Environmental Problems, Their Causes, and Sustainability 1

Outside usesEnergy recovery(steam andelectricity)Incinerator(paper, plastics,rubber, food,yard waste)PipelineShredderSeparatorFood,grass,leavesMetalsRubberGlassPlasticsPaperResidueCompostRecycled to primary manufacturersor reformulated for new productsLandfillandreclaimingdisturbedlandFertilizerConsumer (user)Figure 24-9 Solutions: a generalized materials-recovery facility (MRF) sorts mixed wastes for recycling andburning to produce energy. Because such plants need high volumes of trash to be economical, they discouragereuse and waste reduction.sale to manufacturers as raw materials. The remainingpaper, plastics, and other combustible wastes are recycledor burned to produce steam or electricity to runthe recovery plant or to sell to nearby industries orhomes. Ash from the incinerator is buried in a landfill.Trace the flow of materials through an MRF as diagrammedin Figure 24-9.Such plants are expensive to build, operate, andmaintain. They can emit toxic air pollutants, if not operatedproperly, and they produce a toxic ash thatmust be disposed of safely.MRFs are hungry beasts that must have a large inputof garbage to make them financially successful.Thus their owners have a vested interest in increasingthroughput of matter and energy resources to producemore trash—the reverse of what prominent scientistsbelieve we should be doing (Figure 24-3).To many experts, it makes more sense economicallyand environmentally for households and businessesto separate their trash into recyclable categoriessuch as glass, paper, metals, certain types of plastics,and compostable materials. Then these segregatedwastes are collected and sold to scrap dealers, compostplants, and manufacturers.The source separation approach has several advantagesover the centralized approach. It produces muchless air and water pollution and has lower start-upcosts and operating costs than an MRF. It also savesmore energy, provides more jobs per unit of material,and yields cleaner and usually more valuable recyclables.In addition, it educates people about the needfor waste reduction, reuse, and recycling.To promote separation of wastes for recycling,many communities use a pay-as-you-throw (PAUT)waste collection system. It charges households andbusinesses for the amount of mixed waste picked upbut does not charge for pickup of materials separatedfor recycling.542 CHAPTER 24 Solid and Hazardous Waste