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

1. 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.)2. 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 (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 (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

1. Include: insecticides, fungicides, herbicides

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

2. Example: DDT (dichloro- diphenyl- trichloroethane)

a. structure –

b. is a biological magnification

C. DIOXINS1. Each ring can have up to 4 chlorine atoms

2. Are presented when wastes contain organochlorine compound are burnt

a. Also found in weed killer

3. 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)

1. Have high electrical resistance

2. Used in electrical transformers & capacitors

3. Stays in the environment & accumulate in fatty tissue

4. Reduce reproductive efficiency & impair learning

E. NITRATES1. Sources: intense farming/ artificial fertilizers, acid rain

2. It is soluble not easily removed during sewage treatment

3. 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 Purpose: to remove hazardous materials, reduce

BOD, kill microorganisms There are 3 treatments

A. PRIMARY TREATMENT1. 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

2. Removes: larger insoluble objects

a. removes 30-40% of BOD waste

B. SECONDARY TREATMENT1. 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

2. Removes: 90% of organic matter

3. Substances used:

oxygen & bacteria

C. TERTIARY TREATMENT It is expensive, but necessary Can remove heavy metal ions, nitrates, phosphates, or

organic compounds which primary and secondary treatments cannot

1. 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.)2. 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 (CONT.)3. 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 (CONT.)

4. 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

III. CHLORINE & OZONE TREATMENT

Chlorine Ozone

Effective against bacteria but not viruses

Effective against bacteria & viruses

Cheaper to produce More expensive to produce

Stays in water longer Shorter retention time

Easily liquefied and shipped Must be produced on site because of its high reactivity

Can produce carcinogenic compounds

Oxidized products are less toxic

THE END