| While much of what goes into biodiesel could be | | | | 90 percent, and with 40 million Americans each |
| considered biodegradable waste, the concept | | | | producing an average of more than 1,600 pounds |
| deserves its own section because of its | | | | a year, that's important. WTEs can convert a ton |
| enormous potential. As we said before, biomass | | | | of garbage into 525 kilowatt-hours of electricity |
| happens. When the quantities were relatively low, | | | | (and 300 to 600 pounds of ash). Today, 14 |
| few people considered waste management a | | | | percent of the MSW in the U.S. get incinerated. |
| problem people used to burn trash in their back | | | | But as with landfills. WTEs were not without their |
| yards, or bury, or put it out for the trash truck | | | | own problems. What remains after incineration is |
| without a thought. Industrialization, population | | | | ash, and much of it hazardous. High concentrations |
| growth, and dozens of other factors caused the | | | | of the metals (e.g., lead, cadmium) in the MSW |
| amount of waste produced annually to skyrocket, | | | | remain in the ash, from dyes, inks, batteries, |
| and for a long time everything got dumped into | | | | ceramic materials and more. Pollutants overall |
| old mines, quarries and other big holes: landfills. | | | | have decreased substantially-roughly 85 percent |
| Soon enough it became apparent that in solving | | | | overall-since EPA introduced the Maximum |
| the problem of what to do with the waste, other | | | | Achievable Control Technology (MACT) standards |
| problems had cropped up. Before landfill | | | | in 1995 as part of the Clean Air Act. But U.S. |
| developers thought to line the pits, contaminated | | | | facilities combine their fly ash (airborne) with their |
| water leeched into the aquifers. They attracted | | | | cleaner bottom ash, which brings the overall |
| rats and other scavengers. "Landfill gas" (methane | | | | percentages of toxic materials into compliance |
| and CO2) filled the air, killing surface vegetation | | | | standards for expanded reuse. |
| and contributing in a major way to greenhouse | | | | The newest development is converting the useful |
| gases (1.2 tons of CO2 per ton of municipal solid | | | | biomass energy stored in MSW to feedstock and |
| waste, or MSW). And, quite simply, they stank. | | | | ethanol in biorefineries. A number of processes |
| Still, economics caused most MSW to end up in | | | | are in the R&D and pilot stages, including one in |
| landfills. Then huge incineration plants called | | | | Texas, that uses a biological/chemical process |
| waste-to-energy facilities (WTEs) were built to | | | | that anaerobically digests the biomass into liquid |
| take care of the problem. They do solve some | | | | mixed-alcohol fuels. |
| issues: they reduce the volume of the MSW by | | | | |