The basic premise of biofuels is that they emit less carbon than traditional fossil fuels. When biofuels are burnt, the gases are less toxic than fossil fuels, the handling and storage is safer, and there is a carbon sequestration credit that occurs when growing crops for the use of biofuels
We all know that driving our cars around town creates a lot of GHG emissions that are not helping the global warming crisis. We know that burning fossil fuels for transport energy contributes to pollution and climate change. But does buying ethanol or biodiesel to fuel our cars actually mitigate any of the carbon emissions? Or is this simply another way for fuel producers to scam extra dollars from the concerned citizen’s wallet?
As with all of the topics we will discuss on this website, there is no easy answer as to what is the most environmentally friendly option for fuelling our energy-intensive world. Certainly our transport system is fossil fuel intensive, and searching for new ways to reduce carbon emissions produced by this large system is a start to creating a world that is sustainable (whatever that means). But as the environmental blogger Damian Carrington states; “there are good…
I have been asked by some friends regarding the compulsions for focusing so much on Cellulose when we can do the same in a much simpler manner at a much lower cost with other renewable materials like Sugar cane or corn grains. The reasons may be fairly obvious to many but I will try to capture all arguments together to drive home the point in this post.
1. Food versus Fuel Controversy:
This is the first and foremost reason for pursuing cellulose for ethanol over food based feedstocks like sugar cane or Corn grains. Carbohydrates present in Cellulose ( present mainly in wood, straw, and much of non-edible portions of plant kingdom) cannot be digested by humans. Therefore it doesn’t compete or interfere with food production.
2.Cost of feedstock:
There are two factors that bring down the cost of cellulosic feedstock. They are discussed below:
A group of researchers led by Purdue University scientists believes sweet and biomass sorghum would meet the need for next-generation biofuels to be environmentally sustainable, easily adopted by producers and take advantage of existing agricultural infrastructure.
A sorghum head of seed near to maturity.
Those attributes point to potential adaptability for sorghum. Scientists from Purdue, the University of Nebraska-Lincoln, University of Illinois and Cornell University believe sorghum, a grain crop similar to corn, could benefit from the rail system, grain elevators and corn ethanol processing facilities already in place.
Their article explaining the perspective has been published early online in the journal Biofuels, Bioproducts & Biorefining.
By Elton Alisson Agência FAPESP – Biorefineries, as are called the industrial complexes that produce fuel, electricity and chemicals from biomass, are becoming enterprise capable of converting a wide variety of materials, including agricultural waste, into several products. This process with more energy efficient, economic and environmental benefits compared to conventional technological processes that give rise to only one or two products.
According to Jonas Contiero, a professor at Universidade Estadual Paulista (UNESP), Campus of Rio Claro, the first biorefineries plants were characterized by production of ethyl alcohol by grinding dry grains such as raw materials and have a line of fixed production , which consists of ethyl alcohol in co-products and carbon dioxide. Later, began to emerge in second generation Biorefineries that use technology for grinding “wet”, which enables the production of various final products, depending on demand, using mainly grains as raw materials. There are currently undergoing research…
May 18 (Reuters) – After a decade of promise, advanced biofuels makers are entering a crucial make-or-break period with the first of a new generation of production facilities about to come on line.
The new facilities are designed to take biofuels beyond corn-based ethanol and begin to shift the industry to “advanced” fuels made with a lower carbon footprint derived from products that will not compete with demand for food.
Many of the companies are turning to cellulosic plant materials, animal waste and plant oils to churn out millions of gallons of ethanol, diesel, jet fuel or components for gasoline.
Driving the industry are U.S. government targets stretching out a decade that call for fuel suppliers to blend billions of gallons of the new biofuels into the U.S. gasoline and diesel pools, on top of the corn ethanol that already makes up about 10 percent of the gasoline market.
A biorefinery is a facility that integrates biomass conversion processes and equipment to produce fuels, power, and value-added chemicals from biomass. The biorefinery concept is analogous to today’s petroleum refinery, which produces multiple fuels and products from petroleum.By producing several products, a biorefinery takes advantage of the various components in biomass and their intermediates, therefore maximizing the value derived from the biomass feedstock. A biorefinery could, for example, produce one or several low-volume, but high-value, chemical products and a low-value, but high-volume liquid transportation fuel such as biodiesel or bioethanol. At the same time, it can generate electricity and process heat, through CHP technology, for its own use and perhaps enough for sale of electricity to the local utility. The high value products increase profitability, the high-volume fuel helps meet energy needs, and the power production helps to lower energy costs and reduce GHG emissions from traditional power plant facilities.
There are several platforms which can be employed in biorefineries with the major ones being the sugar platform and the thermochemical platform (also known as syngas platform). Sugar platform biorefineries breaks down biomass into different types of component sugars for fermentation or other biological processing into various fuels and chemicals. On the other hand, thermochemical biorefineries transform biomass into synthesis gas (hydrogen and carbon monoxide) or pyrolysis oil.
The thermochemical biomass conversion process is complex, and uses components, configurations, and operating conditions that are more typical of petroleum refining. Biomass is converted into syngas, and syngas is converted into an ethanol-rich mixture. However, syngas created from biomass contains contaminants such as tar and sulphur that interfere with the conversion of the syngas into products. These contaminants can be removed by tar-reforming catalysts and catalytic reforming processes. This not only cleans the syngas, it also creates more of it, improving process economics and ultimately cutting the cost of the resulting ethanol.
Ethanol from lignocellulosic biomass is produced mainly via biochemical routes. The three major steps involved are pretreatment, enzymatic hydrolysis, and fermentation as shown in Figure. Biomass is pretreated to improve the accessibility of enzymes. After pretreatment, biomass undergoes enzymatic hydrolysis for conversion of polysaccharides into monomer sugars, such as glucose and xylose. Subsequently, sugars are fermented to ethanol by the use of different microorganisms.
Pretreated biomass can directly be converted to ethanol by using the process called simultaneous saccharification and cofermentation (SSCF). Pretreatment is a critical step which enhances the enzymatic hydrolysis of biomass. Basically, it alters the physical and chemical properties of biomass and improves the enzyme access and effectiveness which may also lead to a change in crystallinity and degree of polymerization of cellulose. The internal surface area and pore volume of pretreated biomass are increased which facilitates substantial improvement in accessibility of enzymes. The process also helps in enhancing the rate and yield of monomeric sugars during enzymatic hydrolysis steps.
Pretreatment methods can be broadly classified into four groups – physical, chemical, physio-chemical and biological. Physical pretreatment processes employ the mechanical comminution or irradiation processes to change only the physical characteristics of biomass. The physio-chemical process utilizes steam or steam and gases, like SO2 and CO2. The chemical processes employs acids (H2SO4, HCl, organic acids etc) or alkalis (NaOH, Na2CO3, Ca(OH)2, NH3 etc). The acid treatment typically shows the selectivity towards hydrolyzing the hemicelluloses components, whereas alkalis have better selectivity for the lignin. The fractionation of biomass components after such processes help in improving the enzymes accessibility which is also important to the efficient utilization of enzymes.
The pretreated biomass is subjected to enzymatic hydrolysis using cellulase enzymes to convert the cellulose to fermentable sugars. Cellulase refers to a class of enzymes produced chiefly by fungi and bacteria which catalyzes the hydrolysis of cellulose by attacking the glycosidic linkages. Cellulase is mixture of mainly three different functional protein groups: exo-glucanase (Exo-G), endo-glucanase(Endo-G) and β-glucosidase (β-G). The functional proteins work synergistically in hydrolyzing the cellulose into the glucose. These sugars are further fermented using microorganism and are converted to ethanol. The microorganisms are selected based on their efficiency for ethanol productivity and higher product and inhibitors tolerance. Yeast Saccharomyces cerevisiae is used commercially to produce the ethanol from starch and sucrose.
Escherichia coli strain has also been developed recently for ethanol production by the first successful application of metabolic engineering. E. coli can consume variety of sugars and does not require the complex growth media but has very narrow operable range of pH. E. coli has higher optimal temperature than other known strains of bacteria.
The major cost components in bioethanol production from lignocellulosic biomass are the pretreatment and the enzymatic hydrolysis steps. In fact, these two process are someway interrelated too where an efficient pretreatment strategy can save substantial enzyme consumption. Pretreatment step can also affect the cost of other operations such as size reduction prior to pretreatment. Therefore, optimization of these two important steps, which collectively contributes about 70% of the total processing cost, are the major challenges in the commercialization of bioethanol from 2nd generation feedstock.
Enzyme cost is the prime concern in full scale commercialization. The trend in enzyme cost is encouraging because of enormous research focus in this area and the cost is expected to go downward in future, which will make bioethanol an attractive option considering the benefits derived its lower greenhouse gas emissions and the empowerment of rural economy.
Biomass energy projects provide major business opportunities, environmental benefits, and rural development. Feedstocks can be obtained from a wide array of sources without jeopardizing the food and feed supply, forests, and biodiversity in the world.
Agricultural Residues
Crop residues encompasses all agricultural wastes such as bagasse, straw, stem, stalk, leaves, husk, shell, peel, pulp, stubble, etc. Large quantities of crop residues are produced annually worldwide, and are vastly underutilised. Rice produces both straw and rice husks at the processing plant which can be conveniently and easily converted into energy. Significant quantities of biomass remain in the fields in the form of cob when maize is harvested which can be converted into energy. Sugar cane harvesting leads to harvest residues in the fields while processing produces fibrous bagasse, both of which are good sources of energy. Harvesting and processing of coconuts produces quantities of shell and fibre that can be utilized.
Current farming practice is usually to plough these residues back into the soil, or they are burnt, left to decompose, or grazed by cattle. These residues could be processed into liquid fuels or thermochemical processed to produce electricity and heat. Agricultural residues are characterized by seasonal availability and have characteristics that differ from other solid fuels such as wood, charcoal, char briquette. The main differences are the high content of volatile matter and lower density and burning time.
Animal Waste
There are a wide range of animal wastes that can be used as sources of biomass energy. The most common sources are animal and poultry manures. In the past this waste was recovered and sold as a fertilizer or simply spread onto agricultural land, but the introduction of tighter environmental controls on odour and water pollution means that some form of waste management is now required, which provides further incentives for waste-to-energy conversion.
The most attractive method of converting these waste materials to useful form is anaerobic digestion which gives biogas that can be used as a fuel for internal combustion engines, to generate electricity from small gas turbines, burnt directly for cooking, or for space and water heating.
Forestry Residues
Forestry residues are generated by operations such as thinning of plantations, clearing for logging roads, extracting stem-wood for pulp and timber, and natural attrition. Harvesting may occur as thinning in young stands, or cutting in older stands for timber or pulp that also yields tops and branches usable for biomass energy. Harvesting operations usually remove only 25 to 50 percent of the volume, leaving the residues available as biomass for energy.
Stands damaged by insects, disease or fire are additional sources of biomass. Forest residues normally have low density and fuel values that keep transport costs high, and so it is economical to reduce the biomass density in the forest itself.
Wood Wastes
Wood processing industries primarily include sawmilling, plywood, wood panel, furniture, building component, flooring, particle board, moulding, jointing and craft industries. Wood wastes generally are concentrated at the processing factories, e.g. plywood mills and sawmills. The amount of waste generated from wood processing industries varies from one type industry to another depending on the form of raw material and finished product.
Generally, the waste from wood industries such as saw millings and plywood, veneer and others are sawdust, off-cuts, trims and shavings. Sawdust arise from cutting, sizing, re-sawing, edging, while trims and shaving are the consequence of trimming and smoothing of wood. In general, processing of 1,000 kg of wood in the furniture industries will lead to waste generation of almost half (45 %), i.e. 450 kg of wood. Similarly, when processing 1,000 kg of wood in sawmill, the waste will amount to more than half (52 %), i.e. 520 kg wood.
Industrial Wastes
The food industry produces a large number of residues and by-products that can be used as biomass energy sources. These waste materials are generated from all sectors of the food industry with everything from meat production to confectionery producing waste that can be utilised as an energy source.
Solid wastes include peelings and scraps from fruit and vegetables, food that does not meet quality control standards, pulp and fibre from sugar and starch extraction, filter sludges and coffee grounds. These wastes are usually disposed of in landfill dumps.
Liquid wastes are generated by washing meat, fruit and vegetables, blanching fruit and vegetables, pre-cooking meats, poultry and fish, cleaning and processing operations as well as wine making.
These waste waters contain sugars, starches and other dissolved and solid organic matter. The potential exists for these industrial wastes to be anaerobically digested to produce biogas, or fermented to produce ethanol, and several commercial examples of waste-to-energy conversion already exist.
Pulp and paper industry is considered to be one of the highly polluting industries and consumes large amount of energy and water in various unit operations. The wastewater discharged by this industry is highly heterogeneous as it contains compounds from wood or other raw materials, processed chemicals as well as compound formed during processing. Black liquor can be judiciously utilized for production of biogas using anaerobic UASB technology.
Municipal Solid Wastes and Sewage
Millions of tonnes of household waste are collected each year with the vast majority disposed of in open fields. The biomass resource in MSW comprises the putrescibles, paper and plastic and averages 80% of the total MSW collected. Municipal solid waste can be converted into energy by direct combustion, or by natural anaerobic digestion in the engineered landfill. At the landfill sites the gas produced by the natural decomposition of MSW (approximately 50% methane and 50% carbon dioxide) is collected from the stored material and scrubbed and cleaned before feeding into internal combustion engines or gas turbines to generate heat and power. The organic fraction of MSW can be anaerobically stabilized in a high-rate digester to obtain biogas for electricity or steam generation.
Sewage is a source of biomass energy that is very similar to the other animal wastes. Energy can be extracted from sewage using anaerobic digestion to produce biogas. The sewage sludge that remains can be incinerated or undergo pyrolysis to produce more biogas.
In India, the leading biofuel feedstock today is sugarcane molasses, which is processed to yield bioethanol that can be blended into gasoline (petrol). Sugarcane requires good land and large amounts of irrigation water, which are difficult for the poor to obtain. The bioethanol industry buys its molasses feedstock from the sugar factories. Sugar is the main objective of the sugarcane industry; molasses are simply a byproduct. As such, the unreliability of supply of molasses is a major constraint to biofuels development based on this feedstock.
Even though India is an agrarian economy, the energy potential of agricultural residues has not been realized till now by policy-makers and masses. Most of the biomass wastes are inefficiently used for domestic purposes in absence of reliable and cheaper source of energy. The main crops produced in India are wheat, maize, rice, sorghum, sugarcane and barley. India is among the market leaders in the production of these crops and has tremendous potential to convert lignocellulosic crop residues into ethanol.
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