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Background Information: Main Pollutants – Carbon, Nitrogen, and Phosphorus (C-N-P) Print E-mail
bridges vol. 21, April 2009 / Feature Articles

Wastewater can be separated according to its sources: domestic, municipal, and industrial wastewater. Pollutants from fertilizer use account for a major part of the nutrient load. These agricultural runoffs go straight into the waterbodies, without any treatment. An additional source can be storm water runoff from streets, roofs, and any other sealed surfaces. Old cities often have a combined sewer system - one pipe for both sewage and storm water. This is the case for large parts of Washington, DC., where the wastewater derives from domestic and municipal sources (toilets, baths, showers, kitchens, sinks) and from storm water; industrial and agricultural sources are negligible in the DC wastewater.

       
Pollutant   Source   Impact on Rivers, Lakes, Sea   Removal method in the Treatment Plant  
Organic load (C) Feces, food waste, fat, plant parts, soaps, detergents ... Natural degradation in water bodies causes oxygen depletion; aquatic life dies. Microorganisms degrade organic pollutants aerobically, so aeration is necessary. The augmentation of micro-organisms increases activated sludge volumes. This sludge can be used for land application or energy generation. 
Nitrogen (N) Urine: N is mainly present as ammonium  N is a major nutrient, so fertilization leads to algal bloom; dying algae cause oxygen depletion. Ammonium/ammonia is (fish) toxic. 2-step biological process: Nitrification and Denitrification; first, ammonium is oxidized to nitrates; then nitrates are reduced to harmless nitrogen gas.
Phosphorus (P) Detergents; P is also important in energy metabolism (ATP), genetic information (DNA) Major nutrient, fertilization leads to algal bloom; dying algae cause oxygen depletion. P removal is critical, since it is often the limiting nutrient.  Phosphorus removal can be achieved by chemical precipitation with iron or aluminum chlorides. Biological removal is less common. Limitation or banning of phosphate in detergents differs from state to state.
Large objects, sand, grit, stones Rags, sticks, tampons, cans, fruits ... Ugly, potentially dangerous for aquatic animals. Depending on the material and size, degradation takes very long. Physical removal by screens, sedimentation, flotation. Solids are mostly disposed of in landfill.
Pathogens  Feces Potentially infectious for humans. Chlorination or UV irradiation are most common. While disinfection is mandatory in the US, it is not required in Austria.
Pharmaceuticals Surplus of active ingredients excreted in urine Microorganisms develop resistance to antibiotics; gender change has been observed in fish...  Pharmaceuticals are designed for long life (impact) time; therefore, the common treatment may not fully eliminate them. Experiments with chemical oxidation are not yet widely applied. 
Heavy metals (lead, zinc, copper are most relevant) Industry, pipes, roofs, traffic Chronic poisoning of aquatic life, accumulation in certain species. Industry is well-regulated in the US, but non-point sources are hard to address (roof and pipe runoff).
Chemicals, combustion byproducts Traffic:  Introduced by storm water runoff Chronic poisoning of aquatic life, accumulation in certain species. Sedimentation and aerobic degradation.
Thermal Water as coolant for power plants or industry Changes ecosystem, introduces new species, kills fish.  Not relevant.
       


















































































































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