Water PollutionAPES: Ch. 14

Water Pollution

• Is defined as the contamination of streams, rivers, lakes, oceans, or groundwater with substances produced by human activity that negatively affect organisms.– Has potential to impact both aquatic & terrestrial

organisms– Pollution can either come from point sources or

nonpoint sources

Point Sources vs. Nonpoint Sources

• Point sources are:– Distinct locations like factories or sewage treatment

plants that discharge pollution into a body of water.– Easier to pinpoint source of pollution

• Nonpoint sources are:– Diffuse areas like an entire farming region, suburban

community, or storm run-off from parking lots.– Harder to control pollution from these sources

NONPOINT SOURCES

Urban streets

Suburban development

Wastewater treatment plant

Rural homes

Cropland

Factory

Animal feedlot

POINT SOURCES

Human Wastewater

• This is produced by human activities including:– Sewage, gray water, bathing, washing clothes &

dishes.– Biggest challenge?

• To keep wastewater from contaminating drinking water.• Can be difficult because many use same water source

for drinking, bathing, washing, and disposing of sewage.

Human Wastewater

• Three major reasons wastewater is a concern:– Wastewater naturally undergoes decomposition

by bacteria, which creates a demand for dissolved oxygen (Oxygen Demand).

– Nutrients in released in wastewater decomposition can make water sources eutrophic (Nutrient Release).

– Wastewater can carry a wide variety of disease-causing organisms.

Oxygen Demand

• Oxygen-demanding waste:– Dissolved oxygen in water is used by many animals

in respiration. – Organic matter that enters a body of water &

feeds the growth of decomposers (microbes).– Microbes require oxygen to decompose waste– More waste . . . More oxygen needed

Oxygen Demand

• Measured in terms of biochemical oxygen demand (BOD)– The amount of oxygen a quantity of water uses

over a period of time at a specific temperature.– Lower BOD = body of water is less polluted by

wastewater, whereas, higher BOD = body of water is more polluted by wastewater.

• Normal = 5 to 20 mg of oxygen due to decomposition of leaves, twigs etc.

• High = 200 mg of oxygen due to decomposition of domestic wastewater.

Oxygen Demand

• Dead Zones:– High BOD due to decomposition– Dissolved oxygen is too low for other organisms to

survive (lethal).– Some areas there is so little oxygen that life is

absent.– These areas are called “dead zones”

• Can be self-perpetuating due to dying organisms decomposing causing continued BOD

• Mississippi delta in Gulf of Mexico• UN estimates 200 dead zones globally

Fig. 21-A, p. 507

MississippiRiver Basin

TX

MSLA

Mississippi River

Gulf of Mexico

Ohio River

Mississippi River

Missouri River

Depleted oxygen

LOUISIANA

Gulf of Mexico

Nutrient Release• Products of decomposition:

– Include nitrates (NO3-2) & phosphates (PhO4

-2)

• Additional nutrient sources:– Soaps & detergents

• Provides abundance of nutrients to a body of water – Called eutrophication– Anthropogenic inputs of nutrients is called cultural

eutrophication– Produces algal blooms which die & decompose– Chain of events that leads back to low oxygen– Chesapeake Bay is an example

Pollution of Freshwater Lakes by Cultural Eutrophication

Overgrowth -> Breakdown -> Fish Kills -> Anaerobic Bacteria

Algae, cyanobacteria, water hyacinth, duckweed

Breakdown of these plants consumes oxygen

Less O2 causes organisms to die

Produce toxic HS and flammable CH4

1 2 3 4

Chesapeake Bay

• Point Source - Industry – 60% of phosphates, toxic waste• Non point Source – Agriculture/Municipal – 60% Nitrates,

pesticides

Ocean PollutionDILUTE-DISPERSE-DEGRADE• Can handle a lot of

pollutants• Arguments over safety

– Safer than burying vs. – Delaying pollution

prevention– Promotes degradation of

ocean and connected wetlandsRed Tide – eutrophication in ocean

• Release Toxins• Damage fisheries• Kills birds• Poison Seafood

Fig. 21-10, p. 505

Healthy zoneClear, oxygen-richwaters promote growthof plankton and sea grasses,and support fish.

Oxygen-depleted zoneSedimentation and algaeovergrowth reduce sunlight,kill beneficial sea grasses, useup oxygen, and degrade habitat.

Red tidesExcess nitrogen causesexplosive growth of toxicmicroscopic algae,poisoning fish andmarine mammals.

FarmsRunoff of pesticides, manure, and fertilizers adds toxins and excess nitrogen and phosphorus.

Toxic sedimentsChemicals and toxic metals contaminate shellfish beds, kill spawning fish, andaccumulate in the tissues of bottom feeders.

Construction sitesSediments are washed intowaterways, choking fish and plants, clouding waters, and blocking sunlight.

Urban sprawlBacteria and viruses fromsewers and septic tanks contaminate shellfish beds

Oxygen-depletedzone

Closedbeach

CitiesToxic metals and oil from streets and parking lots pollute waters;

IndustryNitrogen oxidesfrom autos andsmokestacks,toxic chemicals,and heavy metals in effluents flow into bays and estuaries.

Closedshellfish beds

Disease-causing Organisms

• Wastewater carries a variety of pathogens:– Viruses, bacteria, and parasites

• Water-born diseases are:– Cholera, typhoid fever, stomach flu, diarrhea– Worldwide most common: cholera and hepatitis– In USA, hepatitis A & bacterium Cryptosporidium– Large-scale outbreaks are rare in US, but common

in developing world.

Water Born Disease Statistics

• 1.1 billion do not have access to safe drinking water.

• Diarrheal diseases can be prevented by:– Safe drinking water, proper sanitation, & proper

hygiene• 42% of world population lacks access to

proper sanitation– Over half live in China & India– In sub-Saharan Africa only 36% have access

Disease-causing Organisms

• Not feasible to test water for all pathogens • Scientists use indicator species –

– An organism that indicates whether or not disease-causing pathogens are likely to be present.

– Best indicator: fecal coliform bacteria• Generally harmless micro-organisms that live in human

intestines• Most common is Escherichia coli or E. coli

Treatment of Wastewater

• Two most widespread systems for treating human sewage is:– Septic systems – found in rural areas with low

population density.– Sewage treatment plants – found in areas of high

population density such as urban & suburban• System to treat wastewater from large

livestock operations (feed lots) is a manure lagoon.

Septic Systems

• Septic system is a simple system with two components:– Septic tank (1,900 – 4700 L):

• Buried underground near house• Three layers develop:

– Scum layer (top): anything that floats & rises to the top– Sludge layer (bottom): anything heavier than water sinks– Septage (middle): layer of fairly clear water that contains

bacteria, pathogenic organisms, and nutrients (PO4-2, NO3

-2)

Septic Systems

– Leach field:• Septage moves by gravity out of tank to underground pipes

which lie below the lawn• Septage slowly seeps out due to perforations in the pipe.• Septage is filtered by surrounding soil & changed into CO2

and nutrients.• Pathogens can:

– Become part of the sludge– Be outcompeted by other micoorganisms– Be degraded by soil micoorganisms in leach field

– Pro: no electricity needed to run septic system, but sludge needs to be removed periodically.

Sewage Treatment Plant

• Managed by municipalities that are centralized.

• Two steps to treating sewage-– Primary treatment:

• Goal is for solids to settle out of wastewater• Solids are dried & exposed to bacteria that can digest

pathogens; this material is called sludge.• Final product is either dumped in landfills, burned, or

converted into fertilizer

Sewage Treatment Plant

– Secondary Treatment:• Involves the remaining wastewater• Goal is to use bacteria to break down 85 – 90% of

organic matter and convert it into CO2 and nutrients• Processes include –

– Aeration to promote growth of aerobic bacteria (less odoriferous than anaerobic bacteria)

– Secondary wastewater is left in settling ponds for several days to remove any remaining particles

– Disinfection using chlorine, ozone, or UV light kills remaining pathogens

– Final product is released into nearby river, lake, or ocean

Manure Lagoons

• Animal waste problems similar to human waste.

• Only a problem when on a large scale like concentrated feed lots.

• Manure from feed lots contains antibiotics & hormones

• Large amounts of manure are handled in manure lagoons– Large, human-made ponds lined with rubber.

Manure Lagoons

• Manure is broken down by bacteria (same as in sewage treatment plants)

• Manure can be spread of farm fields• Risk of manure lagoons –

– Leaks in rubber can contaminate groundwater– Overflow to adjacent water bodies– Application as fertilizer can runoff to nearby water

bodies