Transcript Water Pollution Chapter 19

Water Pollution
Chapter 19
Types and Effects
• Water pollution: any chemical,
biological or physical change in water
quality that has a harmful effect on
living organisms or makes water
unsuitable for use.
• Table 19-1 Major Categories of Water
Pollutants
How do we measure Water Quality?
• 1) Measure number of coliform bacteria present
in 100-mL sample
– WHO recommends 0 colonies/100mL
drinking
– EPA max level of swimming 200
colonies/100mL
• 2) Measure oxygen demanding waste
– Determined by measuring biological oxygen
demand (BOD): the amount of dissolved O
needed by decomposers to breakdown waste
Sources
• Nonpoint: can’t be traced to any single site of
discharge
– Acid deposit, runoff of chemicals, pesticides,
fertilizer/manure
• Point source: discharge at specific locations
– Factories, sewage treatment, mines, oil
tankers
– Easy to identify, monitor and regulate
Pollution of Freshwater Streams
• Can recover rapidly from degradable, oxygendemanding wastes and excess heat through
dilution and bacterial decay
• These processes do not eliminate
nonbiodegradable or slowly degradable
• The time and distance needed to recover
depend on volume of waste, stream’s volume,
flow rate, temp., and pH level.
Cuyahoga River, Ohio 1959/’69
Pollution of Freshwater Lakes
• Dilution of pollutants in lakes, reservoirs and
ponds less effective
– Contain stratified layers with little vertical
mixing
– Little free flow
– Ponds have small volumes of water
• More vulnerable to contamination by plant
nutrients, oil, pesticides, toxic substances
Eutrophication
• Lakes receive inputs of nutrients and silt eroded
and running off from surroundings
• Eutrophication: natural nutrient enrichment of
lakes
• Near urban or agricultural areas, human
activities accelerate input of plant nutrients
– Results in cultural eutrophication
– Caused mostly by nitrate and phosphate containing
effluents
Groundwater Pollution
• More of a problem because numerous sources
as we dump wastes into storage lagoons, septic
tanks, landfills, hazardous dumps and deep
injection wells.
• Human health risks from contaminants:
petrochemicals (gas, oil)
organic solvents (TCE)
pesticides and arsenic
lead (Pb) and fluoride (F-)
Protecting Groundwater
• Contaminated aquifers almost impossible to
clean up because of large volume,
inaccessibility, and slow movement
• Preventing contamination only effective
method
– Monitor aquifer near landfills and tanks
– Leak detection systems on underground tanks
– Banning/ strictly regulating hazardous waste
19.5
Oceans and pollution
Clean Water Act (1972)
• 1) Make all waters “fishable and
swimmable”
• 2) Require discharge permits of major
polluters
• 3) Identify toxic pollutants and require use
of best practices technology (BPT)
19-5 Ocean Pollution
• Oceans can dilute, disperse, and degrade large
amounts of raw sewage, sludge, oil and some
degradable industrial waste.
• Pro: dumping sludge and hazardous waste into
deep ocean because some organisms are more
resilient in the ocean.
• Con: Feel it would delay pollution prevention and
promote further degradation of this vital system.
Coastal Areas
• Include wetlands, estuaries, coral reefs and
mangrove swamps
• Sustain most of the damage of waste inputs
• Most coastal developing countries dump
sewage into the sea without treatment
• 85% of sewage from cities along
Mediterranean Sea is discharged untreated
Harmful Alga Blooms
• Runoff of sewage and agricultural wastes into
coastal waters introduce large quantities of
nitrates (NO3-) and phosphate (PO43-) plant
nutrients that cause explosive growth of algae.
• The harmful alga blooms (HAB) are called red,
brown, or green tides depending on their color.
• HAB’s can release toxins that damage fisheries
kill fish-eating birds, reduce tourism and poison
seafood.
• Death of the HAB’s deplete dissolved oxygen
and cause the death of marine species.
• These oxygen-depleted zones form in coastal
waters b/c of excessive nonpoint inputs of
fertilizers and animal wastes from land runoff
and deposition of nitrogen from the
atmosphere.
• In these zones, aquatic life dies or moves
elsewhere
• Biggest zone in U.S. waters forms every
summer in Gulf of Mexico near Louisiana and
Mississippi River Basin (Figure 19-13).
What pollutants do we dump
into the Ocean?
• Barges and ships still legally dump large
quantities of dredge spoils (materials containing
toxic metals scraped from bottom of harbors and
rivers to maintain shipping channels) into Atlantic,
Pacific, and Gulf coast
• Many countries dump sewage sludge: gooey
mixture of toxic chemicals, infectious agents,
solids from wastewater treatment plants
– 1992 U.S. banned this practice
Oil Effects on Animals
• Depend on type of oil, amount released,
distance from shore, time of year, weather,
water temperature and currents.
• Volatile hydrocarbons immediately kill
organisms, some others form globules that
float on surface and coat feathers of birds.
• This oil coating destroys the natural insulation
and buoyancy, causing many to drown or die
from loss of body heat
• Most life forms recover from crude oil within 3
years, but refined oil recovery up to 10 years
Oil Effects on Oceans
• Tanker accidents or offshore drilling blowouts
get publicity but are not the main source of
oil pollution.
• Largest input of oil is released into the ocean
during normal operation of offshore wells,
washing tankers and releasing oily water and
from pipeline and storage tank leaks.
• Almost half of oil in the ocean is waste oil
dumped, spilled or leaked into sewers by
cities, industries or at-home oil changes.
Clean Up Oil Spills
• Prevention still best method
– Others remove only part of the oil
– None work well on large spill
• Chemical methods
– Coagulating agents to cause oil to clump or sink
– Dispersing agents to break up oil slicks
• Mechanical methods
– Floating blooms to contain the oil spill or keep it
from moving
– Skimmer boats to vacuum up oil
– Absorbent pads or mesh pillows to soak up oil
Bioremediation
• Biological method of cleanup
• May involve constructing wetlands or
involving plants to soak up organic
nutrients
• Ex: Exxon Valdez oil spill
– Using bacteria to digest the oil coating
– More effective than artificial methods
19-7 Drinking Water Quality
• If no access to clean water, it is taken from
– Shallow groundwater easily contaminated
– Nearby polluted river water
– Mudholes used by animals and humans
• Purification developing countries with no
treatment systems
– Tropical regions: expose water to the sun
– Bangladesh: cloth to strain water
– PUR packet: powdered mixture that removes
pathogenic microorganisms and suspended matter
• U.S. Safe Drinking Water Act of 1974
– Requires EPA to establish national drinking water
standards called maximum contaminant levels
– Privately owned wells not required to meet standards
• Opposition: Congress pressured by waterpolluting industries to weaken Act
– Eliminate national water tests
– No media access of health violations
– Allow states to violate the act if they cannot afford to
comply
– Eliminate water systems use of technology to remove
cancer causing agents
19.6
Preventing/Reducing Surface
Water pollution
Preventing/Reducing Surface Water
Pollution
Clean Up of Nonpoint Pollution:
– Reducing and controlling runoff
– Preserve wetlands to allow nitrate and phosphate to
flow through and be absorbed
Clean Up of Point Source Pollution
– Legal Approach (Basis of efforts to control pollution)
• Federal Water Pollution Control Act of 1972
(renamed Clean Water Act when amended in
1977)
• 1987 Water Quality Act
– Technological Approach
Technological Approach to Point
source Pollution
• Septic Tanks: sewage from each house goes into
holding tank on property
– (25% of all homes)
• Sewer lines: urban areas; waste flow through series of
pipes leading to treatment center
• Some cities have separate lines for sewage and storm
water; some combined lines so if rains flood system,
often discharges untreated sewage into surface water
Sewage Reaches Treatment Plant
• Preliminary: large objects screened
1) Primary Treatment (mechanical process)
1) Removes 60% of the suspended solids and 30% of
oxygen demanding wastes from sewage
2) Grease and oils removed, organic solids sent to
Biosolids treatment
Uses screens to filter out debris such as sticks,
stones and rags
Allow suspended solids to settle out as sludge in
settling tank
• 2) Secondary Treatment (biological process)
– Aeration process (add oxygen)
1) Aerobic bacteria remove 90% of biodegradable,
oxygen-demanding organic waste still left over
Activated sludge process: pump sewage into large
tank and mix for several hours with bacteria-rich
sludge and air bubbles
Then goes to sedimentation tank where
microorganisms and suspended solids settle out
as sludge
• Sludge produced is incinerated, sent to landfill
or treated in biosolids facility
• Secondary removes only tiny fraction of
radioactive isotopes and persistent organic
substances such as pesticides
• 3) Advanced Sewage Treatment
– Water travel through anthracite coal filters that
remove specific pollutants left in water after
primary and secondary
– Sometimes not used because cost twice as
much to build and four times as much to operate
as secondary plants
• Growing interest in using membrane based
technologies reverse osmosis, micro
filtration, ultra filtration and nanofiltration
• Because of Clean Water Act, most U.S. cities
have combined primary and secondary sewage
treatment plants
• **Figure 19-17
• Before discharge, water from all three
processes undergo
– 1) bleaching to remove water coloration
– 2) disinfection to kill disease-carrying bacteria
(chlorination)
Treating Sewage by working with
Nature
• Sewage Walls
– Run along residential block
– Channels sewage through terraced planters that
progressively filter and purify the waste
• Living machines
– Look like aquatic botanical gardens, powered by sun
• Wastewater garden (Figure 19-19)
– Small, low tech artificial wetland to treat sewage
– Water flowing out can be used to irrigate gardens or fields or
flush toilets
The Living
Machine