1 JTI-rapport Lantbruk & Industri 347 Handling of digestate on farm level Lena Rodhe, Eva Salomon and Mats Edström
3 JTI-rapport Lantbruk & Industri 347 Handling of digestate on farm level Economic calculations Hantering av rötrest på gårdsnivå ekonomiska beräkningar Lena Rodhe, Eva Salomon and Mats Edström 2006 Citera oss gärna, men ange källan. ISSN
5 3 Content Preface...5 Summary...7 Sammanfattning...8 Introduction...9 Digestate composition...9 Swedish experience from digested source sorted food residues as fertiliser in cereal production...9 Methods...10 Conditions on farms...10 Liquid digestate...11 Application technology...11 A. Spreading strategy (crop, time)...12 B. Application rate...12 C. Properties of liquid digestate...12 Solid digestate...12 Application technology...12 A. Spreading strategy (crop, time)...13 B. Application rate...13 C. Properties of solid digestate...13 D. Net load capacity...13 Prices...14 Results...14 Liquid digestate...14 Solid digestate...17 Discussions...18 Conclusions...19 References...20
7 Preface 5 Many cities are looking for vehicle fuels and waste management systems that are sustainable and cost effective. In the AGROPTIgas project a full-scale system for co-digestion of biological municipal waste and agricultural feedstock in Västerås has demonstrated a new way to meet these needs. The project has been financed through the EU:s fifth framework and the Swedish Energy Administration. One of the objectives was to study the handling systems for energy crops and digestate. The study of the handling system is one of nine work packages within the project. The ley crop handling system has been studied in an earlier report (JTI-report Kretslopp & Avfall no 32) and the study presented in this report deals with the handling of digestate on farm. Lena Rodhe (AgrD) has been the main writer of this report with help from Eva Salomon (AgrD) and Mats Edström (MSc). Everybody involved in contributing with input to this report is hereby cordially acknowledged. Uppsala July 2006 Lennart Nelson Head of JTI Swedish Institute of Agricultural and Environmental Engineering
9 Summary 7 The farmers are interested in the influence of the digestate properties on the farm economy, how to get a high utilisation of the plant nutrient contents of the digestate and the influence of spreading strategy e.g. application rate and time on the spreading economy. The value of the liquid and solid digestate was investigated by economical calculations in different scenarios. For calculating the profitability of handling liquid and solid digestate on farm level, an economical model was used. The model describes the handling system and the relationships between soil, crop, technology and the organization that influences the profitability of different systems for handling digestate on farms. The revenues are calculated as the sum of nutrients (N, P and K) available to plants. Costs are included for machinery (spreaders), labour and soil compaction. The fixed costs for the tractor for loading the solid digestate and for spreading liquid/solid digestate are considered as overheads. Storage cost was not included. Nor was the cost for the digestate included. The revenues reduced with the costs gives the net present value (Euro t -1 yr -1 ). Including the fixed costs of tractors, costs of storage and possible charge for the digestate, means additional costs and thereby lower net present value For the set conditions, the liquid digestate ( t yr -1 ) were band spread with two tankers each 15 m 3 in growing winter wheat (30 or 20 t ha -1 ) and before sowing in the autumn (20 t ha -1 ). The amount were either divided 2/3 in summer: 1/3 autumn or 1/3 summer:2/3 autumn. The concentrations of the liquid digestate (2.5 % dry matter content) were estimated to 4.8 kg total-n t -1, 3.6 kg total ammoniacal nitrogen (TAN) t -1, 0.4 kg phosphorus (P) t -1, and 4.2 kg potassium (K) t -1. Calculations were also made with concentrations +25% and 25% of the estimated concentrations. The solid digestate (6 500 t yr -1 ) were broadcast spread with two spreaders (12 m working width) before sowing in the autumn (30 t ha -1 ). Two loading capacities (8.4 or 12 t) were included in the calculations. The concentrations of the solid digestate (25% dry matter content) were estimated to 10.9 kg total-n t -1, 3.2 kg TAN t -1, 2.9 kg P t -1, and 3.8 kg K t -1. The net present value for the liquid digestate handled was between 0.48 and 1.98 in Euro t -1 yr -1. A 25% increase in nutrient concentration means an increased value of the liquid digestate by Euro t -1 yr -1. A higher application rate of the liquid digestate in growing crops (30 t ha -1 compared with 20 t ha -1 ) improves the profitability for each spreading strategy with about Euro t -1 yr -1. It is more profitable to spread the main part (2/3) of liquid digestate in the fore season in growing crop at the rate 30 t ha -1 than the main part before sowing in the autumn. With a lower rate, 20 t ha -1 in the growing crop, it is more profitable to apply most of the digestate before sowing in the autumn. The net present value for solid digestate handled was about 4.55 Euro t -1 yr -1. This is a higher value compared with liquid digestate and is explained by the high N and P content, autumn spreading with relatively low soil compaction and lower investment costs for the spreader compared with a slurry spreader. An operation strategy of the biogas plant that results in a digestate with higher nutrient concentration improves the value of the digestate.
10 Sammanfattning 8 Vid användning av rötrest som gödselmedel är det viktigt att ha klart de ekonomiska förutsättningarna för hanteringen på gårdsnivå. Hur får man högsta utnyttjandet av växtnäringen och hur påverkar spridningsstrategin, t.ex. spridningstidpunkt och giva, företagets ekonomi? Syftet med denna studie var att ta fram det ekonomiska värdet av rötresten efter hanteringen på gårdsnivå vid olika scenarier. För att beräkna lönsamheten för att hantera flytande respektive fast rötrest användes en ekonomisk modell tidigare framtagen för stallgödsel. Modellen beskriver hanteringssystemet och förhållandena för mark, gröda, teknik och hantering som påverkar lönsamheten för att hantera rötresten på gårdsnivå. Intäkterna beräknas som summan av den mängd kväve, fosfor och kalium, som är tillgängliga för grödan efter att eventuella hanteringsförluster har dragits bort. I kostnader ingår maskinkostnader, arbete och markpackning. Den fasta kostnaden för traktor för att lasta den fasta rötresten och för att sprida fast eller flytande rötrest har satts som en samkostnad och är därmed inte inkluderad. Lagringskostnader ingår inte i detta fall. Någon eventuell avgift för rötresten är inte heller med i kalkylerna. Intäkter minus kostnader ger ett nettonuvärde för rötresten (Euro t -1 år -1 ). Detta värde minskar om fasta kostnader för lager och traktor eller eventuell avgift för rötresten skulle ingå i kalkylen. Kalkylerna förutsätter en hantering av totalt ton flytande rötrest per år. Rötresten bandsprids med två 15 m 3 tankvagnar i växande höstvete (giva 30 eller 20 t ha -1 ) och innan höstsådd (20 t ha -1 ). Rötrestmängden sprids antingen 2/3 sommar:1/3 höst eller 1/3 sommar:2/3 höst. Näringskoncentrationen hos den flytande rötresten (2,5 % torrsubstanshalt) beräknades till 4,8 kg total-n t -1, 3,6 kg ammoniumkväve t -1, 0,4 kg fosfor t -1 och 4,2 kg kalium t -1. Känslighetskalkyler gjordes också för variationer i näringsinnehållet med +25 % och 25 %. Den fasta rötresten bredspreds (12 m arbetsbredd) med två spridare innan höstsådd (30 t ha -1 ). Beräkningar utfördes för två olika lastkapaciteter, 8,4 eller 12 ton. Näringskoncentrationen hos den fasta rötresten (25 % torrsubstanshalt) beräknades till 10,9 kg total- t -1, 3,2 kg ammoniumkväve t -1, 2,9 kg fosfor t -1 och 3,8 kg kalium t -1. Den flytande rötrestens nettonuvärde uppgick till 0,48 till 1,98 Euro t -1 år -1. En ökad koncentration med 25 % innebar ett ökat värde på rötresten med 0,85 till 1,02 Euro t -1 år -1. Den högre givan 30 ton ha -1 i växande gröda jämfört med 20 t ha -1 ökade lönsamheten med 0,2 0,6 Euro t -1 år -1. Det är också mer lönsamt att lägga huvuddelen av rötresten (2/3) i växande gröda än före sådd vid givan 30 ton ha -1. Vid den lägre givan i växande stråsäd var det däremot mer lönsamt att lägga huvuddelen av rötresten före sådd. Den fasta rötrestens nettonuvärde uppgick till ca 4,55 Euro t -1 år -1. Det är betydligt högre än för den flytande rötresten. Förklaringen till detta är det höga innehållet av N och P, höstspridning med relativt låg markpackning och lägre investeringskostnad för spridare jämfört med den flytande rötresten. Sammanfattningsvis kan sägas att processen vid rötgasanläggningen bör drivas så att rötresten håller höga näringskoncentrationer. Då skapas ett attraktivt gödselmedel som det kan vara lönsamt för lantbrukarna att hantera på sina gårdar.
11 9 Introduction In the AGROPTIgas demonstration project source-separated organic waste is codigested with ley crop in order to produce renewable vehicle fuel as biogas and to establish a sustainable circulation of plant nutrients and organic material between the community and the agriculture sector, thus contributing to a sustainable form of farming (Svensk Växtkraft, 2003). An important aspect of the project is to facilitate recirculation of nutrients in the digested residue (digestate). From the farmers point of view it is important to have knowledge on how the digestate properties (e.g. dry matter content and plant nutrient concentration) and spreading strategy (e.g. application rate and time) influences the economy and the plant nutrient utilisation. The objective of this study was to estimate the economic value of the liquid and solid digestate by making economical calculations with different scenarios based on different spreading times, spreading technology, nutrient concentration and application rate. This study is a part of WP8 (Handling system) in the AGROPTIgas demonstration project. Digestate composition At the time of performing the economical calculations, the biogas plant was still under a starting up phase with increasing nutrient and dry matter contents of the digestate produced. Thereby, the composition of the digestate and the mass-flows within the biogas plant was calculated for a steady state production (Table 1) in order to get the basic data for the economical calculations in both the socio-economic study (WP5) and the study on handling systems (WP 8) of the AGROPTIgas project. The production of liquid digestate was estimated to about tonnes per year and solid digestate about tonnes per year. Table 1. Calculated dry matter and nutrient content (wet basis) in solid and liquid digestate, when the biogas plant has reached steady state and running according to plan Solid digestate Liquid digestate Dry matter, % N-tot, kg/tonne Organic-N, kg/tonne NH 4 -N, kg/tonne P, kg/tonne K, kg/tonne Swedish experience from digested source sorted food residues as fertiliser in cereal production Field trials were carried out during in southern Sweden in order to evaluate the effect of anaerobically digested, source separated food waste originating from households as fertiliser in cereal production (Salomon et al. 2005). The aim was to study the effect of the fertiliser on grain yield in production of spring-
12 10 sown cereals. The field trials were designed as split plot trials with three replications. The digested residues (DR), with a dry matter content of 1 3 %, were compared to mineral fertiliser (all years) and slurry from dairy cattle ( ). Two different spreading strategies were evaluated in 1999 and 2000; spreading at time of sowing as well as spreading when the crop was between 15 and 20 cm high. In 2002 and 2003 a treatment with dewatered DR was included. DR is a fertiliser that can replace mineral fertiliser in the production of springsown cereals, yielding 72 to 105 % of corresponding yield with mineral fertilisers. The yields with DR are slightly higher than the yields with cattle slurry. Yield results vary depending on weather conditions during the growing season. Dry and cold weather has a more negative effect on yield in treatments with DR compared with mineral fertilisers. Another conclusion is that spreading of DR can be extended into the growing season, as long as the crop is supplied with a starter dose at the time of sowing. This is an advantage in case of soil compaction problems. Methods For calculating the net present value of handling liquid and solid digestate on farm level, an economical model was used (Brundin & Rodhe, 1994). The model describes the handling system and the relationships between soil, crop, technology and the organization that influences the profitability of different systems for handling digestate on farms. The revenues are calculated as the sum of nutrients (N, P and K) available to plants. Costs are included for machinery (spreaders), labour and soil compaction. The costs could be divided into variable costs (depends mainly on spreading strategy) and fixed costs (annuity costs for the investment). For the prevailing conditions, storage cost is not included, as the farm companies do not finance it. Nor is the cost for the digestate included. The revenues reduced with the costs gives the net present value (Euro t -1 yr -1 ). Initially, input data have been compiled by: 1) visiting the digestion plant, 2) contacts with the farmer Lars Wretlund, LRF, 3) communication with Researcher Teodorita Al Seadi in the Bioenergy group at SDU, and 4) communication with machinery dealers. The calculations were done with set conditions prevailing in the region and on the farms concerning crop rotation and soil texture. Different spreading strategies were calculated for, as well as different properties of the residuals. For the liquid digestate, a band spreader was used and the spreading times were in growing winter wheat or before sowing in the autumn. The solid digestate was spread before sowing in the autumn. Conditions on farms The main soil type on the farms was clay soil (40% clay) and a 8 year crop rotation was used, Table 2.
13 11 Table 2. Crop rotation and estimated yield in tonnes per ha. For cereals, it is tonnes at 15% water content and for grassland tonnes dry matter per ha Crop Yield, t ha -1 Barley with under sown grass 4.5 Grassland 6.5 Grassland 6.5 Winter wheat 6 Winter wheat 6 Winter wheat 6 Winter wheat 6 Rape seed 2 Liquid digestate Application technology A 15m 3 tanker with boogie (tires 750/60x30.5, tire pressure 200 kpa) and boom with trailing hoses, 12 m working width, is used for spreading (Figure 1). The tanker is equipped with a pump-loading crane for filling. The investment cost for the tanker is SEK or Euro (Henrik Andersson, pers. com., 2006). The fixed costs for the tractor is not included, only the variable costs. The fixed costs for the tractor are considered as farm overheads. Figure 1. Band spreading with a tanker equipped with loading crane and a 12 m boom with trailing hoses.
14 12 In total tonnes liquid digestate is applied with two spreaders (7 500 tonnes per spreader and year). In average, the transportation distance between farm storage and field is 1600 m (one way) given by the survey among the farmers. Soil compaction and crop damage have been calculated according to Brundin & Rodhe (1984). The ammonia losses during storing and after spreading is set to 1% of total nitrogen content during storing, 7% of total ammoniacal nitrogen (TAN) content after spreading in growing wheat and 9% of TAN after spreading in early autumn with incorporation within 4 hours (Karlsson & Rodhe, 2002). A. Spreading strategy (crop, time) 1. Spreading in winter wheat, 2/3 in growing season (May June), and 1/3 before sowing in August. 2. Spreading in winter wheat, 1/3 in growing season (May June), and 2/3 before sowing in August. B. Application rate tonnes per ha in growing crop, 20 tonnes/ha before autumn tillage tonnes per ha at both spreading times C. Properties of liquid digestate 1. Estimated contents: 4.8 kg total-n t -1, 3.6 kg total ammoniacal nitrogen (TAN) t -1, 0.4 kg phosphorus (P) t -1, and 4.2 kg potassium (K) t High contents of nutrients (+25%): 6.0 kg total-n per tonne, 4.5 kg total ammoniacal nitrogen (TAN) t -1, 0.5 kg phosphorus (P) t -1, and 5.25 kg potassium (K) t Low contents of nutrients ( 25%): 3.6 kg total-n t -1, 2.7 kg total ammoniacal nitrogen (TAN) t -1, 0.3 kg phosphorus (P) t -1, and 3.15 kg potassium (K) t -1. Combining the different alternatives in A, B and C gives 12 pre-set scenarios, Table 4. Solid digestate Application technology A solid manure spreader with a single wheel axle (tires 28.1 x 26, tire pressure of 270 kpa), two vertical beaters, 12 m working width is used for spreading (Figure 2). The spreaders have 12 m working width and the net load on road is 7.4 tonnes (DLG, 2003) according to legalisations and for field 12 tonnes (Nordfarm, 2006). The investment cost for the tanker is SEK or Euro (Nordfarm, 2006). A tractor with front loader loads the spreader and the loading capacity is set to 60 t h -1.
15 13 In total tonnes solid digestate is applied with two spreaders (3 750 tonnes per spreader and year). In average, the transportation distance between the heap and field is set to 200 m (one way) as the solid digestate in most cases is placed onto or close to the fields where it will be applied. The fixed costs for loading include the cost for a scope but not for the tractor loader as it is considered as overhead. Figure 2. Solid manure spreader. Photo: Nordfarm (http://www.nordfarm.se) Soil compaction and crop damage have been calculated according to Brundin & Rodhe (1984). The solid digestate will be ploughed into the soil (50% of the cases) or incorporated with a harrow (50%), in both cases within 4 h after spreading. The ammonia losses are set to 20% of total nitrogen content during storage and 35% of TAN after spreading in early autumn with incorporation within 4 hours (Karlsson & Rodhe, 2002). A. Spreading strategy (crop, time) All solid digestate is spread in early autumn before sowing and incorporated into the soil within 4 h after spreading. B. Application rate The application rate is 30 t ha -1. C. Properties of solid digestate Estimated contents: 10.9 kg total-n t -1, 3.2 kg TAN t -1, 2.9 kg P t -1, and 3.8 kg K t -1. Variations in nutrient concentration will influence the result in the similar way as for liquid digestate. D. Net load capacity Two loading capacities are conceivable, 8.4 or 12 t. In public roads the load is limited to 8.4 tonnes with a single axle wagon but on private roads the wagon construction is the limit.
16 14 Prices Table 3 presents some of the data for the calculations. Table 3. Prices (year 2006) from Områdeskalkyl Ss 2006, Agriwise Components Euro SEK* N, per kg P, per kg K, per kg Labour, per hour Fuel, per litre *9.30 SEK=1 Real interest rate: 2.5%. Results Liquid digestate In Table 4 and Figure 3 the set scenarios and the corresponding net present values (Euro t -1 yr -1 ) of the digestate are presented. In all cases the P is utilised in the crop rotation by 100%. The relative high clay content (average 40% clay) of the soil, which delivers K, means an utilisation of 43% of K with a spreading area of 3276 ha. The nitrogen is utilised around 70% when the ammonia loss during storage and after spreading are counted for as well as only a certain part of the organic nitrogen. Autumn spreading means also an additional leakage as a function of the clay content of the soil. The nutrient content of the digestate has a big influence on the profitability for handling digestate on farm level. With a higher concentration, the value of the digestate will increase. Also, a higher application rate improves the profitability. It is more profitable to spread the main part (2/3) of digestate in the fore season in growing crop at the rate 30 tonnes per ha than the main part before sowing in the autumn. With a lower rate, 20 tonnes per ha in the growing crop, it is more profitable to apply most of the digestate before sowing in the autumn.
17 15 Table 4. Set scenarios based on combinations of A. Spreading strategy, B. Application rate in growing crop and C. Properties of digestate and the net present value in SEK and Euro per year per tonne of digestate handled Scenario Spreading strategy Application rate summer, t ha -1 2/3 30 summer 2/3 summer 30 2/3 30 summer Properties Net present value, of digestate Euro*/ t yr Net present value, SEK/ t yr High Estimated contents Low /3 summer 20 High /3 summer 20 Estimated contents /3 summer 20 Low /3 autumn 2/3 autumn 2/3 autumn 1 Euro = 9.30 SEK 30 High Estimated contents Low /3 autumn 20 High /3 autumn 20 Estimated contents /3 autumn 20 Low Euro t -1 yr Scenarios Figure 3. Net present value in Euro per tonne and year of digestate handled and spread with different strategies, rates and nutrient concentrations (storage cost not included). See Table 4 for explanations for the scenarios.
18 16 Variable and fixed costs, revenues and net present value in Euro t -1 yr -1 digestate handled and spread are presented in Table 5 for scenario 2 and 5. The costs for spreading and soil compaction are higher at a rate of 20 t ha -1 in growing crop (Scenario 5) instead of 30 t ha -1 (Scenario 5). On the other hand, the value for TAN is a little bit higher in scenario 5 than in 2 because the amount N applied in Scenario 2 is slightly above the optimal N-rate for winter wheat. Table 5. Variable and fixed costs, revenues and net present value of liquid digestate handled and spread, scenario 2 and 5 (7500 tonnes per spreader) Scenario 2 Scenario 5 Euro t -1 Euro t -1 yr -1 Euro t -1 yr -1 Euro t -1 Euro t -1 yr -1 Euro t -1 yr -1 Costs: Variable Fixed Total Variable Fixed Total Storage Loading Transport Spreading Soil compaction Sum costs Revenues, nutrient content TAN Organic N Phosphorus Potassium Sum revenues Net present value Figure 4 presents the revenues and the costs for the two possible spreading times (2/3 summer, 1/3 autumn) in Scenario 2. The nitrogen revenue is a little higher in summer, but on the other hand the soil compaction/crop damage is higher compared with spreading before sowing in autumn (ploughing after spreading in 50% of the cases). The spreading cost is a bit higher in the autumn because the application rate is only 20 t ha -1. The sums (revenues minus costs) are about the same for the two different application times, around 1.12 Euro t -1. In the set conditions when spreading tonnes yr -1 with one tanker, the fixed cost is 1.82 Euro t -1 yr -1 including the loading crane.
19 17 Value, Euro t -1 yr Sum per spreading time Fixed costs for spreader Loading, transport, spreading Soil/crop compaction N P K -4-6 Summer, in growing crop Autumn, before sowing Figure 4. Revenues (N, P, K), variable costs (loading, transport, spreading), fixed costs for spreader and the sum presented for the two spreading times in the summer in growing crop or in autumn before sowing (Scenario 2). Solid digestate The net present value in Euro per tonne and year of solid digestate handled and spread is rather high compared with the liquid digestate depending on high nitrogen and phosphorus content, autumn spreading with low soil compaction and lower investment costs for the spreader. Variable and fixed costs, revenues and net present value in Euro per tonne and year of digestate handled and spread is presented in Table 6 when 3750 tonnes is spread with one spreader (loading capacity 8.4 tonnes). If increasing the load to 12 tonnes, the loading and transport cost will decrease but on the other hand the cost for soil compaction increase. Thereby the result for the two loading capacities will be about the same.
20 18 Table 6. Variable and fixed costs, revenues and net present value in Euro per tonne and year of solid digestate handled and spread (3 750 tonnes per spreader) Loading capacity 8.4 tonnes Loading capacity 12 tonnes Euro t -1 Euro t -1 yr -1 Euro t -1 yr -1 Euro t -1 Euro t -1 yr -1 Euro t -1 yr -1 Costs: Variable Fixed Total Variable Fixed Total Storage Loading Transport Spreading Soil compaction Sum Revenues, nutrient content TAN Organic N Phosphorus Potassium Sum revenues Net present value Discussions In the calculations, the price for the digestate is set to zero. However, at present the farmers pay for the digestate, which means that the net present value for the digestate should be reduced with this cost. The calculations could thereby be a guideline for setting a reasonable price or a financial compensation to the farmers receiving the digestate. Also, the fixed costs for the tractor (loading, spreading) is not included in our calculations as it is defined as an overhead. When using a contractor for spreading, the farmer has to pay for the fixed costs for the tractor as well. As a reference, the society Maskinring in Enköping gives a price of 1.83 to 3.22 Euro t -1 slurry spread with a tractor and tanker equipped with loader crane, boom with trailing hoses and triple boogie (Maskinring, 2005). This could be compared with the calculated spreading cost (without tractor cost) in Scenario 2 of 2.13 Euro t -1. If less than tonnes liquid digestate is spread per tanker and year the fixed cost will increase and the opposite if higher amounts of digestate is handled with one tanker. However, there is a limit in amount of digestate possible to handle with one tanker. The spreading sequence must not last too long, as the time for spreading will not be optimal. Likely, the farms served by the same tanker have different optimal spreading times and there will be possible to plan the logistic for the tanker. Otherwise, too low spreading capacity will mean that not all digestate will be spread on desired times witch could mean reduced nutrient utilisation, higher soil compaction and/or reduced yield.
21 19 Under the set conditions, it is more profitable for the farmer to spread solid than liquid digestate. It depends on the high nitrogen and phosphorus content of the solid digestate, autumn spreading with low soil compaction and lower investment cost for the solid digestate spreader than for the liquid spreader. Conclusions The net present value for the liquid digestate handled was between 0.48 and 1.98 in Euro per tonne and year. The variation depends mainly on the nutrient content of the digestate. A 25% increase in nutrient concentration of the liquid digestate means an increased value of the digestate of about Euro per tonne and year. A higher application rate of the liquid digestate in growing crops (30 tonnes per ha compared with 20 tonnes per ha) improves the profitability for each spreading strategy with about Euro per tonne and year. It is more profitable to spread the main part (2/3) of liquid digestate in the fore season in growing crop at the rate 30 tonnes per ha than the main part before sowing in the autumn. With a lower rate, 20 tonnes per ha in the growing crop, it is more profitable to apply most of the digestate before sowing in the autumn. In total, the highest net present value for liquid digestate is reached with high nutrient concentrations and the higher rate (30 tonnes per ha) when spreading in growing crop (Scenario 1 and 7). The net present value for solid digestate handled was about 4.55 Euro per tonne and year. This is explained by the high nitrogen and phosphorus content, autumn spreading with relatively low soil compaction and lower investment costs for the spreader compared with a slurry spreader. The fixed costs for the tractor for loading the solid digestate and for spreading liquid/solid digestate are considered as overheads. If allocating these fixed costs to the digestate handled, means additional costs and thereby lower net present value for the digestate handled. An operation strategy of the biogas plant that results in a digestate with higher nutrient concentration improves the value of the digestate.
22 References 20 Agriwise, Områdeskalkyl Höstvete Ss (http://www.agriwise.org) Brundin S.G. & Rodhe L.K.K., Comparisons of Manure Handling Systems Under Swedish Conditions. J. Agric. Engng. Res. 58, DLG, Jeantil Stalldungstreuer EVR 16-12, DLG-Prüfbericht (http://www.dlg.org/de/landwirtschaft/testzentrum/pruefberichte/duengungbe waesserung.html) Karlsson S. & Rodhe L., Översyn av Statistiska Centralbyråns beräkning av ammoniakavgången i jordbruket emissionsfaktorer för ammoniak vid lagring och spridning av stallgödsel. Ett projekt utfört på uppdrag av Jordbruksverket. Uppdragsrapport,, Uppsala. Maskinring, Kalkylexempel Maskinring Enköping-Håbo. Nordfarm, Jeantil EVR vertikalspridare, produktblad. (http://www.nordfarm.se/katalog.php?product=5) Salomon E., Åkerhielm H. & Richert Stintzing A., Anaerobically digested source separated food residues as fertiliser in cereal production. In: Proceedings of 7th FAO/SREN-workshop: The future of biogas for sustainable energy production in Europe. 30 Nov-2 Dec, 2005, Uppsala, Sweden. Svensk Växtkraft, The Växtkraft-project in Västerås. Status report October Personal communication Henrik Andersson, Ranaverken AB, 2006.
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