Download Chapter 17 - Miss

Richard T. Wright
Environmental
Science
Tenth Edition
Chapter 17
Water Pollution and Its Prevention
Copyright © 2008 Pearson Prentice Hall, Inc.
Warm-Up
• Read the introduction to chapter 17 and be able
to answer the following questions
– Where does the Mississippi River end?
– What was a consequence of filling in the wetlands
that drained the Mississippi?
– What is a hypoxic area and why is it bad?
– What caused the hypoxic area?
– What was a solution to lessen the nitrogen problem as
a result of the Harmful Algal Bloom and Hypoxia
Research and Control Act?
– Look up the definition of eutrophic in your glossary.
Dead Zone in the Gulf of Mexico
Pollution – as defined by the EPA
• Pollution: “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 health
effects.”
Pollution Essentials
• Pollution is not usually the result of deliberate actions
– Usually a by-product of essential activities
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Producing crops
Creating comfortable homes
Providing energy
Transportation
Manufacturing
• Exacerbated by growing population and use of nonbiodegradable products
– Resist attack and breakdown by detritus feeders and
decomposers which cause them to accumulate
• Ex – aluminum, plastic, synthetic organic chemicals.
Categories of Pollution
Point vs. Nonpoint Sources
Point Sources
• Relatively easy to identify
and therefore are easier to
monitor and regulate
– Discharge of substances from
factories, sewage systems,
power plants, underground
coal mines, oil wells.
Nonpoint Sources
• Poorly defined and
scattered over broad areas
– Occurs as rainfall and
snowmelt move over and
through the ground
– Picks up pollutants such as
agricultural runoff (farm
animals and croplands), storm
water drainage, atmospheric
deposition
Water Pollution: Point and Nonpoint Sources
Water Quality Standards
• The mere presence of a substance in water
does not necessarily pose a problem
– The CONCENTRATION of the pollutant is the
primary concern
Criteria Pollutants
• To provide standards for assessing water
pollution, the EPA has established the
National Recommended Water Quality Criteria
– EPA listed 167 chemicals and substances as
criteria pollutants and the acceptable
concentration in surface waters
Clean Water Act
• 1972 – Legislation establishing a federal program
to protect and restore the physical, chemical, and
biological integrity of the nations waters
• Requires permits for any discharge of pollution,
strengthens water quality standards, and
encourages the use of best achievable pollution
control technology
• Provides funding for sewage treatment plants
– Amended in 1987
Drinking Water
• Standards are more strict
• EPA established Drinking Water Standards and
Health Advisories
– Cover 94 contaminants and gives maximum
contaminant levels for each
Safe Drinking Water Act
• 1974 – Authorizes EPA to regulate the quality
and safety of public drinking-water supplies,
maintain drinking –water standards for
contaminants, and set requirements for the
chemical and physical treatment of drinking
water
– Amended in 1996
Warm Up
• “Improving Old MacDonald’s Farm” article
Development of Wastewater
Collection and Treatment Systems
• Up through the 1970s, wastewater facilities
would dump untreated sewage directly into
waterways
• Clean Water Act 1972
Video Clip
• Sewage to Tap Water
Pollutants in Raw Wastewater
• Sources
– All tub, sink, and toilet drains from homes and
buildings
• Raw wastewater – 99.9% water, 0.01% waste
Types of Pollutants
• Debris and grit
– Plastic bags, sand, gravel, other objects flushed
• Particulate organic material
– Fecal matter, food wastes, toilet paper
• Colloidal and dissolved organic material
– Very fine particles of organic matter, bacteria, urine,
soaps, detergents, other cleaning agents
• Dissolved inorganic material
– Nitrogen, phosphorus, other nutrients from excretory
wastes and detergents
Removing Pollutants from Wastewater
• Preliminary Treatment
– Removal of debris and grit
– Two steps
• Screening out debris
– With use of bar screen – row of mounted bars
• Settling out particulates
– Grit chamber – water is slowed down to permit grit to settle
Removing Pollutants from Wastewater
• Primary Treatment
– Removal of particulate organic material
• Flows slowly through large tanks called primary
clarifiers
– Organic material (about 30-50%) settles to the
bottom
– Fatty or oily material floats to the top where it is
skimmed off
» Both the material that settles at the bottom and
skimmed off of the top is combined and
referred to as raw sludge
Removing Pollutants From Wastewater
• Secondary Treatment
– Removal of colloidal and dissolved organic
material
• Biological treatment – uses natural decomposers and
detritus feeders
• Feeds on colloids and dissolved o.m to break it down to
carbon dioxide, minerals, and water through cell
respiration
• Oxygen needs to be added so respiration will continue
Secondary Treatment
• Adding oxygen to water
– Trickling filter
– Activated sludge system – what you saw on field
trip
• Air bubbling system and activated sludge is added to
water
– As organisms feed they form clumps and settle
when water is stilled
– Go into second clarifier so organic sludge can settle
out
Trickling Filters for Secondary Treatment
Trickling Filters for Secondary Treatment
Biological Nutrient Removal (BNR)
• To ease eutrophication
– Nitrogen removal
• Denitrification – bacteria convert ammonia and nitrate
back to atmospheric nitrogen
– Phosphorus removal
• Bacteria take up phosphate from solution and store it in
their bodies
Final Cleansing and Disinfection
• Chlorinate water
• More common – use of UV Light
• After these treatments, it is released back into
a surface water source
Removing Pollutants from Sewage: Match
Technology with Function
Technology
Function
Bar Screen
Particulate organics
Grit Screen
Dissolved organics
Primary Treatment
Dissolved inorganics
Secondary Treatment
Large or small debris
Warm-Up
Warm Up
• What are the steps of water purification in a
sewage treatment plant?
Treatment of Sludge
• Raw Sludge
– Gray, foul – smelling, syrupy liquid with a water
content of about 97%
• Pathogens are present in raw sludge because it includes
material directly from toilets
– Considered a biologically hazardous material, but if
properly treated can be used as an organic fertilizer
3 Common Methods to Treat Sludge
• Anaerobic digestion
• Composting
• Pasteurization
Anaerobic Digestion
• Process of allowing bacteria to feed on the
detritus in the absence of oxygen.
– Raw sewage is put into large, airtight sludge
digesters
• End products are CO2, CH4, H20
• Major bi-product is BIOGAS
• Mixture that is about 2/3 CH4, therefore it is flamable
and can be used for fuel
Composting
• Raw sludge is mixed with wood chips, or other
material, to reduce water content
• Mixture is then placed in a windrow
– Long narrow piles that allow air to circulate and
provides oxygen for bacteria to break down
organic matter
Pasteurization
• After raw sludge is de-watered, the resulting
sludge cake is put through ovens that operate
like clothes dryers
• Pasteurized sludge is heated sufficiently to kill
any pathogens
Applied Products
• Milwaukee has rich sludge from brewing
process
• Uses pasteurization to make fertilizer pellets
named Milogranite
Alternative Treatment Systems
• Many homes in rural and suburban areas may
be outside the reaches of the municipal
services
• Currently, 25% of Americans has an on-site
sewage system
• Most Common – Septic Tank and Leaching
Fields
Septic Tanks/Leaching Fields
• Wastewater flows into a tank where organic
material sinks to the bottom
– Acts as primary clarifier in a municipal plant
• Water containing colloidal and dissolved o.m, and
dissolved nutrients will flow onto a leaching field
and gradually percolates into the soil
• O.M that settles in the tank is digested by
bacteria
– Tanks need to be pumped out every so often
Reconstructed Wetland Systems
• Wetlands are capable of absorbing nutrients
– Wetland function jigsaw.
– You are all given a wetland function. You are to
read about the function and put together a poster
and notes-sheet to pass out to your classmates.
– You are to make up a 5 question quiz on your
function to administer at the end of your
presentation
Eutrophication
• Different kinds of aquatic plants
• The impacts of nutrient enrichment
• Combating eutrophication
Different Kinds of Aquatic Plants
• Benthic plants
– Benthos – Greek for deep
– Emergent vegetation
• Grows with the lower parts in water but the upper
parts emerging from the water
– Submerged aquatic vegetation (SAVs)
• Grows totally underwater
• Requires clear enough to allow sunlight
• Absorbs nutrients from bottom sediments
Different Kinds of Aquatic Plants
• Phytoplankton
– Live suspended in the water and are found
wherever sunlight and nutrients are available
• Green filamentous and single cell
• Blue-green single cell
• Diatoms single cell
The Impacts of Nutrient Enrichment
• Oligotrophic: nutrient-poor water
– Fed by watershed that holds its nutrients well
– Limit growth of phytoplankton
• Eutrophic: nutrient-rich water
– Rapid growth of phytoplankton, increases
turbidity
What kind of plants would dominate in
oligotrophic vs. eutrophic conditions?
Eutrophication in Shallow Lakes and Ponds
Oligotrophic
Eutrophic
• As nutrients are
added from
pollution, an
oligotrophic
condition rapidly
becomes eutrophic.
Eutrophic or Oligotrophic?
• High dissolved O2
• Deep light penetration
• High phytoplankton
Eutrophic or Oligotrophic?
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Turbid waters
High species diversity
Good recreational qualities
High detritus decomposition
Eutrophic or Oligotrophic?
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Low bacteria decomposition
Benthic plants
Warm water
High nutrient concentration
BOD
High sediments
Natural and Cultural Eutrophication
• Natural eutrophication
– aquatic succession
– occurs over several hundreds of years
• Cultural eutrophication
– driven by human activities
– occurs rapidly
Combating Eutrophication
• Attack the symptoms
– Chemical treatment
– Aeration
– Harvesting aquatic weeds
– Drawing water down
Combating Eutrophication
• Getting at root cause
– Controlling point sources
– Controlling nonpoint sources
Controlling Point Sources
• Ban phosphate detergents
• Sewage-treatment improvements
Controlling Nonpoint Sources
• Difficult to address runoff pollutants
– Urban
– Agricultural fields
– Deforested woodlands
– Overgrazed pastures
Controlling Nonpoint Sources
• Best Management Practices (BMP): Table
17-2
– Agriculture
– Construction
– Urban
Collecting Pond for Dairy-Barn Washings
Public Policy
• What was the legislative milestone in
protecting natural waters and water supplies
for each of the acts listed in Table 17-3?
Lesson Activity
• In some States, bio-solids are dried, bagged,
and sold commercially for garden use, similar
to cow manure or compost (Milorganite in
Milwaukee for example) How is milorganite
used?
http://www.milorganite.com/