Transcript WasteWater Treatment Plants

Water Treatment
Drinking Water Quality
• 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
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.
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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
Depending on the type of treatment plant and the
quality of raw water, treatment generally proceeds
in the following sequence of stages:
1. Screening
2. Aeration
3. pH correction
4. Coagulation and
flocculation
5. Sedimentation
6. Pre-chlorination and
dechlorination
7. Filtration
8. Disinfection
9. pH adjustment
• As required, other steps will be added, depending on the
chemistry of the treated water.
Initial Stages
1. 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/floc
5. 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 Left
6. Pre-chlorination and dechlorination - mostly
to kills algae and much of the remaining bacteria
7. Filtration (depends on size of plant/volume of water
considerations)
– Usually a sand filter of some size
Final Touches
8. 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 UVlamp
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 nonpotable water (or grey water) is adequate
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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