Svensk spannmålsbaserad drank: Alternativa sätt att tillvarata dess ekonomiska, energi- och miljömässiga potential

Distiller's grain is currently used mainly for animal feed. It can be fed either wet (8.5-28% DM) or dried (90% DM). The main animal groups fed distiller's grain are cattle and pigs, but the product can also be used for other species of farm animal. Distiller's grain can also be used as biogas feedstock, fuel or organic fertiliser. After fermentation, the digestible protein in distiller's grain (primary distiller's grain) remains in essentially unchanged form, while almost all the starch has been consumed. Distiller's grain is therefore a protein feed. Fibre polysaccharides (cellulose and hemicellulose) also remain in distiller's grain. With other processing techniques these can be broken down to fermentable sugars and fermented into ethanol. The distiller's grain from that process, so-called secondary distiller's grain (also called enhanced distiller's grain), can be used in similar applications to normal (primary) distiller's grain and therefore it was also studied in this project. A disadvantage of the secondary processing technique is that some of the amino acids in the distiller's grain protein are broken down. In our economic calculations and life cycle assessment, it was assumed that 50% of lysine and 20% of methionine had been broken down in secondary distiller's grain. Our main objective was to evaluate how distiller's grain can be used in various applications, and to estimate the economic value and production costs for these applications. We also evaluated the environmental impact in terms of e.g. greenhouse gas emissions and energy requirements in the production of ethanol and distiller's grain for the different applications. In addition, we analysed the significance of subjecting the distiller's grain to the additional process in which a proportion of the grain cellulose and hemicellulose is converted into ethanol and secondary distiller's grain is produced. Ruminants, e.g. cattle and sheep, can receive a large proportion of the protein in their feed as wheat distiller's grain. Protein from other sources may be needed so that the total amount of protein behaves as required in digestion. For pigs and poultry, around 10% of the feed may consist of wheat distiller's grain. Piglets are sensitive to the palatability of their protein and therefore it is not certain that they can always eat feed containing wheat distiller's grain. For poultry, the proportion of distiller's grain products in the feed may have to be limited to prevent viscosity problems and wet, sticky manure. For horses, 10-20% of the concentrate can consist of wheat distiller's grain if the animals do not suffer from palatability problems. Distiller's grain can be fired either wet or dry, depending on the heating equipment. Distiller's grain based on grain containing high levels of alkali metals gives an ash with a low melting point, which makes it likely to sinter easily. High concentrations of sulphur and chlorine can cause problems with corrosion. The ash content is quite high, about 5% of DM. The high content of nitrogen (about 5% of DM) makes nitric oxide emissions likely to be high, i.e. similar to those obtained from incineration of rapeseed expeller, which has a similar nitrogen content, and 2 to 3.6-fold higher than for nitrogen-poor fuels. When secondary processing is performed to use part of the cellulose and hemicellulose for the production of ethanol, substances that give problems with firing are concentrated, which increases the likelihood of incinerator problems. In addition, the ash content is higher, while the total heating value decreases as the cellulose and hemicellulose is converted to ethanol. As a fertiliser, primary distiller's grain solids contain about 5.7% nitrogen, 0.8-1.5% phosphorus and 0.9 to 1.9% potassium. Our calculations showed that secondary distiller's grain solids are likely to contain about 7.4% nitrogen, 1.0-2.0% phosphorus and 1.2-2.4% potassium. The mineralisation (release) of organically bound nitrogen is probably slow, as is the case for e.g. rapeseed expeller. Distiller's grain is a suitable substrate for biogas production. The plant nutrients in biodigested distiller's grain are probably more plant-available than prior to digestion. However, distiller's grain is a nitrogen-rich substrate that can cause problems with high ammonium nitrogen concentrations in biogas reactors. This applies to a greater degree to secondary distiller's grain, where the nutrients are concentrated since part of the cellulose and hemicellulose has been converted into ethanol. The yield in the biogas production process should be able to reach 60-70% and in good conditions perhaps 80%. We prepared cost estimates comparing the economic value of distiller's grain stillage derived from the economic value of barley and soybean meal (metabolisable energy and crude protein for cattle and horses, lysine for pigs and poultry, or methionine for poultry) in the feed, forest wood chips for fuel (lower heating value), nitrogen, phosphorus and potassium for use as fertiliser, and the sale of electricity and heat from a large farm biogas plant, including the value of nitrogen, phosphorus and potassium in the digestion residues. In the studies of biogas digestion, cases with both 60 and 80% yield and cases with and without digestion costs were included. Costs were studied for the period 2005-2010. Primary distiller's grain had the highest value when used as feed for poultry (methionine) followed by: feed for horses and cattle, biogas (80%) excluding digestion costs, biogas (60%) excluding digestion costs, poultry feed (lysine) and pig feed, fertiliser, fuel for heating, biogas (80%) including digestion costs and biogas (60%) including digestion costs. Secondary distiller's grain altered the sequence, with feed for horses and cattle giving the highest value followed by: poultry feed (methionine), biogas (80%) excluding digestion costs, biogas (60%) excluding digestion costs, fertiliser, poultry feed (lysine) and pig feed, biogas (80%) including digestion costs, fuel for heating and biogas (60%) including digestion costs. The value of secondary distiller's grain is higher than that of primary distiller's grain for all uses except as feed to pigs and poultry (based on lysine or methionine). The reason for the lower value, when fed to pigs and poultry is that in the secondary process to extract 13% more ethanol, 50% of lysine and 20% of methionine are broken down. The world market prices for barley and soybean meal had a major impact on the value of the distiller's grain, as well as on yield, etc. from the biogas plant. The price of wood chips and manure had slightly less impact on the results, since these products had a lower value from the beginning. Life cycle assessment was carried out on the production of ethanol with system expansion, where the distiller's grain replaced other products depending on its use. The following products were assumed to be replaced depending on the distiller's grain used: soybean meal and barley in animal feed (crude protein for cattle and horses; lysine for pigs and poultry; methionine for poultry); wood chips for fuel; fertiliser NPK at fertilisation; ley and excess fertiliser from biogas feedstock. For primary distiller's grain, the impact on global warming increased in the order: poultry (methionine), horses and cattle, and poultry and pigs (lysine), biogas (80% and 60%), fertilisers and fuel. The order was roughly the same for acidification and eutrophication. For energy consumption, the impact increased in the order: biogas (80% and 60%), fertiliser, fuel, poultry (methionine), horses and cattle, and poultry (lysine) and pigs. For secondary distiller's grain, the impact on global warming increased in the order: horses and cattle, poultry (methionine), biogas (80% and 60%), pigs and poultry (lysine), fertilisers, and fuel. For energy consumption, the corresponding ranking was: biogas (80% and 60%), horses and cattle, poultry (methionine), fertiliser, fuel, and finally pigs and poultry (lysine). The production of ethanol and secondary distiller's grain gives the lowest environmental impact when the secondary distiller's grain is used as feed for cattle and horses, or is used as biogas feedstock. With the other uses of distiller's grain, the production of ethanol and primary distiller's grain gives the least environmental impact. Energy consumption for producing ethanol and secondary distiller's grain, for all uses of distiller's grain, is higher than the production of ethanol and primary distiller's grain. The reason for this is that an energyconsuming additional process is required for the production of ethanol and secondary distiller's grain. Instead of biogas in the system described above, we then assumed that the fuel produced replaced fossil fuel (petrol) directly in light vehicles. In this case the environmental benefits in terms of greenhouse gas emissions were greater than in any other case due to the direct replacement of fossil fuel. In contrast to the other uses of distiller's grain studied here, primary distiller's grain was better than secondary distiller's grain in fuel production as it had more cellulose and hemicellulose left that could be digested to biogas. The energy gain showed a similar result to the greenhouse gases. The energy balance was calculated as the ratio of output energy of ethanol and distiller's grain in terms of lower heating value (net calorific value), and energy consumption in all stages of the entire chain. This extended from the cultivation of winter wheat until the finished ethanol fuel was ready for use as a fuel, or the distiller's grain had been transported to the farm and was ready to be fed to animals. The value obtained was 1.96 for ethanol and primary distiller's grain from an ordinary ethanol process and 1.75 for ethanol and secondary distiller's grain from a process that provides 13% more ethanol from the cellulose and hemicellulose in the grain. When the distiller's grain was not dried, the energy balance improved to 2.84 and 2.22, respectively. If half the area of wheat, barley and triticale in Sweden (almost 400 000 ha) were to be used for ethanol production, nearly 600 000 tonnes of primary distiller's grain would be produced. The current animal population in Sweden could consume about 65% of this, with dairy cows consuming one-third and slaughter pigs barely one-sixth. If even a fraction of the grain cellulose and hemicellulose were to be used for ethanol production, about 470 000 tonnes of secondary distiller's grain would be obtained, of which the current Swedish animal population could consume about 75%, with dairy cows consuming almost two-fifths and slaughter pigs barely one-fifth. There is nothing directly limiting the amount of distiller's grain that can be used for combustion or fertiliser other than the monetary value in these applications. For combustion, a key factor is that thermal power plants can accept fuel sintering (gives slag and deposits in boilers). The maximum potential for heat production according to the above is 2.9 TWh for primary distiller's grain and 2.5 TWh for secondary distiller's grain. If the distiller's grain were to be digested with 80% yield according to the above, the potential would become 2.4 and 2.1 TWh, respectively (as measured by the lower heating value of methane produced). This is substantially more than can be digested in potential biogas plants for other substrates, especially when the distiller's grain products have a high nitrogen content. Our conclusion and recommendation to the industry is that distiller's grain should be used primarily for animal feed. Secondary distiller's grain should be primarily fed to ruminants. Production costs can be high if a biogas plant is built solely for the digestion of distiller's grain. Anaerobic digestion of distiller's grain is currently economically viable primarily in digestion processes where distiller's grain has a additional value, and does not have to be paid for by the biogas plant. Otherwise distiller's grain digestion might be costly. Incineration of distiller's grain should be avoided. Based on areas where there is a shortage of data, suggested topics for future research would be: The characteristics of secondary distiller's grain in feed applications; the potential of distiller's grain as a food commodity; distiller's grain as a potential biogas feedstock in codigestion with other substrates; the properties of distiller's grain fuel alone and together with other fuels in practical applications; the properties of the syrup fraction as a binding agent in the manufacture of feed pellets, fuel pellets and briquettes; life cycle assessment of the biogas from distiller's grain as a replacement fuel in different vehicle fleets; life cycle assessment and economic calculations comparing different potential ethanol crops, and the environmental impact of production of ethanol compared with biogas.