Download Water Pollution: Oxygen Demand, Pathogens, Nutrients, Salts, and Thermal Pollution and more Slides Water and Wastewater Engineering in PDF only on Docsity! • Water that doesn’t evaporate (a rapid process) is available for use by people • Renewable runoff is ~ 46 × 1012 m3/year, order of magnitude more than the current consumption rate • We actually only use (primarily due to costs) 9 to 14 × 1012 m3/year • To maintain balance, there must be runoff water returned to oceans via stream and groundwater flow 16 Docsity.com • Nine water pollutants of interest Water pollutants Oxygen demanding wastes Heavy metals Pathogens Pesticides Nutrients Volatile organic compounds (VOCs) Salts Acidity Thermal pollution 17 Docsity.com 2) Pathogens • Disease producing organisms that grow and multiply within a host ➔ Bacteria: cholera, dysentery, typhoid ➔ Viruses: infectious hepatitis, poliomyelitis ➔ Protozoa: amebic dysentery, giardiasis ➔ Helminths (parasitic worms): schistosomiasis, hookworm 20 Docsity.com • If sewage contaminates drinking water these diseases spread to many. ➔ e.g., cholera epidemic of London 1840’s • Typhoid/cholera epidemic of Chicago 1885: 90,000 people died when untreated sewage was drawn into the public water supply during a storm. • Chlorination of water supplies in US virtually eliminated these problems, but they are severe in many other parts of the world. 21 Docsity.com Two types of infection: WATER BORNE Acquired by ingesting pathogens by drinking water or contact through utensils, food, etc. Contamination from open water handling system — in US giardia is problematic: cysts survive a long time not easily destroyed by chlorination (ex., Cryptosporidium in Milwaukee, 1993) 22 Docsity.com Most of the phosphorus in wastewater is from household detergents (!) tripolyphosphate orthophosphate Orthophosphate is immediately usable by plants. Nitrogen and phosphorus are in wastewater, feedlot runoff, agricultural chemicals. Nitrate (NO3) can be converted to nitrite (NO2) in infants younger than 6 months (in hemoglobin, called methemoglobinemia). Na2P3O10 → P3O105− + H2O → 3PO43− + 4H+ 25 Docsity.com 4) Salts Many salts naturally accumulate in water: Rough measurement of salt content: total dissolved solids (TDS) Fresh water has TDS of < 1500 mg/L Brackish water up to 5000 mg/L Saline water > 5000 mg/L Seawater 30,000 to 34,000 mg/L TDS Drinking water < 500 mg/L (higher: laxative) Animals can tolerate more than 500 mg/L Irrigation requires < 500–2000 mg/L, but plants would prefer < 500 mg/L. Na+ , Ca2+ , Mg+ , K+ , Cl− , SO42− , HCO3− 26 Docsity.com • Irrigation (how?), as well as evaporation from ponds can increase salt concentrations. • As water flows downstream, there is water added from drainage, further increasing salt concentration. 27 Docsity.com
