According to European Union legislation, a hygienisation step is often required before using digestate or other materials from biogas reactors. The standard hygienisation protocol involves treatment at 70 °C for at least one hour. However, alternative protocols are permitted if they can achieve the reduction targets for specific microorganisms. For thermochemical treatments, the required reduction target is a three-log reduction of the roundworm Ascaris sp. This thermochemical treatment can be applied to the bottom sediment of the reception pit or the reactor in biogas production. The objective of this study was to identify conditions for reducing Ascaris suum to acceptable levels as per legislation, enabling the treated sediment to be spread on arable land and avoiding the costly incineration process. The experiment utilized lime (CaO) and predefined temperatures to increase both the pH and temperature of the sediment. The results indicated that using 5% CaO maintained a stable pH above 12.5, and a 15-minute treatment at 65 °C was sufficient for a three-log reduction of A. suum. These conditions, upon approval, can be adopted as national standard protocols for hygienisation of biogas sediment within the European Union and associated states, and potentially worldwide, depending on local legislation

Biogas and fatty acids produced from agricultural biomasses for industrial use.

The Swedish Industrial Biogas Commission is calling for 10 TWh of biogas/year (via digestion and gasification; by 2030). Current production is about 2 TWh/year, mainly from waste and sludge. The supply of organic waste is not sufficient to produce the required biogas.Agriculture has significant amounts of residual biomass that can be digested (mainly manure and straw). With this fact taken into account, this project report also assumesthat smaller parts of the arable land can be used for growing nitrogen-fixing grass/clover ley for biogas production, perhaps in combination with the production of protein feed for agriculture and fatty acids for industry in a biorefinery concept.It is possible to use manure, straw and ley with smaller amounts of waste in the western part of Sweden (Västra Götaland, Skåne and Halland) to produce 3.5 to 5 TWh of biogas/year in large biogas plants (approx. 100 GWh/plant and year) for use in industry. Co-production of fatty acids and biogas is also possible, e.g. at least 16 plants are needed to cover identified industrial needs.There are good opportunities for Bio-CCS, partly at the biogas plant, when biogas becomes biomethane, and partly in the industry where biomethane is used. Negative emissions possible, corresponding reduction of climate gases when biomethane replaces natural gas (5 TWh biomethane with CCS can reduce CO₂ emissions by about ¾ for the chemical and refinery industry segment). CO2 can also be used for production of emethane (Bio-CCU), but electricity shortages are a likely bottleneck.The price of natural gas (including tax) compared to biogas with existing subsidies is estimated to be relatively similar. The current subsidy system is directed towards manure digestion, which only produces about 1/5 of the potential biogas from agricultural biomass, which is why subsidies need to be modified to produce the biogas in demand. Fatty acids can also be produced using primarily pasture and waste via a biological process at a similar price level as today's fossil-based production method.A future investment in building biorefineries, which generate renewable commodities can be one solution for the industrial green transition, with agricultural biomasses, but this can also contribute to the green transition of the agriculture. Difficulties with the studied system is that it is large with many actors, significant investment is needed to be realized, and clear incentives are needed to become an actor in the system also includingthe farmers, and there are technical and biological uncertainties in function. A clear question is who is prepared to take the lead in realizing this?

Hygienisation at biogas plants – Proposal for additional national standard methods To be able to merchandise manure or digestate, the material must be sanitized to en-sure infection control. Swedish biogas facilities today have the choice between using one of two standard methods (at least 1 h at 70 °C, or 10 h at 52 °C) or going through a costly validation process if using alternative parameters. The main aim of this project has been to increase the profitability in the handling of biofertilizers by developing ad-ditional approved national standard methods for hygienization and thereby simplify the validation process. To achieve this, we have conducted interviews with stakeholders to find out which hygienisation parameters are most interesting for them. We have also compared the situation in other European countries and quantitatively and qualitative-ly reviewed scientific studies considering hygiene and inactivation data of microorgan-isms. However, the largest part of the project was laboratory studies where we generat-ed novel inactivation data for the heat-tolerant bacterium Salmonella Senftenberg W775 at different temperatures and time intervals. The requirement for an approved hygienisation is a 5-log reduction of the bacteria. The choice of input parameters in the lab studies was based on literature as well as on the interviews where often preference for hygienization at lower temperature was expressed to save energy and to avoid the need to adapt the equipment to higher temperatures.

Another request that emerged from the interviews was that, in connection with empty-ing vessels, they want to avoid leaving bottom sediment for destruction, which is a cost-ly procedure. Therefore, we have investigated the inactivation data of the roundworm Ascaris suum using limestome combined with heat treatment.

Based on our results, we propose the establishment of the following methods as new Swedish national methods for hygienisation: 1. Heat treatment of substrate for 3.5 hours at 60 °C 3 2. Heat treatment of substrate for 1 hour at 65 °C 3 3. Heat treatment of pure, source-separated food waste for 1 hour at 52 °C 4. Addition of at least 5 mass-% of lime (CaO) to bottom sediment4, and ensuring a temperature of at least 65 °C for at least 15 minutes.

Our assessment and recommendation are that the Swedish regulating authority can use the data regarding proposed treatment methods to approve new or existing biogas plants without the need to carry out a complete validation process including in-situ killing trials.

The potential of producing biogas by digestion from substrates in Västra Götaland, Halland and Skåne has in this study been estimated to approximately 5 900 GWh per year, of which 2 300 GWh are found in Västra Götaland, 650 GWh in Halland and 3 000 GWh in Skåne. The estimated potential is based on the current amounts of the substrate categories food waste, agricultural residues, manure, sludge from sewage treatment plants and industrial organic residues. For each of the three regions, the largest contributor to the current substrate potential is agricultural residues. This category contributes with approximately 3 900 GWh annually in total for the three regions. However, to be able to fully realize the potential of the agricultural residues there are logistic and technical challenges to be solved. Manure accounts for the second largest contribution to the potential, approximately 1 000 GWh per year for the three regions. The conditions to realize the manure potential are good with national production support in place for this substrate category.

The study also includes a brief investigation of future substrate categories focused on marine substrates, grass and hay harvesting, industrial wastewater and biological methanation. From the future substrates, a contribution of a total of 3 600 GWh per year will be added to the estimated potential for the three regions. The largest addition is potential biological methanation of the carbon dioxide streams from the total substrate potential from the current categories, approximately 3 000 GWh annually. Thereafter, the largest contributing future substrate category is industrial wastewater. Including the future substrate flows, a total biogas potential of 9 500 GWh per year was estimated for Västra Götaland, Skåne and Halland together. To realize the potential, close cooperation between substrate owners, gas producers and municipalities are needed together as well as a long-term policy landscape.

BECCS from biogas production

Global CO₂ emissions amount to about 40 Gtonnes/year and they need to be rapidly reduced if we are to meet adopted climate targets. To achieve this, a variety of measures is needed, such as more electrification, reduced use of fossil energy, more renewable energy, energy efficiency improvements and CCS (Carbon Capture and Storage). However, this will not be enough, but will also require so-called negative emissions, which means that CO₂ is removed from the atmosphere through, for example, increased afforestation, increased carbon storage in soil (e.g. biochar), or by capturing and storing CO₂ of biogenic origin in geological formations, also known as bio-CCS or BECCS. At global level, the need for negative emissions is estimated to be in the order of several billion tonnes of CO₂ per year if it shall be possible to reach the 1.5-degree target and net zero emissions by 2050. At national level, Sweden’s target is to achieve net zero emissions by 2045 and from then on to be climate positive. This means that territorial emissions from the 1990 level must be reduced by at least 85% by 2045 and that the remaining 15 % will be eliminated by means of so-called supplementary measures including bio-CCS as an important measure.

The need for bio-CCS is significant and the actors who can deliver biogenic CO₂ at the right quality and at low cost will have good business opportunities in an expected future global marketplace for negative emissions. With this project, we have investigated the opportunities CO₂ from biogas production has to contribute to bio-CCS in Sweden. At biogas plants that produce vehicle gas, there is already equipment to separate CO₂ from biogas, so-called upgrading technologies. By modifying and extending this technology, pure liquid CO₂ can be generated. The CO₂ is then transported to terminals in Swedish ports while waiting for transport by ship to the place for permanent storage.

The project has studied gas purification and liquefaction based on the four most common upgrading techniques: water scrubber, PSA (pressure swing adsorption), membrane separation and amine scrubber. The residual gas (the CO₂-rich gas leaving the upgrading equipment) differs between different upgrading technologies, which affects the need for subsequent purification steps. Results from modelling and simulation have led to two proposed technology chains. For amine scrubbers, a simple process of compression, drying and liquefaction is sufficient to achieve the CCS specification of the liquid CO₂. PSA, membranes and water scrubbers require more advanced gas purification including a two-phase separation and recirculation of gases with low dew point, such as O₂ and CH₄. The recirculated gas is recycled to the inlet of the upgrading process, leading to the double benefit of increased amount of valuable CH₄ product and further reduction of greenhouse gas emissions to the atmosphere. A side effect is that the need for conventional residual gas management is eliminated.

Cost calculations have been carried out for biogas plants with a production capacity of 20, 50 and 120 GWh/year. With an availability of 95% and a CO₂ content of 39% in raw biogas (gas before upgrading), this equates to a CO₂ production of 2,400, 5,900 and 14,200 tons/year, respectively. A starting point for the study has been that systems for large-scale bio-CCS/CCS will be established and that this will lead to the construction of several CO₂ terminals in Swedish ports. Furthermore, it is assumed that these terminals allow third-party access where a supplementary volume of biogenic CO₂ from biogas plants can constitute a portion of the total managed amount. Around each terminal, clusters of biogas plants are estimated to emerge, which each can deliver approximately 20,000–100,000 tons CO₂ per year. The distribution from biogas plants to port terminals may be done by truck transport where the loading capacity amounts to 34 tons of CO₂. After the terminal, CO₂ is transported by ship to the place for permanent storage.

The cost of producing liquid CO₂ from biogas depends on local conditions such as CO₂ flow, O₂ content, upgrading technology, new or existing plant, transport distance to terminal, etc. In order to determine what the cost will be for each individual biogas plant, it is necessary to adapt the calculations to local conditions. Through the project, generic calculations have been carried out which show that large biogas plants have good opportunities to produce liquid CO₂ at competitive costs, but also that there is a strong scaling effect. For example, the cost is about SEK 200–300/tonne CO₂ for new plants with 120 GWh in annual biogas production. With investment support, the cost drops to about SEK 150–200/tonne. For new plants in the intermediate segment (50 GWh/year), the cost is slightly higher, SEK 300–450/tonne (without capital grants) and SEK 190–275/tonne (with capital grants). For smaller plants (20 GWh/year), the cost rises significantly, especially for water scrubbers.

The transport cost up to the terminal is affected by the distance and amount of CO₂ handled. For example, the cost of truck transport from larger biogas plants is about SEK 200/tonne at 100 km one-way to terminal. The total cost of bio-CCS from biogas including terminal handling, ship transport and final storage is affected by many parameters and there are uncertainties in cost estimates along the entire chain. In a calculation example for a biogas plant with membrane upgrading, 100 km of truck transport one way to terminal in Gothenburg and transport and final storage according to Northern Light's concept, the total cost was estimated at SEK 830–1020/tonne CO₂ for larger biogas plants (120 GWh/year).

When the bio-CCS from biogas is introduced, negative emissions arise from two sources, firstly from the final storage itself, which is the main part, and secondly by reducing CH₄ emissions from the upgrading plants, which is a smaller, but not negligible part. The total CO₂ efficiency of the value chain is determined by energy consumption, transport distance, selected storage solution and CH₄ slip before the introduction of bio-CCS. Emissions from truck transport are small in this context. In total, CO₂ efficiency in many cases amounts to close to 100%, i.e. net emissions in the value chain up to final storage are close to zero. For plants that initially had relatively high CH₄ emissions from the upgrading unit, the climate benefit is even greater, with CO₂ efficiency throughout the chain being well over 100%.

A driving hypothesis in the project has been that CO₂ from biogas can be the CO₂ stream in society that is one of the lowest-hanging fruits and that the value chain is well placed to be more cost-effective than other concepts for bio-CCS. Based on the results of the project, we can conclude that the hypothesis is likely to hold. The cost up to the terminal will in many cases likely be lower compared to capture and liquefaction from large point sources. With efficient technology and distribution solutions, biogas producers should be able to contribute to bio-CCS to a fairly large extent, up to about 10% of Sweden's need for negative emissions. For biogas operators, this would mean a broadening of the business where CO₂ is seen as a valuable product which complements the revenues from the production of biomethane. 

The biogas market is facing changes, with gas driven vehicles gradually shifting to electrical drivelines, while new markets are emerging in the areas of industry, heavy road transports and shipping. Those new markets may require huge amounts of biomethane in both compressed and liquid form in the future. Liquid biomethane, even called LBM, bio-LNG or LBG (Liquefied BioGas), can directly replace today's LNG (Liquefied Natural Gas) applications.

Today's facilities for the production of LBG use large-scale conventional technology for the liquefaction, with a capacity of over 10 tpd and high capital costs. A significant part of the high costs is due to the requirement of an extra polishing step after biogas upgrading to remove residual carbon dioxide prior to liquefaction. A new technique using an absorption bed of wood ashes seems to be promising for the polishing of smaller volumes and thus enabling small-scale LBG production (Isaksson, et al., 2018). The technology is called ash filter and is developed at RISE in collaboration with SLU. In a previous study (Isaksson, et al., 2018), small systems with 1−2 GWh/a where ash filters are used for upgrading and polishing, as well as large systems of 30 GWh/a where ash filters are used for polishing only have been evaluated.

The present study focuses on producing LBG from a partial flow of upgraded biogas on larger Swedish biogas plants, where the starting point is that the plant's full capacity cannot be utilized for the production of compressed gas alone. It is thus assumed that there is unused capacity for the production of upgraded biogas that can be further processed to LBG. Processing is done using an ash filter and subsequent drying of the gas, and then liquefying the gas in StirLNG-4 machines. Systems with a liquefaction capacity of 5, 15 and 25 GWh/a, respectively, have been reviewed. The production cost for polishing and liquefaction is just over 4 SEK/kg for the 5 GWh/a system, and about 3 SEK/kg for the larger systems.

The analyzed system also included the LBG distribution. Based on the previous study (Isaksson, et al., 2018), a distribution system has been chosen based on insulated ISO containers permanently mounted on semi-trailers. The calculations show that this system has lower total costs than today's systems with stationary LNG storage and road tankers. In the studied system, ISO containers of different sizes are used for both local storage and transport to customers. Transport distances between 50 and 250 km have been assessed. At short distances, a large part of the distribution costs is due to the customer’s local LBG storage. At larger distances, the actual transport costs become dominant, and it gets increasingly interesting to use large containers.

In total, the cost of production (polishing and liquefaction) and distribution is between 3.5 and 5.5 SEK/kg, depending on the production capacity, distance and container size, which can be compared to the current price of vehicle gas of about 16 SEK/kg (CircleK, 2019). The total cost of raw gas production, upgrading and refueling is about 12.5 SEK/kg (Vestman, Liljemark, & Svensson, 2014). The marginal cost of using unused capacity should therefore be lower than that. Depending on the actual marginal costs, this means that small-scale LBG production from a partial flow of upgraded biogas may be profitable.

Biogasmarknaden står inför förändringar, där traditionella marknadssegment med fordonsgas tappas till elektriskt drivna fordon, medan nya marknader utvecklas med industri, tung trafik och sjöfart som framöver kan komma att efterfråga stora mängder biometan i både komprimerad och flytande form. Flytande biometan kallas i Sverige ofta för LBG (Liquefied BioGas) i anknytning till LNG (Liquefied Natural Gas) och kan direkt ersätta dagens tillämpningar av LNG. Även begreppet bio-LNG används.

Dagens anläggningar för produktion av LBG använder storskalig konventionell teknik för förvätskningen, med en kapacitet på över 10 tpd och höga kapitalkostnader. En del av den höga kostnaden utgörs av att det krävs ett extra poleringssteg efter uppgraderingen av biogasen för att ta bort resterande koldioxid, vilket krävs för att kunna förvätska flödet. En ny teknik som använder sig av en absorptionsbädd av träaska ser ut att vara lovande för polering av mindre flöden och på så vis bädda för småskalig LBG-produktion (Isaksson, et al., 2018). Tekniken benämns askfilter och utvecklas på RISE i samarbete med SLU. Små system med 1–2 GWh/a där askfilter används för uppgradering och polering, samt stora system på 30 GWh/a där askfilter används bara för polering har undersökts i en tidigare studie (Isaksson, et al., 2018).

Den föreliggande studien fokuserar på möjligheten att producera LBG av ett delflöde på större svenska biogasanläggningar, där utgångspunkten är att anläggningens fulla kapacitet inte kan utnyttjas vid produktion av enbart komprimerad gas. Det förutsätts alltså att det finns ledig kapacitet för produktion av fordonsgas som kan vidareförädlas till flytande gas. Förädlingen görs med hjälp av ett askfilter och efterföljande torkning av gasen, för att sedan förvätska gasen i StirLNG-4-maskiner. System med en förvätskningskapacitet på 5, 15 respektive 25 GWh/a har granskats. Produktionskostnaden för polering och förvätskning ligger på drygt 4 kr/kg för 5 GWh/a-systemet, och omkring 3 kr/kg för de större systemen.

Även distributionen ingår i systemet som analyserats. Baserat på den tidigare studien (Isaksson, et al., 2018) har ett distributionssystem valts som bygger på isolerade ISO-containrar som permanent monteras på semitrailer. Beräkningarna visar att detta system har lägre totalkostnader än dagens system med stationära lager och tankbilar. I det studerade systemet används ISO-containrar av olika storlek både som lokalt lager och för transporten till kunderna. Transportavstånd mellan 50 och 250 km har analyserats. Vid korta avstånd utgörs en stor del av kostnaderna av den lokala LBG-lagringen hos kunden. Vid större avstånd blir själva transportkostnaden dominerande, och det blir alltmer intressant att använda stora containrar.

Totalt hamnar kostnaden för produktion (polering och förvätskning) och distribution på mellan 3,5 och 5,5 kr/kg, beroende på produktionskapacitet, avstånd och val av containerstorlek, som kan ställas i relation till dagens pris på fordonsgas på ca 16 kr/kg (CircleK, 2019). Den totala kostnaden för rågasproduktion, uppgradering och tankning är ca 12,5 kr/kg (Vestman, Liljemark, & Svensson, 2014); marginalkostnaden vid användning av ledig kapacitet bör därför vara lägre än så. Beroende på bedömningen av marginalkostnaderna innebär det att det bör finnas affärsmöjligheter för småskalig LBG-produktion genom delströmsförvätskning.