Indirect energy input of agricultural machinery in bioenergy production

Sustainability of bioenergy products should be evaluated by means of an energy analysis that takes into account all relevant direct and indirect energy inputs. Direct energy input is viewed as the major energy consuming factor, and is quite easy to measure. Indirect energy input, however, has received relatively scant attention, so it is likely to be insufficiently analysed and possibly underestimated. This paper reviews the data available and suggests the type of research that would be needed to get a better understanding of the indirect energy input. The analysis addresses questions about the use of energy to produce and maintain agricultural machinery, the allocation of energy to different bioenergy products, and the real use and lifetime of machinery.     

Energy trade-offs between intensive biomass utilization, site productivity loss, and ameliorative treatments in loblolly pine plantations

Loblolly pine plantations are the most important source of forest products in the US and the slash remaining after conventional harvest represents a significant potential source of bioenergy. However, slash removal in intensive harvests might, under some circumstances, reduce site productivity by reducing soil organic matter and associated nutrients. Two complimentary studies in the Gulf Coastal Plain of the southeastern US were designed to test whether harvest intensity (level of biomass removal) could have a negative long-term impact on site productivity. Harvesting tree crowns in addition to the merchantable bole had a negative impact (18%) on pine biomass accumulation by age 7–10 years on 15 of 19 research blocks. Sites at risk of harvest-induced reductions in productivity were relatively unproductive prior to harvest and had low soil phosphorus (P) concentrations. Intensive harvesting, fertilization, and chemical control of non-crop vegetation were all energy efficient; the additional biomass energy gained through these practices was two-orders of magnitude greater than the energy needed to conduct the activities. Harvest of slash for bioenergy in the Gulf Coastal Plain of the southeastern US has the potential to reduce productivity on infertile soils, but fertilization has the potential to restore and even improve productivity on those sites in an energy-efficient way.     

Evaluation of annual bioenergy crops in the boreal zone for biogas and ethanol production

Three annual plant species, maize, hemp and faba bean were tested for suitability as dedicated biomass crops in Boreal conditions. Biomass yields were 10-15 t ha^-1. The crops were analyzed for their composition and tested as raw materials for conversion to methane and to fermentable sugars. The methane yield was 379 ± 16 Ndm³ kg⁻¹ VS⁻¹ from maize, 387 ± 20 Ndm³ kg⁻¹ VS⁻¹ from faba bean and 239 ± 9 Ndm³ kg⁻¹ VS⁻¹ from hemp. Based on the yield per hectare, maize proved to be the most potential raw material source for methane production. Analogous to methane production, maize was the most productive raw material also in standard hydrolysis tests, with a conversion yield of about 80% of the theoretical sugars. Based on the amount of carbohydrates, the highest theoretical yield per hectare was obtained with hemp. However, considering all parameters, including the need for weeding and fertilizers, all three crops studied proved to be attractive options for cultivation in boreal conditions as well as being used as energy crops in boreal climate.     

Cost efficient utilisation of biomass in the German energy system in the context of energy and environmental policies

The possible uses of biomass for energy provision are manifold. Gaseous, liquid and solid bioenergy carriers can be alternatively converted into heat, power or transport fuel. The contribution of the different utilisation pathways to environmental political targets for greenhouse gas (GHG) emission reduction and energy political targets for the future share of renewable energy vary accordingly to their techno-economic characteristics. The aim of the presented study is to assess the different biomass options against the background of energy and environmental political targets based on a system analytical approach for the future German energy sector. The results show that heat generation and to a lower extent combined heat and power (CHP) production from solid biomass like wood and straw are the most cost effective ways to contribute to the emission reduction targets. The use of energy crops in fermentation biogas plants (maize) and for production of 1st generation transportation fuels, like biodiesel from rapeseed and ethanol from grain or sugar beet, are less favourable. Optimisation potentials lie in a switch to the production of 2nd generation biofuels and the enhanced use of either biomass residues or low production intensive energy crops.     

Competition between biomass and food production in the presence of energy policies: a partial equilibrium analysis

Bioenergy has several advantages over fossil fuels. For example, it delivers energy at low net CO₂ emission levels and contributes to sustaining future energy supplies. The concern, however, is that an increase in biomass plantations will reduce the land available for agricultural production. The aim of this study is to investigate the effect of taxing conventional electricity production or carbon use in combination with subsidizing biomass or bioelectricity production on the production of biomass and agricultural commodities and on the share of bioelectricity in total electricity production. We develop a partial equilibrium model to illustrate some of the potential impacts of these policies on greenhouse gas emissions, land reallocation and food and electricity prices. As a case study, we use data for Poland, which has a large potential for biomass production. Results show that combining a conventional electricity tax of 10% with a 25% subsidy on bioelectricity production increases the share of bioelectricity to 7.5%. Under this policy regime, biomass as well as agricultural production increase. A carbon tax that gives equal net tax yields, has better environmental results, however, at higher welfare costs and resulting in 1% to 4% reduction of agricultural production.     

The influence of organic and inorganic fertiliser application rates on UK biomass crop sustainability

Bioenergy and energy crops are an important part of the UK’s renewable energy strategy to reach its greenhouse gas reduction target of 80% by 2050. Ensuring the sustainability of biomass feedstocks requires a greater understanding of all aspects of energy crop production, their ecological impacts and yields. This work compares the life-cycle environmental impact of natural gas and biomass from two energy crop systems grown under typical UK agronomic practice. As reported in previous studies the energy crops provide significant reductions in global warming potential (GWP) compared to natural gas. Compared to no fertiliser application, applying inorganic fertiliser increases the GWP by 2% and applying sewage sludge increases the GWP by a lesser extent. In terms of an equivalent GWP savings per unit area of land, the emissions associated with fertiliser production and application can be offset by a yield increase of <0.2 t/ha. However, very large increases in eutrophication and acidification levels are incurred compared to the natural gas reference case when applying either fertiliser. For sewage sludge the impact of varying the allocation factor between the function of wastewater treatment and that of crop growth is also illustrated.     

Beneficial effects of biochar application to contaminated soils on the bioavailability of Cd,Pb and Zn and the biomass production of rapeseed (Brassica napus L.)

Phytoremediation of soils contaminated by heavy metals was tested by liming (CaCO₃) or adding biochar (1%, 5% and 10%, mass fraction) and by growing rapeseed (Brassica napus L.), a common bioenergy crop. Bioavailable metal concentrations (0.01 mol L⁻¹ CaCl₂ extraction) decreased with increasing concentrations of biochar amendment. The reduction reached 71%, 87% and 92% for Cd, Zn and Pb respectively in the presence of 10% biochar. Twelve weeks after sowing, all plants cultivated on the untreated soil and on the soil amended by biochar at 1% had died, while the plants grew normally on the soil that had the other treatments. Compared to liming, treatment with 10% biochar proved equally efficient in reducing metal concentrations in shoots but the biomass production tripled as a result of the soil fertility improvement. Thus, in addition to C sequestration, the incorporation of biochar into metal-contaminated soils could make it possible to cultivate bioenergy crops without encroaching on agricultural lands. Although additional investigations are needed, we suggest that the harvested biomass might in turn be used as feedstock for pyrolysis to produce both bioenergy and new biochar, which could contribute further to the reduction of CO₂ emission.     

Evaluation the potential economic impacts of Taiwanese biomass energy production

The Taiwanese rice paddy land set-aside program diverts a substantial land area. Given today’s high energy prices and interests in energy security, that set-aside area could be converted to produce bioenergy feedstocks. This study evaluates the economic and environmental impacts of such a policy change using a Taiwanese agricultural sector model. The results show that such a strategy provides increased farm revenue, increased rural employment, increased energy sufficiency and reduced greenhouse gas emissions but also increased government expenditures. These outcomes indicate that the agricultural sector could play a positive role by producing renewable energy.     

Current status and prospects of biomass resources for energy production in Lithuania

Basic biomass sources in Lithuania are comprised of wood, straw, biofuel and biogas. The current status and the problems from using biomass for energy production in Lithuania are analyzed. The possibility of utilizing wood waste, firewood, straw and biogas for energy is evaluated. Forest comprises about 2.05 Mha or 31.3% of Lithuanian land area. About 4.3 million m³ solid volume of wood per year can be used for fuel (843 ktoe). Wood as fuel is used directly or in processed form (briquettes, pellets and chips).Agriculture produces approximately 1.5–2.0 million tons of straw each year for animal feed, litter and olericulture. Around 30–40% (130 ktoe) could be used as fuel for energy production. Boiler houses for combusting the straw have increased and now comprise about 7 MW. Straw is also used for heating private houses.Sources for biogas production include sludge from water cleaning equipment, animal manure and organic waste in food processing companies. Total volume of operating bioreactors comprises about 24 000 m³, and annual production of biogas is 6.3 million m³ per year (3.4 ktoe). By year 2010 the total volume of bioreactors will increase to 35 000 m³ and about 50 000 m³ by 2040.In Lithuania biodiesel and bioethanol are mainly used in blending with conventional fuel. Following the requirements of the European Union (EU), 2% of total consumed fuel per year is to be produced in 2005. By 2010 biofuel should comprise not less than 5.75% of all fuel existing in the market.     

Supply chain optimization of residual forestry biomass for bioenergy production: The case study of Portugal

Within a large set of renewable energies being explored to tackle energy sourcing problems, bioenergy can represent an attractive solution if effectively managed. The supply chain design supported by mathematical programming can be used as a decision support tool to the successful bioenergy production systems establishment. This strategic decision problem is addressed in this paper where we intent to study the design of the residual forestry biomass to bioelectricity production in the Portuguese context. In order to contribute to attain better solutions a mixed integer linear programming (MILP) model is developed and applied in order to optimize the design and planning of the bioenergy supply chain. While minimizing the total supply chain cost the production energy facilities capacity and location are defined. The model also includes the optimal selection of biomass amounts and sources, the transportation modes selection, and links that must be established for biomass transportation and products delivers to markets. Results illustrate the positive contribution of the mathematical programming approach to achieve viable economic solutions. Sensitivity analysis on the most uncertain parameters was performed: biomass availability, transportation costs, fixed operating costs and investment costs.     

Life cycle assessment of different bioenergy production systems including perennial and annual crops

Energy crops are expected to greatly develop in a very short-term bringing to significant social and environmental benefits. Nevertheless, a significant number of studies report from very positive to negative environmental implications from growing and processing energy crops, thus great uncertainty still remains on this argument. The present study focused on the cradle-to-grave impact assessments of alternative scenarios including annual and perennial energy crops for electricity/heat or first and second generation transport fuels, giving special emphasis to agricultural practices which are frequently surprisingly neglected in Life Cycle Assessment studies despite a not secondary relevance on final outcomes. The results show that cradle-to-farm gate impacts, i.e. including the upstream processes, may account for up to 95% of total impacts, with dominant effects on marine water ecotoxicity. Therefore, by increasing the sustainability of crop management through minimizing agronomic inputs, or with a complementary use of crop resides, can be expected to significantly improve the overall sustainability of bioenergy chains, as well as the competitiveness against fossil counterparts. Once again, perennial crops resulted in substantially higher environmental benefits than annual crops. It is shown that significant amount of emitted CO₂ can be avoided through converting arable lands into perennial grasslands. Besides, due to lack of certain data, soil carbon storage was not included in the calculations, while N₂O emission was considered as omitted variable bias (1% of N-fertilization). Therefore, especially for perennial grasses, CO₂ savings were reasonably higher that those estimated in the present study. For first generation biodiesel, sunflower showed a lower energy-based impacts than rapeseed, while wheat should be preferred over maize for first generation bioethanol given its lower land-based impacts. For second generation biofuels and thermo-chemical energy, switchgrass provided the highest environmental benefits. With regard to bioenergy systems, first generation biodiesel was less impacting than first generation bioethanol; bioelectricity was less impacting than first generation biofuels and second generation bioethanol by thermo-chemical hydrolysis, but highly impacting than Biomass-to-Liquid biodiesel and second generation bioethanol through enzymatic hydrolysis.     

Bioenergy in Australia: An improved approach for estimating spatial availability of biomass resources in the agricultural production zones

Bioenergy production from crops and agricultural residues has a greenhouse gas mitigation potential. However, there is considerable debate about the size of this potential. This is partly due to difficulties in estimating the feedstock resource base accurately and with good spatial resolution. Here we provide two techniques for spatially estimating crop-based bioenergy feedstocks in Australia using regional agricultural statistics and national land use maps. The approach accommodates temporal variability by estimating ranges of feedstock availability and the shifting nature of zones of the highest spatial concentration of feedstocks. The techniques are applicable to biomass production from forestry, agricultural residues or oilseeds, all of which have been proposed as biofuel feedstocks.     

Effect of fertilization on the biomass production of coppiced mixed birch and willow stands on a cut-away peatland

This investigation deals with the biomass production of coppiced mixed birch and willow stands growing on a peat cut-away area at Aitoneva, Kihniö (62°12′N, 23°18′E), Finland. The 16-year-old stands were harvested and left to coppice for 14 years, fertilization experiment (control, PK and wood ash fertilization) with three replications was established after the clear cutting. The mother stands before clear cutting (11,000 stems per hectare on average) were dominated by silver birch (69% of the stem number). After clear cutting the number of stems rose 7-fold to 75 500 stems ha⁻¹. Now the stands were dominated by Betula pubescens with 46% out of the total stem number, the share of B. pendula being only 25% and with Salix spp 29%. At the age of 14 years self-thinning had decreased the stem number to 12,800 stems ha⁻¹. The leafless biomass production of the coppiced stands on the control plots was lower than that of the seed originated mother stands had been during the previous rotation. However, with fertilization the 14-year-old coppiced stands reached the same total production as the 16-year-old mother stands had reached. The foliar phosphorus concentrations showed a severe phosphorus deficiency on the controls. Fertilization increased biomass of the stands considerably. After 14 growing seasons the above-ground leafless dry-mass of the fertilized stands was 61.8 (PK-fertilization) and 61.4 t ha⁻¹ (Ash) and that of the control stands 37.6 t ha⁻¹. A single PK fertilizer application had increased the standing biomass by 24 t ha⁻¹ (64%). Even though fertilization increased biomass production it did not increase nutrient concentrations of wood and bark, but rather decreased them. Fertilization decreased the nitrogen concentrations of leafless above-ground biomass.     

Effect of bioaugmentation on hydrogen production from organic fraction of municipal solid waste

In the present study, the effect of bioaugmentation with three bacterial species (i.e. E. coli, Bacillus subtilis and Enterobacter aerogenes) on the hydrogen production from organic fraction of municipal solid waste was evaluated at different bacteria/sludge ratios (0.05, 0.10, 0.15, 0.20, 0.25, 0.30, 0.35 and 0.40). Cumulative hydrogen production, lag phases, and maximum hydrogen production rates were analyzed using modified Gompertz model. The highest cumulative and volumetric hydrogen production of 564.4 ± 10.9 mL and 1.61L_H2/L_substrate respectively was achieved for bioaugmentation with Bacillus subtilis at bacteria/sludge ratio of 0.25. The corresponding highest hydrogen yield was 43.68 mLH₂/gCarbo. For bioaugmentation with E. coli and Enterobacter aerogenes, the maximum cumulative hydrogen production of 423.4 ± 10.6 mL and 486.3 ± 10.6 mL respectively was obtained from bacteria/sludge ratio of 0.20. Corresponding highest hydrogen yields were 32.9 mLH₂/gCarbo and 37.1 mLH₂/gCarbo respectively. Bioaugmentation shortened the lag phases and improved COD removal. Volatile fatty acid generation was also improved with the bioaugmentation.     

Comparative life cycle assessment of the integrated generation of solid fuel and biogas from biomass (IFBB) and whole crop digestion (WCD) in Germany

Today’s bioenergy systems are very different in cultivation, conservation, conversion of the biomass as well as in the form of the final energy. The assessment of bioenergy systems concerning environmental impacts is increasingly up for discussion. Future challenges will be the development of procedures which reconcile high-yielding and efficient approaches with environment friendly production. Against this background the system of Integrated Generation of Solid Fuel and Biogas from Biomass (IFBB) was suggested to increase net energy yields over a wide range of energy crops in order to obtain a higher biodiversity in energy crop cultivation. In the IFBB procedure the ensiled biomass is separated into a liquid phase for biogas production and into a solid fraction for combustion.This work is aimed at the assessment of the IFBB system in comparison to whole crop digestion (WCD). The assessment is based on crop production in a double-cropping system where winter rye and maize are grown subsequently within one growing season. The main parameters investigated are the efficiency of the whole process, primary energy and greenhouse gas savings as well as potentials of acidification and eutrophication according to principles of Life Cycle Assessment. The calculation of energy efficiency shows a superiority of the IFBB system due to a mainly thermal use of the biomass. Savings of fossil primary energy average at a similar level, whereas greenhouse gas savings are slightly higher for WCD. Investigations on acidification and eutrophication show that both bioenergy systems caused higher emissions compared to the fossil-based reference technique.     

Slow expansion and low yields of willow short rotation coppice in Sweden; implications for future strategies

About 16 000 ha of commercial willow Short Rotation Coppice (SRC) fields for production of biomass for energy were planted in the early 1990s in Sweden. The cultivated with SRC area has remained almost stable and was slightly decreased during the last years despite the incentives and predictions for drastic increases. Similar incentives and predictions in other countries have been lately launched. The bioenergy produced in the planted SRC areas in Sweden has been lower than anticipated, partly due to the lower than expected biomass yields and the termination of some willow SRC plantations. Explanations for the low yields are depicted based on analyzing the results of a survey where 175 willow SRC growers participated. Lower biomass yields are attributed to: (i) the low input in management activities; (ii) the choice of land for the willow SRC plantation; (iii) and the level of personal involvement of the farmer. Understanding the reasons to earlier years’ performance of willow SRC is important for development of better performing systems in the future, in Sweden as well as in other countries.     

Determination and comparison of combustion kinetics parameters of agricultural biomass from olive trees

Thermogravimetric curves in air, measured for the different types of agricultural residues from olive trees (leaves, pruning and wood) at different heating rates (5, 10, 20, 40, 100 K/min), are subjected to kinetic evaluation by model-based and model-free methods. It is shown that the combustion process in the samples analyzed can be divided into three stages: water removal, roasting phase and char decomposition. At every stage, the activated energy varies with the mass conversion for the kinetic models considered. Its value was determined by the model-free methods, of which Flynn–Wall– Ozawa and Kissinger–Akahira–Sunose were the most appropriate for this purpose and resulted in similar values of activated energy. Once the activation energy was determined, the order of the reactions and the frequency factors of each stage were calculated by means of the Coats–Redfern model-based method in order to complete the determination of the kinetic triplet. From the results obtained, it was deduced that the most feasible reaction order was one.     

Industrial supply chains and production machinery of forest chips in Finland

Metsäteho Oy surveyed the industrial supply chains used in the production of forest chips in 2006 in Finland. The Metsäteho study also conducted a survey of the production machinery of forest chips used by energy plants in 2007, and provided an estimate of industrial supply chains and future machinery requirements for forest chip production in Finland.The majority of the logging residue chips and chips from small-sized thinning wood were produced using the roadside chipping supply chain in 2006. The chipping at plant supply chain was also significant in the production of logging residue chips. The majority of all stump wood chips consumed were comminuted at the plant, and with only around one fifth comminuted at terminals. The role of the terminal chipping supply chain was also significant in the production of chips from logging residues and small-sized wood chips. It was predicted that the roles of both terminal chipping of logging residues and chipping at the plant will increase by the year 2010. Regarding the production of chips from small-diameter wood, it was estimated that the role of chipping at the plant will also increase in coming years. The proportion of roadside chipping in the production of small-sized wood chips and logging residue chips is expected to decrease.The study estimated that a total of 1100 machine and truck units were employed in the production of forest chips for energy plants in 2007. Increasing forest chip consumption will create considerable demand for additional forest chip production resources in the future.     

Energy and cost analysis of organic fertilizer production in Nigeria

Energy study was conducted in an organic fertilizer production plant in Nigeria, to determine the energy consumption patterns and the associated costs for the production of both powdered and pelletised fertilizer. Analysis was conducted for a daily production of 9000 kg of the finished products. Eight and nine defined unit operations were required for production of powder and pellets, respectively. The electrical and manual energy required for the production of powder were 94.5 and 5.6% of the total energy, respectively, with corresponding 93.9 and 5.1% for the production of pellets. The respective average energy intensities were estimated as 0.28 and 0.35 MJ/kg for powder and pellets. The most energy intensive operation was identified as the pulverizing unit with energy intensity of 0.09 MJ/kg, accounting for respective proportions of 33.4 and 27.0% of the total energy for production of powder and pellets. The energy cost per unit production for powdered and pelletised fertilizer using generator were evaluated as ?2.92 ($0.021) and ?3.87 ($0.028), respectively, with corresponding values of ?1.65 ($0.012) and ?2.00 ($0.014) when electrical energy from the national grid was used. The energy intensities for the production of organic fertilizers were significantly lower than that of inorganic fertilizers.     

Identification of potential areas for biomass production in China: Discussion of a recent approach and future challenges

A standard methodology is needed to recognize potentially suitable areas for sustainable bioenergy crop production. This facilitates better identification of promising crops and cropping systems, logistical and economic studies, and work needed to meet regulatory criteria. A possible approach is built upon three layers of internationally available spatial data: (1) degrading and abandoned areas, (2) potentially suitable land cover classes, (3) exclusion zones such as nature reserves and areas of high biodiversity. For China, areas identified as potentially suitable range from 1.2 to 6.0% of the national territory, depending on different levels of statistical confidence in degrading area status and allowable limits of terrestrial carbon. Verification on the ground showed that about 60% of points tested conformed to the remote suitability assessment in the scenario, which represents the results for the combination of all degrading areas and a terrestrial carbon stock limit of 200 t ha⁻¹. A top-down approach is useful in framing potentially suitable locations, but a complementary bottom-up analysis is still required to ultimately identify areas for sustainable bio-fuel production.