Chapter 21 Wastewater Treatment and Disposal

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Chapter 21Wastewater Treatment and Disposal

• Objectives
• Identify kinds and sources of wastewater
• Describe hazards in wastewater
• Describe ways of treating wastewater
• Describe the products of wastewater treatment,
  including the production and use of biosolids
• Explain important biological, chemical, and
  biogeochemical processes in wastewater treatment

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Terms
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Wastewater and Its Source

• Wastewater is used water that contains dissolved
  or suspended matter
• Kinds of wastewater
• Spent water is water that has been used and can
  no longer serve the purpose for which it was used
  because of contamination
• Domestic wastewater is the wastewater produced by
  humans in their daily lives (gray water is the
  water produced by bathing, cooking, and washing
  dishes and clothes, gray water may be high in
  detergent pollutants)
• Sewage is the wastewater produced by residential
  and commercial sources, it is the water that is
  discharged into sanitary sewers or treated in
  septic systems (sanitary sewers are systems of
  pipes or conduits that carry off sewage)

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Sources of Wastewater

• Homes and business
• Manufacturing wastewater
• Food plants
• Paper mills
• Steel mills
• Electric power plants
• Farm wastewater
• Stormwater (storm sewer is a system of pipes that
  carries runoff from street, buildings, and other
  surface areas)

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Hazards in Wastewater

• Hazardous wastewater is wastewater that is
  potentially dangerous to human health or the
  environment

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1. Infectious Agents

• A waste water infectious agent is any organism
  that can cause disease in humans and other living
  organisms
• The most common infectious agent are
• Bacteria (fecal coliform bacteria are the
  bacteria found in the intestines (colon) of
  mammals)
• Viruses (hepatitis, meningitis, diarrhea, and
  respiratory disease)
• Protozoa (amoebic dysentery, diarrhea, and
  ulcers)
• Worms (tapeworm, roundworms, and whipworms)

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Examples of protozoa often found in wastewater
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Life cycle of the roundworm (Ascaris
lumbricoides) a human parasite
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2. Toxic Waste Substances

• Toxic waste is any materials capable of causing
  injury to humans and other organisms
• The materials can enter the body by inhalation,
  swallowing, or being absorbed through the skin
• Pesticides, detergents, bleach, and heavy metal
  residues are commonly found in wastewater

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3. Organic Matter

• Most organic matter in domestic wastewater is
  easily biodegraded
• The main constituents are undigested food, raw
  food fragments, uneaten cooked food, and paper
• Organic materials provide a good place for the
  growth of infectious agents

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4. Temperature

• The water is warmed and becomes thermal effluent
• Thermal wastewater has several important uses,
  such as growing of fish

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Objectives of Wastewater Treatment

• Remove or destroy pathogenic organisms and
  parasites
• Reduce or remove nutrients to lower pollution of
  groundwater or surface after treatment
• Remove or reduce toxic and organic materials in
  wastewater

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Treatment Systems

• Individual home system
• Commercial system
• Municipal wastewater treatment system
• Urban area
• Big city

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Individual home systems

• A septic tank is a concrete or steel container
  buried in the ground
• The tank serves as a digester where bacteria act
  on the solid materials
• The solids settle to the bottom of the tank
• The liquid passes from the tank into a system of
  underground pipes that from a leaching field
• The pipes have small holes that allow the liquid
  to diffuse into the soil
• Leaching fields should be at least 50 feet from a
  stream and twice that distance from a water well
• Tanks and leaching fields should not be located
  closer than 5 feet to a property boundary
• Septic tanks are cleaned by pumping out the
  sludge, this is done when the scum and sludge at
  the bottom of the tank are closer than 30 cm to
  the top
• Most tanks need to pumped every 2 or 3 years

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General layout of a septic tank system
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Side view inside a septic tank
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Checking a septic tank for pumping involves using
a stick with a flat board on the end to assess
the thickness of the sludge and scum
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Commercial Systems

• Factories and farms often have system to treat
  wastewater from manufacturing and animal
  production
• A lagoon is a type of pond where sunlight,
  bacterial action, and oxygen purify wastewater
  (stabilization pond)
• Aeration is sometimes used to speed bacterial
  action

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Lagoon at a dairy facility
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Tank used to hold and treat wastes from a modern
hog farm production facility
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Municipal Wastewater Treatment Systems

• Municipal wastewater treatment systems are
  designed to serve the needs of towns and cities
• The steps in treatment
• Collection
• Preliminary treatment
• Primary treatment
• Secondary treatment
• Advanced treatment
• Disposal of residue

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General design of a municipal wastewater
treatment system
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This shows primary settling (top left), sludge
thickening (flocculation) (top right), biological
aeration (bottom left), and secondary settling
(bottom right)
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Sludge and Its Use

• Sludge is the semi-solid material formed during
  wastewater treatment
• A sludge digester is a large tank in which the
  settled wastes from wastewater are converted to
  solids and gases by microorganism (methane)
• Biosolids are the dried remains of wastewater
  treatment, they have nutrients needed by plants
  and are used as organic fertilizer

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Liquid sludge from a hog farm is spread on crop
land to increase fertility of the soil
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Biosolids piled at a sewage treatment plant
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Effluent and Its Use

• Effluent is the water that flows from a treatment
  facility or factory into a stream, lake, or ocean
• It is wastewater that has usually been treated to
  prepare it for release

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Process in Wastewater Treatment

• Biological processes
• Chemical processes
• Biogeochemical processes

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Biological Processes

• Bacteria
• Anaerobic bacteria (very slow digesters)
• Aerobic bacteria (septic tank has very little or
  no free oxygen, a major product is methane)
• Clostridium sp. act sugars, amino acids, and
  fatty acids to form organic acids, such as
  acetate, CO2, and H2
• Nitrosomonas and Nitrobacter bacteria convert
  ammonia to nitrate, which is helpful in removing
  excrement from water
• Protozoa help decompose wastes and feed on
  bacteria
• Rotifers feed on bacteria

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Chemical Processes

• Chlorine and ozone are sometimes used to oxidize
  small amounts of organic materials
• Chemical can also be used to help remove toxic
  metals from wastewater
• Chemicals, if used improperly, can kill the
  bacteria that are useful in biodegradation

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Biogeochemical Processes

• Biogeochemical processes are the processes in
  wastewater treatment that transfer nutrients from
  living organisms to physical forms and back to
  living organisms
• Three important biogeochemical processes in
  wastewater treatment are the nitrogen,
  phosphorus, and sulfur cycle

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Nitrogen Cycle

• Ammonification-Nitrogen is protein, such as in
  animal cells, tissues, feces, urine, and other
  materials is converted into ammonium form (NH3 or
  NH4), these forms are poisonous and can kill the
  fish in water if the concentration gets high
• Bacterial nitrification-Bacteria convert the
  ammonium forms to nitrite (N02)
• Oxidation-Nitrite is converted by bacterial
  action into nitrate form (N03)
• Assimilation-The nitrate form is used by plants
  in growing, some may denitrify and enter the
  atmosphere
• Plant consumption by animals-Plants that used
  nitrate to grow are eaten by animals, the animals
  produce feces and urine and later die, leaving
  protein to again go through the nitrogen cycle

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Phosphorus Cycle

• Phosphorus levels are usually 10 to 20 mg/l in
  wastewater
• Excessive phosphorus will at first cause heavy
  algae bloom when it dies off, oxygen depletion
  is a problem
• Eutrophication, a deficiency in oxygen, occurs
  when the water has a nutrient level that is too
  high
• Organic phosphorus compounds include phosphates,
  nucleic acids, and phytin
• Various chemical compounds, such as ferric
  chloride, react with phosphorus to remove it from
  the water

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The phosphorus cycle showing terrestrial and
aquatic processes
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Sulfur Cycle

• Wastewater sources of sulfur are feces and traces
  in natural water supplies
• Bacteria decompose feces, urine, and animal
  proteins into sulfides and sulfites
• Other bacteria convert the sulfites into
  sulfates, which are used by plants
• Some of the sulfur is released from the water in
  sulfate form creating the rotten-egg odor
• Sulfur levels in stormwater are due to acid rain
  and air pollution

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Tests

• What are the major sources of wastewater?
• What hazards may be in wastewater?
• What are the objectives of wastewater treatment?
• What is a septic tank? How does it work?
• What is lagoon? How is water treated in a lagoon?
• What are the steps in a municipal wastewater
  treatment facility?
• What are the three major biogeochemical cycles in
  wastewater?