Chapter 17. What is water pollution Water pollution can be defined as "the presence of a...

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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