Water Pollution • Rapid growth of human pop. And industrial output has resulted in declines in water quality • Waters are contaminated with toxic chemicals, human and animal excrements, heavy metals, pesticides, silt and fertlizers.
Clean Water Act • 1972 Federal Water Pollution Control Amendments Act • 1977 amendments lead to the Clean Water Act • “no one has the right to pollute…” • Congress declares their goal: attainment of wherever possible of water quality” that provides for recreation in and on the water” and the elimination of all pollutant discharges into the nation’s waterways by 1985 (zero discharge goals) • 16% of watersheds are of good quality, 36% moderate quality and 21% had serious quality problems. • In comparison, prior to the Clean Water Act, 95% of all watersheds were polluted. • EPA’s most recent water quality assessment (1998) showed 40% of the rivers, lakes and estuaries are too polluted for fishing and swimming. • In developing countries, 95% of urban sewage is discharged into surface waters untreated.
What are the Sources of Water Pollution? Point Sources Pollutants enter the waterways at well-defined locations. • Sewage tx plants • Industrial facilities Non-Point Sources Those which run off or seep into waterways from broad areas of land. Result from human land-use practices: 1) Agriculture: • Most abundant contaminant is soil • Other contaminants: manure, chemical fertilizers and pesticides. • Control: application of soil erosion prevention techniques; limiting use of fertilizers and pesticides; maintaining a buffer zone between water and livestock.
What are the Sources of Water Pollution? Non Point Sources (cont’d) 2) Construction activities: • Contributes more sediments to water ways than any other activity • Solvents, asphalt, paint, cement wash, oil, tar. • Control: scheduling construction to minimize minimal open land usage during high run off periods; planting while constructing 3) Urban street runoff • Sediments, oils, grease, dirt, heavy metals, pesticides and fertilizers from lawns, animal and bird droppings…. • Control: control public litter; incorporating more urban green spaces; proper disposal of pet wastes; limit use of fertilizers and pesticides; slow release of storm water via tunnels, catchment areas, holding tanks…
Non Point Sources (cont’d) 4) Acid mine drainage iron oxide precipitate formation and sulfuric acid. Iron oxide falls to the bottom and destroys bottom life. Rusty appearance of water. Acid water leaches metals from soil and rocks (Fe, Zn, Mg, Ma, Cu, Ca) Control: sealing openings not efficient; engineered wetlands is promising. 5) Settling of air pollutants Airborne asbestos, Pb, Hg, PCBs and pesticides settle down. Control Strategies for Non-Point Sources: 1) increase land capacity to retain water by establishing soil erosion controls, and 2) minimize pollutant run off into waterways especially during storms What are the Sources of Water Pollution?
Sewage Disposal Why does sewage need to be treated? In order to improve the quality of wastewater to the point it can be discharged in waterways without seriously disrupting the aquatic environment or causing human health problems. This can be achieved by: • killing pathogenic organisms in the sewage • removing as much organic wastes as possible from the sewage to avoid eutrophication of receiving waterways
What is Eutrophication? It means “well fed”: • Nutrients such as nitrates and phosphates (from organic matter such as fertilizers, manure) enter the water body • algae growth is stimulated • some algae release toxins and result in fish deaths. • Also, algae start dying and settle at the bottom. • Decomposing bacteria decompose the algae. • As bacterial population explodes (especially in warmer temperatures), oxygen supply in the water decreases. • Eventually decomposing becomes anaerobic and foul smell results. • Fish and plants are deprived of oxygen (hypoxia) and die off.
Primary Treatment Consists of several physical and mechanical processes to remove the larger suspended solids through screening and sedimentation. Screening Grit chamber Primary clarifier (sedimentation tank RESULT: 50-65% of suspended solids removed; BOD reduced by 25-40% Biochemical Oxygen Demand = an indicator of how much putrescible organic matter is present Municipal Sewage Treatment(POTW)
Secondary Treatment Depends on biological processes, basically accelerated decomposition, to digest organic wastes. Aerobic bacteria are utilized in the presence of an abundance of oxygen. Trickling filters OR Activated sludge process Secondary clarifier (settling tank) RESULT: 90-95% reduction in suspended solids and BOD. But metals, viruses, minerals and other chemicals are not removed. Effluent is either discharged in the oceans far off the coast or piped to large projects (golf courses) where non-potable water is needed. Municipal Sewage Treatment(POTW)
Municipal Sewage Treatment(POTW) Tertiary (Advanced) Treatment Is done when water will be used for drinking, irrigation, recreation or disposal in waterways in such quantities that it could cause eutrophication. • Disinfection Chlorine Filtration Ozonation UV radiation/UV light • Biosolids Mangement • Accounts for 50% of operating costs of a secondary tx POTW.
Septic Systems • 30% of Americans live in unsewered areas and use on-site septic systems • A watertight container made of concrete and fiberglass w/ a min. capacity of 750 gallons • Consists of 2 parts: • A septic tank buried in the ground at some distance from the house to which a pipe is connected • A soil absorption field or sand filter • Sewage in the septic tank undergo partial decomposition by bacteria under anaerobic conditions. • Sludge settles, lighter solids and gases form a scum at the top, the clarified liquid passes thru perforations in the pipe and into the absorption field. • Needs cleaning out every 3-5 years • Accumulation around the pores eventually lead to blockages and failures. Oversuse of water can result in sewage backups.
Waterborne Diseases Bacteria • Thphoid fever, Cholera, Shigella (dysentery), Salmonella and E. coli Viruses • Heapatitis A, poliomyelitis and Rotavirus. • Are resistant to desinfection by chlorination Protozoans • Giardia Lambia, Cryptosporidium, amoebic dysentery. • Are resistant to desinfection by chlorination. • Milwaukee outbreak 1993 of cryptosporidium; 400,000 were affected.
Chemical Contaminants in Drinking Water Synthetic Organic Pollutants PCBs, industrial solvents, pesticides, trihalomethanes Lead Sources: Pb-containing pipes, Pb-containing solder in the pipes or brass faucets. Nitrates • Sources: inorganic nitrates from fertlizers or septic tanks. Example: “blue babies” methhemoglobinemia
SAFE DRINKING WATER ACT1974, 1986, 1996 • The EPA establishes maximum contaminant levels (MCLs) for more than 80 biological, chemical and radioactive pollutants. • These MCLs must be met by water supplied by every community water system (serving 25 people or more or having at least 15 service connections)