How to promote manure-based biogas?

Transcription

1 September 2014 Policy recommendations: How to promote manure-based biogas? Sari Luostarinen, MTT Agrifood Research Finland, FI; Knud Tybirk, Agro Business Park, DK; Elin Einarsson, and Emma Svensson, Jordbruksverket, SE. Photos by Knud Tybirk, Sari Luostarinen, Elin Einarson, Gunnar Laurell and Berit Haggren. Summary and recommendations Manure-based biogas offers significant benefits for the environmental services in agriculture. Thus, its implementation needs to be supported in the Baltic Sea Region (BSR). In the following, we present recommendations for targeted promotion of manure-based biogas based on several BSR projects. Incentives for increased biogas use of solid manure should be created, such as o Funding for technology development of dry fermentation. o Funding for technology development of increasing degradation of solid biomasses via efficient re-treatments. o Support for co-digestion of slurry and solid manure. Manure-based biogas plants utilising wastes and by-products as co-substrates should be given priority in subsidy systems and permission processes. o Energy crops utilisation should be regionally justified so as to avoid harmful consequences for the environment and competition with food and feed production. Manure-based biogas plants with clear plans to optimise the entire manure management chain before and after the plant should be given priority in subsidy systems and permission processes. o Proper solutions for substrate collection, plant design and operation, and storage, spread and potential post-processing of the digestate require development to avoid pollutionswapping between different steps. Energy efficient use of the biogas produced should be a key criteria for the environmental permit and the financial support system. o The best local utilisation of the biogas energy needs to be determined already in the planning phase of the biogas plant.

2 1. Introduction There is plenty of manure produced in the BSR. Some 187 million tons of cattle, pig and poultry manure is annually available, as estimated in the project Baltic Manure. After inclusion of the manure from other farm animals (horses, sheep, goats, fur animals), the amount obviously increases. Manure is an excellent basic substrate for biogas plants due to being constantly available. It also creates a means to utilise the energy and nutrient content in many other organic wastes and by-products from municipalities and industries. This can be achieved via co-digestion with manure. Manure-based biogas production offers several environmental benefits. Biogas is a versatile form of renewable energy which replaces fossil fuels and avoids the emissions thereof. Digestate, the residue of the process, contains all the nutrients in the original substrates, but in a more valuable form: a higher share of nitrogen is readily available for crops. Its fertiliser use replaces mineral fertilisers and avoids the emissions from their production and use. With proper digestate storage and spread, more of the manure nutrients can be directed to crop production and less lost as emissions. To ensure all these benefits, the entire manure management chain before and after the actual biogas plant must be understood and optimised, and pollution-swapping between the different steps avoided. Then manure-based biogas is an efficient way to enhance renewable energy production, nutrient recycling and mitigation of agricultural emissions. The theoretical energy potential of the manure in the BSR has been calculated to be TWh/a as biogas in Baltic Manure. When small farms (<100 animals) were excluded, the techno-economical energy potential became TWh/a. The largest techno-economical manure energy potential lies in Poland (9-19 TWh/a) with Denmark (2-5 TWh/a) and the two North German states with coastline to the Baltic Sea (2-3 TWh/a) following. The other BSR countries could each produce TWh of biogas energy annually. In 2010, 571 TWh of renewable energy was produced in the BSR. The addition of manure-based biogas may seem quite marginal, but when combined with co-digestion of other suitable organic substrates the energy yield can be manifold and it could offer a significant and stable source for renewable energy. Still, only approximately 4.2 million tons of the 187 tons of manure in the BSR (excluding the German states with no data on the amount of manure in biogas production) is currently being directed into biogas plants. With the increasing recognition of manure-based biogas as an integral step in sustainable manure management, renewable energy production and nutrient recycling, the importance of correct policy decisions becomes evident. In this paper, clear recommendations are given as to what kinds of policy measures are needed and which issues need to be taken into account when preparing them. Farm-scale and industrial scale biogas based on manure.

3 2. Solid manure for biogas Biogas technologies for liquid manure, i.e. slurry, are well-developed and utilised. Most of the manure directed to biogas plants is cattle and pig slurry, while solid manures of all farm animals are rarely digested. However, the ratio of slurry and solid manure (deep litter, farmyard manure, dung) differs in different BSR countries. While in Denmark, some 80% of all manure is slurry, in Sweden and Finland the ratio is close to 50:50 and in Poland, nearly 90% of manure is solid. In order to harness the energy and nutrient potential in manure and to minimise the environmental effects of manure, efficient technological solutions for solid manure digestion are required. Technology development to enable more enhanced utilisation of solid manure requires support. Pretreatment of solid manure and other substrates with high dry matter content (e.g. crop residues) may enhance their feasibility for biogas production by improving the degradation. Still, few truly efficient processes with a tolerable energy balance are available. Moreover, dry fermentation processes are not technologically mature. New and improved technologies are needed. Recommendation 1. Support research and development of efficient technological solutions for digestion of solid manure and other substrates with high dry matter content in order to harness the entire energy, nutrient and emission mitigation potential from manure. Another route to increase solid manure use in biogas production is simply via more co-digestion with slurry. This entails also co-digestion of slurry and the solid fraction separated from slurry. At times, it may be beneficial to separate manure on the farm and transport only the solid fraction to a larger biogas plant. Especially recommendable this may become in regions with phosphorus surplus. The solid fraction contains most of the phosphorus and the large biogas plant is able to redistribute the nutrients to a larger area than the manure producing farms alone. This may alleviate the nutrient surplus of one region and the nutrient deficiency of another without the need to use mineral phosphorus. Recommendation 2. Support manure-based biogas plants which co-digest slurry and solid manure. Create support for slurry separation into a transportable, phosphorus-rich solid fraction for digestion and nutrient redistribution in larger biogas plants especially in regions with high animal density and phosphorus surplus. Solid manure and separated fibre fractions are preferred co-substrate.

4 3. Sustainable co-substrates for manure-based biogas Co-substrates improve the economic profitability of manure-based biogas. This is simply because manure alone does not contain enough energy to compensate for the treatment costs. Certainly, in the future the situation will change. This requires a market for the recycled nutrients in addition to the income from energy. Wastes and by-products are the most recommendable co-substrates environmentally and according to the nutrient recycling principles of the future bio-based society. They do not compete with food and feed production and inevitably require some form of treatment. When both their energy and nutrient contents are harnessed via co-digestion with manure, it enhances the environmental benefits of the entire management chain. Still, the choice of wastes and by-products need to be made wisely. Some of them may cause legislative requirements for e.g. hygienisation, making the manure-based biogas plant more complicated and expensive. Recommendation 3. Wastes and industrial by-products are recommended as co-substrates for manure-based biogas after due hygienisation when needed. Production of pure energy crops may cause harmful environmental effects globally mainly due to the related land use changes. In order to use fields for their production, the same amount of food and feed needs to be produced elsewhere, causing potential need for new fields. This usually deteriorates the environmental benefits of energy crops in renewable energy production. However, regionally there is often set aside land available which could be utilised in crop production for biogas production without competition with food and feed production. Moreover, e.g. grass may be recommendable to be added into the crop rotation of cereal farms as it maintains soils structure, takes up surplus nutrients from soil and provides cover for winter periods. In regions with high cereal production, there is often little use for the grass biomass produced making utilisation in biogas production more appealing. Simultaneously uses for other crop residues, such as biomasses from water protective zones, would be created, potentially increasing the interest in building and maintaining them. Recommendation 4. Energy crops may be a good co-substrate in the biogas production, but their production must be regionally justified and bring benefits for the regional environment. They must not compete with food and feed production. Maize and pretreated straw can be co-substrates

5 4. Digestate management The digestate from a biogas digester still contains organic material which continues to degrade in the storage. Especially when digestate temperature remains high, the microbial activity is significant and results in residual methane production. If the storage is open, this methane may be emitted into the atmosphere causing significant greenhouse gas emissions and loss of valuable methane energy. In order to ensure capturing all biogas produced, either the retention time in the digester has to be sufficiently long, or the retention time must be prolonged with a separate post-digestion tank. The residual biogas from post-digestion should be mixed with the reactor-biogas and utilised in energy production. Digestate contains more ammonium nitrogen than raw slurry. This and the higher ph increase potential for ammonia volatilisation. This should be minimised with covered storages as nitrogen is a valuable nutrient and ammonia emissions harmful for the environment. Recommendation 5. Gas-tight post-digestion tank and covered storage tanks are recommended to minimise emissions. Ammonia can also be lost during digestate spread on the field. In order to minimise this, spread with injection or acidification is recommended. Moreover, spreading only during the vegetative season and according to the crops need is recommended so that the crops instantly utilise the nutrients added. This will also minimise the nutrient run-off and help avoid eutrophication of waters. Measures to support proper fertiliser use of manure-based digestate should be implemented. Recommendation 6. Spreading the digestate using injection or acidification technology should be supported and prioritised. Gas tight storage and appropriate field application of digestate is crucial.

6 In large-scale biogas plants, post-processing of the digestate should be developed and implemented especially in regions with surplus of nutrients. Manure-based nutrients cannot be feasibly transported over long distances as slurry-like products. The nutrients have to be concentrated into new fertiliser products. Funding is needed in order to develop reliable, efficient and sustainable technology chains for biorefining manure-based digestate into new fertiliser products. The biogas plants pioneering in post-processing should also be given priority in support systems. Recommendation 7. Economical support is needed for developing technologies for biorefining manure digestate into marketable, transportable fertiliser products. 5. Energy use according to local needs Manure based fertilizer product. Biogas, or the methane it contains, is a versatile fuel which can be utilised to produce renewable heat, heat and power (CHP) and/or biomethane. The important part of planning the energy use of biogas is to make it fit the local needs. It may be that a farm simply wishes to produce heat and only needs a simple boiler with a gas burner. The biogas can also be converted into electricity and heat in a CHP. Then it becomes integral that both energy forms are utilised. Co-operation with local industries may provide users for the heat which cannot be transported very far. Local district heating networks are also advisable and should be promoted. Biogas can also be upgraded to biomethane, which is equal to natural gas and can be injected into the gas grid for storage and for use. Biomethane can also be directly sold as vehicle fuel by setting up a tank station. All energy use of biogas is environmentally friendly and all methods should be promoted. The support system should be flexible to ensure support for all scales and methods, with a focus on integrating biogas energy into the local requirements. Recommendation 8. Support systems for biogas energy should be flexible for all scales in order to ensure support for all locally adapted and efficient gas uses replacing fossil energy.

7 Biogas can be used for heating greenhouses and for tractor fuel. Developments in Finland, Denmark and Sweden in The incentives and bottlenecks for manure-based biogas by 2012 have been reported for each BSR country (Luostarinen 2013a). Therefore, only the recent developments are added here for Denmark, Finland and Sweden. In Finland, little progress has been made since Agricultural biogas production is not receiving any particular subsidies. The investment support in the new rural development programme ( ) appears to remain the same as it was before (max. 30%; programme being negotiated with the EC at the time of writing). The support has been deemed too low to truly kick-start implementation of agricultural biogas production. Small-scale production, as manure-based biogas often is, is still practically excluded from the Finnish feed-in tariff system for biogas electricity. The system has a minimum electrical efficiency requirement of 100 kva, which rules out most of manure-based plants. It also forces to choose either investment support or the tariff and does not allow use of already existing or recycled parts. A working group of the Ministry of Industry and Employment is discussing possibilities to ease small-scale energy production in Finland, but no news of the possible recommendations related to biogas has been given at the time of writing. In Denmark, the Task Force for Biogas reported in May 2014 that biogas production is expected to double by This is accomplished due to increased feed-in tariffs and investment support granted in 2012 for both farm-scale and large co-operative biogas plants. More incentives for biogas energy use are being planned, including e.g. subsidies for electricity production, for upgrading to the natural gas grid, for transportation and for process purposes in industries. Previously the subsidies for electricity and upgrading have been EU ratified. Many large projects are in planning or construction phase, and the Danish natural gas companies are increasingly interested in the technology and the green gas market. The main barriers for further development are as follows, Sources of suitable and sustainable co-substrates for slurry (straw, meadow grass and deep litter deemed the most promising), but few experiences of long-term usage lacking, Biogas plant economy and sale of gas is challenged by e.g. o Other renewable energy sources (woodchips, straw) cheaper for district heating.

8 o The high cost for upgrading and grid injection, though transportation use rapidly evolving: approx. 10 gas stations will be installed in Denmark in Financing of investments generally a challenge due to low economic benefit expected and the overall financial crisis. In addition to this, the environmental permits and local acceptance of biogas plants is often a lengthy and challenging process. In the future, industrial use of biogas and biogas in the transport sector may offer profitable solutions - especially if the natural gas price increases. Around 75% of the predicted increase in biogas production is expected to be upgraded and grid-injected in the future. The Biogas Task Force reports includes recommendations for further biogas development that will be treated politically in 2014/15. In Sweden, biogas production in general is challenged by profitability, and the future of biogas is in shortterm dependent on state support and development of cheaper production technologies. After years of discussion, the negotiations of a special subsidy for manure-based biogas led to the pilot project called compensation for double environmental benefit to be started in end of In practice, it is a subsidy of maximum 0.2 SEK/kWh (around 0.02 Euro/kWh) for manure-based biogas production with a total budget of 240 million SEK (around 26 million Euro) for the next ten years ( ). Despite the demand of digesting manure in existing biogas plants, it is not expected that the amount of new biogas plants will increase. For farm-scale biogas production, a new budget is set for investment support in Rural Development programme also in Sweden. The investment support seems to be similarly constructed as in the last programme with 30% of the investment cost. This support is expected to start in summer 2015.