Drinking Water Quality and Water Treatment

Learning Objectives Identify the major pieces of legislation that protect water quality in the United States (SDWA, CWA) Distinguish between MCLs and MCLGs Describe basic water treatment steps and some common disinfection technologies Describe hard water and its effects Identify and explain common water softening technologies at the molecular level

Water Quality Issues  Is the water we’re drinking safe?  How is it treated to ensure safety?  Can we swim and fish in our rivers? Safe Drinking Water Act, 1974 Clean Water Act, 1972 Both have been amended several times since! visit

Drinking Water Standards 5.10 Sometimes the goal isn’t practical

International Water Supplies WHO/UNICEF Joint Monitoring Programme for Water Supply and Sanitation

Water Supplies in Southcentral Asia Turkmenistan Afghanistan

Source: Sanitation in Southcentral Asia

How is Drinking Water Treated to Make It Safe? Disinfection technologies: chlorination (Cl 2, NaOCl, or Ca(OCl) 2 ) ozonation (O 3 ) UV radiation Fluoridation – to prevent tooth decay

Instrumentation and Measurement of Water Pollutants Atomic absorption spectroscopy is commonly used to measure metals (e.g. lead) Gas chromatography is commonly used to measure organic compounds (e.g. benzene)

Gas Chromatograph

Hard Water contains dissolved minerals such as CaCO 3 Is hard water good or bad? –calcium is good for your bones, right? –causes deposits on pipes, industrial equipment –interferes with soaps

Water Treatment Technologies Water softening (by ion exchange) Na 2 Z (s) + Ca 2+ (aq)  CaZ (s) + 2 Na + (aq) sodium zeolitecalcium zeolite Distillation Reverse Osmosis Carbon Adsorption

Distillation

Reverse Osmosis Systems

Carbon Adsorption

Wastewater Treatment Primary Treatment Secondary Treatment Tertiary Treatment

Primary Treatment Removes large objects from the water –Sticks –Tires –Trash Screening Primary Settling (physical)

Secondary Treatment Uses biologically activated organisms to consume nutrients and other organic constituents Aerobic digestion –Uses organisms that thrive with oxygen –Produce CO 2 Anaerobic digestion –Uses organisms that thrive without oxygen –Produce CH 4 Final settling (physical)

Tertiary Treatment Whatever chemical treatment of remaining water is required Usually includes disinfection (e.g. with chlorine) Can include other chemical treatments depending on the sources of the wastewater