![Development of efficient methane fermentation process and biogas plant technologies Janusz Gołaszewski Center for Renewable Energy Research of the University of Warmia and Mazury in Olsztyn Baltic Eco-Energy Cluster in Gdańsk [email_address] Projekt kluczowy nr POIG.01.01.02-00-016/08 Modelowe kompleksy agroenergetyczne jako przykład kogeneracji rozproszonej opartej na lokalnych i odnawialnych źródłach energii Model agroenergy complexes as an example of distributed cogeneration based on local renewable energy sources](https://image.slidesharecdn.com/10januszgoaszewskien-110919031303-phpapp02/85/410-development-of-efficient-methane-fermentation-process-and-biogas-plant-technologies-janusz-golaszewski-en-1-320.jpg)
![„… with B IOGAS alone we can power the whole world … ” – E.J. Nyns ,[object Object],[object Object],[object Object],[object Object],[object Object]](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
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4.10 - "Development of efficient methane fermentation process and biogas plant technologies" - Janusz Golaszewski [EN]
- 1. Development of efficient methane fermentation process and biogas plant technologies Janusz Gołaszewski Center for Renewable Energy Research of the University of Warmia and Mazury in Olsztyn Baltic Eco-Energy Cluster in Gdańsk [email_address] Projekt kluczowy nr POIG.01.01.02-00-016/08 Modelowe kompleksy agroenergetyczne jako przykład kogeneracji rozproszonej opartej na lokalnych i odnawialnych źródłach energii Model agroenergy complexes as an example of distributed cogeneration based on local renewable energy sources
- 6. Nakicenovic N. 2006. Global Energy Perspectives to 2050 and Beyond. Intern. Conf. „Energy Paths – Horison 2050, Viena. Global Use of Primary Energy – brief history 2011 ~13%
- 7. Source: IEA (World), EUROSTAT (EU-27) Production of primary energy (world, EU-27, Poland) in 2008 -2009 (% of total, based on tonnes of oil equivalent ) 1990 >>> 2008 Energy supply: 103 >>> 144 P Wh P ower supply : 1 2 >>> 20 P Wh
- 8. Primary energy production from renewable energy sources, breakdown by individual source (EU-27, 2008) Source: European Commission . Renewables make the difference . Luxembourg: Publications Office of the European Union 2011
- 9. Primary energy from biomass supply (ktoe) Source: DG Energy, 24 NREAPs waste agriculture and fisheries forestry 2006: domestic + imported 2015, 2020: domestic
- 10. Source: IEA 2010 Climate changes scenarios scenario scenario Reference scenario Nuclear CCS Combustible renewables Energy efficiency n
- 11. 1st p artial recapitulation A gricultural biomass and waste are energy resources with a potential to be significant contributors to the future energy portfolio accompanied by low greenhouse gases emission
- 14. METAN CH 4 The v alue of waste biomass is at least the value of generated energy Neterowicz J., Haglund G. 2011. Energy in Sweden. Mat. Conf. „SymbioCity – Sustainability by Sweden”, Warszawa Sweden – ca 85% of energy in heating grid is from waste Neterowicz J., Haglund G. 2011. Energy in Sweden. Mat. Conf. „SymbioCity – Sustainability by Sweden”, Warszawa Paris – ca 45% of energy in heating grid is from waste Polish Biogas Association Global scale: 800 million ton es of bio waste = 64 billion m 3 of biogas = 32 billion ton es of liquid fuels = 110 GWh of electric energy 2 t waste ~ 1 t coal EU scale: 1 20- 1 40 mil tones (~70% bio waste ) Biow aste
- 15. 2nd p artial recapitulation (nearly) a ny organic agricultural and communal waste is natural feedstock for biogas production – there is a specific environmental pressure to utilize it
- 16. Solar energy – Photosynthesis – Biomass – Decay – Biogas – Methane – Useful e nergy Sunlight + CO 2 + H 2 O + Mineral s form the soil N P K Ca … „ CH 2 O ” + O 2 Organic matter SUBSTRATES PRODUCTS BIOGAS Methane fermentation Methane Hydrogen 100% 20% + 0.2-3% Energy Methabolic processes atmosphere naturally biogas plant Digestate
- 17. Potential of photosynthesis conversion efficiency from solar energy to biomass (chemical energy) Klass D. Biomass for renewable energy and fuels. Encyclopedia of Energy. Oxford: Elsevier Inc.; 2004. How to store and utilize more solar energy? – by increasing the photo-active area of plants (C4 type of photosynthesis (corn, sugarcane) is more efficient, mostly by reduction in photorespiration) Plant productivity = sunlight, water, nutrients plus environmental conditions: temperature, water availability How to reduce water use? – by increasing water use efficiency (corn, sugar cane, miscanthus, cereals – 100-800 kg H 2 O per kg biomass depending on irrigation, fertilization – C4 plants are at the bottom of the range) How to balance the fertilization? – by increasing nutrient use efficiency=decrease cultivation energy inputs (accumulation of nutrients in DM accounts for 5-10% of the mass, current NUE is at most 40% for N, 10% for P, and 40% for K) Crop Type of photosynthesis Photosynthesis conversion efficiency Most of annual crops C3 0.3 Switchgrass C4 0.6 Corn C4 0.8 Willow and poplar C3 0.4 Tropical sugarcane C4 2.6 Tropical Napier grass C4 2.8
- 18. Biomethane cycle in the b iogeochemical carbon cycle CH 4 900 mln t 90% biomass decomposition
- 19. Biogas (methane) cycle Solar energy CO 2 H 2 O Biomass Energy CO 2 H 2 O Nutrients Bioga s Digest ate (biomass) Organic fertilizer Natural decomposition Biogas plant
- 23. Biogas Net energy performance of biomethane per 1 ha for chosen crops in comparison with other biofuels Heat of combustion in comparison with fossil fuels and firewood Szlachta 2008, De Baere 2007, Fachagentur Nachwachsende Rohstoffe e.V. Fuel s Heat of combustion Equivalent of 1 m 3 biogas at the heat of combustion 26 MJ/ m 3 Biogas 17-27 MJ/ m 3 1 m 3 Natural gas 33 MJ/ m 3 0.7 m 3 Diesel 42 MJ/ l 0.6 l Coal 23 MJ/ kg 1.1 kg Firewood 13 MJ/ kg 1.95 kg
- 24. Bioprocesses in biogas production Carboxylic acids (valeric, formic, propanoic, …) Alkohols Gases Acetates CO 2 , H 2 Biogas Simple sugars, alcohols, higher fatty acids, amino acids Carbohydrates Lipid s Proteins Organic matter hydrolitic and fermentative bacteria acidic bacteria acetogenic bacteria methanogenic bacteria 1. Hydrolysis - biopolymers decomposition 2. Acidogenesis - volatile fatty acid s f ormation 3. Acetogenesis - formation of methanogen ic substrates 4. Methanogenesis - biogas formation celullase cel l obiase xylanse amylase l ipase protease Bacteriocides (an.) Clostridia (an.) Bifidobacteria (an.) Streptococci (f. an.) Enterobacteriaceae (f. an.) autotrophs, heterotrophs Acetobacter woodii Clostridium aceticum Clostridium termoautotrophicum . Methanosarcina barkerei Metanococcus mazei Methanotrix soehngenii 70% use acetate s 30% use hydrogen and carbon dioxide
- 25. Bedding added Water added As excreted Covered Lagoon Complete mix Plug-flow Digester Type by Manure Characteristics An example for manure as a feedstock – technical assumptions in the biogas plant project Source: own on the basis of USEPA 2004 Biogas plant – initial technological criteria depend on the substrate
- 26. Chosen parameters of the AD process: pH 5.5-6.5 acetogenic phase and 6.8-7.2 methanogenic phase C:N:P:S =600:15:5:1; COD:N:P:S =800:5:1:0.5 C:N – 15:1-30:1 Substrate: Water (i.e. manure) – 1:1 (~8-10% DM.) Microelements: Fe, Ni, Co, Se, Mo, W (toxic in higher concentration) Inhibitors: antibiotics, pesticides, synthetic detergents, soluble salts of Cu, Zn, Ni, Hg, Cr In dependence on fermentation environment: salts of Na, K, Ca, Mg – facilitation or inhibition depending on the concentration Biogas plant – foundamental criteria Criteria Fermentation process AD stages single-stage two-stage multi-stage Temperature of AD psychrophilic (10-25ºC) mesophilic (35-40ºC) thermophilic (52-55ºC) Flow characteristics Batch (batch, batch/percolation) Continuous (CSTR, PFR) DM in substrate dry fermentation (>15%) wet fermentation (<12%)
- 27. Chosen characteristics of 63 German agricultural biogas plants built in 2007-2009 Source: Bundesmessprogramm, 2009 (FNR) za Linke B. 2009. Biogas plants in Germany – experiences in implementation and processing. Mat. Conf. „Bioenergia w rolnictwie ze szczególnym uwzględnieniem biogazu”, Poznań.
- 31. Feedstock s – mix of land and water biomass Water biomass Terrestrial biomass Laboratory digesters Conservation and conditioning Źródło: Opracowania autorów: Krzemieniewski M., Dębowski M., Zieliński M.
Notas del editor
- This means that a biogas plant with a controllable organic matter degradation process, generating usable biogas and levelling the unfavourable environmental effects, must become a widespread facility. For this solution to be feasible, it is necessary to continually improve the methane fermentation process and technical applications.
- At the beginning I would like to state three theses and in the course of my presentation I will try to discuss them:
- We are considering biogas in the context of a specific balance between energy demand and exploitation of different energy sources, including organic waste and - on the other hand -– the environment with its elements. These two aspects are involved in the policy towards sustainable development and energy safety.
- biomass has always been an important source of energy 150 years ago it was the only energy source but quickly after that people found most efficient energy sources in fossils and since 1950s the primary energy consumption has increased exponentially for the last 20 years renewables have been increasingly more and more importan t , now the y account for 13% of the global use of primary energy
- Between 1990 and 2008, the world energy supply changed significantly, from 103 to 144 P Wh, while the power supply rose from 12 to 20 P Wh. The structure of energy production differs greatly depending on the region. For instance, renewables in the world account for 13%, in the EU-27 - for 17.6% and in Poland for about 8%.
- In the EU-27, the primary energy production from renewable energy sources means mainly production from biomass and waste – 69%, out of which biogas accounts for 5.1%.
- At the same time, in the EU scenario for the total supply of primary energy from biomass for 2015 and 20 2 0, anticipates a 3-fold increase of energy biomass from agriculture and fisheries and 2-fold increase of energy supply from organic waste. So, there are two main sources of biomass which can potentially aid development of biogas plants - biomass from agriculture and organic waste.
- There are two scenarios prepared by the IEA for reduction of CO 2 emission by 2030, one assumes reduction of CO 2 emission below 550 ppm and the other one – below 450 ppm. Among the main determinants which will allow such significant CO 2 reduction will be biomass use (23%), second only to energy efficiency (54%)
- F eedstock or agricultural origin the sector is responsible for 14% of global GHG emissions with methane and nitrous oxide creating a more serious impact on the greenhouse effect than carbon dioxide . Much of the energy from agricultural biomass is simply lost in the decay process and greenhouse gases are released to the atmosphere. So, there is a specific environmental pressure – agricultural waste ought to be utilized as an energy source and, whenever it is, it always adds to sustainable development and supplies the farmer with energy
- The same may refer to communal waste , but here the nature and rate of biodegradation depends on the type of organic material – food waste is quickly biodegradable (half a year), then green garden waste (up to 5 years), but such biomaterials as paper, cardboard, wood, textile waste are hardly biodegradable (15 years) (Nowakowski 1997).
- On the global scale 800 million tonnes of waste is produced every year worldwide. The EU produces 120-140 million tonnes of waste, of which 70% is municipal biowaste. The value of waste biomass is at least the value of generated energy. This common wisdom is understood in a few EU countries, for instance in Sweden over 80% of heat energy is from waste and in Paris this percentage is over 40%
- Any b iomass is a solar energy resource. Biomass is built in the process of photosynthesis, which converts solar energy into biomass energy with the use of CO 2 from the air and water and nutrients from the soil. B iomass begins to decay naturally and biogas with methane is released to the atmosphere or it may be used in a biogas plant to produce useful energy . Let us mention the fact that only 23% of solar energy is absorbed by plants and most of it is used for metabolic processes and only 0.2 to 3% of solar energy is accumulated in organic compounds. Photosynthesis is an extraordinary process, which can serve as a model for any conversion process es when using renewables with the open question - how to convert H 2 O to H 2 effectively using only sunlight to break up the particle? In plants i t is built in the process of photosynthesis which convert solar energy into biomass energy with the use of CO2 from the air and water and nutrients from the soil. When the live cycle ends the biomass begins to decay naturally and biogas with methane is released to the atmosphere or when the decay process is controlled the biogas may be converted to the useful energy. Let us mention that only 23% of solar energy is absorbed by plants while most of it is used for metabolic process es and only 0.2 to 3% of the solar energy is accumulated in organic compounds. It is an extraordinaly process which is a model for everyone dealing with renewables – how to convert H2O to H2 effectively using only sunlight to broke the particle. Biomass from crops or organic waste is a solar energy resource. The main element of biomass in plant and animal organisms is organic carbon. It is built in the process of photosynthesis, which converts solar energy into biomass energy with the use of CO 2 from the air and water and nutrients from the soil. When a living cycle ends, the biomass begins to decay naturally and biogas with methane is released to the atmosphere. Let us mention the fact that only 23% of solar energy is absorbed by plants while most of it is used for metabolic processes and only 0.2 to 3% of solar energy is accumulated in organic compounds. Photosynthesis is an extraordinary process, which can serve as a model for any conversion process when using renewables – how to convert H 2 O to H 2 effectively using only sunlight to break up the particle?
- Plant productivity depends on sunlight, water, nutrients plus environmental conditions such as temperature and humidity. Plants differ in the productivity by the type of photosynthesis conditioned by metabolic processes, denoted as C3 or C4. Plants with C4 photosynthesis, which have a more efficient water economy, also have a higher photosynthetic efficiency but C4 plants are typical of hot climates. And the second remark - m ost plants have growth rates limited by a particular nutrient. However, each nutrient has a maximum uptake requirement, above which it will no longer contribute to the plant’s growth. Considering the above, three questions – each with a relatively obvious answer - can be stated for formulating hypotheses for research.
- Plants and animals respire and through this process CO 2 is released back into the atmosphere. On the other hand, terrestrial and aquatic plants and animals as well as soil require CO 2 for their metabolism. But t here are some other sources of emission which add significantly to the greenhouse effect like natural volcanoes, windstorms, wildfires, and anthropogenic ones, i.e. industry, transportation, households. And in this carbon circulation there is a significant emission of methane .
- So, the methane cycle is an integral part of the carbon cycle. But there is one difference - when controllable, the methane cycle is absolutely neutral to the environment because methane is used for useful energy and the other products of photosynthesis return to the environment and close the cycle.
- The first record on biogas production is from Assyria, the 10 th century BC, and the first biogas plant was built in Mumbai (India) in the mid-19 th century to recycle waste from a leper colony. In Europe, in 1890s biogas was used for lightning streets in Exeter (England) and during WWII it was used as transportation fuel. In 2009, the EU produced 25.2 TWh of electricity from biogas. Leading countries in per capita biogas production are Germany, the UK, Luxembourg, Austria and Denmark; w ith only 2.6 tonne of oil equivalent per capita, Poland holds the 21 st place in the EU The European structure of biogas energy production is dominated by cogeneration (over 60% of all the facilities ), but worth noticing are some advanced programs in Germany on the injection of biomethane directly into a gas supply network and in Sweden on using biogas for public transportation.
- In 2009 primary biogas energy output in EU-27 accounts for 8.3 Mtoe, including 25.2 TWh of biogas electricity. The countries differ in the main substrate of the biogas plants. For example , Germany produces biogas mostly from agricultural feedstock ; the UK , Ital y , France and Spain produce biogas mostly from landfill, and in Sweden and Poland , biogas from sewage sludge dominates . (estimated p otential of electricity: 496 TWh – ( EREC – 2050)
- As already mentioned, organic material consists of organic substances, which turn into biogas in a digestion process, and inorganic substances (minerals and metals), which are ballast in methanogenesis, unaffected by digestion. Biogas is typically made up of 40-70% methane, 20% to 50% carbon dioxide, and usually traces of hydrogen, carbon monoxide and nitrogen. Biogas is an universal fuel it can be used in all solutions designed for natural gas, it can be combusted to produce heat and steam, it can generate electricity attaining electrical efficiency up to 4 0 % or heating efficiency up to 55% it can fuel vehicles after removing the water vapour and sulphide from biogas It can be integrated into the natural gas grid if biogas is upgraded to increase the methane content to at least 97%.
- biogas has a higher calorific value than other biofuels, comparable with coal and twice as high as firewood. a lso, net performance of biomethane per 1 ha of energy crops is two-fold higher than analogues values for biodiesel and bioethanol. biogas used instead of biofuels may reduce CO2 emission 1m3 cattle manure = 22.5 m3 biogas = 146 kWh gross = 36 kg CO 2 - emissions 1 m3 biogas (up to 65% CH4) = 0 . 5 l fuel oil = 1 . 6 kg CO 2 – m3 of biogas as an equivalent of 0.6 L of diesel may reduce CO2 by 1.6 kg 1 m3 biogas = 5 . 5 kg fire wood = 11 kg CO 2
- The simplified scheme of anaerobic degradation process may be established as follows. At first, suspended, colloidal organic matter, i.e. proteins, carbohydrates and lipids, is decomposed into amino acids, sugars, and free long chain fatty acids plus glycerol. It is called hydrolysis. The products in the next stage are converted into ammonia and volatile fatty acids and alcohol. This is acidogenesis. Then, acetic acid, hydrogen and carbon dioxide are formed in the process of acetogenesis. Finally, in the methanogenesis stage, methane and carbon dioxide are formed, 70% from acetic acid and 30% from hydrogen and carbon dioxide.
- The biogas plant system chosen will largely depend on the feedstock to be processed . For example, 'high solid materials', such as a garden and food waste mixture, tend to be processed at a thermophilic temperature using a batch system, while 'low solid materials', such as animal slurry mixed with industrial and municipal food waste, are more likely to be processed at a thermophilic temperature using a continuous flow system. In the presented example for different forms of manure, water or bedding added, affects the consistency of substrate and finally the chosen digester type.
- The foundamental criteria are as follows: the number of AD processes – single-, two-, and multi-stage the temperature reached in the process. Thermophilic processes reach temperatures of up to 60 0 C and mesophilic normally runs at about 35-40 0 C. Theoretically, in hot countries psychrophilic process is also considered. the method of filling substrate, it may be batch or continuous feeding (CSTR continuous stirred-tank reactor , PFR – plug flow reactor) . To overcome peaks and troughs in gas production there is usually multiple batch digesters with staggered changeover times. I n wet AD the feedstock is pumped and stirred and in dry AD it can be stacked Microelements: Fe, Ni, Co, Se, Mo, W (toxic in higher concentration) – Iron, Nickel, Cobalt, Selene, Molybdenum, Wolfram Soluble salts of c ooper, zinc, nickel, mercury, chrome Several operational conditions influence the outcomes of fermentation process including: retention time; pH; relations between different parameters ( COD – chemical oxygen demand ) temperature; type of hydrolyzing biomass; concentration of hydrolyzing biomass i.e. inoculum to substrate ratio; water addition; nutrient addition
- Let us summarize some characteristics of 63 biogas plants built in Germany in 2007-2009, which correspond well to the general characteristics of an average biogas plant. What are they? Biogas generation was mostly a mesophilic process, organic loading rate varied within quite a broad range, from 1 to over 4 kg of VS per m 3 of digester per day, the average methane yield was about 55% of the biogas composition, hydrogen sulphide appeared in a trace amount (<200 mg/Nm3 ) , there were mostly systems with a cogeneration unit and with two modal power capacities of about 250 kW and 500 kW, the calorific value of biogas was 4- 6 kWh/m 3 .
- Depending on the feedstock, biogas plants may be divided into agricultural or recycling ones , i t is also possible to design an agricultural-recycling biogas plant. When considering an agricultural biogas plant, a potential source of biomass could be found in one of the following four groups: (1) biomass of agricultural origin which may be fermented in many various configurations of substrates and acc. to the rule that the superior objective of a biogas plant is to process agricultural waste (the largest potential for biogas production); (2) another potential raw material for biogas is sludge from mechanical and biological wastewater treatment process (sludge from chemical wastewater treatment often has low biogas potential); (3) organic household waste, and (4) organic, bio-degradable waste from industries, in particular slaughterhouses and food-processing industries. When substrate is polluted with heavy metals or harmful chemical substances, then the resulting sludge is treated as waste and should be e.g. incinerated.
- The sources of biomass just mentioned differ in yield and quality depending on the chemical composition of organic compounds and on many physical and chemical propertie s , which are specific for the fermentation process. Theoretically, even the mesophilic process should effectively destroy most of pathogens, including bacteria and viruses (99.9%) which are in excreta of animals, but as regards endo-parasites ( Protozoa, T rematoda, C estoda and Nematoda ) the percentage of neutralized pathogens is only 90%. In the case of organic substance rich with biopol y mers like cellulose , and hemicelluloses the rate of fermentation is limited, so to increase fermentation rate the hydrolysis as a n initial stage of the process is desired.
- The important source of biomass today are dedicated crops but we should mention that their use for biogas purposes is going to be questionable. The problem with them is that today they are mostly the strategic crops and they may compete with food and feed production. So, t he crops in the future biogas plants should be considered as co - substrate s which may be replaced by alternative crops , which do not compete with food production and add to the biodiversity.
- The future b i ogas plant substrate potential is also in water plants , seen here as a single substrate and in mix with other energy crops.
- From the organizational point of view , technology of biogas production may be considered as a modular process, wh ich means that every module - from biomass production, logistics of supply, pretreatment, digestion, homogenization and sanitation, followed by the fermentation process up to biogas and digestate utilization - may have a different technological dimension . So, the standardization at each of the module will enable decreasing costs of biogas plant and a broader implementation. Today, the most common criterion on the biogas plant market is the power installed which guarantees a relatively quick rate of return on investment and profits. At the same time, analysis of the market shows that in the future micro-biogas-plants (power ca 5-50 kWe) and mini-biogas-plants ( ca 50-100 kWe) will be gaining in importance. Now, it is difficult to assume that micro- and small biogas plants will be cost-effective with sale of energy as the only income, but for a farm it will always be an added value generated, i.e. additional energy from the farm and other waste and avoided GHG emission .
- The first module is on biomass sources. In dedicated crops some points should be considered. When we use waste the sanitation of the substrate is often obligatory acc. to the procedures applicable to such substrates due to potential health hazards and epizootics.
- The next modules are logistics of supply and pretreatment with the main goals to reduce energy lost and to initiate biodegradation. The feedstock may be in a different form as fresh biomass, silage, hay, or grass-silage as well as the substrates may compose a sequence of various feedstocks. Feedstock processing begins with pre-treatment. The problem is with biopol y mers which need to be pretreated before fermentation to facilitate the biodegradation of biopol y mers to simpler compounds. In the hydrolysis many methods may be applied, including physical, chemical and biological ones. This module involves also mixing the various feedstock s together to ensure the right consistency and C:N ratio and may also involve the addition of water. The material should also be screened for contaminants at this stage.
- The fundamental part of biogas plant is a digestor which may be a vertical or horizontal tank , insulated and equipped with systems of heating, fi l ling, stirring , biogas and digestate outlets and storage tanks. Besides it should have a monitoring system for fermentation parameters.
- The next module is related to a biogas handling system to remove biogas from the digester and transport it to the end-use. Various components should be considered: piping a gas pump a gas meter a pressure regulator condensate drains a gas scrubber (to avoid corrosion of the equipment) odor control system etc.
- Quality of biogas determine s its use, i.e . when we use the biogas to propel a stationary boiler the biogas may have poorer properties tha n biogas used in gas grid or in transportation. Some of the chemical compounds in biogas should be eliminated but when biogas is used in fuel cells there is no need for elimination of CO. The overall energy efficiency depends on the way the biogas is used, i.e. it may be at the level of 2 5 % in a boiler, over 40% in CHP and over 50% in fuel cells. [1] Ogniwo paliwowe ze stopionym węglanem, MCFC (ang. Molten Carbonate Fuel Cell) [2] Ogniwo paliwowe z zestalonym elektrolitem tlenkowym, SOFC (Solid Oxide Fuel Cell)
- The final and important module is on digestate. Digestate is a nutrient-rich substance produced by anaerobic digestion that can be used as a fertiliser. It consists of leftover indigestible material and dead micro-organisms . the volume of digestate will be around 90-95% of what was fed into the digester. By using digestate instead of synthetic fertilisers derived from natural gas, we can reduce consumption of fossil fuels and reduce our carbon footprint . Digestate can be used straight from the digester, in which case it is called whole digestate. Alternatively it can be separated in to liquor and fibre. Digestate is not compost, although it has some similar characteristics. Compost is produced by aerobic micro-organisms, meaning they require oxygen from the air. When digestate has toxic compounds it should be treated as waste or sewage sludge and the right legal regulations sholuld be applied i such the cases All the nitrogen, phosphorous and potassium present in the feedstock will remain in the digestate as none is present in the biogas. Typical values for nutrients are: Nitrogen: 2.3 - 4.2 kg/tonne ; Phosphorous: 0.2 - 1.5 kg/tonne ; Potassium: 1.3 - 5.2 k g/tonne . However, the nutrients are considerably more bioavailable than in raw slurry, meaning it is easier for plants to make use of the nutrients. T his can be particularly valuable for land within Nitrate Vulnerable Zones (NVZ) where applications of organic nitrogen are restricted.