Chemistry 30S Unit 4: Solutions

1. Chemistry 30SUnit 4: Solutions Lesson 8

2. Learning Outcomes • C11-4-16 Describe examples of situations where solutions of known concentration are important. • C11-4-17 Describe the process of treating a water supply, identifying the allowable concentrations of metallic and organic species in water suitable for consumption.

3. Treatment of Drinking Water • Chemical and physical process • Clean & maintain the quality of our water supplies through the following processes: • Aeration • Coagulation/flocculation • Sedimentation • Filtration • Disinfection

4. 1. Aeration • The addition of oxygen to wastewater or water • Oxygen helps speed up bacterial growth • Bacteria digest many waste products

5. 2. Coagulation/Flocculation • The process by which dirt and other small suspended solid particles are chemically bound, forming flocs • Requires the use of a coagulant or flocculant • This allows for the collection of such particles

6. 3. Sedimentation • Process of letting heavy particles in water settle out into holding ponds or basins before filtration

7. 4. Filtration • Process of passing a liquid or gas through a porous article or mass to separate matter out into suspension • Examples of a porous articles include sand and paper membranes

8. 5. Disinfection • The use of chemicals to kill potentially harmful microorganisms in the water • This is typically accomplished by chlorination, ozone or UV radiation

9. Water Supply • 97% of the world’s water is salt water, leaving 3% usable or fresh water • ~70% of this is frozen • ~30% ground water • ~0.3% surface water • Ground & surface water  our drinking water • Water from lakes, rivers and swamps contain impurities that make it smell and look dirty • May contain harmful chemicals or bacteria that cause disease

10. Water Contamination • May be natural or man-made • Common issues: • Odour • Taste • Colour • Turbidity • Suspended solids • Organic & inorganic pollutants (pesticides, insecticides, etc.) • Heavy metals • Domestic & industrial wastes • Bacteria & viruses

11. Waterborne Diseases • Major public health concern in many areas • 1993 Milwaukee • 400 000 people became sick and over 100 died

12. Winnipeg Water • Since 1919 Winnipeg has used Shoal Lake for its water supply • No outbreaks yet... • Metal and organic pollution are the primary concerns

13. Maximum Allowable Concentration • Metals • Arsenic: 0.01 mg/L • Lead: 0.01 mg/L • Mercury: 0.001 mg/L • Chromium: 0.05 mg/L • Organics • Benzene: 0.005 mg/L • Malathion: 0.19 mg/L • 1,2-dichlorobenzene: 0.2 mg/L

14. Removing Organic Pollutants • Granular activated carbon • Chemicals adsorb to the porous carbon surface • Works quite well for large organics • Pesticides, ringed or branched organics • Not so well for small organics • Simple alcohols & formaldehyde

15. Removing Metallic Pollutants • Hydroxide precipitation • Many metals ions are insoluble with the -OH ion  precipitate out • Works quite well----but can be tricky due to the different pH requirements of various metals

16. Regulation of Drinking Water • Keeping drinking water clean is a joint effort • Federal, provincial & municipal responsibility • Manitoba Drinking Water Safety Act • Sets the standards for public drinking water supplies • Health Canada • Ensures that these standards are met • Water Technicians • Conduct thousands of tests each year to ensure that our water is free of disease-causing bacteria & pathogens • Test results are passed on to provincial and municipal governments