BSc BT (SM) 3rd sem EBT Unit 2. Bioenergy, conventional fuels and biofuels.pdf

Environmental Biotechnology (EBT) Unit 2. Bioenergy, Conventional fuels and Biofuels Fossil fuels as energy source and their impact on the environment. Biomass as source of bioenergy. Types of biomass- plant, animal and microbial. Biofuels from waste; metho...

Environmental Biotechnology (EBT) Unit 2. Bioenergy, Conventional fuels and Biofuels Fossil fuels as energy source and their impact on the environment. Biomass as source of bioenergy. Types of biomass- plant, animal and microbial. Biofuels from waste; methods and processes for utilization of waste for production of biofuels (bioethanol & biodiesel). Modern fuels and their environmental impact. -Dr. Saranya Jayaram  Fossil fuels Fossil fuels are made from decomposing plants and animals. These fuels are found in Earth’s crust and contain carbon and hydrogen, which can be burned for energy. Coal, oil and natural gas are examples of fossil fuels. Coal is a material usually found in sedimentary rock deposits where rock and dead plant and animal matter are piled up in layers. More than 50% of a piece of coal’s weight must be from fossilized plants. Oil is originally found as a solid material between layers of sedimentary rock, like shale. This material is heated in order to produce the thick oil that can be used to make gasoline. Natural gas is usually found in pockets above oil deposits. It can also be found in sedimentary rock layers that don’t contain oil. Natural gas is primarily made up of methane.  The three main kinds of fossil fuels: coal, oil and natural gas are substances formed from the remains of plants and tiny creatures called plankton that lived millions of years ago. As they grew, they captured and stored energy in their bodies from sunlight. They also absorbed carbon dioxide from the atmosphere. When they died, their remains sank to the bottom of the ocean. Layers of sediment built up over them until they were deep underground, subjected to intense pressure and heat. Under these forces, the organic matter in them gradually broke apart and transformed. Plant matter turned into coal and plankton into oil (also called petroleum) and natural gas. These materials contain all the stored energy of the living organisms they once were. Burning them releases all that trapped energy. For over 200 years, humans have relied heavily on fossil fuels as an energy source. Today, 80% of all the energy used in the U.S. comes from them.  According to the U.S. National Academies of Sciences, 81% of the total energy used in the United States comes from coal, oil and natural gas. This is the energy that is used to heat and provide electricity to homes and businesses and to run cars and factories. Unfortunately, fossil fuels are a nonrenewable resource and waiting millions of years for new coal, oil and natural gas deposits to form is not a realistic solution. Fossil fuels are also responsible for almost 3/4th of the emissions from human activities in the last 20 years. Now, scientists and engineers have been looking for ways to reduce our dependence on fossil fuels and to make burning these fuels cleaner and healthier for the environment. Scientists across the country and around the world are trying to find solutions to fossil fuel problems so that there is enough fuel and a healthy environment to sustain human life and activities in the future.  The United States Department of Energy is working on technologies to make commercially available natural-gas-powered vehicles. They are also trying to make coal burning and oil drilling cleaner. Researchers at Stanford University in California have been using greener technologies to figure out a way to burn fossil fuels while lessening their impact on the environment. One solution is to use more natural gas, which emits 50% less carbon dioxide into the atmosphere than coal does. The Stanford team is also trying to remove carbon dioxide from the atmosphere and store it underground—a process called carbon capture and sequestration. Scientists at both Stanford and the University of Bath in the United Kingdom are trying something completely new by using carbon dioxide and sugar to make renewable plastic.  Popular uses of fossil fuels Fuels to drive automobiles and other locomotives. Natural gas for heating water or cooking. Electricity that comes from burning natural gas or coal. Use of products made from fossil fuels, especially oil; all sorts of common goods, including plastics, fertilizers, lubricants and cosmetics, are petroleum-based. Paint and asphalt are all very likely to be petroleum products. Most industries rely on fossil fuels for energy. Examples include industries like manufacturing, agriculture, forestry, fishing, mining, transportation, electricity and construction. These industries also rely on fossil fuels for products such as fertilizers, lubricants, solvents and building materials.  Harmful effects of fossil fuels Unfortunately, burning fossil fuels doesn’t just release energy. It also releases all the carbon the ancient organisms stored in their bodies. The carbon mixes with oxygen in the air to form carbon dioxide, the main greenhouse gas responsible for global warming. And this isn’t the only harmful compound produced. Burning fossil fuels also creates particulate matter, or soot, tiny black particles that damages the lungs when inhaled. It releases harmful sulfur dioxide and nitrogen oxides that react with sunlight to form smog. All these chemicals pollute the air, hurting both humans and wildlife. Air pollution: Extracting, refining and burning fossil fuels release a variety of chemicals that harm human health. These include soot, sulfur and nitrogen oxides and leaked methane. All these chemicals pollute air, increasing risks of respiratory diseases. Pollution poses the greatest risk in low-income communities, which are usually closer to fossil fuel pipelines, refineries and power plants.  Water pollution: Fossil fuel use pollutes the water in a variety of ways. These include oil spills, runoff from strip mines, wastewater injection from fracking and wastewater from refineries. Nitrogen oxides produced by burning fossil fuels also contribute to water pollution. They precipitate out of the air and wash into waterways, changing the water chemistry in ways that threaten aquatic life. Like air pollution, water pollution has an outsized impact on low- income households and people of color. Small, low-income communities are much more likely than other communities to lack access to safe drinking water and to better water facilities. Water use: Plants that burn fossil fuels use large amounts of freshwater for cooling. This drains local water supplies, leaving less for farming and other uses. Some power plants return the water to rivers, lakes, and oceans, but this causes problems as well. The water leaves the plant much hotter, and it contains lower levels of dissolved oxygen. This threatens the health of fish and other water-dwelling creatures.  Global warming: The biggest threat fossil fuels pose is their effect on global temperatures. Fossil fuels are the largest source of greenhouse gas emissions responsible for global warming. This includes CO2 and N2O from burning fossil fuels and methane leaked from gas wells and pipes. When fine particles such as soot land on snow or ice, they make their surface darker. This causes it to absorb more heat from sunlight and melt faster. As the snow cover vanishes, the land surface gets darker still, absorbing heat even faster. This is one of the reasons ice and snow in many areas now melt earlier and faster, reducing freshwater supplies. Climate change is the greatest environmental threat we face today. It increases the severity of all kinds of weather disasters and increases the melting of icecaps and glaciers, causing sea levels to rise. And much of the increased CO2 in the atmosphere is being absorbed into the ocean, making it more acidic. This threatens various kinds of wildlife, including fish and coral reefs. Countries near the equator are suffering from more extreme heat. Indigenous peoples in the Arctic, which is warming faster than other parts of the globe, are losing the wildlife crucial to their traditional way of life. Island nations and low-lying coastal areas, such as Bangladesh, are at risk from sea level rise. Low-income countries have the greatest danger from extreme weather and natural disasters.  Acid rain: The sulfur and nitrogen oxides created by burning fossil fuels don’t just pollute the air. They also react with water and other substances to form acid rain. Acid rain harms plants, trees, fish and other wildlife. It can also damage buildings and other structures.  Biomass Energy Biomass is renewable organic material that comes from plants and animals. Biomass contains stored chemical energy from the sun that is produced by plants through photosynthesis. Biomass can be burned directly for heat or converted to liquid and gaseous fuels through various processes. Biomass was the largest source of total annual U.S. energy consumption until the mid-1800s. In 2022, biomass accounted for nearly 5% of U.S. total primary energy consumption. Biomass is used for heating and electricity generation and as a transportation fuel. Biomass is an important fuel in many countries, especially for cooking and heating in developing countries.  Sources of biomass energy include: * Wood and wood processing waste like firewood, wood pellets, and wood chips, lumber and furniture mill sawdust and waste and black liquor from pulp and paper mills. * Agricultural crops and waste materials like corn, soybeans, sugar cane, switchgrass, woody plants, algae and crop and food processing residues, mostly to produce biofuels. * Biogenic materials in municipal solid waste like paper products, cotton and wool products, and food, yard and wood wastes. * Animal manure and human sewage for producing biogas (renewable natural gas). Biomass is converted to energy through various processes, including: * Direct combustion (burning) to produce heat. * Thermochemical conversion to produce solid, gaseous and liquid fuels. * Chemical conversion to produce liquid fuels. * Biological conversion to produce liquid and gaseous fuels. Processes for production of biomass Direct combustion is the most common method for converting biomass to useful energy. All biomass can be burned directly for heating buildings and water, for providing industrial process heat and for generating electricity in steam turbines. Thermochemical conversion of biomass includes pyrolysis and gasification. Both processes are thermal decomposition processes wherein biomass feedstock materials are heated in closed, pressurized vessels called gassifiers at high temperatures. The processes mainly differ in the temperatures and in the amount of oxygen present during conversion. * Pyrolysis entails heating organic materials to between 800° F and 900° F (400° C and 500° C) in the nearly complete absence of free oxygen. Biomass pyrolysis produces fuels such as charcoal, bio- oil, renewable diesel, methane and hydrogen. * Hydrotreating is used to process bio-oil (produced by fast pyrolysis) with hydrogen under elevated temperatures and pressures in the presence of a catalyst to produce renewable diesel, renewable gasoline and renewable jet fuel.  * Gasification entails heating organic materials to between 1,400° F and 1,700 F (800° C and 900° C) with injections of controlled amounts of free oxygen or steam into the vessel to produce a carbon monoxide- and hydrogen-rich gas called synthesis gas or syngas. Syngas can be used as a fuel for diesel engines, for heating and for generating electricity in gas turbines. It can also be treated to separate the hydrogen from the gas, and the hydrogen can be burned or used in fuel cells. The syngas can be further processed to produce liquid fuels. * A chemical conversion process known as transesterification is used for converting vegetable oils, animal fats and greases into fatty acid methyl esters (FAME) to produce biodiesel. Anaerobic decomposition is the process where microorganisms, usually bacteria, break down biomass in the absence of oxygen. * In an anaerobic environment, biomass decays and produces methane, which is a valuable energy source. This methane can replace fossil fuels. * In addition to landfills, anaerobic decomposition can also be implemented on ranches and livestock farms. Manure and other animal waste can be converted to sustainably meet the energy needs of the farm. By-products of biomass production Biological conversion of biomass includes fermentation to make ethanol and anaerobic digestion to produce biogas. Ethanol is used as a vehicle fuel. Biogas, also called biomethane or renewable natural gas, is produced in anaerobic digesters at sewage treatment plants and at dairy and livestock operations. It also forms in and may be captured from solid waste landfills. Properly treated renewable natural gas has the same uses as fossil fuel natural gas. Biomass is the only renewable energy source that can be converted into liquid biofuels such as bioethanol and biodiesel. * Biofuel is used to power vehicles and is being produced by gasification in various countries. * Ethanol is made by fermenting biomass that is high in carbohydrates, such as sugarcane, wheat or corn. * Biodiesel is made from combining ethanol with animal fat, recycled cooking fat or vegetable oil. Biofuels do not operate as efficiently as gasoline, they can be blended with gasoline to efficiently power vehicles and machinery, and do not release polluting emissions.  Biochar, produced during pyrolysis, is valuable in agricultural and environmental use. When biomass rots or burns (naturally or by human activity), it releases high amounts of methane and carbon dioxide into the atmosphere. However, when biomass is charred, it sequesters (stores) its carbon content. * When biochar is added back to the soil, it can continue to absorb carbon and form large underground stores of sequestered carbon (in carbon sinks) that can lead to negative carbon emissions and healthier soil. * Biochar also helps enrich the soil. It is porous. When added back to the soil, biochar absorbs and retains water and nutrients. When wood is processed into paper, it produces a high-energy, toxic substance called black liquor. Until the 1930s, black liquor from paper mills was considered a waste product and dumped into nearby water sources. However, black liquor retains more than 50% of the wood’s biomass energy. With the invention of the recovery boiler in the 1930s, black liquor could be recycled and used to power the mill. In the United States, paper mills use nearly all their black liquor to run their mills, and the forest industry is one of the most energy-efficient in the nation.  Biomass is rich in hydrogen, which can be chemically extracted and used to generate power and to fuel vehicles. Stationary fuel cells are used to generate electricity in remote locations, such as spacecraft and wilderness areas. Yosemite National Park in the U.S. state of California, for example, uses hydrogen fuel cells to provide electricity and hot water to its administration building. * Hydrogen fuel cells may hold even more potential as an alternative energy source for vehicles. * Currently, hydrogen fuel cells are used to power buses, forklifts, boats, and submarines, and are being tested on airplanes and other vehicles. * However, there is a debate as to whether this technology will become sustainable or economically possible, because the energy that it takes to isolate, compress, package, and transport the hydrogen does not leave a high quantity of energy for practical use. Some of the leading biomass feedstocks include (top row) switchgrass, copra (coconut), cotton, jatropha; (middle row) municipal solid waste (msw), sunflowers, palm nuts, canola; (bottom row) wheat, sugar cane, wood, and rice. Types of Biomass  Wood waste: wood and its waste are the best source of biomass. Its combustion generates heat and steam which can be further used to produce electricity. All forms of wood that include wood chips, wood pallets, logs, sawdust and even tree bark can be used to produce the required energy. Animal waste: animal waste includes animal manure, animal waste and waste from livestock. All these can be considered as raw materials for biomass. The dairy industry too contributes to a large extent. Agricultural waste: agricultural waste is a huge source of raw material to the biomass industry. Different types of agricultural waste can be utilized to create energy. Waste can be in the form of leaves, husk, shells and animal waste. All these come under renewable energy source that are even beneficial to the environment. Another important characteristic of this agricultural waste is that it can be used for organic farming as manure and used for cooking and heating purposes.  Biomass crops: certain crops are grown so that it can be further used for biomass energy. Some of the commonly grown biomass crops are corn varieties for ethanol production and soybean oil for the production biodiesel. The heat produced can be used for generating electricity. Dairy manure: dry manure is from livestock. The manure collected in bulk from farms are washed and dried. This is used for the combustion in biomass plants to generate heat for the production of electricity. Landfills: landfills are a traditional method in which waste is buried underground so that it decomposes. This buried waste decomposes to form biomass and produces biogas. This energy can be utilized to generate heat and energy. Mill residue: the residue from the wood mills like wood chips and wood powder can be effectively utilized in biomass plants. Alcohol fuels: alcohol fuel such as ethanol is produced through a process of fermentation which is widely used by automobile industry. Advantages of biomass energy Renewable source: this is mainly because of the raw materials that are used, which are available throughout. Their procurement and regrowth is easy. Cheaper: the production of biomass energy is comparatively cheaper as compared to fossil fuesl. The raw materials are cheaply available. Hence, the low cost in the generation of electricity reduces the bills of the common man. Variety products: biomass energy is versatile as it creates a lot of products. Biomass can be converted into various forms in the presence and absence of oxygen. Some of the byproducts are ethanol, biogas, syngas, bio-oil and bio-char. Clean gas: biomass energy is a cleaner gas as compared to other forms of energy. Green house gases are not emitted during combustion of organic matter. Minimal pollution is the outcome. Lesser amount of carbon is emitted during the process which is absorbed by plants for their survival and life cycle. Disadvantages of biomass energy Constant and continues supply of biomass is required for the generation of biomass energy. Compared to the input of raw materials, the outcome is comparatively less. All the raw materials used are waste products that can cause pollution and foul smell. The storage of biogas and its transportation is difficult due to less advanced technology. Large space is required for the building of production plants. Huge investment is required for biomass production plants. More and more biomass crops are grown which in turn reduces the fertility of the soil. Production of bioethanol from organic waste: The composition of food waste relies on its source of production which mainly consists of a mixture of carbohydrates (cellulose, starch, hemicellulose), proteins and lipids. Food waste can be utilized to produce biofuels or energy in various ways: a) biodiesel can be produced by transesterification of oils and fats, b) bioethanol or biobutanol can be produced by fermentation of carbohydrates, c) biogas can be produced by anaerobic digestion, d) hydrogen can be produced by dark fermentation, e) hydrothermal carbonization, f) pyrolysis and gasification and g) incineration. Bioethanol is considered to be a cleaner biofuel. According to few reports during the process of combustion the net emission of carbon dioxide is zero, however, reports are also available demonstrating the presence of carbon dioxide emission. But because it is biogenic it has zero impact on the environment. Therefore, bioethanol was established to have a vast advantage as an environmentally sustainable fuel.  Bioethanol is one of the most interesting biofuels due to its positive impact on the environment. Currently, it is mostly produced from sugar- and starch-containing raw materials. However, various available types of lignocellulosic biomass such as agricultural and forestry residues and herbaceous energy crops could serve as feedstocks for the production of bioethanol, energy, heat and value-added chemicals. Lignocellulose is a complex mixture of carbohydrates that needs an efficient pretreatment to make accessible pathways to enzymes for the production of fermentable sugars, which after hydrolysis are fermented into ethanol. Despite technical and economic difficulties, renewable lignocellulosic raw materials represent low-cost feedstocks that do not compete with the food and feed chain, thereby stimulating the sustainability.  Bioethanol serves mostly in the transport sector as a constituent of mixture with gasoline or as octane increaser (ethyl tertiary butyl ether - ETBE consisting of 45% per volume bioethanol and 55% per volume of isobutylene). Bioethanol is mixed with gasoline at the volume fractions of 5, 10 and 85%. A total of 85% bioethanol by volume can only be used in flexible fuel vehicles (FFV), while mixtures of 5 and 10% by volume can be used without any engine modifications. However, problems related to the use of bioethanol are: corrosive effect on fuel injector and electric fuel pump (bioethanol is hygroscopic in nature), engine startup problem in cold weather conditions (pure ethanol is hard to vaporize) and the tribological effect on lubricant properties and engine performance. Bioethanol inside lubricant significantly reduces the properties and performance of engine oil because it is miscible with water, but immiscible with oil and hence leads to emulsion formation (bioethanol-water-oil mixture), which causes serious engine failures.  Predictions of the world bioethanol production (a) and consumption (b) by 2024. Source: OECD/Food and Agriculture Organization of the United Nations. OECD-FAO Agricultural Outlook 2015. Paris, France: OECD Publishing; 2015. https://doi.org/1787/agr_outlook-2015-en  Different types of biomass have a potential as raw materials for bioethanol production. Because of their chemical composition, i.e. carbohydrate sources, they mostly form three groups: (i) sugar-containing raw materials: sugar beet, sugarcane, molasses, whey, sweet sorghum, (ii) starch-containing feedstocks: grains such as corn, wheat, root crops such as cassava and (iii) lignocellulosic biomass: straw, agricultural waste, crop and wood residues. However, these sugar- and starch-containing feedstocks (first generation) compete with their use as food or feed, thus influencing their supply. Therefore, lignocellulosic biomass (second generation) represents an alternative feedstock for bioethanol production due to its low cost, availability, wide distribution and it is not competitive nature with food and feed crops.  The most employed microorganism for bioethanol production from sugar-containing feedstocks is Saccharomyces cerevisiae due to its capacity to degrade sucrose into hexoses (glucose and fructose). S. cerevisiae requires small amounts of oxygen for fatty acid and sterol synthesis during bioethanol production, so aeration is an important bioprocess parameter. S. cerevisiae does not tolerate higher sugar and salt concentrations in the medium or higher temperatures. The Melle-Boinot process is the typical process for bioethanol production in batch fermentation. It consists in broth preparation and sterilization followed by yeast fermentation. Fermented broth goes through the centrifugal separation, whereas the liquid part of the broth moves on to ethanol separation stage (usually distillation) and the yeast is recycled for the next fermentation in order to achieve higher cell concentrations.  There are two major processes for bioethanol production from corn starch: dry-grind (67%) and wet mill process (33%), both using yeasts (Saccharomyces cerevisiae, Saccharomyces pastorianus, Schizosaccaharomyces pombe and Kluyveromyces sp.) that are capable of metabolizing starch hydrolysates. In this process, the whole corn is milled (hammer or roller mill) and mixed with water to obtain a mash. The mash is cooked in a jet cooker at 80–90°C for 15–20min. During jet cooking α-amylase (relatively small amounts) is added in order to support liquefaction. Additional α-amylase is added during secondary liquefaction, which occurs for 90min at 95 °C. After that, the mash is cooled to 60°C and mixed with the glucoamylase to hydrolyse the starch into sugars which can be further metabolized to ethanol by yeast. Saccharification and fermentation often occur simultaneously. The bioprocess usually takes place at pH=4.8–5.0 and 30°C for 48h. The fermented broth is then distilled to produce a 95% by volume ethanol. Dehydration of the 95% by volume ethanol requires molecular sieves in order to obtain 99.5% by volume ethanol.  The most often used steps in the bioethanol production from lignocellulose-containing raw materials are: (i) pretreatment of cellulose and hemicellulose to become more accessible in the subsequent steps, (ii) acid or enzymatic hydrolysis of polysaccharides into simple sugars, (iii) microbial fermentation of the simple sugars (hexoses and pentoses) to ethanol and (iv) separation and concentration of ethanol. Production of biodiesel from organic waste: Biofuel production in industrialized countries is abundantly available from wide range of feed stocks which includes the waste from agriculture, municipal (MSW), domestic and industrial solid waste. Sawdust, wood chips, discarded logs and other wood processing wastes can also be utilized as feed stocks for biofuels. The biofuels of second generation are generated from lignocellulosic materials (like jatropha, cassava, switch grass, wood and straw) and biomass remains, while the first- generation biofuels are obtained from edible food crops (like sugarcane, wheat, barley, corn, potato, soybean, sunflower and coconut). Food-grade virgin oils of high quality are developed via the chosen feedstock while waste oils such as used cooking oils are used to derive low-cost biodiesel. To aim for the reduction in material cost in the generation of biodiesel, waste cooking oils can be put to use in place of virgin oil as feed stocks.  The most commonly used types of biofuels are biodiesel and bioethanol which are obtained mostly from vegetable oils, seeds and lignocelluloses. Biodiesel can act as substitute diesel and bioethanol can be utilised as petrol. Biofuel can also be produced through the conversion of biomethane and bio-briquette which are produced from agro-industrial bio-waste and aquatic plant wastes.  Food waste is converted to fatty acids and biodiesel through direct transesterification using alkaline or acid catalysts or by the transesterification of microbial oils produced by various oleaginous microorganisms. Many yeast strains can produce microbial oils which can be used as the substitute of plant oils due to their similar fatty acid compositions. They can also be used as a raw material for biodiesel production. Microalgae have the ability to fix carbon dioxide ten times higher than the terrestrial plants. They are hence also used for the production of biofuels, by extraction of their lipid content and concentration of biomass, salts, nitrate and carbon dioxide. Modern fuels and their environmental impact  One of the most economical methods to generate renewable energy is waste utilization, which is coupled with its complementary benefit of cleaning the environment. Inevitable production of significant amounts of biomass waste and residues from different sectors across world, can prove to be an essential resource to produce energy if economically viable and efficient technologies are brought into development. There exist various drawbacks for the production of energy from biomass: it is not cheap, it requires lot of investment in setting up plants for biomass energy generation, it requires continuous supply of large amounts of biomass waste, yield is generally low especially due to storage and transportation of bioenergy, inadequate design and/or poor operation of MSW combustion systems for the generation of electricity could lead to the emissions of trace organics like furans, polychlorinated dioxins, lead, mercury and cadmium. Therefore, continuous development of a satisfactory control technology, which helps in preventing the harmful volatile emission during waste-to-bioenergy processes is necessary.  The use of non-renewable resources for energy production is not environment friendly and economic at all. In the near future we are going to face severe energy crisis which can prevent our social and economic growth. Hence we must focus on the use of renewable resources for the energy generation. The problem of energy crisis worldwide can be solved by genomics. Hence now a days researchers are focusing to generate energy from renewable resources, like from bacteria, algae, bio-mass, through genomics. Thus genetic engineering may replace the fossil fuels one day. The main obstacle is to develop bio-fuels at a large scale through an efficient method. Hence the knowledge of genomics can break down this obstacle and make biomass more promising in the production of biofuels