Environmental Problems, Their Causes, and Sustainability 1

OdorsOdors may cause illness orindicate presence of harmful gases.Dust ParticlesParticles of dried sludge carry virusesand harmful bacteria that can be inhaled,infect cuts or enter homes.BUFFERZONEExposureChildren may walk orplay in fertilized fields.SludgeLivestock PoisoningCows may die after grazingon sludge-treated fields.GroundwaterContaminationHarmful chemicalsand pathogens mayleach into groundwaterand shallow wells.Surface RunoffHarmful chamicalsand pathogens maypollute nearby streams,lakes, ponds, andwetlands.Figure 22-17 Natural capital degradation: some potential problems with using sludge from sewage treatmentplants as a fertilizer on croplands. The EPA says that sludge is safe to use if applied following its guidelines.Scientists and people who have gotten sick from exposure to sludge fertilizer claim the guidelines areinsufficient and not adequately enforced.and hazardous chemicals from reaching sewage treatmentplants and thus from getting into sludge and thewater discharged from such plants.He suggests several ways to do this. One is to requireindustries and businesses to remove toxic andhazardous wastes from water sent to municipal sewagetreatment plants. Another is to encourage industries toreduce or eliminate toxic chemicals use and waste.Another suggestion is to have more households,apartment buildings, and offices eliminate sewage outputsby switching to waterless composting toilet systemsthat are installed, maintained, and managed by professionals.Such systems would be cheaper to install andmaintain than current sewage systems because they donot require vast systems of underground pipes connectedto centralized sewage treatment plants. Theyalso save large amounts of water. They work great. Iused one for 15 years.xHOW WOULD YOU VOTE? Should we ban the dischargeof toxic chemicals into pipes leading to sewage treatmentplants? Cast your vote online at http://biology.brookscole.com/miller14.Solutions: How Can We Treat Sewageby Working with Nature? EcologicalPurificationNatural and artificial wetlands and other ecologicalsystems can be used to treat sewage.John Todd has developed an ecological approach totreating sewage, which he calls living machines (Figure22-1). More than 150 cities and towns in the UnitedStates use natural and artificial wetlands to treatsewage as a low-tech, low-cost alternative to expensivewaste treatment plants.For example, the coastal town of Arcata, California,created some 65 hectares (160 acres) of wetlands betweenthe town and the adjacent Humboldt Bay. Themarshes and ponds, developed on this land that wasonce a garbage dump, act as an inexpensive naturalwaste treatment plant. The project cost less than halfthe estimated cost of a conventional treatment plant.Here is how it works. First, sewage goes to sedimentationtanks, where the solids settle out as sludgethat is removed and processed for use as fertilizer.Next, the liquid is pumped into oxidation ponds,512 CHAPTER 22 Water Pollution