Environmental Problems, Their Causes, and Sustainability 1

Cleaned gasElectrodesCleaned gasDirty gasDust dischargeDirty gasa. Electrostatic Precipitator b. Baghouse FilterBagsFigure 20-18 Solutions: fourcommonly used output or controlmethods for removing particulates(a, b, c, d), and SO 2 (d) from theexhaust gases of electric powerand industrial plants. Of these,only baghouse filters remove manyof the more hazardous fine particles.All these methods producehazardous materials that must bedisposed of safely, and except forcyclone separators, all of them areexpensive. Modern wet scrubbersremove 98% of the SO 2 and 98%of the particulate matter in smokestackemissions, but they are expensiveto install and maintain.Cleaned gasCleaned gasDust dischargeDirty gasDirty gasCleanwaterWetgasDirty waterDust dischargec. Cyclone Separator d. Wet ScrubberFigure 20-19 (p. 458) lists ways to reduce emissionsfrom motor vehicles, the primary culprits in producingphotochemical smog. One way to make significant reductionsis to get older, high-polluting vehicles off theroad. According to EPA estimates, 10% of the vehicleson the road in the United States emit 50–70% of vehicularair pollutants. But people who cannot afford tobuy a newer car often own old cars. One suggestion isto pay people to take their old cars off the road, whichwould result in huge savings in health and air pollutioncontrol costs.In 2003, a team of research engineers workingwith grants from the National Science Foundation andan oil company found a way for oil refineries, powerplants, and vehicles to use a class of chemicals calledzeolites to do a better job than other alternatives in removingsulfur impurities from diesel fuel, jet fuel, andgasoline. This adsorption process, which is carried out atroom temperature and pressure, should be cheaper,easier, and more effective than using expensive catalyticconverters that operate at high temperatures andpressures to remove sulfur. Stay tuned to see if thistechnology works as projected and is implemented.Good news. Over the next 10–20 years air pollutionfrom motor vehicles should decrease from increaseduse of partial zero-emission vehicles (PZEVs) that emit almostno air pollutants because of improved engineand emission systems, hybrid-electric vehicles (Figure18-9, p. 385), and vehicles powered by fuel cellsrunning on hydrogen (Figure 18-10, p. 385).Bad news. The growing number of motor vehiclesin urban areas of many developing countries is contributingto the already poor air quality there. Many ofthese vehicles are 10 or more years old, have no pollutioncontrol devices, and continue to burn leadedgasoline.http://biology.brookscole.com/miller14457