Water Pollution

1

99-00 S.6 Chemistry Project
Chemistry and Society
water pollution and solid waste
2
Muscle Mak (19) Joe Hor (8)
3
Water Pollution

• Introduction
• Cause of water pollution
• Effects of water pollution on the environment
• Water quality

4
Nowadays, our surrounding waters have been
assaulted with a heavy burden of pollutants.The
most obvious damage has been to coastal zones,
where fouled waters and littered beaches have
resulted in a reduction of resorts suitable for
swimming.The longer we use our surrounding
waters as a giant garbage dump the more difficult
and cost the cleanup will be.
Introduction
5
Cause of water pollution

• Livestock waste
  - from pigs and
  poultry
• Oil spillage
  - from ships
• Residues of pesticides
  - from farms
• Detergents in sewage
  - from commercial and
  domestic wastewater
• Industrial effluents
  - from dyeing and
  electroplating factories

6
Effects of water pollution
on the environment

• Livestock waste
• When an excessive amount of organic matter is
  discharge into water, the existing aquatic
  micro-organisms will grow and multiply rapidly.
• The oxygen dissolved in water is rapidly
  depleted. Because of the lack of oxygen,
  anaerobic micro-organisms begin to break down
  partially the organic matter, releasing
  foul-smelling and toxic gases like CH4, NH3 and
  H2S.
• As a result, the aquatic organisms will die.

7

• Oil Spillage
• The effects of oil spillage may include the
  following
• Oil clogs the feathers of sea birds and prevent
  them from flying or swimming, oil interferes with
  the insulation provided by the feathers, so the
  birds may die of cold or pneumonia.
• As oil is immiscible with water and floats on
  water, it blocks the oxygen supply to the sea
  water.
• As oil is toxic, it kills marine life.
• Residues of pesticides
• Pesticides cause immediate toxic effects on
  aquatic life and accumulate along the food chain
  until a toxic level is reached.

8

• Detergents in sewage
• Detergents may speed up the eutrophication,
  because
• phosphates in some detergents are nutrients
  to algae.
• Detergents may cause foaming in rivers and lakes,
  because some synthetic detergents with branched
  hydrophobic chains cannot be biodegraded within a
  short time.
• Industrial effluents
• The toxic materials present in industrial
  effluents vary with the industry involved.
• They may contain toxic metal ions of Cd, Cr, Cu,
  Hg, Ni, Pb and Zn cyanides, polychlorinated
  hydrocarbons, organic solvents, acids and bases.

9
Water Quality

• 1. Dissolved Oxygen (DO)
• Dissolved Oxygen (DO) is an indicator of the
  oxygen content in water, It is measured in
• a. mg of O2 per dm of water, or
• b. percentage saturation of dissolved oxygen
• The maximum concentration of dissolved oxygen in
  water at 16C is 10 mg dm . If a water sample
  contains 6mg dm of dissolved oxygen at 16 ,the
  saturation of DO is then
• 6/10 x 100 60
• The sample is said to be 60 saturated with
  oxygen.

10

• The amount of dissolved O2 in water is important
  for aquatic life. Fishes normally require 4-6 mg
  dm of DO for survival.
• Depletion of oxygen may be caused by biological
  degeneration of water matter.
• The larger the amount of organic matter in the
  waste water,the lower is it DO.

11
Quality standards for water of different uses
12

• 2. Biochemical Oxygen Demand (BOD)
• Biochemical oxygen demand (BOD) is an indicator
  of the water pollution. It is the amount of
  oxygen required to break down the organic matter
  present in a water sample.
• If water has a high BOD, it indicates that a lot
  of organic waste is present and a lot of oxygen
  is required to break down the organic matter in
  the waste.
• If water has a low BOD, it indicates the presence
  of a small amount of organic matter and there is
  little organic pollution.
• Natural clean water has a BOD is about 1 to 4 mg
  dm .

13

• If BOD is greater than the amount of oxygen
  replenished by air, then some fishes and aquatic
  life may die organic debris accumulates, and
  anaerobic micro-organisms begin to multiply,
  producing unpleasant odours.
• BOD is determined in the laboratory by incubating
  a sample of water for five days in the dark at 20
  C and measuring the amount of oxygen consumed.
  The BOD determined in this way is also known as
  five-day BOD, BOD5.
• BOD5 value is commonly used to indicate the
  relative oxygen requirements of treated effluents
  and polluted waters.

14
Major producers of chemical waste in Hong Kong
15
Oil Spillage
16
Polluted water
17
A dead bird in polluted water
18
Solid Waste

• Solid Waste in Hong Kong
• Disposal of Solid Waste
• A. Incineration
• B. Landfilling
• Pollution Problems associated with the Disposal
  of Plastics
• Solving the Plastic Pollution Problem
• A. Development of Degradable Plastics
• B. Recycling of Plastics

19
Solid Waste in Hong Kong

• In Hong Kong,an average of 25,000 tonnes of
  solid waste were disposed of daily due to human
  activities of domestic households, commercial and
  manufacturing business and construction site in
  the territory.
• This quality amounts to about 4kg of waste per
  head of population.
• Some of the waste are potentially recyclable,
  e.g. metals, plastic, paper and glass.

20
Disposal of solid waste

• A. Incineration
• About 1/4 to 1/5 of solid wastes in Hong Kong is
  disposed by incineration.
• Advantages of incineration
• reduces the volume of the waste by
  approximately 85
• kills the disease-causing organisms at high
  temperature
• makes no risk of groundwater pollution
• Disadvantages of incineration
• it may produce toxic air pollutants and
  increase
• the incidence of acid rain and photochemical
  smog

21

• B. Landfilling
• About 4/5 to 3/4 of the solid waste is
  disposed by landfilling. The solid wastes are
  compressed and covered with soil on landfill
  sites.
• Advantage of landfilling
• only very small amounts of harmful air pollutants
  are released.
• Disadvantage of landfilling
• the potential environmental problems associated
  with landfilling of waste result mainly from the
  generation of landfill gas and leachate.

22
Pollution problems associated with the disposal
of plastics

• The tremendous amount of plastic items used today
  creates waste disposal problems. Moreover, the
  use of plasticizers and CFCs in the manufacture
  of plastics produce ecological and environmental
  problems.
• Landfilling and incineration are two main ways to
  disposal of plastic wastes.
• Problems associated with the landfilling of
  plastics As plastic are chemically
  tailored for long life, they do not generally
  undergo decomposition in the landfill site. Thus
  the plastic waste can last for a long period in
  the environment. The plastic wastes in landfills
  may delay the reuse of landfills for other
  purpose.

23

• Problems associated with the incineration of
  plastics If plastics are burned away by
  incineration, in addition to CO2, toxic gases may
  be formed, e.g. burning PVC or other
  chlorine-containing polymer gives HCl. HCl may
  contribute to the formation of acid rain.
• Plastics wastes in sea endanger aquatic lives,
  e.g. plastics bags or fragments of plastic foam
  may be mistakenly eaten by fishes, since plastics
  are not digestible, the fragments of plastic will
  clog their digestive tracts, the small fishes
  will eventually die. Sea animals have been
  suffocated to death by plastic bags.
• Plasticizers from the degradation of plastics may
  pollute water as they are released from landfill
  as leachate, e.g. PCBs are once common
  plasticizers that are found to be very stable in
  the environment and pose health hazard. Other
  common plasticizers such as phthalates are also
  found in leachate, they are safer than PCBs but
  are still harmful to us.

24
Solving the Plastic Pollution Problem

• A. Development of Degradable Plastics
• Biopolymers - They are polymers made by living
  organisms, e.g. poly(hydroxybutyrate), PHB,
  is a natural polyester made by certain bacteria.
  Micro-organisms found in soil and natural water
  sources are able to break down the polymer. The
  degradation of PHB in the environment is usually
  completed within 9 months. However, PHB is 15
  times more expensive than poly(ethene).
• Photodegradable plastics - Light-sensitive
  functional groups such as carbonyl group (CO)
  can be incorporated into the polymer chains. The
  long polymer chains will be broken down under the
  action of sunlight into shorter fragments which
  can then be biodegraded by micro-organisms in
  soil.

25

• Synthetic biodegradable plastic - made by starch
  or
• cellulose incorporated into the polymer
  during production.As
• micro- organisms digest the starch or
  cellulose, the plastic is
• broken down into tiny pieces.The very small
  pieces left over
• have a large surface area which greatly
  speeds up their
• biodegradation.
• Degradable plastics have been used for marking
• six-pack beverage rings, trash bags and
  disposable diapers.
• B. Recycling of plastic
• Direct recycling - This apply only to
  thermoplastic.
• The plastic in the waste are separated,
  cleaned,
• pulverized, and remoulded into plastic
  items.

26
Coding system developed by the society of the
Plastic Industry for sorting out plastics
PETE - Polyethylene HDPE - High density
polyethylene V - Polyvinyl chloride (PVC) LDPE -
Low density polyethylene PP - Polypropylene PS -
Polystyrene OTHER- All other resins
27

• Disadvantages of direct recycling
• the regenerated plastics usually have properties
  due to repeated thermal and mechanical
  processing,and can only be used for articles
  which are not subjected to high stress. Recent
  development on recycled plastics focuses on
  converting the plastic products with short
  service lives, such as foam, wrap and containers,
  to products with longer service lives, such as
  construction materials and plastic pipes.
• It is not very economical to separate the
  plastic items from the other wastes at present.
  Moreover, plastic products are very difficult to
  be classified.
• Plastic products contain different dyes. It is
  very difficult to remove them from the recycled
  plastics , the recycled plastics are usually
  black in colour.

28

• Recycling of energy - This applies to most
  plastic.
• The plastic wastes are burned in the
  incinerators. The
• calorific values contained in plastics are
  quite high.
• Advantages of recycling of energy
• The energy obtained from burning plastic waste
  can be
• used for heating or generation of
  electricity.
• It is not necessary to separate the plastics.
• Less dumping area is required.
• Disadvantages of recycling of energy
• Burning plastic produces toxic gases,e.g. PVC
  will give HCI.
• Expensive scrubber systems have to be used to
  remove
• them.

29

• Recycling of chemicals by pyrolysis - This
  applies to all plastics
• Similar to cracking, the plastic wastes can be
  pyrolyzed (decomposed at high temperature
  in the absence of air) at 600-900 C to give
  useful small molecules similar to those obtained
  from the fractional distillation of crude oil.
  These small molecules are mainly hydrocarbons.
• The small molecules are separated by fractional
  distillation.
• Some of the small molecules (e.g.CH4 ) can be
  used directly as fuels while other larger
  molecules may be employed in plastics production
  or used for other purposes.

30

• Advantages of pyrolysis
• The products are useful raw materials for the
  manufacture of plastics-reduces the use of
  petroleum.
• It is not necessary to separate the plastics.
• Less dumping area is required/saves more land for
  other uses.
• Disadvantages of pyrolysis
• Burning plastics produces toxic gases, e.g.PVC
  will give HCI. Expensive scrubber systems have to
  be used to remove them . The capacity of handling
  plastic waste by a pyrolysis plant is also small
  compared to the total amount of plastic waste
  produced.At present, the running cost of disposal
  of plastic by pyrolysis is much more expensive
  than landfilling.

31
(No Transcript)
32
Solid Waste
33
Solid Waste
34
The End