Water Treatment

•Much of the world's drinking water is contaminated and poses serious health threats

•U.S. Safe Drinking Water Act of 1974 requires EPA to establish national drinking water standards

•Alternates to Tap Water:•Bottled water- is it really from natural spring? Also, puts too many plastic bottles in landfill!

•Home filters- point of entry/use

Drinking Water Quality

Water Quality Standards

• The EPA (Environmental Protection Agency) sets Maximum Contaminant Levels (MCLs) for drinking water

• There are standards for numerous contaminants, two of which cause an immediate health threat if exceeded• Coliform bacteria -because they may indicate presence

of disease-causing organisms• Nitrate - can cause ‘blue baby syndrome”—nitrate

reacts with blood and blood can’t carry as much oxygen

WATER POLLUTION CONTROLS

Point Reduction• A single identifiable location produces pollution,

i.e. a discharge pipe, drainage channel, well, etc.

• Eliminate lead from gas- decreased lead in water• Better handling of oil (double hulled ships)• Banning of DDT & PCB’s in 1970’s• IPM to reduce pesticides, use fewer fertilizers• Recycling• Industries must separate their wastes to remove

metals which can be sold to other companies that use it for their products

Non-Point Reduction• Generally due to runoff, precipitation, leaching,

etc. where there isn’t a single pollution source• Much harder to control and identify

• Preserving wetlands to filter pollutants• Urban runoff- recycle waste oil instead of

sending down drains, pick up trash, minimize fertilization & pesticide application in your yard, banning phosphate detergent use

MUNICIPAL WATER PURIFICATION PLANTS

Treats water to send to homes for municipal use.

Municipal Water Purification Plant

Water Treatment Plant Stages

1. Screening2. Aeration3. pH correction4. Coagulation and

flocculation

5. Sedimentation6. Pre-chlorination and

dechlorination7. Filtration8. Disinfection9. pH adjustment

Depending on the type of treatment plant and the quality of raw water, treatment generally proceeds in the following sequence of stages:

• As required, other steps will be added, depending on the chemistry of the treated water.

Initial Stages1. Screening - removal of

any coarse floating objects, weeds, etc.

2. Aeration - dissolving oxygen into the water – promotes helpful bacteria

growth– precipitates nuisance metals

like iron and manganese.3. pH correction - preparing

for coagulation and to help precipitate metals – mimics acid rain on soils.

isis.csuhayward.edu/alss/Geography/ mlee/geog4350/4350c4f01.ppt

4. Coagulation and flocculation –

• add coagulating agent• causes agglomeration

(clumping) - sludge/floc5. Sedimentation –• Floc settles out and is

scraped and vacuumed off the bottom of large sedimentation tanks.

• Water is carefully decanted off the top

Filtering Out What’s Left6. Pre-chlorination and dechlorination - mostly

to kills algae and much of the remaining bacteria7. Filtration (depends on size of plant/volume of water

considerations)– Usually a sand filter of some size

Final Touches8. Disinfection - water completely

free of suspended sediment is treated with a powerful oxidizing agent usually one of three types:– Chlorine– Chloramine (chlorine then

ammonia)– Ozone- more expensive– UV-light

9. pH adjustment - desired range of 6.5 to 8.5 pH units.

Possible Additional Steps• Heavy metal removal• Troublesome organics: Activated carbon

filters for pesticides, phenols and MTBE (gasoline additive)

WASTEWATER TREATMENT PROCESS

Wastewater Treatment

• Usually refers to sewage treatment, or domestic wastewater treatment

• Process of removing contaminants from wastewater, both runoff and domestic, using the same processes of purification that would occur in a natural aquatic system

Wastewater Treatment Types of treatment systems include:

• Septic Tanks treat small volumes of waste (e.g., from a single household, small commercial/industrial)

• WasteWater Treatment Plants (WWTPs) treat larger volumes of municipal or industrial waste.

SEPTIC TANKS

• In rural areas or in particular urban communities in the U.S., human wastewater will be treated through individual septic tank systems – Microorganisms breakdown waste– Wastewater is filtered thru soil & rocks of

leachfield– If no leachfield, septic truck sucks out waste &

sends to WWTP.• Septic tanks are easier & faster to install than

sewage system, but prevent fast recycling of water back to ecosystem.

Septic Tanks

• Approx. 22 million systems in operation ( 30% of US population)

• Suitability determined by soil type, depth to water table, depth to bedrock and topography

• Commonly fail due to poor soil drainage

WASTEWATER TREATMENT PLANTS

(WWTP’S)

Preliminary treatment

• Remove large objects via screens• Ex: sticks, rags, toilet paper, tampons• Clog equipment in sewage treatment plant

Treatment stages - Primary treatment

• Typical materials that are removed during primary treatment include– fats, oils, and greases (aka FOG)– sand, gravels and rocks (aka grit)– larger settlable solids including human waste

Treatment stages - Secondary treatment

• Degrade biological content (dissolved organic matter) of the sewage– Ex: human waste, food waste, soaps, detergent

• Added bacteria and protozoa into sewage • Requires aeration to keep oxygen levels high to

promote decomposition• Sludge is sent to landfill or incinerated. If no

toxic metals present, could be used for fertilizer

Sludge Treatment - Composting

• aerobic process• requires the correct

mix of carbon, nitrogen, oxygen and water with sludge

• Generate large amount of heat

Sludge disposal

• Superheat sludge and convert into small granules that are rich in nitrogen– Sell it to local farmer as fertilizer

• Spread sludge cake on the field• Save landfill space

Treatment stages – Tertiary treatment

• remove disease-causing organisms from wastewater

• 3 different disinfection process– Chlorination– UV light radiation– Ozonation

Chlorination

• Most common• Advantages: low

cost & effective• Disadvantages:

chlorine residue could be harmful to environment

UV light radiation• Damage the genetic

structure of bacteria, viruses and other pathogens.

• Advantages: no chemicals are used

• water taste more natural

• Disadvantages: high maintenance of the UV-lamp

Ozonation

• Oxidized most pathogenic microorganisms• Advantages: safer than chlorination

fewer disinfection by-product• Disadvantage: high cost

Advanced Treatment

• Nitrogen removal– Ammonia (NH3) → nitrite (NO2

-)→ nitrate (NO3-)

• Phosphorous removal– Precipitation with iron or aluminums salt

• Lead to eutrophication!!• May cause algae bloom

Summary

Link to Water Filter

Reusing Wastewater• Cannot directly mix treated wastewater with treated

raw water and supplied as potable (drinking) water.• Can use a dual plumbing system to supply wastewater

into facilities for specific, approved uses for which non-potable water (or grey water) is adequate – Processing water in manufacturing process– Irrigation– Car washing– Toilets

Alternatives to WWTP• Effluent sewerage- several septic tanks connected

to one mini-treatment plant- no drainfield• Use artificial wetlands

– Fairly common in Europe, limited usage in US– Sewage/contaminated water is piped to holding ponds,

sediment settles, water passed to wetland where plant roots filter & cleanse, microorganisms decompose

Questions