1. Waste water treatment List the primary pollutants found in waste water and identify their sources. Outline the primary, secondary and tertiary stages of waste water treatment, and state the substance that is removed during each stage. Evaluate the process to obtain fresh water from sea water using multi- stage distillation and reverse osmosis.

2. Waste water treatment: why? Presence of nitrates and phosphates in polluted water is harmful to humans. Excessive nitrate level affects oxygen transport by interacting with hemoglobin in young infants. Blue Baby Syndrome Heavy Metals are toxic. e.g) Mercury, Lead, Cadmium They reacts with the necessary ions in the body like Calcium, Magnesium or Zinc. They affect ecological issues such as biomagnification in food chain, declination of fish population etc.

3. Waste water treatment: why? Purpose of waste water treatment: Remove toxic materials and other microorganisms Toxic materials and microorganisms harms human and other living organisms in the water. Reduce the BOD Aquatic region with high level of BOD is unfavorable condition for the fish.

4. Water pollutants (1) pollutantssources pesticidesagriculture dioxinsDioxins are from: * The incineration of waste materials that contain Organochloro compounds. * Consists in some weed killers (herbicides) 10,000 times more poisonous than the cyanide ion PCB’s: polychlorinated biphenyls;  electrical insulators, molecules added to plastics  overexposure result in a disease called chloracne which is a skin condition which produces cysts containing a straw coloured liquid; other symptoms are loss of appetite, nausea, vomiting and weakness  most PCB’s have low toxicity for humans

5. Water pollutants (2) pollutantssources organic matter Sewage, agricultural run off e.g. cleaning out of stables, cow sheds, food industry nitratesOver-use of fertilizers results in leaching of nitrates into rivers/run-off of fertilizers, animal and human waste. phosphatesUse of phosphate-containing detergents

6. Water pollutants (3) heavy metals pollutantssources mercury mercury cell e.g. used in the electrolysis of brine - greatest dischargers; batteries; mercury salts used as fungicides to reduce formation of moulds on seeds (seed dressing) lead lead paints lead based solder in water pipes and fittings; car exhausts (leaded petrol); car batteries cadmium by-product of the extraction of zinc and lead; cadmium is always found near zinc used in pigments in ceramics; zinc-plating always contains some cadmium; rechargeable batteries

7. Primary treatment: physical methods: filtration flocculation sedimentation removes: insoluble solids and liquids most suspended particles some oxygen-demanding wastes (organic matter) (http://en.wikipedia.org/wiki/Sewage_treatment#Filter_beds_.28oxidising_beds.29

8. Secondary treatment: activated sludge http://en.wikipedia.org/wiki/Activated_sludge

9. Secondary treatment:trickler filter http://en.wikipedia.org/wiki/Trickling_filter

10. Secondary treatment removes 90% organic waste reducing BOD methods: activated sludge trickle bed filter

11. Secondary treatment Activated sludge: oxidation of organic waste by aerobic bacteria encouraged by aeration Trickling filter beds: rotating pipes sprinkle waste water over stones which have bacteria and algae growing on them which consume the waste and some nitrates.

12. Tertiary treatment methods: activated carbon-bed: organic waste is oxidized into CO 2 and H 2 O by the carbon activated by heat, also removes dioxins and PCBs denitrifying bacteria: nitrates into N 2 chemical precipitation: heavy metal ions are precipitated out by adding anions which form insoluble salts with them (see next slide); also removes phosphates reverse osmosis and ion exchange: nitrates.

13. Tertiary treatment: precipitation ions like cadmium, lead, mercury and phosphate ions can be precipitated by adding ions which form insoluble compounds with the heavy metal or phosphate ions to precipitate phosphates, aluminium or calcium ions are added which form insoluble phosphates; these phosphates then precipitate out 3Ca 2+ (aq) + 2PO 4 3- (aq)  Ca 3 (PO 4 ) 2 (s) 2Al 3+ (aq) + PO 4 3- (aq)  AlPO 4 (s) to precipitate heavy metal ions, hydrogen sulphide gas is added; the heavy metal ions form their sulphide salts which have very low solubilities: Pb 2+ (aq) + H 2 S (g)  PbS (s) + 2 H + (aq)

14. Ion exchange X = resin beads Equation of exchange: X – Cl - + NO 3 -  X – NO 3 + Cl -