chapter 17. what is water pollution water pollution can be defined as "the presence of a...
TRANSCRIPT
WATER POLLUTION AND ITS
PREVENTION
Chapter 17
1. Water pollution
What is water pollution Water pollution can be defined as
"the presence of a substance in the environment that because of its chemical composition or quantity, prevents the functioning of natural processes and produces undesirable environmental and (human) health effects."
Categories of Water Pollutants
Main groups of water pollutants
1. Biodegradable Rapidly degradable (non-persistent) Slowly degradable (persistent)
2. Non-biodegradable
Water Pollutants: sources
a. Non-pont-source pollutants: agricultural runoff, storm-water drainage, atmospheric deposition.
b. Point-source pollutants: discharges from factories, sewage systems, power plants, underground coal mines, oil wells.
Strategies to bring water pollution under control:1. Reduce or
remove the sources
2. Treat the water to remove pollutants or convert them to harmless forms.
Water pollutants: types
a. Pathogens
b. Organic wastes
c. Chemical pollutants
d. Sediments
e. Nutrients
Pathogens Infectious
agents that cause sickness and death
Come from excrement from humans and other animals that are infected
Disease Infectious Agent
•Typhoid fever •Salmonella typhi (bacterium)
•Cholera Vibrio cholerae (bacterium)
•Salmonellosis •Salmonella sp. (bacteria)
•Diarrhea •Echerichia coli,•Campylobacter sp. (bacteria)•Cryptosporidium pavum (protozoan)
•Infectious hepatitis •Hepatitis A virus
•Poliomyelitis •Poliovirus
•Dysentery •Shigella sp. (bacteria)•Entamoeba histolytica (protozoan)
•Giardiasis •Giardia intestinales (protozoan)
•Numerous parasitic diseases
•(Roundworms, flatworms)
Public heath Before mid 1800s: epidemics were common in cities
(typhoid fever, cholera)
After: connection between disease and sewage-carried pathogens
Today: public health measures Purification and disinfection of public water supplies with
chlorine and other agents Sanitary collection and treatment of sewage wastes Maintenance of sanitary standards in all facilities in which food
is processed or prepared for public consumption Public education in personal and domestic hygiene practices
Sanitation = good medicine Good health is a result of the prevention of disease through
public-health measures Population in areas where here is little or no sewage
treatment are extremely vulnerable to deadly epidemics.
Organic wastes Includes leaves, grass clippings, trash, etc.
Enter water as a consequence of runoff or excessive aquatic plant growth
As bacteria and detritus feeders decompose organic matter, they consume O2 dissolved in water.
BOD (biochemical oxygen demand): measures the amount of organic material in water in terms of how much oxygen will be required to break it down. Fishes and shellfish are killed at an OD of 2 to 3 ppm A BOD value for raw sewage is around 250 ppm
Chemical pollutants
Inorganic chemicals: include heavy metals (lead, mercury, cadmium, nickel, etc), acids from mine drainage and acid precipitation, and road salts.
Organic chemicals: include petroleum products, pesticides, industrial chemicals (PolyChorinated Biphenyls, cleaning solvents and detergents)
Sediments Erosion from farmlands, deforested slopes,
overgrazed rangelands, construction sites, mining sites, stream banks and roads increase the load of sediments.
Nutrients
Inorganic chemicals carried in solution in all bodies of water are classified as nutrients.
Include phosphorus and nitrogen Stimulate undesirable plant growth in
the bodies of water. Sources include sewage outfalls,
agricultural runoff, lawns and gardens, golf courses and storm drains.
Water quality standards
National Recommended Water Quality Criteria (EPA) provides standards for assessing water pollution.
Lists 158 chemicals and substances as criteria pollutants and recommends concentrations for fresh water, salt water and human consumption
Water quality standardsCriteria maximum concentration (CMC):
highest single concentration beyond which environmental impacts may be expected
Criterion continuous concentration (CCC): highest sustained concentration beyond which undesirable impacts may be expected
Drinking water standards and health advisories: enforceable under the authority of the Safe Drinking Water Act (SDWA)○ Maximum Contaminant levels (MCLs)
Arsenic as a example:
Listed as a human carcinogen CMC and CCC values are 340 and 150
g/L for freshwater bodies, and 69 and 36 g/L for saltbodies.
Drinking water MCL concentration is 10 g/L
Other applications to the water quality criteria National pollution discharge elimination
system program (NPDES): addresses point-source pollution and issues permits to regulate discharges from industrial sources.
Total maximum daily load program(TMDL): evaluates all sources of pollutants entering a body of water, especially non-point sources
2. Eutrophication
Types of aquatic plants
BenthicSubmerged aquatic vegetation (SAV)Emergent vegetation
Phytoplankton (algae, protists, cyanobacteria
Oligotrophic = low in nutrients
What is an oligo-trophic body of water?
What is a Eutrophic Body of Water? Eutrophic = well nourished
How do you create a Eutrophic Body of Water? 1. Nutrient enrichment,
natural or cultural
2. Increased phytoplankton growth resulting in increased turbidity
3. Loss of sunlight, food and habitat
4. Depletion of dissolved oxygen from decomposition of phytoplankton by decomposers
How to Stop Eutrophication
1. Attack the symptoms:
Chemical treatments (with herbicides)
Aeration
Harvest aquatic weeds
Draw water down
How to Stop Eutrophication2. Attack the root cause:
Control point-source pollutants○ Ban the sale of phosphate detergents○ Regulate the maximum alowable level of
phosphates○ NPDES permits
How to Stop Eutrophication2. Attack the root cause:
Control non-point-source pollutants○ EPA regulations through the TMDL program
include:○ Identify pollutants○ Estimate pollution comming from all sources○ Estimate the ability of the body of water to
assimilate pollutants○ Determine the maximum allowable pollution load○ Allocate the allowable level of pollution among the
different sources
How to Stop Eutrophication2. Attack the root cause:
Best management practices (BMPs)○ Practices used to minimize erosion, runoff and
leaching○ Methods of soil conservation
When washings from animal facilities are flushed directly into natural waterways, they contribute significantly to eutrophication. This may be avoided by collecting the flushings in ponds from which both the water and the nutrients may be recycled.
How to Stop Eutrophication2. Attack the root cause:
Recovery○ Govenrment practices for the management of
watersheds○ Lake washington
3. Sewage Management and Treatment
History of sewage treatment
Late 1800s: human excrement was disposed in the outdoor privy
Louis Pasteur and other scientists showed that sewage borne bacteria were responsible for many infectious diseases
Human wastes started to be disposed through drain systems
The flush toilet was introduced
Water became unfit to swim in because of sewage contamination
1900: Sewage treatment systems were developed
What is in Raw Sewage 1. Debris and grit: plastic bags, coarse sand, gravel
2. Particulate organic matter: fecal matter, food wastes, garbage, toilet paper
3. Colloidal and dissolved organic matter: urine, soaps, detergents and cleaning agents.
4. Dissolved inorganic matter: nitrogen, phosphorus, and other nutrients
5. Pathogens: bacteria, protozoa, virus
6. Heavy metals, pesticides, and various other toxic compounds
How Do We Remove These Substances from the Water?
Preliminary Treatment - debris and grit removed by a bar screen and grit chamber
How Do We Remove These Substances from the Water?
Primary Treatment - particulate organic matter removed by primary clarifiers
How Do We Remove These Substances from the Water?
Secondary Treatments - colloidal and dissolved inorganic matter removed by trickling filter systems or activated sludge systems
How Do We Remove These Substances from the Water? Biological Nutrient Removal - dissolved inorganic matter removed
by bacterial denitrification and bacterial uptake of phosphorusa. Can also be done inorganically by using chemical processes·Lime causes phosphate to precipitate as insoluble calcium phosphate ·Ferric chloride causes phosphate to precipitate as insoluble ferric phosphateb. Removal of the dissolved inorganic matter is not standard treatment though it is becoming more common
Final Clarification and Disinfection Meant to eliminate pathogens Disinfecting agents
chlorine gasSodium hypochlorite (chlorox)Ozone gasUltraviolet light
Discharge
BOD values are 10 to 20 ppm (200 ppm in the incoming sewage)
Many cities are still operating with lower quality treatments or with no treatment at all.
Treatment of sludge
Raw sludgeMost is disposed in landfills with no previous
treatmentIt is considered a biologically hazardous
materialIt is a nutrient-rich organic material with
potential to be used as organic fertilizerMethods for treating sludge include:
○ Anaerobic digestion○ Composting○ Pasteurization
Anaerobic digestion Raw sludge is put into large
airtight tanks (sludge digesters)
Anaerobic bacteria break down the organic matter
End products include carbon dioxide, methane and water (biogas)
Treated sludge is called biosolid
Dewatered it becomes a sludge cake
Composting
Raw sludge is mixed with wood chips Placed in piles that allow air circulation Aerobic bacteria and other decomposers
break down organic material to rick humus-like material
Pasteurization
The sludge cake is put through ovens to be pasteurized
The product is dry, odorless organic pellets.
Alternative Treatment Systems On site wastewater
treatment systems
Using effluents for irrigation
Reconstructed wetland systems
4. Public Policy
Public Policy
EPA is responsible for overseeing water Depends on laws passed by Congress
Clean water act (CWA) of 1972○ Required permits for all point source
discharges of pollutantsClean water state revolving fund program
(SRF)○ Gives funds to local governments to build
treatment facilities
Problems and progress Problems
Non point source pollution
Construction of new wastewater treatment facilities
Storm water discharges Sewer overflows Wetlands protection Animal feeding
operations
Progress The number of people
served by adequate sewage has increased
Soil erosion has been reduced
Two-thirds of the nation’s waterways are safe for fishing and swimming
Many rivers have been cleaned up and restored
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hefty-fines-on-polluters/ http://bio4esobil2010.wordpress.com/2011/06/01/e
utrophication/ http://www.squamlakes.org/programs/phosphorus.
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