Water Treatment

WATER TREATMENT

By Loan QuanIB Chemistry SLJanuary 23, 2013

I. PRIMARY POLLUTANTS

Found in:Heavy metalsPesticidesDioxinsPolychlorinated (PCBs)Organic matterNitrates & 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, agriculture2) 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. Lead1) source – lead paint, pipes, pottery2) 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. Cadmium1) source – metal plating, rechargeable

batteries, zinc refining products2) h.h. – kidney & lung cancer, makes zinc

ineffective in the body3) envir. h. – toxic to fish, birth defects in

mice

B. PESTICIDES

1. Include: insecticides, fungicides, herbicidesa. 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 cellsa. symptoms: liver cirrhosis, heart & memory damage, depression, chlorance – skin diseaseb. malfunction in fetuses

D. POLYCHLORINATED BIPHENYLS (PCBS)

1. Have high electrical resistance2. Used in electrical transformers & capacitors3. Stays in the environment & accumulate in fatty

tissue4. Reduce reproductive efficiency & impair

learning

E. NITRATES1. Sources: intense farming/ artificial fertilizers, acid rain2. It is soluble not easily removed during sewage treatment3. 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 cancera) nitrate nitrite nitrosamineb) 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 removed1) flocculation – allows particles to clump together by adding chemical to speed up sedimentation processa) adds: aluminum sulfate & calcium hydroxide precipitate of aluminum hydroxideAl2(SO4)3 + 3Ca(OH)2 2Al(OH)3 + 3 CaSO4

2. Removes: larger insoluble objectsa. removes 30-40% of BOD waste

B. SECONDARY TREATMENT1. Method: aeration/ activated sludge process

a. passes through an aeration tank, which is enriched with oxygenb. the sludge settles in sedimentation tank, aerobic bacteria is added to break down organic matter = activated sludge process

2. Removes: 90% of organic matter3. 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 precipitationa. removes: heavy metal ions & phosphate1) phosphate ions decrease by adding calcium or aluminum ion

3Ca2+ +2PO43- Ca3(PO4)2

Al3+ + PO43- AlPO4

2) heavy metals precipitate as sulfide saltCd2+ +H2S CdS +2H+

C. TERTIARY TREATMENT (CONT.)2. Reverse osmosis

a. Osmosis: movement of solvent (water) from dilute to concentrated

solutionb. Semi/partially permeable membrane:

allows solvent to pass through, but solute particles cannotc. 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 behindd. Advantage –  significantly reduces salt, most other inorganic material present in the water, and some organic compoundse. 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 boiled2) anything don’t evaporate stays at the bottom to be removed3) steam is condensed by pipesb. Advantage – removes pathogensc. 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 H2Ob. Removes salt from sea waterc. Very expensive

III. CHLORINE & OZONE TREATMENT

Chlorine OzoneEffective 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