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Water Treatment. By Loan Quan IB Chemistry SL January 23, 2013. I. Primary Pollutants. Found in: Heavy metals Pesticides Dioxins Polychlorinated (PCBs) Organic matter Nitrates & Phosphate. A. Heavy Metals. It’s poisonous a. Examples: mercury, lead, cadmium

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water treatment

Water Treatment

By Loan Quan

IB Chemistry SL

January 23, 2013

i primary pollutants
I. Primary Pollutants
  • Found in:

Heavy metals



Polychlorinated (PCBs)

Organic matter

Nitrates & Phosphate

a heavy metals
A. Heavy Metals
  • It’s poisonous

a. Examples: mercury, lead, cadmium

b. The metal ions interfere with other ions in the body (ie. Ca2+, Mg2+, Zn2+)

a heavy metals cont
A. Heavy Metals (cont.)
  • Sources and health hazard of heavy metals

a. Mercury

1) source – paint, batteries, agriculture

2) health hazard – nerves & brain damages, symptoms: depression, blindness, insanity,

3) environmental hazard – inhibit growth & kill fish production; biological magnification in food chain

***biological magnification – the builds up of toxic level over time within each successive link in the food chain

a heavy metals cont1
A. Heavy Metals (cont.)

b. Lead

1) source – lead paint, pipes, pottery

2) h.h. – burning pain in mouth; constipation/diarrhea; severe: kidney, heart, liver failure; brain damage in kids

3) envir. h. – toxic to plants & domestic animals; biological magnification in food chain

a heavy metals cont2
A. Heavy Metals (cont.)

c. Cadmium

1) source – metal plating, rechargeable batteries, zinc refining products

2) h.h. – kidney & lung cancer, makes zinc ineffective in the body

3) envir. h. – toxic to fish, birth defects in mice

b pesticides
B. Pesticides
  • Include: insecticides, fungicides, herbicides

a. Poisonous  cause pollution when washed off land & into water

  • Example: DDT (dichloro- diphenyl- trichloroethane)

a. structure –

b. is a biological magnification

c dioxins
C. Dioxins
  • Each ring can have up to 4 chlorine atoms
  • Are presented when wastes contain organochlorine compound are burnt

a. Also found in weed killer

  • Stays in fat and liver cells

a. symptoms: liver cirrhosis, heart & memory damage, depression, chlorance – skin disease

b. malfunction in fetuses

d polychlorinated biphenyls pcbs
D. Polychlorinated biphenyls (PCBs)
  • Have high electrical resistance
  • Used in electrical transformers & capacitors
  • Stays in the environment & accumulate in fatty tissue
  • Reduce reproductive efficiency & impair learning
e nitrates
e. Nitrates
  • Sources: intense farming/ artificial fertilizers, acid rain
  • It is soluble  not easily removed during sewage treatment
  • Set limit of nitrate in drinking water: 50 mg dm-3

a. High level can interact with hemoglobin & affect oxygen transport

b. Risk in babies:

1) nitrate converts to nitrite

2) nitrite oxidized Fe2+ to Fe3+

3) decreases oxygen- carrying capacity  form methaemoglobin (blue baby syndrome)

c. Risk in adults:

1) can cause cancer

a) nitrate  nitrite  nitrosamine

b) nitrosamine = carcinogenic

ii waste water treatment
II. Waste- Water Treatment
  • Purpose: to remove hazardous materials, reduce BOD, kill microorganisms
  • There are 3 treatments
a primary treatment
A. Primary Treatment
  • Method: filtration/ screening

a. waste water passes into sediment tank  sludge at the bottom is removed

1) flocculation – allows particles to clump together by adding chemical to speed up sedimentation process

a) adds: aluminum sulfate & calcium hydroxide  precipitate of aluminum hydroxide

Al2(SO4)3 + 3Ca(OH)2 2Al(OH)3 + 3 CaSO4

  • Removes: larger insoluble objects

a. removes 30-40% of BOD waste

b secondary treatment
B. Secondary Treatment
  • Method: aeration/ activated sludge process

a. passes through an aeration tank, which is enriched with oxygen

b. the sludge settles in sedimentation tank, aerobic bacteria is added to break down organic matter = activated sludge process

  • Removes: 90% of organic matter
  • Substances used:

oxygen & bacteria

c tertiary treatment
C. Tertiary Treatment
  • It is expensive, but necessary
  • Can remove heavy metal ions, nitrates, phosphates, or organic compounds which primary and secondary treatments cannot
  • chemical precipitation

a. removes: heavy metal ions & phosphate

1) phosphate ions decrease by adding calcium or aluminum ion

3Ca2+ +2PO43- Ca3(PO4)2

Al3+ + PO43-  AlPO4

2) heavy metals precipitate as sulfide salt

Cd2+ +H2S CdS +2H+

c tertiary treatment cont
C. Tertiary Treatment (cont.)
  • Reverse osmosis

a. Osmosis:

movement of solvent (water) from dilute to concentrated solution

b. Semi/partially permeable membrane:

allows solvent to pass through, but solute particles cannot

c. Methods:

1) sea water is pressurized with at least 70atm (osmotic pressure)

2) pure water passes through the semi- permeable membrane

3) solute (salt) is left behind

d. Advantage – significantly reduces salt, most other inorganic material present in the water, and some organic compounds

e. Disadvantage - damaged membranes are not easily detected  not be able to know if the system functions normally or not

c tertiary treatment cont1
C. Tertiary Treatment (cont.)
  • Distillation

a. Methods:

1) sea water is heated & passed into evacuated chamber in order to be boiled

2) anything don’t evaporate stays at the bottom to be removed

3) steam is condensed by pipes

b. Advantage – removes pathogens

c. Disadvantage – expensive to maintain; take 2-5 hours to make 1 gallon of water

c tertiary treatment cont2
C. Tertiary Treatment (cont.)
  • Ion exchange

a. Resins/ zeolites are used to exchange nitrate ions with hydroxide ions

1) X-OH- + NO3-(aq) X-NO3- + OH-(aq)

2) Y-H++ M+(aq) Y-M++ H+(aq)

3) H+ and OH- combine to form H2O

b. Removes salt from sea water

c. Very expensive