Environmental Problems, Their Causes, and Sustainability 1

AdvantagesLarge potentialsupply in someareasModerate costsNo net CO 2increase ifharvested andburnedsustainablyPlantation canbe located onsemiarid landnot needed forcropsPlantation canhelp restoredegraded landsCan make use ofagricultural, timber,and urban wastesT rade-OffsSolid BiomassDisadvantagesNonrenewable ifharvestedunsustainablyModerate to highenvironmentalimpactCO 2 emissions ifharvested andburnedunsustainablyLow photosyntheticefficiencySoil erosion, waterpollution, and lossof wildlife habitatPlantations couldcompete withcroplandOften burned ininefficient andpolluting open firesand stoveswhen oil becomes too scarce or expensive. Ethanol canbe made from sugar and grain crops (sugarcane, sugarbeets, sorghum, sunflowers, and corn) by fermentationand distillation. Gasoline mixed with 10–23% pureethanol makes gasohol, which can be burned in conventionalgasoline engines.Figure 18-27 lists the advantages and disadvantagesof using ethanol as a vehicle fuel compared togasoline. Ethanol could be produced from surplusgrain crops. But industrialized agriculture uses moreenergy in the form of petroleum-based vehicle fuel,fertilizers, and pesticides than the energy obtained byburning ethanol produced by such crops. Thus, there isa net energy loss from growing grain crops, convertingthe grain to ethanol, distilling the ethanol, and distributingand burning it as a motor vehicle fuel. The U.S.government gives large subsidies to corn growers toproduce ethanol as part of the national energy policy.Critics see this as a politically motivated giveaway andwaste of money that could be used to support morepromising renewable energy alternatives.xHOW WOULD YOU VOTE? Do the advantages of usingliquid ethanol as a fuel outweigh the disadvantages?Cast your vote online at http://biology.brookscole.com/miller14.T rade-OffsFigure 18-26 Trade-offs: general advantages and disadvantagesof burning solid biomass as a fuel. Pick the singleadvantage and single disadvantage that you think are the mostimportant.AdvantagesEthanol FuelDisadvantagesBacteria in large digesters can also convert municipalgarbage and sewage to methane gas. Wells drilledinto about 300 large landfills in the United States recovermethane produced by the decomposition of organicwastes and burn it to produce enough electricityto meet the needs of a million homes. BMW’s automobilefactory near Spartanburg, S.C. gets more than afourth of its electricity and a tenth of its heat by burningmethane gas piped in from a nearby landfillowned by Waste Management.High octaneSome reduction inCO 2 emissionsReduced COemissionsCan be sold asgasoholLarge fuel tankneededLower driving rangeNet energy lossMuch higher costCorn supply limitedMay compete withgrowing food oncroplandHigher NO emissionsWhat Are the Advantages and Disadvantagesof Using Liquid Ethanol and MethanolProduced from Biomass as a Fuel? MixedSignalsSome believe we can rely much more onethanol and methanol as a fuel, but othersdisagree.Some analysts believe that liquid ethanol producedfrom biomass could replace gasoline and diesel fuelPotentiallyrenewableCorrosiveHard to start in coldweatherFigure 18-27 Trade-offs: general advantages and disadvantagesof using ethanol as a vehicle fuel compared to gasoline.Pick the single advantage and single disadvantage that youthink are the most important.http://biology.brookscole.com/miller14399