Biomass Energy All flesh is grass ~ Isaiah 40.6-8 CHAPTER 6 Biomass energy refers to the energy of all products derived from living organisms. Just like fossil fuels, biomass is formed by the Sun which, through photosynthesis, converts carbon dioxide and water into organic matter. However, unlike fossil fuels that take millions of years to form, biomass can be produced in a short period of time. In fact, this is how the human body converts food into the energy it needs to perform daily tasks. Many of the materials we use and much of the by-products of our activities are biomass; they can be burned directly or converted into liquid and gaseous fuels such as methanol, ethanol, biogas and synfuel. Although only a tiny fraction of the solar energy that reaches the earth is converted into biomass, it can fulfill all the world’s energy needs. Currently, biomass contribution to overall energy consumption is small. However, if energy contained in food is included, biomass provides about 15% of all the energy consumed in the world and, after oil, coal, and natural gas, is our fourth largest energy resource.1 Until the mid nineteenth century, wood provided 90% of energy used in the United States, before better coal technology and the discovery of petroleum reduced the demand for biomass. Today, about 3% of the US energy demand is supplied by biomass, mostly for residential heating and cooking in the form of firewood, but also indirectly as feedstock for the production of liquid and gaseous biofuels.2 Some developing countries, mainly China and India, satisfy as much as one third of their total energy needs from biomass. Tires, pulp, paper, wooden products, foodstuff, rice husks, peanut shells, fruit pits and animal waste are all examples of biomass. Municipal solid wastes are, for the most part, derived from plants and other organic matter. Unfortunately, they contain a variety of other substances that are highly toxic and could pose a health hazard if burned; due to these toxic components many people do not consider them to be biomass. Although biomass energy is renewable, it is not clean, and when burned, like other conventional fuels, it produces pollution. The emissions are lower, however. Furthermore, the carbon dioxide produced from the combustion of biomass offsets that used up during its formation, maintaining zero net production of this dangerous greenhouse gas. In this chapter, we will discuss the mechanism for the formation of biomass, its resources, and its many applications. 1 2 E xcluding food energy (See Chapter 1), wind energy is the fourth largest energy resource. E IA International Energy Annual Report, 1998. Overview When the earth was formed about 5 billion years ago, it was nothing more than a collection of extremely hot cosmic dust with no atmosphere. With time, these particles lumped together by the force of gravity forming an early atmosphere of mostly hydrogen and helium. This was followed by volcanic eruptions which produced water vapor, nitrogen, methane, sulfur, and a few other gases present in today’s volcanoes. No free oxygen was yet present. As earth cooled, water vapor turned into liquid, filling up oceans. Small amounts of oxygen gas appeared only after sun’s ultraviolet radiation broke up the water molecules. The condition was now just right for carbon dioxide and water to react through a process called photosynthesis, making the simpler organic compounds. As by-products, oxygen and ozone were also formed. As the atmosphere thickened, dinosaurs, birds, more complex animals, and eventually the primary form of man appeared. Photosynthesis Photosynthesis (photo=light; synthesis=build) is the crucial link between the sun and the chemical energy stored in all living organisms. It involves the removal of carbon dioxide from the atmosphere by plants and the combination of it with water and other nutrients from the soil to form carbohydrates. Carbohydrate molecules contain carbon (carbo-), hydrogen (hydr-), and oxygen (ate). In the process, oxygen is released into the atmosphere. For photosynthesis to occur, sunlight is needed. The overall reaction can be written as: 6 CO2 + 6 H2O 12 CO2 + 11 H2O or more generally: carbon dioxide + water + sunlight carbohydrate + oxygen Sunlight Sunlight C6H12O6 + 6 O2 C12H22O11 + 12 O2 (6-1) (6-2) In this reaction, two important tasks are accomplished. Firstly, carbon is “fixed”, that is, converted from its inorganic form (carbon dioxide) to its organic form (carbohydrates in the form of glucose or sugar). Secondly, the sun’s dispersed light-energy is transformed into concentrated chemical energy. Once sugar is formed, it can be converted to starch for storage or combined with other nutrients such as nitrogen, phosphorous and sulfur to create more complex molecules such as proteins. Proteins are the building blocks of life, essential to the growth of the body as well as the brain. The best sources of proteins are meat, fish, eggs and milk. But does all of the energy in the sunlight participate in photosynthesis? The light required for photosynthesis must be of the right frequency, around the red end of the visible light spectrum. To capture light for 120 Chapter 6 - Biomass Energy Sulfur-Based Life Digging Deeper ... Until only a few decades ago, biologists thought that organisms in the deep ocean lived only on the debris of marine plants and dead animals falling from the surface to the bottom. Because of the high concentration of deep-sea plants near hydrothermal (volcanic) vents, it is presumed that another mechanism called chemosynthesis is responsible for producing this form of life.i According to this hypothesis, these organisms utilize chemicals rather than photosynthesis to metabolize carbon dioxide and water to form carbohydrate. Examples of vent animals include snails, crabs, limpets, mussels and tube worms. Little, C.S., and Vrijenhoek, “Are hydrothermal vent animals living fossils?” TRENDS in Ecology and Evolution, V. 18, Tube worms Image: NASA Ocean Planet, Smithsonian No. 11, November 2003. i photosynthesis, plants have special pigments called chlorophyll; these absorb only the red and blue portions of sunlight, reflecting the green. This is why many leaves appear green. Lower frequency light does not have sufficient energy so plants do not absorb it. Higher frequency light is too strong and the excess energy is wasted. The result is that photosynthetic efficiency is at a maximum for red light,3 drops abruptly to zero for lower energies (infrared light), and falls slowly for photons of higher energies (blue and green lights). The net effect is that only 32% of solar energy participates in photosynthesis.4 In addition to chlorophyll, plants have two other pigments to trap light in regions that chlorophyll misses. Carotenes absorb blue and blue-green light and anthocyanins absorb green and yellow light and are responsible for the leaves’ yellow, orange, brown or red colors common during the fall season.5 Photosynthesis in Water Photosynthesis is not only responsible for the production of food on land, but also for manufacturing microscopic single-celled plants called phytoplankton in the oceans. Phytoplankton is responsible for the nourishment of the entire marine food web. The lives of all animals that live in the sea -- with the exception of hydrothermal vent organisms (See box “Sulfur-Based Life”) -- depend on phytoplankton for energy and minerals. The rate of photosynthesis is highest, not at the surface, but at a depth of about 10-20 meters where light intensity is not too high. As we go deeper, the rate of photosynthesis slows and eventually stops.6 Food Chain and Food Web Plants use the energy stored by photosynthesis for their own growth, to acquire nutrients, to fight off insects and to create the oxygen required for respiration. Respiration is the reverse of photosynthesis; carbohydrate and oxygen are converted to carbon dioxide and water. In addition, a relatively large amount of energy is released and captured throughout the Near 6700 angstroms. One angstrom is equal to 10 -4 m icrons or 10 -10 meters (1 oA=10 -4 μ m=10 -10 m) Thorndike, E. H., Energy and Environment , Addison-Wesley Publishing, 1976. p.33. 5 Sunlight not only provides the energy for photosynthesis, but also causes chlorophyll to break down. In fact, plants continuously have to work to produce new chlorophyll to replace that which was destroyed. During autumn, in preparation for winter, trees absorb as much nutrients as they can before the leaves fall. As chlorophyll d isappears another pigment called carotene, which holds up better in the sunlight, remains. Since carotene absorbs blue and blue-green, the leaves appear yellow. 6 The study of algae growth in the euphotic zone shows that maximum photosynthetic activity occurs at a depth of only 10-20 m beneath the surface of water. The warmer surface temperatures limit the amount of carbon dioxide that can be dissolved. Below this point, the photosynthesis becomes light-limited, and so decreases with depth. 3 4 121 C Digging Deeper ... Living with Carbon Dioxide* arbon dioxide (CO2) is a colorless, odorless gas that is 1.5 times as heavy as air. It is a component of all carbonated beverages. With water it forms carbonic acid, which has a mildly acid taste. As a by-product of fermentation in yeast , it is CO2 that makes dough rise. The gas is easily liquefied by compression because of its relatively high critical temperature. When liquid CO2 is allowed to evaporate, the vapor freezes to a snow-like solid at -56.2ºC. The solid vaporizes without melting (sublimates) because its vapor pressure is one atmosphere at -78.5ºC. This property makes solid CO2, or dry ice, valuable as a refrigerant that is always free of messy liquids. Carbon dioxide is also an efficient fire extinguisher because most substances will not burn in it. It is also easily generated and, best of all, it is cheap. Air containing as little as 2.5 percent CO2 will extinguish a flame. Although the gas is not toxic, high concentrations will cause suffocation. The atmosphere contains only 0.04 percent CO2 by volume, but still serves as a huge reservoir of the gas, which supports the photosynthetic activities of plants. Because a liter of water at 20ºC can dissolve 0.9 liters of CO2, oceans and lakes serve as rather sizable reservoirs of the compound as well. Although the oceans keep the CO2 levels of the atmosphere relatively constant, the levels have increased detectably in the last few years due to the increase in the rate of burning of fossil fuels. The early atmosphere contained no free oxygen. Almost all the earth’s oxygen was bound in water and metal oxides. Carbon dioxide was also absent from the early atmosphere. Organic compounds would remain stable for a very long time under these conditions. It is therefore reasonable to assume that sea was the suitable laboratory to synthesize the first living organisms. In an environment devoid of oxygen, molecules could come together freely and experiment. Occasionally particles reacted to form new species. Colloidal aggregates grew to form molecules of larger size and higher complexity. For life to exist, a continuous influx and outflow of matter and energy must persist. In the absence of oxygen, only fermentation could provide such a mechanism. Energy is all that was needed for a cell to survive. Alcohol and carbon dioxide were waste products that had to be discarded. Gradually, the concentration of carbon dioxide dissolved in oceans increased until the water became saturated and CO2 escaped into the atmosphere, making photosynthesis processes possible. * Excerpts from a physics text currently under preparation jointly by this author and Professor Igor Glozman, Department of Physics, Highline Community College, Des Moines, Washington 98198. Photosynthesis CO2 + H2O (sunlight) Respiration Carbohydrate + O2 process (Figure 6-1). One major difference between the two processes is that while photosynthesis is possible only in the presence of sunlight (daytime), respiration occurs continuously, regardless of whether or not there is light (day and night). Humans continuously utilize respiration as the source of energy for daily activities. C6 H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (6-3) This is the energy that ultimately, through the food chain, passes on to other living organisms to sustain life. The simple food chain starts from plants (producers) and passes on to other animals (consumers) through three or more stages called trophic (nutritional) levels. At the base of the food pyramid are autotrophs, which are responsible for the primary food production. Autotrophs (self-feeders or producers) are those organisms, such as green plants, algae, and certain bacteria that convert inorganic compounds into energy-rich organic compounds, mostly by photosynthesis.7 Heterotrophs (other-feeders) are those organisms that cannot produce their own food, but rather feed on other organisms. Trees and most other plants are autotrophs. All animals, including humans, are heterotrophs, as are many microscopic organisms. Heterotrophs can be Figure 6-1 Photosynthesis and respiration. Carbon dioxide and water, through the process of photosynthesis, are turned into organic carbon. During respiration, the reverse happens and plants’ and animals’ organic carbon is broken down into carbon dioxide and water. 7 Biomass may also be produced without sunlight through the utilization of certain inorganic compounds called chemo-autotrophs. 122 Chapter 6 - Biomass Energy divided into primary consumers or grazers (herbivores), colloquially referred to as vegetarians, and secondary consumers (carnivores), or meat-eaters. A simple three-level food chain is grassgsheepgwolf. Plantginsectg froggman is an example of a simple four-level food chain. Things are not always that simple in nature, however, as there are multiple types of prey for a single predator. Each link in the food chain can itself be linked with many other food chains, making a complex set of feeding relations which is more accurately called a food web. Although nutrients undergo cyclic processes, energy is not cyclical (See Figure 6-2). Organisms use energy as fuel to help their movements and growth. In this fueling process, some energy is discarded as waste heat. To keep the system operating, as energy degrades, the sun must replenish it. Energy Flow through the Biosphere Heat Heat Sun Producers Consumers Heat = Energy Nutrient Pool Decomposers = Nutrients Figure 6-2 The flow of nutrients and energy through biological systems. Note that while nutrients are recycled over and over again, the sun must continuously supply energy. [Adapted from Masters, G. M.,”Introduction to Environmental Science and Technology,” John Wiley & Sons, 1974.] As was discussed above, photosynthesis is not only responsible for providing energy for a plant’s own growth, but must also provide food for other consumers as they are passed through one trophic level to the next. The photosynthetic capacity, i.e., the rate at which solar energy is fixed by plant photosynthesis varies with temperature, rainfall and the biochemistry of the plant. The rate of gross production is therefore dependent not only on the amount of sunlight, the nutrient supply, and the stability of the surface water in an area, but also to geography. Overall, it is estimated that a mere 1% of the incident solar energy is responsible for the production of all plants, and only a portion of this energy is used for a plant’s own respiration. The remainder is used by consumers and decomposers and is referred to as the net production. Additional losses cause efficiency to drop at each level of consumption beginning with plants; as a result, only ten percent of the energy is converted from one trophic level to the next (See box “Rule of 10”). For example, only 10% of the energy contained in plants is used to warm an herbivore and make it grow. The rest is excreted as waste. Similarly, our body uses only 10% of the energy we take in as food (plants or meat) for our various needs. Question: Plenty of sunshine is often treated as a necessary condition for growing plants. Does plant production increase with light intensity? Answer: Yes, to a certain extent. As light intensity increases, the chlorophyll traps more light, but as traps are filled, additional light will not be useful and may actually harm the plant. The demand for food production increases because of two factors: the increase in population and change to a more affluent diet. At the present rate of growth, it is estimated that by mid-century, the world population will increase to between 8 and 11 billion before gradually stabilizing. Affluent diets enriched with animal fat, meat, dairy, and eggs use up as much as three times more biomass than vegetarian diets (Figure 6-3). Heat Heat Solar Energy 1000 calories 100 calories Human 10 calories Heat Heat Heat Solar Energy 1000 calories 100 calories Cow 10 calories Human 1 calories Figure 6-3 Energy flow in vegetarian and non-vegetarian diets. [Adapted from http://Humboldt.earthsave. org.] 123 Digging Deeper ... Rule of 10* H umans extract about 95 percent of the potential (chemical) energy available in food, but convert only about 10 percent of this energy into useful work, such as lifting weights and building muscle tissue. The rest is turned into heat and dispersed into the environment. Every time any organism eats another, some of the energy stored in the prey is released to the predator. Each of these storage steps along a food chain is called a trophic level. Estimates of energy loss between trophic levels vary widely but, on average, only about 10 percent of the energy fixed (captured and stored) by plants is ultimately stored by herbivores. Only about 10 percent of the energy that herbivores accumulate ends up being stored in the living tissues of the carnivores that eat them; and only 10 percent of that energy is successfully converted into living tissue by carnivores on the third trophic level. This pattern of energy loss is known as the ecological rule of 10. Inefficient energy chains create the so-called ecological pyramid, in which each trophic level contains only one-tenth as much living tissue as the level beneath it. For instance, consider a person who decides to eat only red meat to gain one pound in weight. That person must then eat 10 pounds of beef. The cattle that produced the 10 pounds of flesh must have originally eaten about 100 pounds of fodder. That’s why it makes good ecological sense that the larger animals, such as elephants, are vegetarians. By feeding at or near the base of the ecological pyramid, the larger animals make much more efficient use of energy, and the given ecosystem can support many more of them. Of course, the ultimate source of energy on earth is the sun. Through photosynthesis, plants use most of energy they get from sunlight to grow roots, pump water, and so on. As a result, they convert only about one percent of the sun’s energy into chemical energy, which is then stored in their molecules. Evidently, this is enough to provide for the whole planet, and even keeps gardeners busy. * Excerpts from a physics text currently under preparation jointly by this author and Professor Igor Glozman, Department of Physics, Highline Community College, Des Moines, Washington 98198. Raising domestic animals and livestock such as cows, sheep, goats, pigs, horses, and camels was a major factor that led to the development of ancient societies. These animals not only provided meat, milk, and milk products such as butter, cheese, and yogurt, but also fertilizer and plowing power needed to grow various plants. In fact, these mammals yielded several times more energy over their lifetime than if they were slaughtered and consumed as meat.8 Question: In India, cattle are considered sacred and cannot be slaughtered for food. How does this practice contribute to the food shortage in India? Answer: Although on the surface this practice may appear unjustifiable, it is actually an effective way to combat hunger. Cattle are fed mostly with grass and crop wastes, but provide milk and other dairy products, which are sources of highquality protein. Besides producing food, cow dung is used as fuel and a source of high-quality fertilizer. Question: W hat are the consequences of vegetarian and nonvegetarian diets on total energy consumption? Answer: R aising livestock for meat is a very inefficient way of generating food. For example, it takes far more resources (fuel, water, 8 Diamond, J., Guns, Germs, and Steel: The Fate of Human Societies , W. W. Norton and Company, 1999. p. 88 124 Chapter 6 - Biomass Energy etc.) to produce a kilogram of meat than a kilogram of corn. Adding in all the energy used for transportation, feedlot, and storage, it takes the equivalent of one gallon of gasoline to produce one pound of grain-fed beef. In other words, to provide the yearly average beef consumption in an American family, we require over 260 gallons of fossil fuel.9 The rate of food production varies widely among developed and developing countries. Modern agricultural machinery, better fertilizers, and more complex irrigation techniques have allowed developed countries to produce food at a rate exceeding the rate of their population increase. Unfortunately, the same cannot be said for developing and underdeveloped countries. In these countries, although yearly food production has remained relatively constant, the population has been steadily increasing. As a result, the amount of food per capita has been decreasing dramatically, and many countries have faced severe food shortages and even famine. Furthermore, the food surplus in the richer countries that was traditionally exported to the poorer countries is now being used either to feed the increasing appetite of the local population or is exported to other developing countries. At the same time, much of the high-quality food produced in less-developed countries is being exported to industrial countries. For example, for the last few years, the United States has been the world’s largest importer of beef and fish while Latin America has been the major exporter of this same products.10 Units Food energy is usually expressed in Calories. One Calorie (with a capital C) is equal to the heat energy that is required to raise the temperature of one kilogram of water by one degree centigrade. A smaller unit of thermal energy is a calorie (with a small c), which is 1/1000th of the food calorie: 1 Calorie = 1 kilocalorie = 1,000 calories = 4,184 joules Unfortunately, the calorie notation can cause some confusion. What should be remembered is that when we talk about a food calorie, we are talking about kilocalories, whether capitalized or not. The same is true when we talk about weight; we usually mean mass, especially when we are using terms such as “weight loss.” Energy of Food Production Food production has become less and less efficient as we have replaced the traditional pre-industrial non-mechanized practices with modern agricultural technologies and farming practices. Food production efficiency defined as the ratio of energy output (energy content of foods) to the energy input (energy used to produce, process, package, and 9 R ifkin, J., Beyond Beef: The Rise and Fall of the Cattle Culture , Penguin Press, N.Y., 1992. United Nations Food and Agricultural Organization (http://www.hsus.org/ace/352). 10 125 transport food) has decreased from roughly 100 in the pre-industrial era to less than 1 today.11 The reason for this huge loss in efficiency is that much of the commercial production and delivery of our food on all stages (planting, irrigation, feeding and harvesting, processing, packaging and distribution) depends heavily on oil as the primary source of energy. Fossil fuel is important in cultivating the land, planting seeds, manufacturing fertilizers and pesticides, irrigating, and harvesting. Fossil fuel is also needed in the construction of roads and the transportation of farm workers and food. As a result, only one in every 7-11 calories of energy is available through food. Efficiencies of around 15% in Europe and 9% in the United States have been reported.12 Metabolism Table 6-1. Energy Expenditure (above basal)* Activity Sleeping Eating, Reading Sitting, standing , office work Walking (average speed) Walking downstairs Walking upstairs Golf Jogging Running Tennis Dancing (ballroom) Dancing (disco) Skiing (downhill) Skiing (cross county) Bicycling (20 km/hr) Horseback riding, trotting Horse racing, galloping Boxing (sparring) *For an average person (70 kg) Cal/h 60 80 100 180 205 500 140 400 600 400 300 430 300 600 450 450 550 620 W 70 93 116 210 240 580 163 465 700 465 350 500 350 700 520 520 640 720 It takes energy to stay alive. Whether we are eating or participating in rigorous exercise, we metabolize food as a source of energy. Even when we are not doing any work or are sleeping, we consume food energy. The minimum energy needed for survival and to maintain equilibrium of all vital functions (nervous, cardiovascular, respiratory, and digestive systems) when a body is at rest (sedentary) is called the basal metabolic rate (BMR). The brain and the liver, two organs which jointly make up only 4% of body weight, are responsible for half of all metabolic activity. As chemical energy in food converts to heat, body temperature tends to rise. To maintain a constant temperature, the body reacts by transferring the energy to the circulatory system and to the skin, where it eventually dissipates into the environment. BMR varies with sex, body size, general health, and age, and is generally higher in males and for heavier, healthier, and younger animals. BMR is about 1.45 watts for a rat, 80 watts for an average sized person, and 266 watts for a medium size cow.13 BMR does not account for any physical activity, so additional energy is needed to carry out daily tasks (See Table 6-1). Physical activities can be divided into aerobic and non-aerobic activities. During aerobic activities, oxygen breaks down carbohydrates, fat, and protein and converts them to energy. Examples of aerobic exercises are dancing, jogging, swimming, and biking. Anaerobic activities burn carbohydrates without oxygen with maximum bursts of energy of short duration. Examples are weight lifting, pushups, chin ups, and sprinting. The amount of daily energy needed is different for different people and can vary with gender, weight (mass), and levels of physical and mental activity. As a rule of thumb, it is usually assumed that an average man requires 2,500 Calories, whereas an average woman needs only 1,800 Calories per day in food intake. Example 6-1: W hat is the minimum number of calories that an Green, B. M., E ating Oil – Energy Use in Food Production, Westview Press, Boulder, Colorado, 1978. 12 Günther, F., “Fossil Energy and Food Security,” E nergy & Environment, Volume 12, Number 4, July 2001, pp. 253-272. 13 Faughn, J., L ife Science Applications for Physics , Harcourt, 1998. 11 126 Chapter 6 - Biomass Energy Metabolism and Animal Kingdom U FYI ... nlike their cold-blooded neighbors, warm-blooded animals must always maintain a constant body temperature, irrespective of the temperature of the environment. In cold climates, they fight against losing too much heat; in hot climates, they try to stay cool by dissipating excess heat. The rate at which heat is generated in and lost from an animal’s body depends very much on the size of the animal. Larger animals have more mass to “feed” and therefore generate more metabolic heat. Larger animals also have more surface area from which heat is lost. While it would seem that the larger animals have to contend with a greater heat loss, it is the specific heat loss (i.e., heat loss per unit body mass) that is more relevant to the animal’s survival. Since mass is proportional to L3 and surface area is proportional to L2, the specific heat loss is actually proportional to 1/L (or M-1/3). In other word, as the metabolic rate is lost through the body surface, it is logical to expect that an organism will adjust its BMR to overcome heat losses through the surface (skin) proportional to M2/3. A similar relationship has also been found for plants. Amazingly, we can actually predict (or at least rationalize) certain patterns of behavior of different animals on the basis of simple scaling arguments. A very small animal must compensate for its lost body heat by an almost continual intake of food. A mouse eats a food equivalent of about one-quarter of its body weight daily. The tiny shrew will die of starvation if forced to go without food for more than about 3 hours. A giant elephant, on the other hand, faces the opposite problem of getting rid of excess heat. It’s no wonder that elephants take every opportunity to cool themselves off at waterholes. We can therefore understand why a mouse might want to be in a warm spot, while an elephant in a cool one. For insects, the surface to volume ratio is so much larger than that of any warm-blooded animal that they cannot possibly eat fast enough to maintain a constant body temperature. What to do then? Fortunately for the insects, the body temperature of a cold-blooded creature matches that of the surroundings. This provision of nature greatly reduces heat loss and consequently the Mass (kg) insect’s food requirements. average person needs to barely stay alive? Solution: Assuming BMR of 80 W, the daily caloric intake must be at least 80 W = 80 J 1 kcal 24 x 3600 s 1 kJ x x x = 1650 kcal/day s 4.1868 kJ 1000 J day Question: How much weight does a starving male (zero food intake) lose in one week? Answer: Assuming an average person requires 2,500 kilo-calories of food to meet his daily energy needs, and that each gram of fat metabolizes 9 Calories (37.6 MJ/kg), he burns 2,500/9=277 grams of his body fat each day (1.9 kilograms in one week). It is no surprise that people are known to survive many weeks without food.14 Question: W hich one has a higher BMR, a tall and thin person or a short and fat person? Answer: For the same mass, tall thin persons have a greater skin surface area and thus lose heat to the environment faster. They should have a higher BMR to maintain the equilibrium body temperature. 14 They still need to drink water to prevent dehydration that may occur in a few days. Basal Metabolic Rate (W) 127 The Origin of Life Digging Deeper ... T he simplest living organisms were developed about 3.5-4.0 billion years ago from organic molecules produced by chemical reactions in an atmosphere consisting principally of water vapor, carbon dioxide, ammonia, and methane, and devoid of oxygen (anaerobic), fueled by ultraviolet light from the sun. In addition, a substantial amount of organic molecules are believed to have been brought to earth by impacts from asteroids, comets, and meteors common during the early stages of earth’s formation. There is strong evidence that the chemical reactions near deep-sea vents have also contributed. The minerals in the early primordial soup facilitated the coalescence of these molecules to form longer RNA (ribonucleic acid) strands that could replicate themselves. Some strands of the RNA molecules eventually combined to form DNA (deoxyribonucleic acid), the building block of what we know as life today. The first microorganisms were chemoautotrophs that had access to very few enzymes and obtained their energy from inorganic molecules (such as those near hydrothermal vents and hot springs). As life evolved, other mechanisms, mainly photosynthesis, played more important roles. Early photosynthesis involved hydrogen sulfide, not water, and therefore produced no oxygen. Photosynthesis involving water evolved later, producing oxygen that was built up over the years in earth’s atmosphere. In the beginning, oxygen reacted immediately with other organic and inorganic material and no molecules were released into the atmosphere; in the process, many early life forms became extinct. It took at least one billion years before oxygen concentrations rose to significant levels. As a result of the new chemistry, two types of molecules were formed: simpler single-organism prokaryotic molecules lacking a cellular structure (bacteria) and more complex eukaryotic cells (which ultimately led to the creation of a cell nucleus). These cells proved to be the key in the manufacturing of more complex molecules called adenosine triphosphate (ATP), which captured and transferred the energy that cells need for building all cellular components. Cells can be viewed as tiny chemical factories which provide processes needed to make complex organic molecules needed by all living organisms. With time, the cellular structures became more and more complex, eventually leading to multi-cellular species such as plants and, eventually, animals. Early plants and animals lived in oceans where there were plenty of nutrients and they were protected from harmful ultraviolet radiation. As atmospheric oxygen converted to ozone, plants and animal could increasingly survive land environment and life as we know it today flourished. Food Waste Heat Question: W hich organism has a higher basal metabolic rate, a hummingbird or an elephant? Answer: Hummingbirds are very small birds, weighing approximately 2.5-4.5 grams. Because small birds have proportionately larger surfaces in relation to their body mass, they can lose heat faster and therefore have higher metabolic rates. Gram by gram, hummingbirds have the highest metabolic rate of any animal, roughly 12 times that of a human being and 100 times that of an elephant. Their BMR is around 29 W, which means they need to consume 600 Calories of food every day. No wonder each day they have to visit hundreds of flowers to gather enough nectar to survive. The Human Heat Engine Muscle Work Figure 6-4 Human body is a heat engine, taking input energy in the form of food, converting a part of it into muscle work, and rejecting the waste heat as sweat and other excrements. The human body functions like an engine, converting part of the food’s chemical energy into useful mechanical energy when muscle cells carry out physical work, and dumping the rest into the environment (Figure 6-4). The conversion efficiency is about 17%, that is, only about one in every six units of energy in the food we eat is converted to muscle work. What remains is used as internal energy in our muscles, essential to maintaining our body temperature (through sweating and other forms of heat losses collectively called waste heat) or stored in body in form of fat . Metabolic efficiency is not the same for all people, and can vary between 15-25% 128 Chapter 6 - Biomass Energy depending on gender, weight, condition of health, athletic abilities, and age. Although maximum power can be quite high, average power output is not and is limited to around 20 W of mechanical energy per kilogram of body mass. By combining the food production efficiency (~10-15%) and metabolic efficiency (~15-25%), a net figure for the human power efficiency is calculated at around 1.5-3.75%. In other words, on average, each unit of mechanical (muscle) energy comes at the expense of 17 to 66 units of primary (fossil) energy. Example 6-2: Can we harness waste energy from the human body to perform work? What is the maximum power that can be utilized using this energy? Solution: Assuming ambient temperature of 25oC, the Carnot efficiency is 298 = 3.87 % 310 where waste is taken to be at the body temperature of 37oC. While sitting, an average person can expend 116 W, of which 4.5 W is available in the form of useful power. η = 1Example 6-3: Compare the cost of power generated by human muscles to that from nuclear or coal power plants. Solution: An average human consumes 2,500 Calories of food every day. Each Calorie is equal to 1,000 calories or 4,180 joules, and each kilowatt-hour is 3.6x106 joule, so 2,500 kcal = 10,450 kJ = 2.9 kWh This amount of energy can be supplied by about 2 pounds of steak and 10 slices of bread for an average cost of $10 (or $300 a month for food cost). The energy cost is therefore estimated at around $3.45/ kWh. The cost of electricity being charged to American consumers varies between 8-15 cents per kilowatt-hour, which is an order of magnitude cheaper than the cost of energy delivered by humans. No wonder machines are rapidly replacing people whenever possible. Food, exercise, and dieting The energy required by our body is provided by the food we eat. The major food categories are carbohydrates (mainly sugar, bread, and rice), proteins (primarily meat, milk, and eggs), and fats. In addition, most plant-based foods contain other nutrients like vitamins, minerals, and water which are drawn up from their roots during growth. Although they are small in quantity, these are essential ingredients in metabolizing the calories stored in food. The human body metabolizes these foods differently. While each gram of fat yields 9.5 kilocalories when burned, carbohydrates and proteins yield only 4.3 and 5.3 kcal of energy, respectively. Carbohydrates and proteins take some time to digest into simple sugars, whereas sugar is instantly metabolized. The energy contents (calorific values) of some 129 Food: The Facts Did You Know That ...? • It takes 127 calories of energy (aviation fuel) to transport one calorie of lettuce across Atlantic, 97 calories to transport 1 calorie of asparagus from Chile, and 66 units of energy to fly one calorie of carrot from South Africa. • Every year around 20 million people die as a result of hunger or malnutrition. • It takes 10,000 kilocalories of food to supply the roughly 3,000 kilocalories consumed per day by an average American. • It takes about 5.5 kilograms of protein in the feed to produce 1 kilogram of poultry and about 8 kilogram to produce one kilogram of pork. common foods are given in Table 6-2. Table 6-2. Food Calories (all values are averaged) Food Apple, large Bacon, 2 strips Banana, small Beer, one glass Bread and butter (one slice) Butter (one teaspoon) Cake, a slice Chicken, fried (1/2 breast) Cheeseburger Cookie, chocolate chip Coke, one glass Doughnut Egg (one) French fries (regular) Ice cream (one scoop) Steak (1/4-lb) Mayonnaise (1 tbsp) Milk, one glass Milk shake Orange Juice (one glass) Pizza, cheese, one slice Potato chips, one serving Hamburger Spaghetti, one serving kcal 100 100 90 150 80 36 350 230 350 50 110 150 80 250 300 200 92 166 420 120 180 110 275 400 Physiologists and physicians have studied, but differ in opinion on the root causes of weight gains by people. Some attribute the propensity to gain weight to a special gene and hormonal imbalance. Others believe bodies develop fat cells during childhood that become active as the body ages. Still others attribute obesity solely to overeating. No matter what the actual medical reason for weight gain, to maintain our weight, the total energy intake by food must balance the energy expenditure of normal basal metabolic rate and that expended by work and other physical activities. If the energy intake exceeds the energy expenditure, the excess energy is stored as fat. As a rule of thumb, we need to burn roughly 3,500 extra Calories to lose one pound of fat. Example 6-4: According to one study15, since the 1960s, the average individual living in the United States has increased caloric intake by about 250 Calories each day. How much weight would one gain by staying on the new diet? Solution: The total excess intake of energy over one year is: 250*365 = 91,250 kcal. The added weight is 91,250/3,500 = 26 lbs (11.8 kg). Example 6-5: A 50-kg woman is jumping rope at a rate of 50 times a minute for 15 minutes. Each jump on average raises the center of mass 0.5 m. How much energy does this woman consume? Solution: The work performed per jump is W = mgh = 50x9.8x0.5 = 245 J. Total work performed is (15 minutes)x(50 jumps/minute)x(245 J/jump) = 183,750 J = 44 kilocalories. Example 6-6: A 110-lb (50 kg) woman pedals a stationary bike for 20 minutes at an average speed of 20 km/h (12.5 mph). Calculate power consumption rate, total Calories burned and the metabolic equivalent (METs). 1 MET is defined as the energy expenditure rate in kcal per hr per kilogram of body mass. Solution: Referring to Table 6-1, energy expenditure rate (power) is given as 450 kcal/hr or 520 W. Total calories burned is E = P.t = 450 kcal/hr x 20 min = 150 kcal. The metabolic equivalent is calculated as 15 Thompson, D. J., et al., “Lifetime health and economic consequences of obesity,” A rchives of Internal Medicine, 159:2177-83 (1999). 130 Chapter 6 - Biomass Energy the power (450 kcal/hr) divided by her weight (50 kg), or 9 METs. Example 6-7: It is experimentally found that in the photosynthetic reaction given by Equation 6-1, for each mole of carbohydrate (CH2O), 112 kcal of light energy is needed. What is the amount of energy supplied to our body through the consumption of one 12-oz cola containing 36 grams of sugar (glucose)? Solution: The respiration reaction is the inverse of equation 5-1; for each mole of glucose (180 g) we consume 6x112 = 672 kcal (Calories) of energy is taken in. The soda contains 36x672/180 = 134 Calories. Example 6-8: How many stairs should a 60-kg woman climb to burn off a chocolate chip cookie that has 100 Calories? Solution: To maintain her weight, the woman needs to burn off 100 Calories. Assuming there are no other losses (friction from shoes and air currents, for example), this energy must be compensated for by the work that she does against gravity (i.e. gain in the potential energy), or 100 kcalx4.18 kJ/kcal = 418 kJ. The height she needs to climb is h = E/mg = 418,000/(60x9.81) = 710 m. Assuming each step is 20 cm in height, she must climb up 710/0.20 = 3,550 steps! In reality, the human body is only about 20% efficient at converting chemical energy into gravitational potential energy. In other words, 80% of the metabolic energy generated goes into heat. Consequently, the number of steps is really smaller by a factor of 5, but it still is a pretty big number, something to think about before you take another cookie. Example 6-9: A 90-kg (200-lb) man has a cheeseburger, regular fries, and a glass of beer for lunch and a milk shake for dessert. How long would it take him to burn off the calories, if (a) he returns to continue his routine office work or (b) he goes to a gym and bicycles at a moderate speed? Solution: The total caloric intake can be calculated using data in Table 6-2, as 350+150+250+420 = 1,170 Calories. An average person (70-kg) can burn off calories at the rate of 100 Calories/hr by sitting in his office or 450 Calories/hr by bicycling. Since the rate of energy consumption is higher for a heavier person, the 90-kg man burns calories faster at the rate of 100x90/70 = 129 Calories/hr doing office work, and 450*90/70 = 579 Calories/hr bicycling. The time Did You Know That ...? EX 6.6 Solid Wastes in the United States: The Facts • The United States generates 200 million tons of solid waste a year-- about 3 tons for every person, twice that of an average European. • Every year we dispose of 6 billion plastic diapers and 200 million pounds of plastic soda bottles. • The garbage from a typical American household consists of roughly 66% paper and other organics and 24% glass, metal, and plastic. The remaining 10% are rubber, textile, and other wastes. • McDonald’s produces over 34,000 tons of polystyrene cups, boxes and trays annually. 131 needed is 1170/129 = 9 hours of office work, or 1170/579 = 2 hours of bicycling. Clearly, the best way to lose the weight is by eating less. Exercising has many health benefits, but not necessarily the most effective for losing weight. Example 6-10: In order to maintain constant weight, we must consume about 2,000 kilocalories of food energy per day of inactivity. How long could you live off your fat? Solution: In two days of starvation and inactivity one would be able to lose about 4,000 kcal or about one pound of fat. On the average, 15% of an adult male’s weight is in the form of body fat, and 22% for the adult female. Therefore, assuming about 30 pounds per person, we could, in principle, live for about two months (30x4100/2000 = 61.5 days) simply by burning off our own fat. Example 6-11: Suppose a 65-kg person spends 8 hours sleeping, 1 hour performing moderate physical labor, 4 hours engaging in light activity, and 11 hours working at a desk or relaxing. Is this person likely to gain weight if he maintains a 3500-Cal daily diet? Solution: Referring to table, we calculate the energy expenditure to be (8x70+1x460+4x230+11x115) x 3600 = 11.5 MJ = 2800 Cal/day. Since this person is taking in 3500 Cal and burning only 2,800 Cal, he will gain weight. Among health care professionals, perhaps the best known method for assessing body size is the Body Mass Index (See box “Body Mass Index”). Other factors, such as the waist-to-hip ratio, may also be important in determining the ideal weight for a healthy person. Power Generation by Biomass Biomass is not only the source of our food, but also plays an important role in meeting our energy demands as a fuel. Wood can be burned directly in fireplaces or used in boilers to produce steam. Some developing countries, FYI ... Body Mass Index B ody mass index (BMI) is defined as body mass divided by height squared. It is an empirical formula defined by the National Institute of Health (NIH) to measure Height, cm Healthy Height, feet Healthy obesity and provide a guideline for weight control. Mass, kg Mass, lbs BMI = M [ kg2] h2 m (i) 150 155 160 165 170 175 180 43-56 46-60 49-64 52-68 55-72 58-77 62-81 5’ 0” 5’ 2” 5’ 4” 5’ 6” 5’ 8” 5’ 10” 6’ 0” 97-128 104-136 110-145 117-155 125-164 132-174 140-184 According to this scale, adults with a BMI between 19 and 25 are considered to have a healthy weight, those below 19 are underweight, between 25 and 30 are overweight, and above 30 are considered obese. For easy reference, the recommended weights for adults of different heights are tabulated in metric and US units. 132 Chapter 6 - Biomass Energy such as India, use animal dung for heating and cooking purposes. In more developed countries, special plants are cultivated to be used specifically as biomass fuel. These include herbaceous plants (such as sugarcane, corn, cotton, sorghum, and bamboo), aquatic plants (such as algae and seaweeds), and crop residues (wheat and rice straws, and dead and dying trees, stalks, leaves, and cobs). The most suitable plants are perennial plants such as switch grass, poplar, willow, maple, and sycamore. These plants need little fertilizer or pesticide, and can help to reduce soil erosion. Another source of biomass fuel is municipal solid waste (trash) consisting of everyday items such as product packaging, paint, yard waste, bottles, cans, newspaper, rubber, leather, textiles and other household items.16 In 2001, the US produced 229 million tons of waste, divided equally among residential, commercial, and construction sectors (Figure 6-5). This represented a 2.6-fold increase since 1960, equivalent to 2.2 kg per person per day. Of all the garbage collected in the United States, roughly threequarters is biodegradable and can be considered biomass. Over 72% of this is buried in landfills, about 15% is incinerated, and the rest is recycled or reused (Figure 6-6). Direct Burning (Incineration) Biomass can be burned in incinerators for heat, mixed with coal and used directly for heating, or converted to electricity in power plants. Conventional incinerators directly burn biomass to heat water and generate steam that runs a steam turbine. In modern incinerators, biomass is first converted into producer gas, which can then be burned inside gas turbines. In some instances, the waste heat from the gas turbine may be used to drive a secondary steam turbine, converting more of the fuel energy into electricity in what are commonly referred to as combined heat and power (CHP) units. Finally, the waste heat from these secondary plants is hot enough for hot-water and space heating that would otherwise be lost to the atmosphere. According to the US Department of Energy, domestic capacity for biomass generation utilizing combustion could reach 20-30 GW by the year 2020. About four-fifths of all biomass energy used today comes from burning wood and wood scraps. The remainder is from crops, garbage, landfill, and alcohol fuel. Materials used for direct incineration are usually scrap wood and sawdust produced by timber companies, solid wastes and garbage, and landfill gases. Most energy generated by biomass fuel is used locally. Burning trash has the advantage of producing electricity and heat, and also reducing the volume of trash. The main problem with incinerators is that many of the pollutants associated with combustion remain and are released to the atmosphere. Some newer technologies burn these materials 16 Figure 6-5 Municipal solid wastes constitute a major source of energy. Source: National Renewable Energy Laboratory, Photographic Information Exchange U.S. Waste by Type (2001) Metals Glass 8% 5% Plastics 11% RLT 7% Food Wastes Wood 11% 6% Yard Trimming 12% Other 3% Paper 37% (a) U.S. Waste by Sector (2001) Other 14% Construction debris 21% Residential 32% Commercial 33% (b) Composition of municipal solid waste in the U.S, (a) by type, and (b) by sector. RLT refers to rubber, leather, and textiles. Source: US EPA 2001 Facts and Figures. http:// www.epa.gov/garbage/pubs/msw2001.pdf. Figure 6-6 The word “municipal” implies anything that is operated and controlled by elected local city or county officials. 133 FYI ... Biomass from Animal Waste H ow much electricity can be utilized from the average daily droppings of the three most common farm animals? Answer: • Cow 3.0 kWh • Pig 0.2 kWh • Chicken 0.012 kWh Table 6-3. Calorific values for different biomass fuels Source Heating Value* (MJ/kg) 21.5 13.0 19.7 19.7 20.4 21.3 18.5 49.8 20.0 27.0 Sugar cane Municipal solid waste Garbage Newspaper Hardwood Pinewood Grass Methane Methanol Ethanol * Lower heating value at much higher plasma temperatures. Plasma is gas heated (usually by passing strong electric currents through it) to temperatures around 10,000 o C, causing electrons to be stripped off the atoms. At these temperatures, hydrocarbons, PCBs, and other toxins break down, allowing them to be burned completely. The residues are mixed with soil and harden into inert and harmless rocks suitable for road gravel. Incineration accounts for 10-15% of all garbage generated in the US and for only a tiny one-tenth of one percent of all electricity supplies.17 Biomass has lower calorific values as compared to fossil fuels. Table 6-3 compares the calorific (heating value) of several biomass fuels with fossil fuels. Thermochemical Conversion In thermochemical conversion (also called pyrolysis or gasification) dry biomass is decomposed to simpler molecules (gaseous methane and liquid methanol) by high heat. No or little oxygen is used in the process, and no chemical reactions are involved. The methane can be collected and sold by natural gas utilities; methanol (also called wood alcohol) is of great interest in reformers to produce hydrogen for fuel cells or used directly in alternative fuel vehicles. Coal or other carbonaceous materials can be gasified to produce hydrogen, synfuel, and other valuable products (See Chapter 14). Biochemical Conversion Biochemical conversion could be either anaerobic or aerobic. In anaerobic conversion, biomass is put in anaerobic digesters, where it is exposed to microorganisms in the absence of oxygen and allowed to decay. The oldest form of biochemical conversion is the fermentation of grapes, corn, and barley by microscopic yeast to produce wine, beer, and other alcoholic beverages. The same process can be utilized to produce ethanol (also called grain alcohol) and other synthetic fuels. High-moisture herbaceous plants and marine crops are most suitable for biological digestion. Fuel alcohol is produced by cooking the biomass and converting the starch into sugar. The sugar is then allowed to ferment. Ethanol can be removed by distillation and can be used directly, or be blended with gasoline and used as fuel in internal combustion engines. New processes use enzymes to break down the cellulose part of the plants, allowing the entire plant (and not just the starch) to be utilized. 17 O ffice of Technology Assessment, “From Pollution to Prevention: A Progress Report on Waste Reduction,” Washington, D.C., 1987. 134 Chapter 6 - Biomass Energy Ethanol Enigma Digging Deeper ... E thanol is formed by fermenting sugar in grains such as corn, wheat, and rice, in much the same way that beer, wine, and liquors are made. The process is not new; in fact it has been around for many centuries. Before the Civil War, ethanol was used in the United States mainly as a lantern fuel and as a lubricant. In order to finance the war, US president Abraham Lincoln imposed a tax on liquors. Since ethanol was produced by fermentation of grains, it was taxed heavily and people turned to kerosene, which was poisonous and not suitable for drinking. The “Spirit Tax” was eventually repealed in 1906, and ethanol became an ideal fuel to run internal combustion engine once again. Fuel ethanol made a partial comeback, but the introduction of Prohibition in 1919 killed any chances of ethanol becoming a major fuel source. To make combustion more uniform, ethanol continued to be used as an additive, however. To increase market share, oil companies opted for lead additives, which soon proved to be a major health concern. In 1933, Prohibition ended and ethanol was put to new uses in making synthetic rubber and the production of ethanol soared again. A decade later, as WWII came to an end, grains found new market and ethanol production was curtailed one more time. Lead continued to be the primary additive for many years until the increasing level of emission from automobile exhaust forced new regulations that resulted in development of catalytic reactors, which were poisoned by the lead additives in gasoline. Even after lead was removed from gasoline, oil companies chose aromatics like benzene, toluene, and MTBE. Benzene was eventually phased out in 1990s and many states are now passing legislations to ban MTBE. Ethanol, as an alternative fuel or as an additive, has generated renewed interest. As we will show in Chapter 14, ethanol has a higher octane than gasoline and, because it is oxygenated, burns cleaner. The effect on production of the greenhouse gases is less certain. It was commonly presumed that, since ethanol is a biomass, no net greenhouse gases are produced. Recent studies, however, rebuke this claim on ground that to produce biofuels, virgin forests and grasslands must be cleared. About 2.7 times more carbon is stored in terrestrial soils and plant material than in the atmosphere, and this carbon is released when these areas are cleared (often by burning) and the soil is tilled. Cellulosic and sugar-based ethanol are considered best. The United States, under pressure from corn-producing states uses corn as source of its biofuel. Corn farming requires more land andonly yields 1/4 more energy out than the fossil energy you have to put in.i In addition, serious environmental problems, such as higher food prices, soil erosion and nutrient leaching, and substantial demand on the world’s land and water resources may not warrant production of biofuels in a large scale. i From Proceeding of the National Academy of Science of the USA, July 2006. The main source of bioethanol is sugar-containing plants, corn in the United States and sugar cane in Brazil. Sugar from these plants is fermented by yeast and bacteria to reduce carbohydrate to ethanol and carbon dioxide according to: C6H12O6 2 C2H5OH + 2 CO2 Some energy of course is needed to produce the plant, to harvest it and ferment it into a biofuel. The ratio of the amount of energy produced when biofuel is burned to the amount of energy used to make the biofuel is the fossil energy replacement ratio (FER). FER is around 1.2-1.4 for corn ethanol, and about 8 for sugarcane. Therefore, it can be argued that not only can corn ethanol be economically viable substitute for fossil fuels, its impact on the production of greenhouse gases would be minimal. Another important byproduct of anaerobic digestion is biogas. Biogas is a mixture of methane, carbon monoxide, and carbon dioxide gas which occurs naturally in the bottom of swamps, marshes and landfills, 135 or is produced by the fermentation of human and animal wastes. Biogas is a well-known fuel for cooking and lighting in a number of countries. Biogas can be converted to liquid biofuels, which can potentially replace petroleum fuels. Biochemical conversion is also possible in presence of air or oxygen (aerobic conversion). These processes occur at much higher temperatures, and generally do not produce appreciable amount of useful fuel gases. Summary Biomass is a result of photosynthetic activities where carbon dioxide and water, in the presence of sunlight, combine to form carbohydrates. The conversion efficiency is rather low, however; only 0.3% of the incoming solar energy is converted to the chemical energy stored in plants. In contrast, as we will see in later chapters, solar cells can convert up to 40% of the solar energy directly into electricity. Biomass is considered by many as a renewable source of energy. Others point out that in order for biomass to be truly renewable, the rate of cultivation of new trees must be equal to that of biomass consumption. That is to say, for every tree that is cut down and burned, another tree must be replanted. Even if biomass were entirely renewable, it is not a clean source of energy. As is the case with fossil fuels, burning biomass creates major air pollutants such as carbon monoxide and particulates. In addition to these pollutants, biomass produces aldehydes which, although not carcinogenic, produce an unpleasant odor at high concentrations. Since there are low levels of sulfur and nitrogen in biomass, fewer products that cause acid rain are formed. Biomass, however, does not contribute to global warming and is relatively low in sulfur; it therefore contributes little to the acidity of the environment. Besides pollution, biomass as a source of energy has been controversial for other reasons. Harvesting forests for fuel wood and lumber will ultimately lead to deforestation. Crop farms will not be able to produce such crops for a very long time, as soil erosion and massive use of herbicides and fertilizers will reduce their productivity. Furthermore, these farms are built on lands which could otherwise produce the food-crops necessary to feed many parts of the world. Burning trees, dung, and other animal wastes deprives the soil of its essential nutrients, reduces the yields, and makes the land less capable of supporting natural vegetation. It is therefore, important to use plants that are not suitable for food consumption, and are planted in marginal land unsuitable for food crops. Trash and municipal solid wastes have become a major problem for many 136 Chapter 6 - Biomass Energy countries. Trash must be stored in landfills, shipped away to areas with lower population densities, or simply burned. Landfills are filling up fast, especially near towns. They are polluting, may leak hazardous chemicals into the ground and water, and are breeding grounds for rats, flies, and microbes that cause diseases, rot foods, and may react to produce other unwanted products. Hauling trash is not popular with its potential recipients. Incinerators are appealing to many because they reduce trash volume by 60-80% and produce energy at the same time. Incinerators, however, produce deadly smoke and ash, which require expensive scrubbers, filters, and other control equipment. Furthermore, many toxic metals such as mercury, lead, and cadmium cannot be effectively removed and will eventually find their way into the ground or be released into the atmosphere. Recycling seems to be a sensitive solution to the problems of waste disposal. The problem with this approach is that it encourages waste, which ultimately increases energy use and generates a considerable amount of air pollutants. In addition, recycling demands consuming additional energy-- as much as 25% of the energy used in manufacturing the original material. The only solution to our trash problem is to create less trash. This means we must produce only goods that are essential, made of materials that are harmless to the environment, last longer, and have been designed to be disposed with minimal waste when they are no longer needed. Additional Information Books 1. Sims, R., Bioenergy Options for a Cleaner Environment in Developed and Developing Countries, Elsevier, 2003. 2. Tillman, D., Combustion of Solid Fuels & Wastes, Academic Press, 1991. 3. Biofuels for Transport: Global Potential and Implications for Energy and Agriculture, The Worldwatch Institute, 2007. Periodicals 1. Biomass and Bioenergy, Science Direct Elsevier Science Publishing Company. Government Agencies and Websites 1. National Renewable Energy Laboratory: Biomass Research (http:// www.nrel.gov/biomass). 2. US Department of Energy (http://www1.eere.energy.gov/biomass). Non-Government Organizations and Websites 1. Biomass Energy Research Association (http://www.bera1.org). 2. American Bioenergy Association (http://www.biomass.org). 137 Exercises I. Essay Questions 1. Why are most plant leaves green? Why do they turn yellow in the fall? 2. What does it mean to “fix” carbon? How can this be done? 3. What is a hydrothermal vent? Why do deep-sea organisms mostly grow near these vents? 4. Describe the processes of aerobic and anaerobic conversion. Give examples of physical activities that involve these conversions. 5. What are the various trophic levels? How does energy transfer from one trophic level to another? 6. What are the differences between thermochemical and biochemical conversions? Between the processes of aerobic and anaerobic conversion? 7. A basketball player is using an average 400 watts of power during a basketball match. How long does he have to play to burn off a Big Mac (750 Calories)? Assume a metabolic efficiency of 25%. 8. What is the BMR value for a 70 kg woman who is 155 cm tall? Is she overweight or underweight? If she is overweight, and if she intends to reduce her weight by aerobics only (no dieting) over 6 months, for how long does she have to exercise every day? 9. If the US were to meet its entire energy need (100 Quads) from sugarcane, how many tons of sugarcane would have to be planted? 10. Describe the difference between gross and net production. What are the factors that limit production efficiency from one trophic level to the next? 11. Which has a higher metabolic rate, a hummingbird or a human? How does size of an animal affect its metabolic rate? II. Multiple Choice Questions 1. Biomass a. Is a form of solar energy b. Can be used to produce electricity c. Refers principally to wood, and animal and human waste d. Will likely increase in use because it is a free source of energy e. All of the above 2. Which of the following are considered to be carbon sequesters? a. Fossil fuels b. The oceans c. Thermafrost and tundra d. The atmosphere e. All of the above 3. During photosynthesis, a plant a. Creates energy b. Absorbs energy c. Gives off energy d. Transmits energy e. Reflects energy 4. Humans use chemical energy contained in food a. To maintain their body temperature b. To enable their bodies to move c. To perform mechanical work d. To feed neurons for transmitting electrical signals e. All of the above 5. Biomass energy refers generally to a. Wood and agricultural products b. Solid waste c. Landfill gases d. Alcohols e. All of the above 6. If 0.1% of solar energy that falls on earth is captured by plants, and 2% of that energy is involved in photosynthesis, what fraction of sunlight that hits the earth is converted to food? a. 0.2 b. 0.02 c. 0.002 138 Chapter 6 - Biomass Energy d. 0.0002 e. 0.00002 7. Which of the following statements is incorrect? a. Autotrophs are mainly green plants and algae formed through photosynthesis. b. Heterotrophs cannot produce their own food. c. Heterotrophs can be divided into herbivores or vegetarians, and carnivores or meat-eaters. d. Nutrients are recycled over and over through biological systems. e. None of the above. 8. What kind of organisms can produce their own food? a. Autotrophs b. Herbivores c. Heterotrophs d. Carnivores e. All of the above 9. Which trophic level is represented by the greatest biomass in any ecosystem? a. Herbivores b. Primary carnivores c. Producers d. Secondary carnivores e. Top carnivores 10. What kind of organisms are at the top of the food web? a. Autotrophs b. Herbivores c. Heterotrophs d. Carnivores e. None of the above 11. If you eat a frog that eats insects, which in turn eat plants, you would be a a. Producer b. Primary consumer c. Secondary consumer d. Tertiary consumer e. Trophic consumer 12. Pyrolysis is a. Burning biomass at a very high temperature The process of hydrogenation of biomass by adding steam Breaking down the biomass matter by using heat in the absence of oxygen Thermochemical conversion at room temperature Disintegration by microscopic organisms in the absence of oxygen b. c. d. e. 13. Wood and other biomass account for about ____ percent of US energy consumption. a. 0.1 b. 1 c. 3 d. 10 e. 25 14. Respiration is a. An intermediate step in photosynthesis b. Another name for photosynthesis c. The reverse of photosynthesis d. Same as sweating e. Photosynthesis in water 15. Incineration a. Is becoming the most popular way to produce energy at very low costs b. Is considered as a good and inexpensive alternative to solid waste disposal c. Is not clean and produces harmful by-products that are highly toxic to humans and animals d. Is best for disposing of metals and plastics e. All of the above 16. “Rule of 10” refers to a hypothesis that states a. Roughly 10% of solar energy is involved in photosynthesis b. Biomass constitutes about 10% of US energy needs c. Humans use about 10% of their daily energy needs from food d. Only 10% of the energy contained in a given trophic level can be converted to the level below e. Humans convert roughly 10% of the energy contained in their food to useful muscle work 139 17. The human body works as a heat engine, converting ______ percent of the food energy to mechanical energy necessary to carry daily physical activities, while disposing the rest as waste heat. a. Less than 1% b. Between 1 to 5% c. About 15-25% d. About 60% e. Above 90% 18. Thermal treatment of biomass to methane is called a. Pyrolysis b. Incineration c. Fermentation d. Burning e. Decomposition 19. Which of the following statements is not correct? a. Body mass index is a measure of body’s mass in proportion to height. b. Body mass index is calculated as body mass divided by height. c. Body mass index is calculated as body mass divided by height squared. d. According to the National Institute of Health studies, a healthy body should have a body mass index of between 19 and 25. e. None of the above. 20. The minimum energy required for a body to maintain all its vital organs function under rest is called a. Body mass index b. Basal metabolic rate c. Body’s maximum respiration d. Survival index e. None of the above III. True or False? 1. Biomass accounts for almost all the renewable energy used in the United States. 2. When burned, biomass does not contribute to any greenhouse gases. 3. Biodiversity refers to the number of species present in a given place at a given time. 140 4. Photosynthesis is possible only in air and in the presence of sunlight. 5. Photosynthesis was the first process to occur in nature after earth sufficiently cooled down, following its formation 5 billion years ago. 6. Heterotrophs are organisms that cannot produce their own food, but are fed by other organisms. 7. An organism which is fed by a producer is called a secondary consumer. 8. Autotrophs are placed at the base of food pyramid and are responsible for primary food production. 9. Net productivity is the gross productivity minus that which is metabolized by the producer. 10. BMR is generally higher for males and for heavier and healthier animals. 11. For two persons of a similar mass, the BMI is lower for the person who is taller. 12. To use 200 kilocalories in muscle energy, you need between 800-1000 kcal in food energy. 13. Biomass is a type of solar energy. 14. Biomass is stored chemical energy in plants. 15. Humans can convert about one-half of the energy contained in food they eat to muscle work. IV. Fill in the Blanks 1. In addition to chlorophyll, plants trap light via two other pigments called ___________ and ______________. 2. The reverse process to photosynthesis where carbohydrate and oxygen react to produce carbon dioxide and water is called _______. 3. Half of all metabolic activities happen in two organs in the body: the ________ and the ________. Chapter 6 - Biomass Energy 4. The three major food categories are _________, ____________, and ____________. 5. Roughly two-thirds of garbage from American households is made of _________. V. Project I - Creationism and Evolution How life was formed has been debated by scientists and theologians for a long time, without reaching consensus. Scientists strongly favor the theory of evolution as laid out by the noted British biologist, Charles Darwin (1809-1882). Theologians, however, believe that the odds of amino acids combining to form the necessary proteins by undirected means is so minute that the proteins needed for life could never have come into existence by chance or any natural processes. In this project you are asked to research arguments for and against each theory and answer the following questions: a. What constitutes life? How can we distinguish living from non-living organisms? b. How do different religions (Buddhism, Judaism, Christianity, Islam, etc.) view the origin of life? Are there any discrepancies among these religions in this regard? c. Is there any contradiction between Christianity and the theory of evolution? Explain. d. What are the main features distinguishing evolutionists and creationists in regard to the origin of life? e. Is there a scientific basis for the creationists’ point of view? What are they? Do these arguments withstand the accepted methods of scientific inquiry? f. How does the doctrine of “Intelligent Design” differ from traditional creationists? g. Does science rule out divine intervention? Project II - Life in the Universe Life as we know it is made of mainly four elements -oxygen, carbon, hydrogen and nitrogen. A few other elements, notably calcium, phosphorous, potassium and sulfur, provide the bulk of nutrients we need to sustain life. Most oxygen is bound to hydrogen to form water, whereas carbon makes up cellular structure. In this project you are asked to research the web resources to find whether other forms of life can or cannot be sustained on Earth or any other place on the Universe. In particular try to answer the following questions: 1. What is unique about carbon that makes it so suitable for forming much of the internal structure of living organisms on Earth? (Hint: look at molecular structure of carbon and how it binds with other molecules). 2. Why do some scientists (and science-fiction writers) propose other forms of life, especially those based on silicon, as a possibility? Why is carbon-based life more prevalent over siliconbased life? What makes silicon less favorable? 3. What other elements have been suggested and why? 4. Why it is highly unlikely to have any other form of life such as nitrogen-based or iron-based life forms in the universe? Project III - Diet and Exercise In this project you are asked to keep a daily log of your daily food intake and tasks you perform. Then you are asked to estimate your caloric intake and the calories you burn as a result of daily routine, work, and exercise. For better estimates, it is recommended that you collect and average data for three 24-hour periods. Basic Information: Sex: _____ (male/female) Mass: _____ kg Height: _____ cm 1. Make a table listing all the foods you consumed. Categorize them into breakfast, lunch, dinner, and snacks. 2. Make a list the activities you performed and their durations. Now do the following calculations: 1. Find the average daily total intake of food calories. Take the three-day average. 2. Estimate the average daily total calories from carbohydrates, protein, and fat, respectively. Assume 9 Calories per gram of fat and 4 Calories 141 3. 4. 5. 6. per gram of protein and carbohydrates. 7. Carry the energy balance by taking the difference Calculate the average power you put out assuming between your daily energy expenditure and energy you maintain a similar diet throughout the year. from food intake. Calculate your BMR. According to Harris and 8. Calculate your daily calorie needs by multiplying Benedict19, BMR can be accurately calculated using your BMR by: the following equations. BMR is basal metabolic a. 1.200 if you are inactive (do little or no rate in kcal/day; M is body mass in kg, H is height exercise) in cm, and A is age in year. b. 1.375 if you are somewhat inactive (light Men: BMR= 66 +13.7*M +5*H -6.8*A exercise 1-3 times a week) Women: BMR=655 +9.6*M +1.8*H -4.7*A c. 1.550 if you are moderately active (moderate Estimate the total non-BMR calories burned exercise 3-5 times a week) through various activities. Which of the activities d. 1.725 if you are active (extraneous exercise were aerobic and which ones were anaerobic? 5-7 times a week) Calculate your total daily energy expenditure by 9. If you maintain a fairly similar routine for the entire adding total BMR and non-BMR calories. What is year, how much mass should you expect to gain or power per mass (kW/kg)? to lose? Work Sheet for Project III Name: ___________________ Mass: ______ kg Food Intake: Height: _______ m Breakfast: _______________ _______________ _______________ Lunch _______________ _______________ _______________ Total: ______ Calories Activities: _______________ Activity Sleeping Sitting/Watching TV Walking Reading Total BMR: ____________ Calories Total non-BMR: ________ Calories Total: _______________ Calories Driving Cooking Washing dishes Working: (describe) __________ Power per kilogram: ____________ kW/kg Sex: ___ Calories _______ _______ _______ Calories _______ _______ _______ _______ Calories _______ _______ _______ _______ _______ _______ _______ _______ _______ Snack _______________ _______________ _______________ Dinner _______________ _______________ _______________ _______________ Activity Light exercise __________ __________ Medium exercise __________ __________ Strenuous exercise __________ __________ _______ ( __ ) _______ ( __ ) _______ ( __ ) _______ ( __ ) _______ ( __ ) _______ ( __ ) Calories _______ _______ _______ Calories _______ _______ _______ _______ Calories (a/n)* Net Energy Intake: Mass gain / loss: ____________ Calories ____________ kg Calorie needs _____________ kilocalories * (a/n) aerobic/anaerobic 19 H arris, J. A. and Benedict, F., “A Biometric Study of Basal Metabolism in Man,” Washington, D.C. The Carnegie Institution, 1919. 142