Transcript Slide 1
Introduction to Water Treatment CAEE 201 Introduction to Infrastructure Engineering Drexel University 21 May 2007 21 July 2015 Mark H. Weir E.I.T. 1 Water Use and Demand • • • • Users Factors in Water Use Trends Fire Demands – National Board of Fire Underwriters – Insurance Services Office • Figures 4.3 and 4.4 in Handout Q 1020 P 1 0.01 P Q 18CO X P A • Forecasting Demand 21 July 2015 Mark H. Weir E.I.T. 2 Each Type of User in a Community Must be Considered • Residential are encompassing 600 acres – Housing density of 4 houses per acre – High value residence with 1000 gpm fire flow requirement • A city block has the following buildings: – – – – 200-room hotel with 35 employees and one kitchen. Public laundry facility with 22 washers and dryers. Small card shop. News Stand selling magazines, refreshments and snacks. 21 July 2015 Mark H. Weir E.I.T. 3 Water Treatment • Water carries excreta – Pathogens – Water and waste disposal – Stormwater runoff • Surface wash and transport of fecal material. • Deadly outbreaks – Cholera – Typhoid 21 July 2015 Mark H. Weir E.I.T. 4 Water Treatment Regulations • Principle law regulating drinking water safety. – Safe Drinking Water Act (SDWA) • 1974 • United States Environmental Protection Agency (USEPA) • 1832 Paisley, Scotland – First municipal water filtration plant – 1852 first law passed in London “all waters should be filtered” • In the U.S. – Interstate Quarantine Act (1893) • Surgeon General U.S. Public Health Service (USPHS) “…make and enforce regulations prevent introduction, transmission or spread of communicable diseases.” 21 July 2015 Mark H. Weir E.I.T. 5 Water Treatment Regulations in the United States • 1913 comprehensive review of drinking water • concerns. 1914 first federal drinking water standards – – 100 organisms mL 10 organisms mL total bacterial plate counts Escherichia coli • SDWA includes various amendments made for • further contaminants (i.e. lead etc.) States must at least match the federal regulations 21 July 2015 Mark H. Weir E.I.T. 6 Water Treatment for Human Health • Microorganisms are responsible for a wide spectrum of diseases. – Orally ingested. – Bacterial pathogens. – Viral pathogens. – Protozoan pathogens. – Helminths 21 July 2015 Mark H. Weir E.I.T. 7 Disinfection Giardia Cryptosporidium • Purpose – Why is disinfection needed • Protozoan – Cryptosporidium Oocyst – Giardia Cyst Campylobacter Norovirus • Bacteria – Campylobacter • Virus – Norovirus Pictures Courtesy U.S. Center for Disease Control cdc.gov 21 July 2015 Mark H. Weir E.I.T. 8 What makes a Disinfectant? • Disinfection Sterilized • Destruction of pathogenic microorganisms • Considerations – – – – – – – Effective destruction of pathogenic microorganisms. Nontoxic to humans or domestic animals. Nontoxic to fish and other aquatic species. Easy and safe to store transport and dispense. Economic. Easy and reliable analysis in water. Residual protection in drinking water. 21 July 2015 Mark H. Weir E.I.T. 9 Disinfection Kinetics • Described by first-order law studied by Chick advanced by Watson dN kN where k C n dt N ln C n N0 • Inactivation constant is specific to microorganism and disinfectant. 21 July 2015 Mark H. Weir E.I.T. 10 Disinfection Continued • Chlorine gas • Chlorine Dioxide • Ozone – 1774 – 1825 • Waste treatment in France – 1831 • Cholera epidemic in Europe – prophylactic – No residual for distribution • UV radiation – Again no residual • Others – Heat • Boil orders – pH extremes – Silver, copper (other metals) 21 July 2015 Mark H. Weir E.I.T. 11 Disinfection is Chemistry • Chlorine. – Effective disinfectant • Very effective for distribution system residual. – Chlorine gas, sodium hypochlorite and solid calcium hypochlorite are all chemically equivalent. – Amount of chlorine present is available chlorine Cl2 + 2 e2ClOCl- + 2 e- + 2 H+ Cl- + H2O – Calcium hypochlorite – Sodium hypochlorite 21 July 2015 Ca(OCl)2 Na(OCl) Mark H. Weir E.I.T. Safer to handle than chlorine gas 12 Disinfection Chemistry • Free available chlorine – Cl2 HOCl and OCl- • HOCl is a very strong disinfectant – Reacting with enzymes essential to metabolic processes in living cells. Ca(OCl)2 Ca2+ + 2OClH+ + OClHOCl • There is a demand to chlorine other than in disinfecting. – Reducing agents – Organic mater – Ammonia 21 July 2015 Mark H. Weir E.I.T. 13 Chlorine Demand Chlorine Residual (mg/L) Chlorine Demand Curve 1 0.8 Applied Chlorine 0.6 0.4 0.2 0 0 0.5 1 1.5 2 Chlorine Dose (mg/L) Drinking water with 1 hours contact time 21 July 2015 Mark H. Weir E.I.T. 14 Example of Chlorine Demand • Use the chlorine demand curve to determine the daily amount of NaOCl to obtain combined residual of 0.4 mg/L and free residual of 0.5 mg/L – 1 hour contact time – 6.34 Mgal/day (24,000 m3/day) 21 July 2015 Mark H. Weir E.I.T. 15