effect of bleaching on the methane potential of softwood CTMP fibres was likely related to a higher degree of deacetylation and improved accessibility of the hemicellulose. In conclusion, fibres from kraft and sulphite pulping are promising substrates for methane production irrespective of raw material or bleaching, as well as fibres from CTMP pulping of hardwood.

Kraft fibre sludge from the pulp and paper industry constitutes a new, widely available substrate for thebiogas production industry, with high methane potential. In this study, anaerobic digestion of kraft fibresludge was examined by applying continuously stirred tank reactors (CSTR) with sludge recirculation.Two lab-scale reactors (4L) were run for 800 days, one on fibre sludge (R1), and the other on fibre sludgeand activated sludge (R2). Additions of Mg, K and S stabilized reactor performance. Furthermore, theCa:Mg ratio was important, and a stable process was achieved at a ratio below 16:1. Foaming was abatedby short but frequent mixing. Co-digestion of fibre sludge and activated sludge resulted in more robustconditions, and high-rate operation at stable conditions was achieved at an organic loading rate of 4 gvolatile solids (VS) L1 day1, a hydraulic retention time of 4 days and a methane production of230 ± 10 Nm L per g VS.

With the final aim of reducing the energy consumption and increase the methane production at Swedish pulp and paper mills, the methane potential of 62 wastewater effluents from 10 processes at seven pulp and/or paper mills (A-G) was determined in anaerobic batch digestion assays. This mapping is a first step towards an energy efficient and more sustainable utilization of the effluents by anaerobic digestion, and will be followed up by tests in lab-scale and pilot-scale reactors. Five of the mills produce kraft pulp (KP), one thermo-mechanical pulp (TMP), two chemical thermo-mechanical pulp (CTMP) and two neutral sulfite semi-chemical (NSSC) pulp. Both elementary and total chlorine free (ECF and TCF, respectively) bleaching processes were included. The effluents included material from wood rooms, cooking and oxygen delignification, bleaching (often both acid- and alkali effluents), drying and paper/board machinery as well as total effluents before and after sedimentation. The results from the screening showed a large variation in methane yields (percent of theoretical methane potential assuming 940 NmL CH4 per g TOC) among the effluents. For the KP-mills, methane yields above 50% were obtained for the cooking effluents from mills D and F, paper machine wastewater from mill D, condensate streams from mills B, E and F and the composite pre-sedimentation effluent from mill D. The acidic ECF-effluents were shown to be the most toxic to the AD-flora and also seemed to have a negative effect on the yields of composite effluents downstream while three of the alkaline ECF-bleaching effluents gave positive methane yields. ECF bleaching streams gave higher methane yields when hardwood was processed. All TCF-bleaching effluents at the KP mills gave similar degradation patterns with final yields of 10-15% of the theoretical methane potential for four of the five effluents. The composite effluents from the two NSSC-processes gave methane yields of 60% of the theoretical potential. The TMP mill (A) gave the best average yield with all six effluents ranging 40-65% of the theoretical potential. The three samples from the CTMP process at mill B showed potentials around 40% while three of the six effluents at mill G (CTMP) yielded 45-50%.

Increased viscosity and the presence of extracellular polymeric substances (EPS) and soluble microbial products (SMP) are important factors that may negatively affect wastewater treatment processes, e.g. foaming, inefficient mixing or poor dewatering. Many industries, including the pulp and paper industry, are running their production processes at shifting conditions, leading to large variations in wastewater composition to downstream treatments. The aim of this study was to investigate how changes in organic loading rate (OLR) and hydraulic retention time (HRT) affect the viscosity and production of EPS and SMP during anaerobic digestion of pulp and paper mill sludge. Two lab-scale continuous stirred tank reactors (CSTRs) were operated for 800 days at 37⁰C. The OLR was increased and the HRT was decreased in steps. Reactor fluid was sampled once a month for rheological characterization and analysis of EPS and SMP.

Our results demonstrated a clear positive correlation between viscosity and the production of EPS and SMP. OLR, magnesium and potassium were important for EPS and SMP formation and the protein fraction of SMP was negatively correlated to HRT and sludge retention time. The production of EPS and SMP was important in foam formation and sludge bulking, either directly through their surface-active properties, or indirectly by increasing the viscosity. Sludge bulking was avoided by more frequent mixing. In conclusion, rheological measurements and estimates of EPS and SMP contents could prove valuable tools to avoid the severe consequences of sludge bulking and foaming in full-scale applications.

Society is largely moving into electric mobility to achieve net -zero emissions, with the choice of electrification as the sole viable option for decarbonizing personal road transport. While this perspective has some merits, it overlooks the potential of biomethane produced through anaerobic digestion (AD) as a carbon -negative solution. Biomethane from AD offers not only carbon -neutrality but the possibility of being carbon -negative, with estimates suggesting it could provide 10 % of the world 's primary energy consumption by 2050. AD provides socio-environmental advantages, including improved quality of life and employment opportunities, a particularly relevant topic in developing countries. The technology is mature, cost-effective, and applicable across various sectors and therefore it is imperative that it is considered as an alternative or complementation to electrification of road transport.

Background: This paper gives insight into whether biofuels for road transport can play an important role in a Swedish county in the year 2030, and contributes to knowledge on how to perform similar studies.

Methodology: A resource-focused assessment, including feedstock from the waste sector, agricultural sector, forestry sector and aquatic environments, partially considering technological and economic constraints.

Results: Two scenarios were used indicating that biofuels could cover almost 30 and 50%, respectively, of total energy demand for road transport.

Conclusion: Without compromising food security, this study suggests that it is possible to significantly increase biofuel production, and to do this as an integrated part of existing society, thereby also contributing to positive societal synergies.

Connectedness through cooperation with other sectors regarding feedstock, energy, products and by-products is important for environmental performance of industrial production. The aim of this study is to provide a better understanding of the level of connectedness in the Swedish biofuels for transport industry, involving producers of ethanol, biogas and biodiesel. In interviews, the CEOs of four important companies provided information about current strategies, historic and planned development. The production systems are dynamic and have changed significantly over time, including material and energy exchanges between traditionally separate industries. Interesting development was noted where revised business strategies have led to changed cooperation structures and thus altered material and energy flows. Fuel and raw material prices are very influential and all of the respondents said that political decisions to a large extent affect their competitiveness and emphasised the importance of clear long-term institutional conditions, ironically very much in contrast to the current situation within EU and Sweden.

Recycling and reducing household waste are political goals internationally, nationally and locally. In Sweden, households in apartment buildings seem to sort their waste to a lesser extent than households in single-family houses. This paper analyses the challenges of the diffusion of a new waste management system in apartment buildings, and focuses on a municipal housing company and the actions of its area managers. It is argued that area managers can be regarded as street-level bureaucrats who act as collectors of tenants everyday practices in the studied implementation process. The study is based on interviews, document analysis and observations.

In this article, the development of biogas for transport in the municipality of Linköping, Sweden, is studied in order to contribute to a better understanding of the conditions for socio-technical transitions towards sustainability. Linköping municipality, 1976 [kommunfullmäktige] Motion om utredning angående eldrivna fordon. Dnr 1976.278. Using concepts from multi-level perspectives and socio-technical perspectives on system builders, the study focuses on three time periods: During the first time period (1976–1994), a niche for biogas developed amongst dedicated actors in small networks representing energy and public transport within the municipality. That is, biogas was entirely connected to the vision of a ‘green’ public transport. Second, between the years of 1994 and 2001, the biogas producing company acted as a system builder and initiated a large-scale biogas production through close cooperation in networks with other actors. As a result, biogas reached a phase of technological maturity and also gained some support from national investment programs. Finally, from 2001 the expansion of biogas became clearer as the biogas production spread into a regional arena but also reached for new customers, like personal cars. Unforeseen spin-offs like the formation of new private companies and development of research were important results of the transition. Thereby, the transition is a move towards a new socio-technical regime. A conclusion from the study is that the development of biogas was highly influenced by national support and pressure, but was mainly driven by local actors – system builders – that could steer the processes and had endurance as well as capability to mobilize resources in order to fulfill their purposes.

The anaerobic digestion of food waste can not only enhance the treatment of organic wastes, but also contributes to renewable energy production and the recirculation of nutrients. These multiple benefits are among the main reasons for the expansion of biogas production from food waste in many countries. We present methodological insights and recommendations on assessing the environmental and economic performance of these systems from a life-cycle perspective. We provide a taxonomy of the value chain of biogas from food waste which describes major activities, flows, and parameters across the value chain with a relatively high detail. By considering the multiple functions of biogas production from food waste, we propose a few key performance indicators (KPI) to allow comparison of different biogas production systems from the perspectives of climate impact, primary energy use, nutrients recycling, and cost. We demonstrate the operational use of our method through an example, where alternatives regarding the heat supply of the biogas plant are investigated. We demonstrate how global and local sensitivity analyses can be combined with the suggested taxonomy and KPIs for uncertainty management and additional analyses. The KPIs provide useful input into decision-making processes regarding the future development of biogas solutions from food waste. (C) 2020 Elsevier Ltd. All rights reserved.

As a result of rapid development in China and the growth of megacities, large amounts of organic wastes are generated within relatively small areas. Part of these wastes can be used to produce biogas, not only to reduce waste-related problems, but also to provide renewable energy, recycle nutrients, and lower greenhouse gases and air polluting emissions. This article is focused on the conditions for biogas solutions in Guangzhou. It is based on a transdisciplinary project that integrates several approaches, for example, literature studies and lab analysis of food waste to estimate the food waste potential, interviews to learn about the socio-technical context and conditions, and life-cycle assessment to investigate the performance of different waste management scenarios involving biogas production. Xiaoguwei Island, with a population of about 250,000 people, was chosen as the area of study. The results show that there are significant food waste potentials on the island, and that all studied scenarios could contribute to a net reduction of greenhouse gas emissions. Several socio-technical barriers were identified, but it is expected that the forthcoming regulatory changes help to overcome some of them.

In the transition towards fossil-free transports, there is an increasing interest in upgraded biogas, or biomethane, as a vehicle fuel. Liquefied biogas has more than twice as high energy density as compressed biogas, which opens up the opportunity for use in heavy transports and shipping and for more efficient distribution. There are several ways to produce and distribute compressed and liquefied biogas, but very few studies comparing them and providing an overview. This paper investigates the energy balance, environmental impact and economic aspects of different technologies for upgrading, liquefaction and distribution of biogas for use as a vehicle fuel. Furthermore, liquefaction is studied as a method for efficient long-distance distribution.

The results show that the differences between existing technologies for upgrading and liquefaction are small in a well-to-tank perspective, especially if the gas is transported over a long distance before use. Regarding distribution, liquefaction can pay back economically after 25–250 km compared to steel container trailers with compressed gas, and reduce the climate change impact after 10–30 km. Distribution in gas grid is better in all aspects, given that it is available and no addition of propane is required. Liquefaction can potentially expand the geographical boundaries of the market for biogas as a vehicle fuel, and cost reductions resulting from technology maturity allow cost-effective liquefaction even at small production capacities.

The heavy transport sector is facing a growth within technology and infrastructure for use of natural gas. This opens an opportunity for the biogas market to grow as well, especially in the form of liquefied biogas (LBG). This study presents an investigation of the energy balance, environmental impact and economic aspects of current technologies for production of LBG: mixed refrigerant cycle, nitrogen cycle, pressure reduction and cryogenic liquefaction. Calculations are based on a review of recent literature and data from the biogas industry. The results show that mixed refrigerant cycle is the most economic and energy efficient technology for liquefaction of upgraded biogas, followed by nitrogen cycle. The lowest electricity use and environmental impact is achieved if the liquefaction process is preceded by amine scrubber upgrading. Pressure reduction liquefaction is inexpensive and can be an alternative in areas connected to a high-pressure gas grid, but as a method for liquefaction it is not very efficient as only about 10% of the incoming gas is liquefied and the rest remains in its gaseous form. Moreover, addition of propane for distribution in the natural gas grid increases the environmental impact compared to other distribution pathways. The cryogenic technology has a higher energy use than other liquefaction technologies but compensates by also including CO₂ separation, which could make it suitable if there is no existing upgrading facility in place. However, there are technical difficulties to overcome and it is not widely implemented.

Several previous studies reported stimulatory effects on biogas process performance after trace metal supplementation. However, the regulation of the bioavailability in relation to chemical speciation, e.g. the role of sulfide is not fully understood. The objective of the present study was to determine the effect of sulfide on chemical speciation and bioavailability of Co and Ni in lab-scale semicontinuous stirred biogas tank reactors treating stillage. The chemical forms and potential bioavailability of Co and Ni were studied by sequential extraction, analysis of acid-volatile sulfide (AVS), and simultaneously extracted metals. The results demonstrated that Ni was completely associated to the organic matter/sulfide fraction and AVS, suggesting low potential bioavailability. Cobalt was predominantly associated to organic matter/sulfide and AVS, but also to more soluble fractions, which are considered to be more bioavailable. Process data showed that both Co and Ni were available for microbial uptake. Although the actual bioavailability of Co could be explained by association to more bioavailable chemical fractions, the complete association of Ni with organic matter/sulfides and AVS implies that Ni was taken up despite its expected low bioavailability. It was concluded that extensive Co- and Ni-sulfide precipitation did not inhibit microbial uptake of Co and Ni in the reactors.

Addition of Co and Ni often improves the production of biogas during digestion of organic matter, i.e. increasing CH4-production, process stability and substrate utilization which often opens for higher organic loading rates (OLRs). The effect of Co and Ni addition was evaluated by measuring methane production, volatile solids reduction, pH and concentration of volatile fatty acids (VFAs). A series of six lab-scale semi-continuously fed biogas tank reactors were used for this purpose. The chemical forms and potential bioavailability of Co and Ni were examined by sequential extraction, acid volatile sulfide extraction (AVS) and simultaneously extracted metals. Furthermore, the sulfur speciation in solid phase was examined by sulfur X-ray absorption near edge structure spectroscopy. The effect of Co and Ni deficiency on the microbial community composition was analyzed using quantitative polymerase chain reaction and 454-pyrosequencing. The results showed that amendment with Co and Ni was necessary to maintain biogas process stability and resulted in increased CH4-production and substrate utilization efficiency. 10-20% of the total Co concentration was in dissolved form and should be regarded as easily accessible by the microorganisms. In contrast, Ni was entirely associated with organic matter/sulfides (mainly AVS) and regarded as very difficult to take up. Still Ni had stimulatory effects suggesting mechanisms such as dissolution of NiS to be involved in the regulation of Ni availability for the microorganisms. The microbial community structure varied in relation to the occurrence of Ni and Co. The acetate-utilizing Methanosarcinales dominated during stable process performance, i.e. when both Co and Ni were supplied, while hydrogenotrophic Methanomicrobiales increased together with VFA concentrations under Co or Ni deficiency. The increase was more pronounced at Co limitation. This study demonstrates that there are good possibilities to improve the performance of biogas processes digesting sulfur-rich substrates by supplementation of Co and Ni.

Policy integration between autonomous policy sectors is a tool for managing interdependent technical systems to avoid suboptimization. Biogas, regarded as a renewable energy carrier usable in the energy and transport systems, is produced from organic material such as municipal organic waste (MOW). It is connected to a number of systems and policy sectors, making biogas management an instructive case for studying policy integration processes. Swedish biogas production has increased in recent years, and in the Stockholm region there has been enormous interest in biogas production for vehicle use since the early 2000s. In this paper biogas will be discussed in the perspective that it is or has potential to be a vital part of three systems: waste, energy, and transportation. The aim is to analyse whether policy integration occurs between the systems and to explore if boundary objects can play a role when understanding policy integration processes. In examining the biogas development process, regional policy documents and interviews with stakeholders in the biogas process are used. The results indicate consensus among regional actors that biogas should be used in vehicles and that MOW should be collected for this purpose, indicating congruence of understanding of biogas. Biogas functions as a boundary object in these cases and contributes to high policy integration between the energy and waste systems. Despite consensus that biogas should be used in the transport system, there is little policy integration between the energy and transport sectors. The policy sectors of transport infrastructure and spatial planning are not concerned with fuel or biogas issues. Public transport policy focuses on the use of biogas for their vehicles, but even if biogas serves as a boundary object it is not developing into policy integration processes. The conclusion is that biogas development has resulted in integrated policymaking between the energy and waste sectors and biogas has served as a strong boundary object which has spurred that development. Between the energy and transport sectors there is little policy integration, and biogas is not a boundary object in the cases of transport infrastructure and spatial planning policy sectors. What this case shows is that if there is a lack of presence of a boundary object it suggests no preconditions for policy integration processes to start.

Biogas production through anaerobic digestion may play an important role in a circular economy because of the opportunity to produce a renewable fuel from organic waste. However, the production of biogas may require energy in the form of heat and electricity. Therefore, resource-effective biogas production must consider both biological and energy performance. For the individual biogas plant to improve its energy performance, a robust methodology to analyse and evaluate the energy demand on a detailed level is needed. Moreover, to compare the energy performance of different biogas plants, a methodology with a consistent terminology, system boundary and procedure is vital. The aim of this study was to develop a methodology for analysing the energy demand in biogas plants on a detailed level. In the methodology, the energy carriers are allocated to: (1) sub-processes (e.g., pretreatment, anaerobic digestion, gas cleaning), (2) unit processes (e.g., heating, mixing, pumping, lighting) and (3) a combination of these. For a thorough energy analysis, a combination of allocations is recommended. The methodology was validated by applying it to two different biogas plants. The results show that the methodology is applicable to biogas plants with different configurations of their production system.

There are several ways to improve biogas production in anaerobic digestion processes and a number of strategies may be chosen. Increased organic loading in existing plants will in most cases demand the introduction of new substrate types. However, to substantially increase the Swedish biogas production new, large-scale biogas plants digesting new substrate types need to be established.

Better utilization of existing digester volumes can be linked to: 

• Increase of organic loading rates and/or reduced hydraulic retention time
• Optimizing the anaerobic microbial degradation by identifying rate-limitations, its causes and possible remedies such as:
• Nutrient and trace element balances
• Needs and availability of trace element
• Process design aiming at an increase of the active biomass (e.g. recirculation of reactor material, two stage processes)
• Process inhibition (enzymatically regulated product inhibition and toxicity)
• Improved pre-treatment to increase degradation rates and VS-reduction
• Mixing and rheology
• Better monitoring and control
• Co-digestion with more high-potential substrates

The present report reviews a number of fields that are linked to improvements in the biogas production process as based on the bullets above.

A well-working, active biomass is a prerequisite for efficient biogas production processes, why factors affecting microbial growth are crucial to obtain stable processes at the highest possible organic load/lowest possible hydraulic retention time.

The microorganisms need nutrients, i.e. carbon, nitrogen, phosphorus, calcium, potassium, magnesium and iron as well as trace elements such as cobalt, nickel, manganese, molybdenum, selenium and tungsten for growth. The need of nutrients and trace elements varies with the substrate digested, the organic loading rate, the process design (e.g. the reactor configuration, the degree of recirculation etc). In addition, the complexity of the chemical reactions controlling the bioavailability of the trace metals is wide, why optimal addition strategies for trace elements needs to be developed.

Substrates as food wastes, sewage sludge, cattle manure, certain energy crops and algae are good bases to obtain processes with good nutrient- and trace element balances. These kinds of substrates can often be implemented for “mono-substrate” digestion, while substrates dominated by carbohydrates or fats needs to be co-digested or digested in processes modified by  e.g. nutrient- and trace element additions, sludge recirculation, etc. Protein-rich substrates often include enough nutrients, but can give other process problems (see below).

Iron, cobalt and nickel are the nutrients/trace elements given most attention so far. However, molybdenum, selenium and tungsten have also, among others, been shown effective in different AD applications. The effects have, however, mainly been shown on turnover of VFAs and hydrogen (resulting in increased methane formation), while just a few studies have addressed their direct effect on rates of hydrolysis, protein-, fat- and carbohydrate degradation. Selenium- and cobalt-containing enzymes are known to be involved in amino acid degradation, while selenium and tungsten are needed in fat- and long chain fatty acid degradation. Enzymes active in hydrolysis of cellulose have been shown to be positively affected by cobalt, cupper, manganese, magnesium and calcium. This implies that trace element levels and availability will directly affect the hydrolysis rates as well as rates and degradation pathways for digestion of amino acids, long chain fatty acids and carbohydrates. However, their effect on hydrolysis seems neglected, why studies are needed to map the metals present in active sites and co-factors of enzymes mediating these primary reactions in AD. Further investigations are then needed to elucidate the importance of the identified metals on the different degradation steps of AD aiming at increased degradation rates of polymeric and complex substrates. It should also be noted that the degradation routes for amino acid degradation in AD-processes, factors governing their metabolic pathways, and how ATP is gained in the different pathways seem unknown. The different routes may result in different degradation efficiencies, why a deeper knowledge within this field is called for.

Trace metals added to biogas reactors have positive effects on the process only if they are present in chemical species suitable for microbial uptake. Interaction of biogenic sulfide with trace metals has been identified as the main regulator of trace metal speciation during AD. Fe, Co and Ni instantaneously form strong sulfide precipitates in biogas reactors but at the same time show very different chemical speciation features. The soluble fraction of Co widely exceeded the levels theoretically possible in equilibrium with inorganic sulfide. The high level of soluble Co is likely due to association with dissolved organic compounds of microbial origin. Fe and Ni speciation demonstrated a different pattern dominated by low solubility products of inorganic metal sulfide minerals, where their solubility was controlled mainly by the interactions with different dissolved sulfide and organic ligands. To our knowledge, the information about chemical speciation of other trace metals (Se, Mo, and W among others) and its effects on the bioavailability in anaerobic digestion environments is rare. Providing information on the metal requirements by processes linked to their bioavailability in biogas reactors is identified as a key knowledge needed for maximizing the effect of metals added to biogas reactors. Further research is also needed for development and design of proper metal additive solutions for application in full scale biogas plants. A practical approach is to supplement trace metals in specific chemical forms, which are either suitable for direct bio-uptake or will hamper undesirable and bio-uptake-limiting reactions (e.g. mineral precipitation).

Recirculation of reactor material as a way to enrich and maintain an active microbial biomass (and, thus, an increase in the substrate turnover rate) in tank reactors has been tested for digestion of fat within BRCs project DP6. The methane yield increased from 70 to 90% of the theoretical potential at a fat-loading rate of 1.5 g VS/L and day. The same strategy has been successful during digestion of fiber sludge from the pulp and paper industry, i.e. the recirculation has been crucial in establishment of low hydraulic retention times. Also degradation of sewage sludge (SS) would likely be improved by recirculation as the retention time of the solid SS is prolonged in such a system. However, this remains to be tested. The recirculation concept also needs to be evaluated in larger scale reactors to form a base to include extra costs and energy consumption vs. the benefits from increased yields.

To divide the anaerobic digestion process into two phases, where the hydrolytic/acidogenic and the syntrophic/methanogenic stages of anaerobic digestion are separated, might be a way to enhance degradation of lignocellulosic materials as the hydrolysis of these compounds may be inhibited by the release of soluble sugars. It should be noted that the natural AD of ruminates is phase-separated and improvements in AD can likely be achieved using these natural systems as a starting point. Also the degradation of aromatic and chlorinated species is likely enhanced by phase separation. One way to obtain such systems is to combine a leached bed for hydrolysis of insoluble material with a methanogenic reactor treating the leachate. Plug flow reactors might be another possibility as well as membrane reactors, which physically separates the hydrolyzing and methanogenic phases.

Inhibition caused by toxic levels of ammonia (protein- and ammonia rich substrates), fat-rich substrates and long chain fatty acids (LCFAs), aromatic compounds, salts etc. have been reported in many cases and some remedies are suggested. Ammonia can be stripped off as a measure to overcome too high levels. Another option is to adjust pH of the reactor liquid by addition of acid shifting the ammonia-ammonium balance in the system towards less free ammonia. A decrease in alkalinity by acid addition might also affect the availability of trace elements as solubility of trace metal mineral phases is generally higher at lower pH. LCFA degradation has been shown to benefit from periodic additions of fat and is, thus, an effective strategy to minimize inhibition by the release of the LCFA. Adsorption to zeolites has also been shown to abate the inhibition by LCFA. The best way to avoid inhibition is, however, to keep the processes nutritionally well balanced and using concepts suitable for the actual substrate mix digested (i.e. sludge recirculation, phase separation etc.) in order to obtain the highest possible degradation rate for problematic compounds, thus, avoiding accumulation of inhibitory components such as LCFA and aromatics. High ammonia and salt levels can often be regulated by the substrate mix.

The hydrolysis is often reported as rate limiting in digestion of complex polymers in balanced anaerobic digestion systems, while the methanogensis is regarded as rate-limiting for more easily degraded substrates. As mentioned above the effect on methane formation rates by the addition of trace elements have been shown in numerous studies, while their effect on the hydrolysis and acidogenic AD steps are much less studied. Thus, the effects of the trace elements on the early steps in the AD-chain need to be investigated further.

To obtain high-rate hydrolysis, effective and energy efficient pre-treatment methods are crucial for a large number of substrates. The rate of hydrolysis is to a large extent dependent on the properties of the organic compounds in the substrate e.g. carbohydrates, proteins, fat or lignocellulosic material as well as particle size and pre-treatment methods applied. The establishment and colonization by sessile microorganisms and biofilms is highly important for efficient and high rate hydrolysis. Microbial formation of organic compounds and the availability of surfaces are factors influencing these key processes, which in turn are tightly coupled to the growth conditions for the hydrolyzing microorganisms. This is an area recently brought up as an issue for detailed research.

Mixing is mostly needed for effective high-rate biogas production, but too extensive mixing can destroy the syntrohpic interactions necessarily taking place during AD. However, the efficiency of the mixing system design in relation to colonization, presences of dead zones, changes in viscosity/rheology, etc. seem unclear and this area thus calls for further attention. 

In high-loaded efficient processes a monitoring program following parameters e.g. organic loading rate, gas-production, VS-reduction, pH and VFA-levels is needed. This can be achieved through sampling and analysis off line, but there are of course benefits with on-line monitoring. A number of different methods have been suggested and tested, and some titration- and spectroscopic methods are applied, but none seems commonly in use. The reasons for the low interest to apply these methods may be the need for expertise on calibration, validation and multivariate analysis of most on-line methods, high maintenance demands (cost and time), and l functional problems related to fouling, gas bubbles, sensor location, disturbing particles etc.

New substrates with the highest potential for use in existing or new biogas plants seem to be forestry-based biomass, certain energy crops and macro-algae. Both the energy crops and the macro-algae can be chosen to give nutritionally well balanced AD-processes, while AD on forestry biomass demands nutrient supplements. For both the energy crops and the macro-algae sustainable cultivation systems need to be developed. Crop rotation systems should be employed to minimize tillage as well as fertilization- and pesticide utilization at highest possible TS-yields. System analyses aiming at sustainability and economy of TS and methane yields per ha including needs of nutrient supplements should therefore be performed.

In all three cases (forestry biomass, energy crops and algae) pre-treatment methods to create high internal surface areas are needed. However, the pre-treatment methods chosen need to be highly energy- and resource efficient to obtain sustainable systems (a positive energy balance). New plants will for profitability likely need to be large with highly developed infrastructure for substrates supply and distribution of the produced biogas/electricity nearby. Process concepts aiming at highest possible loading rates at shortest possible retention time will be needed, which likely are met by including both phase-separated process systems and systems for sludge recirculation.

It should also be noted that the lignin in substrates from forestry biomass needs to be used for production of e.g. polymeric materials or as a fuel to obtain reasonable energy balances for AD of lignocellulose. Pre-treatment methods obtaining separation of lignin is therefore needed. A substantial research and development is in progress within this field.

The possibilities for AD within the pulp and paper industry are interesting, especially if specific effluents within the pulp- and paper production units are selected and the raw material for the pulp and paper production is chosen considering the biogas yields of the residues.

In BRC EP3 focus has been on new industries. The goal has been to find some new industries where biogas production is a resource‐efficient way to take advantage of material flows that are not used today. From this goal seven activities were formulated and are in short: (A1) Present biogas solutions, (A2) Overview of new industrial sectors in Sweden regarding biogas production, (A3) Possibilities and impossibilities process‐wise, (A4) Energy and environmental impacts, (A5) Societal aspects, (A6) Selection of case studies, and (A7) Case study design. These activities needed different angles of approach and therefore a variety of methods were used in the project, e.g. literature studies, calculations, measurements, interviews and workshops. The results from the activities are presented in short below.

A1: International comparison of biogas production at industrial sites, for example, is impossible to carry out as different classifications are used in different countries. In A1 a way to categorize biogas plants is proposed and discussed.

A2: By screening and geographically pin‐pointing the food industry, eight clusters were chosen for deeper studies. A mapping of biogas potential was thereafter carried out in these clusters. The activity shows great potentials for some of the clusters regarding biogas production.

A3: Process‐related feasibility for opportunities for the clusters studied in A2 is targeted. The general conclusion is that there are no severe aspects that imply that one should not continue working with a specific cluster or a specific substrate found in those clusters, regarding biogas production.

A4: Each cluster found in A2 is assessed in terms of environmental aspects (climate, acidification and eutrophication), energy balance and economy, which were found being the most important assessment criteria when it comes to efficient biogas solutions. The results show, for example, that even though some of the clusters hold a large potential for biogas production some of these clusters do not imply profitable solutions or environmental advantages compared to the present situation of using the substrates. Moreover, the study shows that the end use of the biogas (electricity, heat and vehicle fuel) has significant influence on the results. It is shown that each cluster has a unique combination of substrates and unique alternatives for use of both substrates and produced biogas, implying different beneficial solutions. Sometimes the beneficial solutions differ dependent on what assessment criterion used.

A5: Societal aspects were explored for each cluster found in A2. It is shown that there are differences between the clusters regarding institutional and organizational prerequisites. Important areas have been identified on both a national level (e.g. taxes) and regional level (e.g. cooperation between public and private sectors).

A6: When selecting case studies it is found that the following aspects needs to be considered: (1) biogas potential, (2) character of substrates and other materials, (3) environmental aspects (climate, acidification and eutrophication), (4) influence on energy balances (5) economy, (6) use of biogas, and (7) societal aspects.

A7: When designing case studies the same aspects as for A6 applies. However, when designing the case study it is also vital to consider where to put the system border and also consider the localization of the production unit (e.g. internal at a company or detached).

Moreover, integration of biogas solutions with other types of material or energy flows has to be considered.

All the stated parts in “Motivation and aim” are addressed in the project. Consequently, the target of the project is achieved.

The Swedish pulp and paper industry is the third largest exporter of pulp and paper products worldwide. It is a highly energy-demanding and water-utilising industry, which generates large volumes of wastewater rich in organic material. These organic materials are to different extents suitable for anaerobic digestion (AD) and production of energy-rich biomethane. The implementation of an AD process within the wastewater treatment plant of a mill would increase the treatment capacity and decrease the overall energy consumption due to less aeration and lower sludge production and in addition produce biomethane. Despite the many benefits of AD it is only applied at two mills in Sweden today. The reason for the low implementation over the years may be due to problems encountered linked to the complexity and varying composition of the wastewaters. Due to changes in market demands many mills have broadened their product portfolios and turned towards more refined products. This has increased both the complexity and the variations of the wastewaters´ composition even further, as the above changes can imply an increased pulp bleaching and utilisation of more diverse raw materials within the mills.

The main aim of this thesis was therefore to generate knowledge needed for an expansion of the biomethane production within the pulp and paper industry. As a first step to achieve this an evaluation of the biomethane potential and the suitability for AD of wastewaters within a range of Swedish pulp and paper mills was performed. Thus, around 70 wastewater streams from 11 different processes at eight mills were screened for their biomethane potential. In a second step, the impact of shifts in wood raw material and bleaching on the AD process and the biomethane production was investigated and further evaluated in upflow anaerobic sludge bed (UASB) reactors.

The screening showed that the biomethane potential within the Swedish pulp and paper industry could be estimated to 700 GWh, which corresponds to 40% of the Swedish biomethane production during 2014. However, depending on the conditions at each specific mill the strategy for the establishment of AD needs to differ. For mills producing kraft pulp the potential is mainly found in wastewaters rich in fibres, alkaline kraft bleaching wastewaters and methanol-rich condensates. The biomethane potential within thermo-mechanical pulp- (TMP) and chemical thermo-mechanical pulp (CTMP) mills is mainly present in the total effluents after pre-sedimentation and in the bleaching effluents as these holds high concentrations of dissolved organic material. The screening further showed that the raw material used for pulp production is an important factor for the biomethane potential of a specific wastewater stream, i.e. hardwood (HW) wastewaters have higher potentials than those from softwood (SW) pulp production. This was confirmed in the lab-scale UASB reactor experiments, in which an alkaline kraft bleaching wastewater and a composite pulping and bleaching CTMP wastewater were used as substrates. AD processes were developed and maintained stable throughout shifts in wastewater composition related to changes in the wood raw materials between SW and HW for the kraft wastewater and spruce, aspen and birch for the CTMP wastewater. The lower biomethane production from SW- compared to HW wastewaters was due to a lower degradability together with a higher ratio of sulphuric compounds per TOC for the SW case. The impact of shifts between bleached and unbleached CTMP production could not be fully  evaluated in the continuous process mainly due to technical problems. However, due to the large increase in dissolved organic material when bleaching is applied, the potential biomethane production will increase during the production of bleached pulp compared to unbleached pulp. Based on the biomethane potentials obtained for one of the included CTMP mills, their yearly production of biomethane was estimated to 5-27 GWh with the lowest and the highest value corresponding to the production of unbleached spruce pulp vs. bleached birch pulp.

Thus, the results of the investigations presented in this thesis show that the UASBreactor is suitable for AD of wastewaters within the pulp and paper industry. The results also show that challenges related to variations in the organic material composition of the wastewaters due to variations in wood raw materials could be managed. The outcome of the thesis work also imply that the production of more refined products, which may include the introduction of an increased number of raw materials and extended bleaching protocols, could increase the potential biomethane production, especially if the pulp production will make use of more HW.

This study evaluates the biomethane potential of composite pulping and bleaching chemical thermo-mechanical pulp (CTMP) wastewaters in relation to their composition of organic compounds, as well as to their sulphur contents. The biomethane potential was determined in batch experiments and the CTMP wastewaters from production of bleached spruce-, birch- and aspen pulp and unbleached spruce pulp were analysed for dissolved lignin, carbohydrates, wood extractives, acetic acid and total sulphur content. The biomethane potential obtained for the wastewaters ranged from 350 to 670 NmL g TOC^-1 with the highest yield for wastewater from the production of bleached birch CTMP followed by bleached aspen-, bleached spruce- and unbleached spruce CTMP. The main differences in wastewater composition were related to the raw material used for the pulp production, i.e. softwood vs. hardwood. The compounds mainly promoting the biomethane production were acetic acid, xylose, wood extractives, triglycerides and steryl esters, whereas dissolved lignin, sulphur, arabinose, mannose, lignans and free fatty-/resin acids lowered the potential. However, the individual contribution of each variable was not possible to evaluate due to covariations among them.

In this  study we have investigated the role of biogas solutions to support increased resource efficiency on the island Gotland,  including recovery and redistribution of nitrogen (N) and phosphorus (P) within the agricultural sector. First, we  analyzed the potential for  expanding energy and nutrient recovery from organic residues using biogas solutions. Our findings suggest that the biogas production could expand to 165 GWh, from the current 36 GWh (2020), with manure accounting for a potential  110 GWh biogas annually if all were digested. Comparing the nutrients contained in organic feedstock with the crop nutrient demand on Gotland showed that for N the  demand is 2.4 times higher than the supply. In contrast, the calculations showed a 137 tonnes P surplus, with distinct excess areas in the center and southern part of the island.

We then compared scenarios with different numbers (3 - 15) of biogas plants with respect to   efficient nutrient redistribution and transport costs. Spatial constraints for new plants, e.g. need for roads with a certain capacity  and permit issues, were accounted for by  adding local information to a national data set. We identified  104 potential locations (1 km$^2$ grid cells) and used an optimization model to identify the most suitable locations for minimized transport costs. Optimal  (meeting the crop demand with no excess) redistribution of all nutrients contained in the feedstock, as raw digestate from biogas plants, would result in an export of 127 tonnes of P from the island. The model results indicated that if all potential feedstock would be digested in three additional biogas plants and nutrients redistributed for optimal reuse, the total transport  cost would be 2.6 million SEK annually, excluding the costs for nutrient export from the island (3.7 million SEK). If instead 10 or 15 smaller plants would be built, the transport cost would drop to 1.8  million SEK, with the same amount of P being exported. Comparing the scenarios with different number of biogas plants (3 - 15), showed that some locations are more suitable than others in terms of distance to feedstock and

to fields with fertilizer demands. Finally, a preliminary analysis of the amount of crop residues indicated that this type of feedstock could add a substantial amount of biogas production, but more extensive analyses are needed to assess  the feasibility to realize part of that potential.

Anaerobic digestion of alkaline kraft elemental chlorine-free bleaching wastewater in two mesophilic, lab-scale upflow anaerobic sludge bed reactors resulted in significantly higher biogas production (250 ± 50 vs. 120 ± 30 NmL g [Formula: see text]) and reduction of filtered total organic carbon (fTOC) (60 ± 5 vs. 43 ± 6%) for wastewater from processing of hardwood (HW) compared with softwood (SW). In all cases, the gas production was likely underestimated due to poor gas separation in the reactors. Despite changes in wastewater characteristics, a stable anaerobic process was maintained with hydraulic retention times (HRTs) between 7 and 14 h. Lowering the HRT (from 13.5 to 8.5 h) did not significantly affect the process, and the stable performance at 8.5 h leaves room for further decreases in HRT. The results show that this type of wastewater is suitable for a full-scale implementation, but the difference in methane potential between SW and HW is important to consider both regarding process dimensioning and biogas yield optimization.

BACKGROUND: Chemical thermo-mechanical pulp (CTMP) mills holds a large biomethane potential in their wastewater. Their broadened market has involved increased bleaching and utilisation of different raw materials. Therefore, the main aim of this study was to obtain and maintain a stable anaerobic digestion (AD) process, with a high methane yield and total organic carbon (TOC) reduction, when digesting CTMP wastewater, from different production protocols including shifts in raw material and bleaching. A lab-scale upflow anaerobic sludge bed (UASB) reactor was used for the tests.

RESULTS: The variations in raw material (aspen, birch and spruce) and consequently in TOC-loading (3.6-6.6 kg TOC m^-3 and day^-1) did not affect the UASB process negatively. Methane production values from 360 to 500 NmL g TOC^-1 were obtained, with the highest yield for wastewater from the production of birch- followed by aspenand spruce pulp. The acetic acid and fTOC reduction ranged 90 to 95% and 61 to 73%, respectively.

CONCLUSIONS: The stable process performance maintained during shifts in raw material for pulp production show that AD is feasible for CTMP mills with a diversified product portfolio. Furthermore, the increased use of hardwood and bleaching will most likely increase their potential as a biomethane producer.

Green public procurement can play an important role in reducing the environmental impact of societies. While its uptake is continuously growing, barriers to its use still remain. One barrier previously identified in literature is related to the lack of accessible and easy to use tools that help standardize the development of criteria in green tenders. In this paper, to help overcome this barrier, a method is presented that can be used to develop green public procurement tools that follow previous studies recommendations about including life-cycle assessment-based data and basing procurement criteria on national environmental objectives. The method was then applied to develop a procurement tool for green procurement of public transport services in Sweden based on the Swedish environmental quality objectives. Results from the assessment of 18 pre-defined fuel systems are shown together with an illustrative example of how the tool can be used in the process leading up to procurements to set relevant criteria and during the procurement to adjust incoming tender prices. The results showed that waste-based biomethane and hydrogenated vegetable oil systems were well aligned with the Swedish environmental quality objectives due to being able to contribute positively to several objectives. Crop-based biofuels, on the other hand, performed worse due to negative effects from agricultural practices. The performance of the electric vehicle systems depended in large on how the electricity was generated, where renewable sources and low carbon sources performed better than non-renewable alternatives.