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Theoretical Review
Energy crops
Energy crops are plants cultivated with low maintenance costs with the aim to exploit its energy content. Energy crops production is an emerging field in agricultural science and industry which is enforced by the Renewable Energy Sources Act in Europe. The new paradigm in the agriculture industry is the shift from crops for food production to the production of energy crops for fuel purposes. Regarding qualitative aspects, increase in protein content of food crops will be replaced by maximizing the dry matter content or yield per area unit in energy crops. In other words, plants high in glucose and sugars can be used as energy crops while lignin and cellulose contents are not suitable, since these two hydrocarbons cannot be digested in current biofuel production processes such as the bioethanol production. (Sticklen, 2008).
Energy crops consist of a « closed-loop process » which they grow particularly for their potential to generate energy. Crops such as switch grass, woody crops (e.g. Willow, Poplar and Cottonwoods, hybrid Willows) and sugarcane are being studied in order to investigate their potential to serve as an energy crop for fuel production (McKendry, 2002). The advantage of these crops is that they are short-rotation and multiple–harvesting crops, which grow after each harvest without the need of re-planting (Sims. 2001). Crops such as corn and sorghum serve as dual purpose with the ability to be grown for fuel and the leftover by-products could be used for other purposes, including animal food and fertilization.
Sugarcane is a tropical crop which is processed into raw sugar and molasses. Since alcohol is a result of fermentation of sugars, it could be easily gained by converting sugar crops such as sugarcane and sugar beets into alcohol. Forage and sugar beets are known as energy crops due to high organic dry matter yield per hectare and are also easily ensiled and stored for the use through the whole year.
One the main factors influencing the development of energy crop production for biofuels is market developments in relation to politics in the field of agriculture and energy. Regress in the legal promotion of energy crops will result in the collapse of recent developments of energy crop production (Rode et al.2005).
Main issues facing biofuels
Since the development of biofuels, many issues have raised from the use of biofuels as the replacement of fossil fuel. “Food crisis” is the main issue of biofuel development since apart from monoculture of energy crops for biofuel production, a large portion of food crops are being fed to vehicles while based on UNDP statistics more than 1.02 billion people of the world population are suffering from famine (FAO, 2009). The rapid increase of energy crop demands as a source of biofuel has lead to other important social-economical issues as follow (Global Forest Coalition, 2006):
• Increased land competition which results in further land concentrations, demotion of small-scale agriculture and the extensive conversion of forests and other ecosystems
• Drastic increase in food prices leading to hunger, malnutrition and poverty amongst the poorest sectors of society due to the conversion of arable land for growing fuel crops
• Extensive use of agrochemicals e.g. fertilizers and pesticides which deteriorate and decline human health and ecosystems
• Destruction and pollution of watersheds e.g. rivers, lakes and streams
• Local and regional climate extremes such as droughts
• Extensive use of genetically modified organisms (GMO) leading to extraordinary risks
• Destruction of the traditions, cultures, languages and spiritual values of indigenous peoples and rural communities
Biofuel life cycle
Fossil fuels are limited for use in vehicles due to high emissions and the high contribution to global warming. Biofuel alternative to vehicle fuel is also a major issue of debates today since the biofuel life cycle consists of major industries of agriculture, biofuel production processes and transportation which have considerable emissions and other related environmental issues. In the following sectorthe three main industries and the major operations in the life cycle of biofuels will be mentioned.
Agriculture industry
Agriculture is the process of exploitation of soil, water and air by humans in order to fulfill their principle need of hunger and shelter and is in close connection with the ecosystem which bears upon all living beings. By increase in the global population and evolution of techniques, agriculture is no longer a simple mean of earning livelihood, but has become an industry which deals with major amounts of matter and energy. Today, agriculture is a major industry affecting economic activities and employment in the society.
Agriculture is also one of the main targets for climate change effect studies since it is intimately affected by climate and on the other side it affects the climate as a major origin of emissions. As an example, the studies published by IPCC indicate that between 1970 and 1990 direct emissions of greenhouse gases (GHGs) from this sector grew by 27% (IPCC, 2007). Apart from energy crisis the global water crisis is facing the world and the agriculture sector is the largest consumer of water, up to 75%, particularly due to inefficient management and non-sustainable practices (Cornish et al., 2004). Therefore mitigation measures and sustainability issues are of great importance in the subject of agriculture production and management.
Energy in agriculture is mainly used for irrigation and ground water pumping, farm machinery such as threshers and tractors and also transportation. While neglecting the direct emissions from fuel combustion, the major emissions from agricultural operations are due to fertilizer production, mismanagement of soil and water, tillage, and inappropriate cropping patterns (Giampietro, 2003). Fertilizers are one of the largest sources of emissions in the agriculture sector, for example agricultural soil naturally release nitrogen dioxide that is increased by fertilization and study’s of the United States Environmental Protection Agency (EPA) show that 38% of nitrogen dioxide is of fertilizer applications (EPA, 2006). The beginning of the green revolution in agriculture (1943-1970), caused a great increase in emissions from the agriculture sector, for example, “Intensification” which is the cultivation of bicrops has increased the emission from soil due to distribution of hybrid seeds, high consumption of fertilizers and pesticides, and irrigation.
Today, biofuel extracted from agriculture and livestock waste is an alternative to fulfill the expanding need to fuel our automobiles. Energy crop plantation for fuel application is a major issue such as the need of intensification, nutrient depletion, soil erosion, followed by massive energy inputs and emission outputs solely from the agriculture industry.
Production process of arable crops
Energy crops, as any other crop, are produced in a process of operations which require energy and emit gases, and are of great concern for sustainable management and development .The agricultural operation considered in this report for energy crops are the following stages (campus et al., 2004):
Ploughing: The initial stage of crop cultivation is ploughing, which includes soil preparation operations for sowing seeds and planting crops. In this group of operations the upper layer of soil is turned over in order to improve the soil structure for supporting the newly grown plant, efficient aerations and water penetration and also incorporating the residue from the previous crop into the soil. Ploughing reduces the frequency of weeds in the field and eases later planting processes. Most tractors and agricultural machinery used in this stage consume fossil fuels which have high contribution to energy consumption in the agricultural operations. Emissions in this step are direct emissions from fuel consumption in agricultural machinery and soil disturbance. In this report direct fuel consumption of machinery and the fuel consumption in the industrial production processes have been considered.
Seeding: This group of operations is done for preparing the soil bed for sowing and germination of plant seeds by machine or hand sowing. Machinery such as tractor driven seed drills combined with rollers is used. Since the soil disturbance in this stage is low in comparison with other stages, energy consumption and emissions are low too.
Fertilization and chemical application: Studies show that the major problem of fossil fuel use in industrial farming is not transportation of material and food or fueling machinery; but chemicals. More than 40 % of energy consumption in agriculture and food system goes towards the production of artificial fertilizers and pesticides (Center for Sustainable Systems, 2009).
Fertilizers: Plant productivity is limited by the lack of nutrients therefore fertilizers are applied in order to improve crop growth which could be either organic or mineral substances (Gellings and Parmenter, 2004)
• Mineral fertilizers: This group of fertilizers are artificially produced from minerals and fossil resources. The most energy intensive mineral fertilizers are nitrogen while phosphate fertilizers are produced from resources of phosphate rock (Table 1, Figure 2).
• Organic fertilizers: This group of fertilizers are composed from organic and mineral substances. Organic fertilizers are mainly wasted materials and processed residues such as manure, compost and even the biogas digestate from the biogas plant (Gellings and Parmenter, 2004).
Fertilizers, chemical pesticides, hybrid seeds, and special feed supplements for livestock are characterized as an indirect energy consumer on the farm and a majority of this energy consumption is accomplished away from the farm. Tractors, irrigation pumps, and other types of agricultural equipment are considered as direct energy consumers (Gellings and Parmenter, 2004).
The main aim of fertilizer application is to maintain soil fertility and increase crop yield. Since 1900s, fertilizer applications have grown extensively and in many developing countries continue to grow at a steady rate. By increase in world population fertilizers have become an important element in worldwide food production since fertilizers enable higher yields on less crop area than it would be required without the use of fertilizers. In spite of their benefits, production of fertilizers has high energy consumption, particularly natural gas. Due to energy limitations and high fuel costs it is necessary to implement energy efficiency measures in the production and use of fertilizers (Table 2).
Chemical plant protection: This stage consists of chemicals such as pesticides, herbicides, and fungicides, applied to protect plants against biological invaders which reduce the plant performance. These agents can cause problems to the environment and human health. They cause decrease in biodiversity on a large scale and human health problems by leaking into surface water and finally to drinking water. Since there is a small amount of material and energy flow related to pesticide production in relation to the total amount of all material flows in the overall life cycle, therefore in this report we will not analyze pesticides in detail (Hamilton and Crossley, 2004). Harvesting: This stage includes operations of cutting, silage, cleaning, and storage in order to harvest the crop from land. Harvest is an energy intensive operation. After harvest energy crops are stored and stocked to be transported to the biofuel production plant. Raw materials for biofuel plants are first cleaned from dust and compressed in order to reduce the amount of oxygen and finally stored in special storage containers (Crofcheck et al., 2006)
Ensilage: Silage is the high–moistened forage that is fermented in the silo and stored, the process is called ensilage. Plant material suitable for ensiling are high in moisture, ranging from 55-75% which depend on the degree of compression, amount of water lost during storage and the storage construction. The reason for ensiling is that it influences the quality of silage. The silage must be compressed by tractors driven on the laid silage in the storage, in order to eliminate the oxygen as much as possible before covering the silage. After four to six weeks the silage is ready (Wegener et al., 2005).
Ecological effects of energy crop cultivation
Biofuels were firstly produced as fuel alternatives with the main aim of reducing emissions of greenhouse gases. Many prior studies found that the biofuel production will reduce greenhouse gases since the feedstock of biofuel industries, which were plants and crops, sequestered carbon during their growth on the field. Today results show that energy crop production on arable land has major ecological effects such as narrow crop rotations and intensive production systems which is a great issue between nature conservation and the agriculture industry. Energy crop production and its occupation have the following effects (Rode et al., 2005):
• Soil compaction which causes interference with other functions in soil such as the activity of vital micro-organisms. Soil compaction is the result of traffic of agricultural machines and mainly depends on factors such as soil quality, frequency, time and duration of machines used, and the weight and type of machine tires.
• Soil erosion largely depends on the kind of crop covering the soil, cultivation operations, topography, and crop rotation.
• Decrease in biodiversity as well as landscape features and their habitats. Cultivation of energy crops for biofuel production is a shift from biodiversity to monoculture in agriculture which increases the risk of crop failure followed by global food crisis.
• Soil depletion is one of the main results of energy crop cultivation. Monoculture of energy crops for biofuel purposes will extract nutrients and elements from soil leading to soil nutrient depletion.
• Food crisis for humans and animals
• Pests and aliens tend to survive in monoculture croplands
But with response to the high prices of energy crops farmers worldwide tend to convert food cropland, forest and grassland to croplands where grain or crops diverted to biofuel feedstock are cultivated. Studies on switch grass grown on U.S. corn lands for biofuel production, shows that emissions will increase by 50% which raises concerns about large biofuel mandates and emphasizes the importance and value of using waste products for biofuel production (Searchinger et al. 2008). Many opponents believe that biofuels increase greenhouse gas emitions since more land is being cleared. Biofuel production has also large impacts on ecosystems such as forests and rural livelihoods which are expected to accumulate rapidly. In countries such as Brazil which is a large scale exporter of biofuels, monocultures of crops such as sugarcane, corn, oil palm, soybean etc. is required. Monocultures of crops are not only a cause of ecological disasters but also the main cause of rural depopulation and deforestation worldwide.
Biofuel industrial plants
Biofuel plants vary in function and technology based on the kind of biofuel produced, for instance a biogas plant which its energy production is based on anaerobic digestion of biological material is a plant which constitutes of high resistant tanks, pipes and pumps and requires well maintenance of the whole system. Pretreatments of the raw material for the biogas plant depend on the kind of feedstock. While the bioethanol industrial plant performs fermentation on sugar crops in order to produce alcohol. In such an industry stages are more complex in order to pretreat the feedstock and there are by-products which should be cared (Anderson et al., 2003).
Transportation
Today transportation is a system standpoint in every industry and the global transportation emits 14% of the total CO2 emissions (WRI, 2006).Transportation consists of all modes of trucks, railroads, barges, and ocean vessels. The agricultural supply chain is a major user of the world’s transportation system therefore energy consumption and emissions of the transportation sector in agricultural studies should be taken into account in planning and assessing of the industry.
Bioethanol in Brazil
Ethanol
Awareness of current energy supplies, commitments to national and international climate change protocols and strong evidence of the large contribution of the transportation sector to global warming has focused the world’s attention on renewable and environmental friendly fuels. One of the various biofuel alternatives is ethanol from sugarcane crop which is the first production source of ethanol. Today the major suppliers of bioethanol production are Brazil and the US, holding 89% of the world’s bioethanol production (Wiessner, 2008). Bioethanol in Brazil is extracted from the sugarcane while maize is the main energy crop in the United States for bioethanol production. In 2008, Brazil produced 37.3% of the world’s total bioethanol used as fuel (Licht, 2001; The World Bank 2008). The use of bioethanol from biomass as a fuel was innovated in Brazil as a result of high fossil fuel prices and limitation of fossil fuel resources. Therefore the bioethanol production has great correlation with fuel prices. Bioethanol production was peaked in the 1980s and reduced as fossil fuel prices declined. Later on higher oil prices, reduced cost of bioethanol production, design of dual-fuel vehicles and environmental aspects such as the climate change lead to increase in bioethanol production. Today many countries are commencing the infrastructure and facilities for bioethanol fuel installation mainly due to environmental pollution by the transportation sector.
Bioethanol production (reaction)
The reaction below is common for the production of bioethanol in beverages and more than half of the industrial bioethanol. Simple sugar is the raw material for the reaction, and by a biological agent sugar is fermented to bioethanol and CO2 ( Donal O’Leary. 2000) C6 H12 O6 CH3CH2 OH + 2 CO2
The main biological agent in the reaction of bioethanol is yeast such as Zymomonase mobilis. (Gunasekaran and Chandra, 1999). The Feedstock for bioethanol production is biomass high in sugar, such as follow:
• Crops: sugarcane, corn, sugar beet, sorghum, switch grass, barley, kenaf, potatoes, sweet potatoes, cassava, sunflower, grain, wheat, straw, cotton
• Waste residues: bagasse, molasses
Bioethanol composition
Bioethanol is a straight-chain alcohol, with the chemical formula of C2H5OH. It is known as pure alcohol, which is volatile, flammable. Bioethanol used as fuel could have different compositions which differ in application (Donal O’Leary. 2000):
• Anhydrous ethanol: 100% pure ethanol suitable for blending with gasoline
• Hydrous ethanol: mixture of 95% ethanol and 5% water
Application of ethanol
Fuel: The major use of ethanol is as fuel and fuel additive for vehicle engines and motors. Ethanol as fuel could be hydrous or anhydrous differing in purity in the distillation stage. Many countries have replaced gasoline consumption with a mixture of a certain percentage of bioethanol and gasoline which is called gasohol. Brazil has the largest bioethanol fuel industry.
Industry: Bioethanol is used as a chemical in industrial processes, also in industries of paint, perfumes and cosmetics and medicine and as an antiseptic. Bioethanol is an effective agent against bacteria and fungi and some viruses while not effective against bacterial spores.
Beverages (portable alcohol): The smallest share of bioethanol is among the beverages since beverages have other sources such as fruits and malt. Main bioethanol beverage markets are China, Russia, USA, Brazil and Japan. Bioethanol in beverages is expressed by volume fraction of bioethanol, percentage or alcoholic proof unit (Licht, 2001).
Ethanol industry
Ethanol (C2H5OH) is a clear and colorless liquid. All industrial ethanol is a mixture of 95% ethanol and 5% water and known as, 95% alcohol. Industrial ethanol is produced through five main stages as follow (Donal O’Leary. 2000):
Conversion of biomass to fermented sugars: In this stage a solution of sucrose from biomass is prepared and yeast is added, the mixture is then heated up to 250°C and 300°C. The enzyme, invertase, which is present in yeast, acts as a catalyst to convert the sucrose into glucose (C6H12O6) and fructose (C6H12O6) which are fermented in the next stage. In case of sugarcane based ethanol, this step is not performed.
Table of contents :
Chapter 1: Introduction
1.1. Historical background
1.2 Aim and objectives
Chapter 2: Theoretical Review
2.1. Energy Crops
2.2. Main issues facing biofuels
2.3. Biofuel life cycle
2.3.1. Agriculture Industry
2.3.1.1. Production process of arable crops
2.3.1.2. Ecological effects of energy crop cultivation
2.3.2. Biofuel industrial plants
2.3.3. Transportation
2.4. Bioethanol in Brazil
2.4.1. Ethanol
2.4.1.1. Bioethanol production (reaction)
2.4.1.2. Bioethanol composition
2.4.1.3. Application of ethanol
2.4.1.4. Ethanol industry
2.4.1.5. Ethanol as fuel
2.4.2. Sugarcane
2.4.2.1. Plant physiological
2.4.2.2. Sugarcane cultivation
2.4.2.3. Sugarcane for Ethanol Production
2.4.3. Ethanol in Brazil
2.4.3.1. Sugarcane Industry in Brazil
2.4.3.2. Industrial operations
2.5. Biogas in Sweden
2.5.1. Biogas
2.5.1.1 Biogas Production
2.5.1.2. Biogas Composition
2.5.1.3. Applications of biogas
2.5.1.4. Biogas as Fuel
2.5.1.5. Biogas industrial plant
2.5.1.6. Biogas upgrading
2.5.2. Sugar beet
2.5.2.1. Plant physiology
2.5.2.2. Sugar beet cultivation
2.5.2.3. Sugar beet for biogas production
2.5.3. Biogas in Sweden
2.5.3.1. Potential of the agriculture sector
Chapter 3: Methodology
Chapter 4: Results
4.1 Biogas
4.1.1 Energy input
4.1.2 Emissions
4.2 Ethanol
4.2.1 Energy inputs
4.2.2Emissions
4.3 Comparison of Biogas and Bioethanol
Chapter 5: Discussion
Chapter 6: Conclusions and Recommendations
References
