Environmental Problems, Their Causes, and Sustainability 1

22 WaterPollutionWaterPollutionControlCASE STUDYLearning Nature’s Waysto Purify SewageSome communities and individuals are seeking betterways to purify sewage by working with nature. EcologistJohn Todd designs, builds, and operates innovativeecological wastewater treatment systems calledliving machines (Figure 22-1).This ecological purification process begins whensewage flows into a passive solar greenhouse or outdoorsites containing rows of large open tanks populatedby an increasingly complex series of organisms.In the first set of tanks, algae and microorganisms decomposeorganic wastes, with sunlight speeding upthe process. Water hyacinths, cattails, bulrushes, andother aquatic plants growing in the tanks take up theresulting nutrients.After flowing though several of these natural purificationtanks, the water passes through an artificialmarsh of sand, gravel, and bulrush plants to filter outalgae and remaining organic wastes. Some of theplants also absorb (sequester) toxic metals such aslead and mercury and secrete natural antibiotic compoundsthat kill pathogens.Next the water flows into aquarium tanks. Snailsand zooplankton in these tanks consume microorganismsand are in turn consumed by crayfish, tilapia,and other fish that can be eaten or sold as bait. After10 days, the clear water flows into a second artificialmarsh for final filtering and cleansing.The water can be made pure enough to drink byexposing it to ultraviolet light or by passing it throughan ozone generator, usually immersed out of sight inan attractive pond or wetland habitat. Selling the ornamentalplants, trees, and baitfish produced as byproductsof such living machines helps reduce costs.Operating costs are about the same as for a conventionalsewage treatment plant.Some communities and industries are workingwith nature by using natural and artificial wetlandsto purify wastewater, as discussed later in thischapter.Ocean Arks InternationalWater pollution is related to air pollution, landusepractices, climate change, energy use, solid andhazardous waste, and the number of people, farms,and industries producing sewage and other wastes.These connections explain the need to solve waterpollution problems by integrating them with policiesfor the problems just listed. Otherwise, environmentalistswarn we will continue to shift environmentalproblems from one part of the environment toanother.Figure 22-1 Solution: Ecological wastewater purification by aliving machine. At the Providence, Rhode Island, Solar SewageTreatment Plant, biologist John Todd demonstrates how ecologicalwaste engineering in a greenhouse can be used to purifywastewater in an ecological process he invented. Todd and othersare conducting research to perfect solar-aquatic sewagetreatment systems based on working with nature.