Water Pollution

Core Case Study: Using Nature to Purify Sewage

 Ecological wastewater purification by a

living machine

.

 Uses the sun and a series of tanks containing plants, snails, zooplankton, crayfish, and fish (that can be eaten or sold for bait).

Figure 21-1

WATER POLLUTION: SOURCES, TYPES, AND EFFECTS



Water pollution

is any chemical, biological, or physical change in water quality that has a harmful effect on living organisms or makes water unsuitable for desired uses.



Point source

: specific location (drain pipes, ditches, sewer lines).



Nonpoint source

: cannot be traced to a single site of discharge (atmospheric deposition, agricultural / industrial / residential runoff)

Table 21-2, p. 495

Major Water Pollutants and Their Effects

 A fecal coliform bacteria test is used to indicate the likely presence of disease-causing bacteria in water.

Figure 21-2

Major Water Pollutants and Their Effects

 Water quality and dissolved oxygen (DO) content in parts per million (ppm) at 20 °C.

 Only a few fish species can survive in water less than 4ppm at 20 °C.

Figure 21-3

POLLUTION OF FRESHWATER STREAMS

 Flowing streams can recover from a moderate level of degradable water pollutants if they are not overloaded and their flows are not reduced.

 In a flowing stream, the breakdown of degradable wastes by bacteria depletes DO and creates and

oxygen sag curve

.

• This reduces or eliminates populations of organisms with high oxygen requirements.

Biological Oxygen Demand

• Measures the amount of oxygen consumed by microorganisms in decomposing organic matter in stream water • Also measures the chemical oxidation of inorganic matter (extraction of dissolved oxygen (DO) via chemical reaction) • Directly affects the amount of DO in rivers and streams (the greater the BOD, the more rapidly oxygen is depleted in the stream)

Biological Oxygen Demand

• Sources of BOD include debris; dead plants and animals; animal manure; wastewater treatment plants; feedlots; urban stormwater runoff • The consequences of BOD are the same as those with low DO (aquatic organisms become stressed, suffocate, and die)

Water Pollution Problems in Streams

 Dilution and decay of degradable, oxygen demanding wastes and heat in a stream.

Figure 21-4

POLLUTION OF FRESHWATER STREAMS

 Most developed countries have sharply reduced point-source pollution but toxic chemicals and pollution from nonpoint sources are still a problem.

 Stream pollution from discharges of untreated sewage and industrial wastes is a major problem in developing countries.

Global Outlook: Stream Pollution in Developing Countries

 Water in many of central China's rivers are greenish black from uncontrolled pollution by thousands of factories.

Figure 21-5

POLLUTION OF FRESHWATER LAKES

 Dilution of pollutants in lakes is less effective than in most streams because most lake water is not mixed well and has little flow.

 Lakes and reservoirs are often stratified and undergo little mixing.

 Low flow makes them susceptible to runoff.

 Various human activities can overload lakes with plant nutrients, which decrease DO and kill some aquatic species.

Cultural Eutrophication



Eutrophication

: the natural nutrient enrichment of a shallow lake, estuary or slow moving stream, mostly from runoff of plant nutrients from the surrounding land.



Cultural eutrophication

: human activities accelerate the input of plant nutrients (mostly nitrate- and phosphate-containing effluents) to a lake.

 85% of large lakes near major population centers in the U.S. have some degree of cultural eutrophication.

POLLUTION OF GROUNDWATER

 Groundwater can become contaminated with a variety of chemicals because it cannot effectively cleanse itself and dilute and disperse pollutants.

 The drinking water for about half of the U.S. population and 95% of those in rural areas comes from groundwater.

Coal strip mine runoff Polluted air Pumping well Deicing road salt Pesticides and fertilizers Waste lagoon Accidental spills Hazardous waste injection well Buried gasoline and solvent tanks Gasoline station Cesspool, septic tank Water pumping well Landfill Sewer Leakage from faulty casing Discharge Confined aquifer Groundwater flow Fig. 21-7, p. 501

POLLUTION OF GROUNDWATER

 It can take hundreds to thousand of years for contaminated groundwater to cleanse itself of

degradable wastes

.



Nondegradable wastes

(toxic lead, arsenic, flouride) are there permanently.



Slowly degradable wastes

(such as DDT) are there for decades.

Solutions Groundwater Pollution Prevention Cleanup Find substitutes for toxic chemicals Keep toxic chemicals out of the environment Install monitoring wells near landfills and underground tanks Require leak detectors on underground tanks Pump to surface, clean, and return to aquifer (very expensive) Inject microorganisms to clean up contamination (less expensive but still costly) Ban hazardous waste disposal in landfills and injection wells Store harmful liquids in aboveground tanks with leak detection and collection systems Pump nanoparticles of inorganic compounds to remove pollutants (may be the cheapest, easiest, and most effective method but is still being developed) Fig. 21-9, p. 504

OCEAN POLLUTION

 Oceans, if they are not overloaded, can disperse and break down large quantities of degradable pollutants.

 Pollution of coastal waters near heavily populated areas is a serious problem.

 About 40% of the world’s population lives near on or near the coast.

 The EPA has classified 4 of 5 estuaries as threatened or impaired.

Industry Nitrogen oxides from autos and smokestacks, toxic chemicals, and heavy metals in effluents flow into bays and estuaries.

Cities Toxic metals and oil from streets and parking lots pollute waters; Closed beach Urban sprawl Bacteria and viruses from sewers and septic tanks contaminate shellfish beds Construction sites Sediments are washed into waterways, choking fish and plants, clouding waters, and blocking sunlight.

Closed shellfish beds Farms Runoff of pesticides, manure, and fertilizers adds toxins and excess nitrogen and phosphorus.

Red tides Excess nitrogen causes explosive growth of toxicmicroscopic algae, poisoning fish and marine mammals.

Oxygen-depleted zone Toxic sediments Chemicals and toxic metals contaminate shellfish beds, kill spawning fish, and accumulate in the tissues of bottom feeders.

Oxygen-depleted zone Sedimentation and algae overgrowth reduce sunlight, kill beneficial sea grasses, use up oxygen, and degrade habitat.

Healthy zone Clear, oxygen-rich waters promote growth of plankton and sea grasses, Fig. 21-10, p. 505

OCEAN POLLUTION

 Harmful algal blooms (HAB) are caused by explosive growth of harmful algae from sewage and agricultural runoff.

Figure 21-11

Oxygen Depletion in the Northern Gulf of Mexico

 A large zone of oxygen depleted water forms for half of the year in the Gulf of Mexico as a result of HAB.

Figure 21-A

Case Study: The Chesapeake Bay – An Estuary in Trouble

 Pollutants from six states contaminate the shallow estuary, but cooperative efforts have reduced some of the pollution inputs.

Figure 21-12

OCEAN OIL POLLUTION

 Most ocean oil pollution comes from human activities on land.

 Studies have shown it takes about 3 years for many forms of marine life to recover from large amounts of

crude oil

(oil directly from ground).

 Recovery from exposure to

refined oil

(fuel oil, gasoline, etc…) can take 10-20 years for marine life to recover.

OCEAN OIL POLLUTION

 Tanker accidents and blowouts at offshore drilling rigs can be extremely devastating to marine life (especially diving birds, left).

Figure 21-13

Solutions Coastal Water Pollution Prevention Reduce input of toxic pollutants Cleanup Improve oil-spill cleanup capabilities Separate sewage and storm lines Ban dumping of wastes and sewage by maritime and cruise ships in coastal waters Ban ocean dumping of sludge and hazardous dredged material Protect sensitive areas from development, oil drilling, and oil shipping Sprinkle nanoparticles over an oil or sewage spill to dissolve the oil or sewage without creating harmful by-products (still under development) Require at least secondary treatment of coastal sewage Regulate coastal development Recycle used oil Use wetlands, solar-aquatic, or other methods to treat sewage Require double hulls for oil tankers Fig. 21-14, p. 509

PREVENTING AND REDUCING SURFACE WATER POLLUTION

 The key to reducing nonpoint pollution – most of it from agriculture – is to prevent it from reaching bodies of water.

 Farmers can reduce runoff by planting buffers and locating feedlots away from steeply sloped land, flood zones, and surface water.

PREVENTING AND REDUCING SURFACE WATER POLLUTION

 Most developed countries use laws to set water pollution standards, but such laws rarely exist in developing countries.

 The U.S. Clean Water Act sets standards fro allowed levels of key water pollutants and requires polluters to get permits.

 EPA is experimenting with a

discharge trading policy

similar to that for air pollution control.

Reducing Water Pollution through Sewage Treatment

 Septic tanks and various levels of sewage treatment can reduce point-source water pollution.

Figure 21-15

Reducing Water Pollution through Sewage Treatment

 Raw sewage reaching a municipal sewage treatment plant typically undergoes: 

Primary sewage treatment

: a physical process that uses screens and a grit tank to remove large floating objects and allows settling.



Secondary sewage treatment

: a biological process in which aerobic bacteria remove as much as 90% of dissolved and biodegradable, oxygen demanding organic wastes.

Reducing Water Pollution through Sewage Treatment

 Primary and Secondary sewage treatment.

Figure 21-16

Reducing Water Pollution through Sewage Treatment

 Advanced or tertiary sewage treatment:  Uses series of chemical and physical processes to remove specific pollutants left (especially nitrates and phosphates).

 Water is chlorinated to remove coloration and to kill disease-carrying bacteria and some viruses (disinfect).

Reducing Water Pollution through Sewage Treatment

 Sewage sludge can be used as a soil conditioner but this can cause health problems if it contains infectious bacteria and toxic chemicals.

 Preventing toxic chemicals from reaching sewage treatment plants would eliminate such chemicals from the sludge and water discharged from such plants.

Dust Particles Particles of dried sludge carry viruses and harmful bacteria that can be inhaled, infect cuts or enter homes.

Groundwater Contamination Harmful chemicals and pathogens may leach into groundwater and shallow wells.

Odors Odors may cause illness or indicate presence of harmful gases.

BUFFER Sludge ZONE Surface Runoff Harmful chemicals and pathogens may pollute nearby streams,lakes, ponds, and wetlands.

Exposure Children may walk or play in fertilized fields.

Livestock Poisoning Cows may die after grazing on sludge-treated fields.

Fig. 21-17, p. 513

Reducing Water Pollution through Sewage Treatment

 Natural and artificial wetlands and other ecological systems can be used to treat sewage.

 California created a 65 hectare wetland near Humboldt Bay that acts as a natural wastewater treatment plant for the town of 16,000 people.

• The project cost less than half of the estimated price of a conventional treatment plant.

Using Laws to Protect Drinking Water

 While most developed countries have drinking water quality standards and laws, most developing countries do not.

 The U.S Safe Drinking Water Act requires the EPA to establish national drinking water standards (

maximum contaminant levels

) for any pollutant that may have adverse effects on human health.

Solutions Water Pollution • Prevent groundwater contamination • Reduce nonpoint runoff • Reuse treated wastewater for irrigation • Find substitutes for toxic pollutants • Work with nature to treat sewage • Practice four R's of resource use (refuse, reduce, recycle, reuse) • Reduce air pollution • Reduce poverty • Reduce birth rates Fig. 21-18, p. 517

What Can You Do?

Water Pollution • Fertilize garden and yard plants with manure or compost instead of commercial inorganic fertilizer.

• Minimize your use of pesticides.

• Do not apply fertilizer or pesticides near a body of water.

• Grow or buy organic foods.

• Do not drink bottled water unless tests show that your tap water is contaminated. Merely refill and reuse plastic bottles with tap water.

• Compost your food wastes.

• Do not use water fresheners in toilets.

• Do not flush unwanted medicines down the toilet.

• Do not pour pesticides, paints, solvents, oil, antifreeze, or other products containing harmful chemicals down the drain or onto the ground.

Fig. 21-19, p. 517