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Download Water Pollution Major Pollutants Oxygen-Demanding Waste
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Major Pollutants Water Pollution Some substance or condition that so degrades water quality that it cannot be used for a specific purpose • Oxygen demanding wastes - ex. Sewage • Pathogens • Inorganic chemicals • Trace organic chemicals – ex. PCB • Plant nutrients • Sediment • Radioactive substances • Heat • Point source – comes from a single effluent – Sewage treatment plant effluent • Non-Point Source – large number of sources – Urban run-off Oxygen-Demanding Waste • • • • Sewage Agricultural waste Food processing waste Pulp mill waste • Organic matter decays – Degraded by bacteria – Bacteria use up oxygen – Oxygen concentration goes to 0 • Kills fish • Foul odors 1 • Stream flows past point source of organics • Stream eventually recovers – Dilution – Invasion of new oxygen – Organics used up • Stream cleans itself Water Bourne Pathogens • • • • • • Typhoid and paratyphoid Cholera Dysentery Weanling diarrhea Viruses Legions of parasites • Nearly all caused by fecal contamination of drinking water Coliforms Most Pathogens are too rare to detect So what do we do? • E. coli – Common in vertebrate feces – Provides Marker of fecal contamination • Culture and count coliforms – Easy to do 2 Criteria • Drinking water – no coliforms • Swimming – 200/100ml • If water exceeds these limits, it must be chlorinated Wastewater Treatment Mimics Stream • Primary treatment – Remove large material • Secondary treatment – Remove organics • Tertiary treatment – Remove plant nutrients Secondary Treatment Methods • Activated sludge – Aerate in tank – Get froth that is removed • Trickling Filters – Waste trickled over a bed of gravel • Stabilization Ponds Waste Stabilization Ponds – Put waste in ponds • Septic tanks – Put tank in ground and pipe sewage to it – Allow sewage to percolate into ground Plant Nutrients as Pollutants Nitrates and Phosphates 3 • You can work hard to remove all of the organic matter from sewage, but plant nutrients are still left • Plants in lakes and streams take nutrients and recreate the organic matter • Result is a bright green soup!!! • Process called EUTROPHICATION Is Eutrophication Bad? It depends on who you are • Good – if you want to produce food from the water – Some fish grow better • Bad – if you want to use the lake for recreation – Causes tastes and odors – Degrades water for recreational use How to reverse eutrophication • Remove nutrients from lake – Tertiary treatment of sewage • Removes nutrients – Reduce non-point sources of nutrients • Fertilizers • Leaky septic tanks The Dead Zone Eutrophication of the Sea 4 • Region of Gulf of Mexico off the Mississippi Delta • Scientists noticed that oxygen levels were dropping • Seems to be caused by excess nutrients coming into Gulf from the Mississippi – Mainly nitrates • Source of nutrients unclear – Maybe Midwest farmlands 5
