Energy Crops For Biogas Production Research Articles

Sweet Sorghum as a Potential Fallow Crop in Sugarcane Farming for Biomethane Production in Queensland, Australia

Biogas from lignocellulosic feedstock is a promising energy source for decentralized renewable electricity, heat, and/or vehicle fuel generation. However, the selection of a suitable energy crop should be based on several factors such as biomass yields and characteristics or biogas yields and economic returns if used in biorefineries. Furthermore, the food-to-fuel conflict for the use of a specific energy crop must be mitigated through smart cropping techniques. In this study, the potential use of sweet sorghum as an energy crop grown during the fallow periods of sugarcane cultivation was evaluated. Nine sweet sorghum cultivars were grown on sandy loam soil during September 2020 in North Queensland, Australia. The overall results showed that the crop maturity had a profound influence on chemical composition and biomass yields. Further, the total insoluble and soluble sugar yields varied among the tested cultivars and were dependent on plant height and chemical composition. The biomass yields ranged from 46.9 to 82.3 tonnes/hectare (t/ha) in terms of the wet weight (w/w) of the tested cultivars, with the SE-81 cultivar registering the highest biomass yield per hectare. The gross energy production was determined based on the chemical composition and methane yields. Biochemical methane potential (BMP) studies in batch experiments at 37 °C showed that methane yields of 175 to 227.91 NmL CH4/gVSadded were obtained from the tested cultivars. The maximum methane yield of 227.91 NmL CH4/gVSadded was obtained for cultivar SE-35. However, SE-81 produced the highest methane yields on a per hectare basis (3059.18 Nm3 CH4/ha). This is equivalent to a gross energy value of 761.74 MWh/year or compressed biomethane (BioCNG) as a vehicle fuel sufficient for 95 passenger cars travelling at 10,000 km per annum. Overall, this study demonstrated that sweet sorghum is a potential energy crop for biogas production that could be cultivated during the fallow period of sugarcane cultivation in Queensland.

Cost–Benefit Analysis for Supply Chain of Renewable Gases from Perennial Energy Crops: The Case of Lithuania

The increasing production of renewable gases has been driving attention to perennial energy crop production, particularly the problem of choosing an attractive and effective way to produce the supply chain from the farmer to the biogas plant. The production of perennial energy crops for renewable gases may provide an excellent chance for a sustained bioeconomy and help to minimize the total environmental effect of the section. This study aims to demonstrate the scenarios associated with the production of five perennial energy crops, namely, Miscanthus, Switchgrass, Perennial Ryegrass, Common Sainfoin, and Lucerne, for renewable gases in the supply chain. The investigation was carried out utilizing cost–benefit methodology, during which a net benefit identification was executed by comparing the internal rate of return (IRR), payback period (PBT), and net present value (NPV), in addition to the benefit-cost ratio (RBC). According to the results, the best and most attractive perennial energy crops for biogas production include Miscanthus and Switchgrass. Perennial Ryegrass, Common Sainfoin, and Lucerne are not attractive crops for the supply chain of renewable gases. The earned revenue is too small to cover the costs of cultivation.

The potential of spineless cactus as a drought tolerant energy crop for biogas production: a geographic analysis of potential impact depending on water use efficiency (WUE) and mean annual rainfall (MAR) in South Africa

ISHS X International Congress on Cactus Pear and Cochineal: Cactus - the New Green Revolution in Drylands The potential of spineless cactus as a drought tolerant energy crop for biogas production: a geographic analysis of potential impact depending on water use efficiency (WUE) and mean annual rainfall (MAR) in South Africa

Influence of the Fertilization Method on the Silphium perfoliatum Biomass Composition and Methane Fermentation Efficiency

Biogas production is one of the solutions for replacing fossil fuels, which promotes the widespread use of green energy. The aim of this study was to determine the potential of Silphium perfoliatum as an energy crop for biogas production, as well as the effect of different fertilization doses (0, 85 and 170 kg N ha−1) on the production potential (NL CH4 kg−1 VS) of Silphium perfoliatum. The study investigated the use of different feedstocks, such as raw and ensiled Silphium perfoliatum biomass. The methane production ranged between 193.59 and 243.61 NL CH4 kg−1 VS. The highest biogas production potential was achieved with the biomasses which were cultivated with the highest fertilization dose (170 kg N ha−1), both for raw and ensiled crop biomasses, although the difference from the other fertilization doses was not significant. The feedstock (biomass and silage) and digestate parameters were investigated as well. The use of Silphium perfoliatum for biogas production seems very promising since its methane production potential was found to be similar to that of the most common energy crop, such as maize, indicating that Silphium perfoliatum can compete in the future with maize.

Moringa oleifera Lam. as an energy crop for biogas production in developing countries

Moringa oleifera Lam. (moringa) is a typical plant of tropical climates used as food, feed, and natural medication. This plant, rich in oil, could be valorized in the bioenergy sector, as infeed to produce biofuel, useful to save fossil sources, and to limit GHG emissions. This paper has evaluated its potential methane production by the anaerobic digestion process, in comparison to corn and giant cane, two typical food and non-food energy crops. Biogas production has been correlated to the content of fats, waxes, resins, cellulose, hemicellulose, proteins, and lignin in the three plants and to the different carbon types detected by solid-state nuclear magnetic resonance (NMR) technique. Chemical and spectroscopic analysis showed that organic matter of moringa contains more than 40% of fats having high potential to produce biogas. Although the quantity of biogas produced from corn was higher, among the three samples, the content in methane for corn and moringa was not statistically different. In particular, the methane yields for the giant cane, moringa, and corn were 363 ± 11, 442 ± 9, and 452 ± 12 m3 Mg DM−1 respectively: moringa produced less biogas but it was richer in methane. Methane concentration was positively correlated to the sum of fats, waxes, resins, hemicellulose, and proteins (R2 = 0.97; n = 3; p < 0.05). All these results seem to indicate that effectively moringa can be used as substrate to produce biogas by anaerobic digestion. When combined with small-scale low-tech digesters, this can represent a good opportunity for bioenergy production in developing countries.

Biogas production from submerged macrophytes\u2014a case study of regional biomass potentials in Germany

BackgroundUtilization of energy crops for biogas production has been controversially discussed in Germany due to negative environmental effects and the “food vs. fuel” debate. This led to a search for alternative substrates focusing on material from landscape management measures. Aquatic biomass is harvested during water body management, yet it has not been considered for energy generation.MethodsThe information where and which amount of biomass is collected by aquatic de-weeding operations in rivers and lakes was gathered via a nationwide survey. In addition to that, the amount of aquatic plant biomass potentially available in water bodies was estimated exemplarily for the flowing waters of Baden-Württemberg—by using data from the European Water Framework Directive surveys.ResultsThe survey revealed 172 locations of de-weeding operations in flowing waters and 93 in standing waters. These locations are concentrated in lowland rivers of the North German Plain as well as the Upper Rhine Plain. Standing water de-weeding operations were reported mainly from the foothills of the Alps. The overall amount of biomass harvested per year is 36,244 t of fresh biomass. Taking into account missing data, a maximum of 100,000 t of fresh biomass per year can be estimated for Germany. The case study on plant biomass de-weeded from waters in Germany revealed that only a small part of the total aquatic plant biomass is actually harvested.ConclusionsThe amount of biomass harvested and removed from water bodies in Germany is considerably lower than the harvest of other substrates from landscape management measures such as mowing of meadows or trimming of trees and hedges. However, larger amounts are accumulating locally, concentrated in some regions or at specific water bodies, e.g., reservoirs, for which regional value chains could be established. In order to make the exploitation of these local potentials economically viable, changes regarding the economic and technological framework are required.

Towards high-biomass yielding bioenergy crop Silphium perfoliatum L.: phenotypic and genotypic evaluation of five cultivated populations

Cup plant (Silphium perfoliatum L.) represents a promising alternative to silage maize as an energy crop for biogas production. This non-food plant possesses a highly ecological value due to its long blooming period, ability to grow in low-input agriculture and positive influence on soil structure. So far, there have been almost no breeding attempts for the cup plant, and all field experiments showing its high biomass yield were conducted by using only a few cultivated populations of unclear ancestry.Comprehensive assessment of five such populations for their biomass and methane yield parameters revealed substantial genetic variations indicating the possibility of improving these traits through selection and breeding. Higher biomass yield is likely to be achieved by breeding for secondary traits such as plant height, shoot diameter and internode number as well as photoperiod response. For increasing the methane production, reduced lignin or fibre content in the biomass seems to be important.Genetic relationships among the populations were estimated using tunable genotyping by sequencing (tGBS) technology. Genetic structure and phylogeny analyses revealed that all the plants belong to the same gene pool and share a common ancestry. Four out of five populations demonstrate a low genetic differentiation, whereas the fifth one represents a clear example of population stratification. To achieve a successful domestication and breeding of this new high-yielding perennial crop, a broader base of genetic diversity needs to be ensured and complemented by innovative breeding strategies driven by molecular genetic and modern genomics approaches.

Evaluating Bioenergy Cropping Systems towards Productivity and Resource Use Efficiencies: An Analysis Based on Field Experiments and Simulation Modelling

Silage maize (Zea mays L.) is the dominating energy crop for biogas production due to its high biomass yield potential, but alternatives are currently being discussed to avoid environmental problems arising from maize grown continuously. This study evaluates the productivity and resource use efficiency of different bioenergy crops and cropping systems using experimental and simulation modelling derived data. The field experiment consisted of two years, two sites differing in soil texture and soil water availability, different cropping systems and increasing nitrogen (N) supply. Continuous (two years) perennial ryegrass and two crop rotations including winter cover crops (double cropping system) and combining C4 and C3 crops were compared with continuous maize (maize–maize). The productivity of the crops and cropping systems in terms of dry matter (DM) yield was analyzed with respect to the fraction of light interception and light use efficiency (LUE). In addition, water use and water use efficiency (WUE), N uptake, and N use efficiency (NUE) were quantified. DM yield of the double cropping system was similar to that of continuous maize, due to a prolonged leaf area duration, compensating for the intrinsic lower LUE of C3 crops. Perennial ryegrass was less productive than the other crops/cropping systems. Nitrogen uptake and consequently N demand of perennial ryegrass and the C3 crops of the crop rotations were higher than for maize–maize. Groundwater recharge was mainly site-dependent, but was at both sites higher for maize than for the crop rotations or the perennial ryegrass system. Our results indicate that, in terms of biomass productivity, optimized rotations are feasible alternatives to maize–maize, but trade-offs exist in terms of water and N use efficiency.

Aerobic deterioration of corn stalk silage and its effect on methane production and microbial community dynamics in anaerobic digestion

Ensilage is a commonly used method of preserving energy crops for biogas production. However, aerobic deterioration of silage is an inevitable problem. This study investigated the effect of aerobic deterioration on methane production and microbial community dynamics through anaerobic digestion (AD) of maize stalk silage, following 9days air exposure of silage. After air exposure, hydrolytic activity and methanogenic archaea amount in AD were reduced, decreasing the specific methane yield (SMY); whereas lignocellulose decomposition during exposure improved the degradability of silage in AD and enhanced SMY, partially compensating the dry matter (DM) loss. 29.3% of the DM and 40.7% of methane yield were lost following 0–9days exposure. Metagenomic analysis showed a shift from Clostridia to Bacteroidia and Anaerolineae in AD after silage deterioration; Methanosaetaceae was the dominant methanogenic archaea.

Biotechnological application of sustainable biogas production through dry anaerobic digestion of Napier grass.

Napier grass (Pennisetum purpureum), represents an interesting substrate for biogas production. The research project evaluated biogas potential production from dry anaerobic digestion of Napier grass using batch experiment. To enhance the biogas production from ensiled Napier grass, thermal and alkaline pre-treatments were performed in batch mode. Alkali hydrolysis of Napier grass was performed prior to batch dry anaerobic digestion at three different mild concentrations of sodium hydroxide (NaOH). The study results confirmed that NaOH pretreated sample produced high yield of biogas than untreated (raw) and hot water pretreated samples. Napier grass was used as the mono-substrate. The biogas composition of carbon dioxide (30.10%), methane (63.50%) and 5ppm of H2S was estimated from the biogas. Therefore, fast-growing, high-yielding and organic matter-enriched of Napier grass was promising energy crop for biogas production.

Biogas production from energy crops in northern Greece: economics of electricity generation associated with heat recovery in a greenhouse

Herein a techno-economic assessment was performed on an energy-crop-based biogas plant coupled with a greenhouse for utilizing thermal energy produced by cogeneration. Seven energy crops were evaluated: triticale, maize, alfalfa, sunflower, clover, barley and wheat. According to the evaluation, triticale was the most competitive energy crop under selected climate conditions for northern Greece. Although maize displays higher biomass yield and biogas potential than the drought-resistant crop triticale, it has high irrigation demand that contributes significantly to total production costs. For a triticale-based biogas production to become economically feasible, agricultural arable area larger than 500 ha, or biogas plant size larger than 1000 kWel, is required. However, with public funding, biogas production becomes feasible at smaller area (>250 ha) or biogas plant size (>500 kWel). The inclusion of a greenhouse into the design of the biogas plant contributes positively to the economic viability of the entire system. Under this scenario, greenhouse financial income accounts for about 17–18% of total income. Results of a sensitivity analysis suggest that the selection of an appropriate energy crop for biogas production should be based principally on both digestibility (specific methane yield) and biomass yield per hectare, these factors being more critical than biomass production costs.

Drought Tolerance and Water‐Use Efficiency of Biogas Crops: A Comparison of Cup Plant, Maize and Lucerne‐Grass

AbstractThe cup plant (Silphium perfoliatum L.) is discussed as an alternative energy crop for biogas production in Germany due to its ecological benefits over continuously grown maize. Moreover, a certain drought tolerance is assumed because of its intensive root growth and the dew water collection by the leaf cups, formed by fused leaf pairs. Therefore, the aim of this study was to estimate evapotranspiration (ET), water‐use efficiency (WUE) and the relevance of the leaf cups for the cup plant's water balance in a 2‐year field experiment. Parallel investigations were conducted for the two reference crops maize (high WUE) and lucerne‐grass (deep and intensive rooting) under rainfed and irrigated conditions. Root system performance was assessed by measuring water depletion at various soil depths. Transpiration‐use efficiency (TUE) was estimated using a model approach. Averaged over the 2 years, drought‐related above‐ground dry matter reduction was higher for the cup plant (33 %) than for the maize (18 %) and lucerne‐grass (14 %). The WUE of the cup plant (33 kg ha−1 mm−1) was significantly lower than for maize (50 kg ha−1 mm−1). The cup plant had a lower water uptake capacity than lucerne‐grass. Cup plant dry matter yields as high as those of maize will only be attainable at sites that are well supplied with water, be it through a large soil water reserve, groundwater connection, high rainfall or supplemental irrigation.

Computing the biomass potentials for maize and two alternative energy crops, triticale and cup plant (Silphium perfoliatum L.), with the crop model BioSTAR in the region of Hannover (Germany).

BackgroundLower Saxony (Germany) has the highest installed electric capacity from biogas in Germany. Most of this electricity is generated with maize. Reasons for this are the high yields and the economic incentive. In parts of Lower Saxony, an expansion of maize cultivation has led to ecological problems and a negative image of bioenergy as such. Winter triticale and cup plant have both shown their suitability as alternative energy crops for biogas production and could help to reduce maize cultivation.ResultsThe model Biomass Simulation Tool for Agricultural Resources (BioSTAR) has been validated with observed yield data from the region of Hannover for the cultures maize and winter wheat. Predicted yields for the cultures show satisfactory error values of 9.36% (maize) and 11.5% (winter wheat). Correlations with observed data are significant (P < 0.01) with R = 0.75 for maize and 0.6 for winter wheat. Biomass potential calculations for triticale and cup plant have shown both crops to be high yielding and a promising alternative to maize in the region of Hanover and other places in Lower Saxony.ConclusionsThe model BioSTAR simulated yields for maize and winter wheat in the region of Hannover at a good overall level of accuracy (combined error 10.4%). Due to input data aggregation, individual years show high errors though (up to 30%). Nevertheless, the BioSTAR crop model has proven to be a functioning tool for the prediction of agricultural biomass potentials under varying environmental and crop management frame conditions.

Comparing energy crops for biogas production – Yields, energy input and costs in cultivation using digestate and mineral fertilisation

Analyses of six crops grown in southern Sweden for biogas production (hemp, sugar beet, maize, triticale, grass/clover ley, winter wheat) showed varying performance regarding methane yield per hectare and energy input and costs in the production and supply of crops as biogas feedstock. The highest biomass and biogas yield was observed for sugar beet. Crops with lower risk of negative environmental impact in cultivation, such as ley and hemp, produced less than half the methane energy yield per hectare. Triticale, also having less risk of negative environmental impact, gave an energy yield similar to that of winter wheat grain and maize.Replacing most of the mineral fertiliser with biogas digestate did not, with the exception for hemp, influence crop yields per hectare, but energy input in cultivation decreased by on average 34% for the six crops tested. For hemp and sugar beet the biogas feedstock costs for the freshly harvested crop per GJ methane were close to that of the economic reference crop, winter wheat grain. For maize, beet tops and first and second year ley, the feedstock costs were lower, and for triticale much lower. When ensiled crops were used for biogas the feedstock costs increased and only those of triticale silage remained slightly lower than the cost of dried wheat grain. However, all feedstock costs were so high that profitable biogas production based solely on ensiled crops would be difficult to achieve at present Swedish biogas sales prices.

Alkaline hydrogen peroxide pretreatment of energy crops for biogas production

AbstractIn this study, the influence of alkaline hydrogen peroxide (H2O2) pretreatment of the three different plant sources: Miscanthus giganteus, Sorghum Moench, and Sida hermaphrodita, for biogas production was investigated. The influence of temperature, reaction time, and H2O2 concentration on the efficiency of biomass degradation and on the further methanogenic fermentation were studied. The results obtained after chemical pretreatment indicate that using H2O2 at alkaline conditions leads to the decomposition of three major structures: lignin, hemicellulose, and cellulose. The best results were achieved for the process performed at 25°C for 24 h with the use of a 5 mass % H2O2 solution. Although the degradation level was very high for all three plant sources, the biogas production from the energy crops pretreated chemically was strongly inhibited by byproducts and the residual oxygen formed after H2O2 decomposition. This fact indicates that alkaline H2O2 pretreatment is a very promising method for plant material degradation for further biogas production, but pretreated biomass must be separated from supernatant before the fermentation process because of the high concentration of inhibitors in the hydrolysates. The best results were obtained for Sida with biogas and methane production of 2.29 Ndm3 and 1.06 Ndm3, respectively.

Energy crop production in double-cropping systems: Results from an experiment at seven sites

Energy crop production for fermentation in biogas plants significantly increased in the last years. At present maize is the most common energy crop for biogas production due to high dry matter and methane yields together with advanced breeding activities. In Germany nearly 80% of all energy crop biogas production is based on maize for silage. This dominance frequently causes environmental risks like soil erosion, nutrient losses and increased use of pesticides. Furthermore it puts societies’ acceptance towards biogas production increasingly at risk. Thus, the development of innovative cropping systems is essential for a sustainable energy crop production.This paper reviews results from 3 years field trials at seven locations with 12 different double-cropping systems (turnip rape, rye and mixture of rye–winterpea as first crops and maize, sorghum, sunflower and mixture of maize–sunflower as succeeding second crops) in comparison with three sole crops systems as references: maize and sunflower after mustard as catch crop and energy rye, harvested at dough ripeness as whole-crop silage.Double-cropping systems with rye or rye–pea as first crop and maize as second crop achieved highest DM yields of 23tDMha−1 on average, followed by sole cropped maize and double-cropping system of turnip rape and maize. Sole-cropped sunflowers had the lowest yield with nearly 15tDMha−1, followed by winter rye harvested at dough ripeness. Yields of other double-cropping systems had an intermediate position between those treatments. Methane yield per hectare was positively correlated with DM yield. Double cropping systems mostly achieved lower DM contents than sole cropping systems due to later sowing and altered photoperiodic influences. Further research on cultivars suitable for late sowing dates is necessary.Methane yield of crops was very similar with 282–298Nlkg−1 oDM, except for sorghum with 255Nlkg−1 oDM on average. Hence, differences in chemical components did not result in large changes regarding to methane yield, again except for sorghum, probably due to higher lignin contents.Double-cropping systems had mostly higher yield stability than sole cropping systems. The cultivation of two crops within 1 year may also spread the risk of weather extremes among two crops (or more if mixtures are grown) resulting in higher yield stability. This property is getting increasingly important with regard to climate change. Hence, double-cropping systems may contribute to a more sustainable energy crop production.

Regional energy concepts – based on alternative biomass cultivation for rural areas and its efficient energy usage

In the German electric energy market, the share of regional and decentralized power generation based on renewables has become more and more signifi cant. The following study describes the initiative of the energy and utilities company ‘EnBW Energie Baden-Wurttemberg AG’ (EnBW) in Germany to investigate regional energy concepts based on agricultural biomass. The study focuses on two aspects: the development of more sustainable approaches for energy crops cultivation and the effi cient use of cogeneration heat produced by bioenergy-driven power plants in rural areas. For the development of concepts and tools, a study area including two counties in the South-West of Germany were chosen. This article focuses on the work done on the county of Ravensburg. Geographic information system (GIS) tools are used to collect data about current land use practices related to energy crops. Subsequently, the suitability of new and more sustainable energy crops for biogas production based on current production regimes is investigated by following a modeling approach. The approach followed includes the screening of new agricultural substrates as substitutes for maize, which is currently the dominant energy crop for biogas production in Germany, the modeling of new substrate mixtures, and the measurement of the methane potential of energy crop samples in a biogas laboratory. Bioenergy-driven power plants are usually implemented nearby high biomass potentials—in rural areas, where heat demand is scarce. Optimizing heat use in combined heat and power (CHP) generators is a major issue for the future of bioenergy. The effi cient utilization of residual heat is one of the targets of the upcoming update of the German Renewable Energy Sources Act in 2012. Therefore, the profi table operation of biogas plants increasingly depends on the level of heat use which can be reached. The possibilities for heat supply to potential consumers in rural areas have been investigated using a GIS methodology on an object-based level for residential and tertiary/industry sectors. Building age and type have been used as parameters to estimate the annual heat consumption. Scenarios illustrating a renovation rate of the investigated objects (buildings) have been calculated. For the purpose of verifi cation and calibration, measurements of the heat demand of more than 3,000 houses have been used. Furthermore, on the basis of existing biogas plants, a techno-economic comparison of heat networks with micro gas networks for the distribution of renewable energy to demand sites have been performed.

Comparative environmental performance of three different annual energy crops for biogas production in Northern Italy

Abstract Bioenergy is becoming increasingly important for agriculture. However, the use of first generation crops for biofuels and bioenergy production is controversial due to their competition with food and feed. The cultivation of three different energy crops – wheat, maize and triticale – for biomass in order to produce biogas in Lombardy, in the Po Valley (Italy), was evaluated in this study to quantify their environmental profiles and identify the best biomass source from an environmental perspective. The choice of these cropping systems was based on the fact that they are well-known and extensively cultivated for energy purposes in Italy. The standard framework of the Life Cycle Assessment (LCA) was followed in this study and detailed inventories for these crops were designed. The environmental profile was analysed in terms of abiotic depletion, acidification, eutrophication, global warming, ozone layer depletion, photochemical oxidants formation, human toxicity and ecotoxicity. In addition, an energy analysis was performed using the cumulative energy demand method. According to the results, the selection of the best biomass source depends on several factors such as the functional unit and biomass yield. Therefore, a sensitivity assessment was done in order to identify these differences. Moreover, the most critical processes throughout the life cycle of the cropping systems were identified and improvement alternatives were proposed, specifically for the mineral fertilization (one of the most important hot spots). Thus, different scenarios built on alternative nitrogen based fertilizers were assessed in detail and discussed, resulting in the identification that the use of calcium ammonium nitrate instead of urea should improve the environmental profile regardless of the energy crop. Finally, the combination of triticale or wheat with maize classes 300, 400 and 500 in rotation systems was done in order to achieve similar biomass yields, per ha, to the maize classes 600 and 700, which were also evaluated. The best results were obtained for maize classes 600 and 700 regardless of the functional unit considered in all the categories assessed except in GWP, where triticale with maize 400 and with maize 500 were the best options.

A Multi-Criteria Assessment of Energy Crops for Biogas Production

This paper presents the system for the assessment of energy crops for biogas production. The system is based on simulation modelling and multi criteria decision analysis. The deterministic simulation system consists of deterministic production simulation models that enable different types of costs calculations for the production of energy crops, electrical and heat energy in biogas production. Simulation model results were further evaluated using a qualitative multi-attribute modelling methodology (supported by the software tool DEX-i) and quantitative analytical hierarchical process – AHP (supported by the software tool Expert Choice 2000TM). The analysis showed that by using current model the most relevant alternative used for energy crop for biogas production is maize. The maize results in the best multicriteria evaluation EC = 0.248 and DEX-i evaluation = appropriate. The best alternative for maize is sorghum with multicriteria evaluation of EC = 0.201 and DEX-i evaluation = less appropriate.

Methane production through anaerobic digestion of various energy crops grown in sustainable crop rotations

Biogas production is of major importance for the sustainable use of agrarian biomass as renewable energy source. Economic biogas production depends on high biogas yields. The project aimed at optimising anaerobic digestion of energy crops. The following aspects were investigated: suitability of different crop species and varieties, optimum time of harvesting, specific methane yield and methane yield per hectare. The experiments covered 7 maize, 2 winter wheat, 2 triticale varieties, 1 winter rye, and 2 sunflower varieties and 6 variants with permanent grassland. In the course of the vegetation period, biomass yield and biomass composition were measured. Anaerobic digestion was carried out in eudiometer batch digesters. The highest methane yields of 7500 – 10 200 m N 3 ha - 1 were achieved from maize varieties with FAO numbers (value for the maturity of the maize) of 300 to 600 harvested at “wax ripeness”. Methane yields of cereals ranged from 3200 to 4500 m N 3 ha - 1 . Cereals should be harvested at “grain in the milk stage” to “grain in the dough stage”. With sunflowers, methane yields between 2600 and 4550 m N 3 ha - 1 were achieved. There were distinct differences between the investigated sunflower varieties. Alpine grassland can yield 2700 – 3500 m N 3 CH 4 ha - 1 . The methane energy value model (MEVM) was developed for the different energy crops. It estimates the specific methane yield from the nutrient composition of the energy crops. Energy crops for biogas production need to be grown in sustainable crop rotations. The paper outlines possibilities for optimising methane yield from versatile crop rotations that integrate the production of food, feed, raw materials and energy. These integrated crop rotations are highly efficient and can provide up to 320 million t COE which is 96% of the total energy demand of the road traffic of the EU-25 (the 25 Member States of the European Union).