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.

The transition to a circular economy relies on systems that facilitate waste recovery and recirculation of resources. These systems are based on certain enabling technologies. The aim of this paper is to explain how socio-economic structures influence the diffusion of such technologies. It applies a framework built on societal embedding and varieties of capitalism to compare the diffusion of anaerobic digestion (AD) in Sweden in northern Europe and Paraná in southern Brazil. Both Sweden and Paraná have experienced accelerated diffusion of AD, but there are significant differences in the respective diffusion patterns. The comparative analysis points to a tradeoff between system complexity and speed of diffusion. It illustrates how AD can be presented as a solution to various problems, and it further shows how the specific problems that gain attention shape diffusion patterns. By showing how socio-economic structures influence the appointment of problem owners, their agency, and legitimate forms of institutional support, the analysis demonstrates how economic systems condition technology diffusion.

Policy mixes are needed to overcome the different barriers hindering sustainability transitions. This creates the need for policy coherence. Policy coherence studies in sustainability transitions literature are dominated by European cases, limiting their generalizability. This article analyzes policy mixes related to biogas systems and their related coherence issues, and, how that influences biogas production and use in Brazil. We identified policy coherence within and between biogas related sectors and over time, showing how the pre-conditions for biogas production, distribution and use differ considerably between the Brazilian states. This points to a need for decentralized governance structures to enable policy differentiation, as a complement to policy coherence. The article concludes that the characteristics of biogas systems as being locally embedded constitutes a challenge in hierarchical market economies such as Brazil, where policy development, resource mobilization and allocation are highly centralized.

This study analysed to what extent biogas solutions can improve the nutrient recovery of biobased industrial clusters in different sectors. Three cases representing the agricultural, marine and forest sectors were analysed quantitatively using mass flow analysis. Adding a biogas plant facilitated production expansion and development of collaborative waste management, e.g. a wheat processing biorefinery with a mill and agricultural actors, or a pulp and paper mill with the aquaculture industry. In the marine- and forest-based cases, this decreased the total nitrogen (N) and phosphorous (P) input by 18% while increasing the recovery rate; e.g. for P from 32 to 96% for the marine-based and from 52 to 91%, for the forest-based. The impact in the agro-based case was minor as the actors were already operating with a high nutrient recovery. For the marine-based case, the impact was due to a huge increase in P recovery for the aquaculture actor while for the forest-based case, N from the aquacultural sector could be reused in the wastewater treatment. For the agro- and marine-based cases, adding a biogas plant also resulted in less transports and more local nutrient recycling; the total transport of organic waste, by-products and biofertilizers (in km x tonne) was reduced by 40% and 90%, respectively. The results demonstrate that biogas solutions can stimulate the development of biobased industrial symbiosis with integrated waste management, and contribute to more efficient recycling of key resources, which is essential for the transition to a circular society.

This study examined whether the abundance and expression of microbial 16S rRNA genes were associated with elemental concentrations and substrate conversion biokinetics in 20 full-scale anaerobic digesters, including seven municipal sewage sludge (SS) digesters and 13 industrial codigesters. SS digester contents had higher methane production rates from acetate, propionate and phenyl acetate compared to industrial codigesters. SS digesters and industrial codigesters were distinctly clustered based on their elemental concentrations, with higher concentrations of NH3-N, Cl, K and Na observed in codigesters. Amplicon sequencing of 16S rRNA genes and reverse-transcribed 16S rRNA revealed divergent grouping of microbial communities between mesophilic SS digesters, mesophilic codigesters and thermophilic digesters. Higher intradigester distances between Archaea 16S rRNA and rRNA gene profiles were observed in mesophilic codigesters, which also had the lowest acetate utilization biokinetics. Constrained ordination showed that microbial rRNA and rRNA gene profiles were significantly associated with maximum methane production rates from acetate, propionate, oleate and phenyl acetate, as well as concentrations of NH3-N, Fe, S, Mo and Ni. A co-occurrence network of rRNA gene expression confirmed the three main clusters of anaerobic digester communities based on active populations. Syntrophic and methanogenic taxa were highly represented within the subnetworks, indicating that obligate energy-sharing partnerships play critical roles in stabilizing the digester microbiome. Overall, these results provide new evidence showing that different feed substrates associate with different micronutrient compositions in anaerobic digesters, which in turn may influence microbial abundance, activity and function.

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.

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.

Den svenska pappers- och massaindustrin är den tredje största exportören av massa och pappersprodukter och en viktig industriell aktör i Sverige. Det är en industri med hög energi- och vattenanvändning, som genererar stora mängder avloppsvatten rika på organiskt material. Detta organiska material kan via anaerob nedbrytning användas för att producera energirik biometan. Användandet av anaerob behandling, som ett steg i brukens vattenrening, genererar inte bara biometan utan kan också öka reningskapaciteten och minska energiförbrukning och kostnader tack vare minskat behov av luftning och minskad slamproduktion. Trots de många fördelarna med anaerob behandling är den idag bara tillämpad på två bruk i Sverige. En av orsakerna till detta kan vara processproblem som relaterats till avloppsvattnens komplexitet samt varierande sammansättning och flöden. Många pappers- och massabruk har utökat sina produktportföljer med bl a mer förfinade produkter, som en följd av en förändrad marknad. Dessa förändringar har ökat avloppsvattnens komplexitet och variation än mer, då ovan exempelvis kan medföra en ökad produktion av blekt massa samt att fler typer av träråvaror används vid ett och samma bruk.

Huvudsyftet med föreliggande avhandling är att bidra med kunskap för en ökad produktion av biometan inom pappers- och massaindustrin. Som ett första steg genomfördes en övergripande utvärdering av ca 70 avloppsvattenströmmar från totalt 11 olika processer vid åtta svenska pappers- och massabruk med fokus på biometanpotential samt lämplighet för anaerob behandling. I ett andra steg utvärderades hur skiften i träråvara samt blekning påverkar biometanproduktionen samt processtabiliteten för en kontinuerlig anaerob nedbrytningsprocess i en UASBreaktor.

Den initiala utvärderingen visade att den svenska pappers- och massaindustrin skulle kunna bidra med 700 GWh biometan per år, vilket motsvarar 40% av biometanproduktionen i Sverige under 2014. Beroende på utformningen av det enskilda bruket kommer strategier för implementering av anaeroba processer att se olika ut. För bruk som producerar sulfatmassa återfanns huvuddelen av biometanpotentialen i fiberrika avloppsvattenstömmar, alkaliska blekeriavlopp samt metanolrika kondensat. För bruk som producerar termomekanisk- (TMP) eller kemitermomekanisk (CTMP) massa föreligger biometanpotentialen framförallt i avloppsvatten rika på löst organiskt material såsom totalavlopp efter sedimentering och blekeriavlopp. Den initiala utvärderingen visade också att användandet av lövved ger en högre biometanpotential jämfört med barrved. Dessa resultat kunde bekräftas vid kontinuerliga experiment med anaerob nedbrytning i UASB-reaktorer, där ett alkaliskt blekeriavlopp från ett sulfatmassabruk och ett kombinerat massaproduktions- och blekeriavlopp från ett CTMP-bruk användes som substrat. Stabila anaeroba processer etablerades och bibehölls vid förändrad avloppsvattensammansättning på grund av skiften i träråvara (löv- och barrved för sulfatmassabruket samt gran, asp och björk för CTMP bruket). Den lägre produktionen av biometan för barrved jämfört med lövved kunde förklaras med en lägre nedbrytbarhet samt ett ökat svavelinnehåll i relation till mängden organiskt material. Skiften mellan avloppsvatten från blekt- och oblekt CTMP massa kunde inte utvärderas fullständigt i den kontinuerliga processen på grund av tekniska problem. Produktionen av blekt massa ökar dock mängden organiskt material i  avloppsvattnet, vilket medför att mer biometan kan produceras jämfört med då oblekt massa produceras. Baserat på biometanpotentialerna för ett av i studien ingående CTMP bruk uppskattas den årliga produktionen av biometan till 5-27 GWh, där den lägsta produktionen motsvarar oblekt granmassa och den högsta produktionen motsvarar blekt björkmassa.

Sammanfattningsvis visar studien att UASB-reaktorer är lämpliga för anaerob behandling av avloppsvatten inom pappers- och massaindustrin. Vidare visar resultaten från de kontinuerliga försöken att de utmaningar som medförs av den varierande sammansättningen av avloppsvattnens organiska material knutet till träråvaran kan hanteras. Slutligen, breddade produktportföljer samt produktionen av mer förfinade produkter, vilket kan innebära en ökad massablekning och ett ökat användande av olika träråvaror, kan öka brukens potentiella biometanproduktion, särskilt om mer lövved används för massaproduktion.

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 three Scandinavian peatlands we studied to what extent plant and microbial community compositions are governed by local-scale microhabitat, with a special interest in the effect of aspect (i.e. exposition of slopes). Despite differences in solar irradiance between the south- and north-facing slopes, maximum temperature was elevated in the south-facing slopes at the most northern site only. Pore-water nutrient concentrations were not affected by aspect, yet dissolved organic carbon concentrations were higher in the south-facing microhabitats. This was likely caused by higher vascular plant biomass. Plant and microbial community composition clearly differed among sites. In all three sites, microhabitat (i.e. prevailing water-table depth) affected the plant and microbial community compositions. Aspect, however, did not affect community composition, even though microclimate significantly differed between the south- and the north-facing aspects at the northernmost site. Our results highlight the complex link between plant community composition, microbial community and environmental conditions, which deserves much more attention than currently in order to fully understand the effects of climate change on peatland ecosystem function.

The microbial community of 21 full-scale biogas reactors was examined using 454 pyrosequencing of 16S rRNA gene sequences. These reactors included seven (six mesophilic and one thermophilic) digesting sewage sludge (SS) and 14 (ten mesophilic and four thermophilic) codigesting (CD) various combinations of wastes from slaughterhouses, restaurants, households, etc. The pyrosequencing generated more than 160 000 sequences representing 11 phyla, 23 classes, and 95 genera of Bacteria and Archaea. The bacterial community was always both more abundant and more diverse than the archaeal community. At the phylum level, the foremost populations in the SS reactors included Actinobacteria, Proteobacteria, Chloroflexi, Spirochetes, and Euryarchaeota, while Firmicutes was the most prevalent in the CD reactors. The main bacterial class in all reactors was Clostridia. Acetoclastic methanogens were detected in the SS, but not in the CD reactors. Their absence suggests that methane formation from acetate takes place mainly via syntrophic acetate oxidation in the CD reactors. A principal component analysis of the communities at genus level revealed three clusters: SS reactors, mesophilic CD reactors (including one thermophilic CD and one SS), and thermophilic CD reactors. Thus, the microbial composition was mainly governed by the substrate differences and the process temperature.

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%.