Water Pollution-Oxygen Consuming
Wastes
General types of water pollutants
? Disease-causing agents (Pathogens)
? Oxygen-consuming agents
? Plant nutrients
? Toxic substances
– Heavy metals
– Pesticides
? Dissolved solids
? Acids
? Suspended solids and sediments
? Oil
? Radioactive substances (Radionuclides)
? Heat (thermal pollution)
Oxygen and aquatic life
? Animals and plants living in an aquatic habitat
depend on oxygen dissolved in the water for their
survival.
? The availability of O2 in water sets the boundary
between aerobic and anaerobic life,This has
implications on:
– Water quality
– Health of ecosystem
? Oxygen in water comes from dissolution of
atmospheric O2.
Dissolved oxygen
The amount of dissolved
oxygen (DO) depends on
the temperature and the
altitude of the water.
Relates to atmospheric
pressure
Biological oxygen demand
? Energy is acquired by oxidation of organic material,In
this process,oxygen is required.
CH2O + O2 = CO2 + H2O
12 mgC 32mg
1mgC 2.7mg O2
? At 20oC,DO=9 mg/l,therefore,only ~3.4mg of CH2O
can be oxidized by the O2 in a liter of water.
? When the concentration of organic material is high,
water can be easily depleted of DO.
? Biological oxygen demand (BOD) is the amount of O2
(in milligram) required by microorganisms to carry out
the oxidation of organic carbon in one liter of water.
– BOD5,the oxygen consumed by microorganisms in five days.
BOD,example problem
What is the BOD of water in which 10 mg of sugar
is dissolved in a liter? How does this compare with
the O2 solubility at 20oC?
Oxygen-consuming wastes
? Organic waste materials released into the water can
rapidly deplete dissolved oxygen.
? When water is overloaded with organic materials,
oxygen-consuming (aerobic) bacteria proliferate,
? As a result,DO is consumed more rapidly than it can be
replaced from the atmosphere.
? When DO<5ppm,fish start to die.
? If DO drops further,invertebrates and aerobic bacteria
will be unable to survive.
? In the absence of DO,anaerobic bacteria take over to
decompose organic material ? The water begins to
smell unpleasant.
DO variation with the distance from organic waste charge
point
Sources for organic wastes
? Human and animal sewage
? Industrial waste from paper mills,tanneries,
and food-processing plants
Typical BODs for wastes from various processes
Type of discharge BOD
(mg O2/liter waste water)
Domestic sewage 165
All manufacturing 200
Chemicals and allied
products
314
Paper 372
Food 747
Metals 13
Decomposition products of organic compounds
Element in org,
compound End products of decomposition
Aerobic conditions Anaerobic conditions
Carbon CO2 CH4
Nitrogen NO3- NH3 and amines
Sulfur SO42- H2S
phosphorus PO43- PH3 and other P
cmpds
Three definitions of oxidation and reduction
oxidation Reduction
In terms of oxygen Gain of oxygen Loss of oxygen
In terms of hydrogen Loss of hydrogen Gain of hydrogen
In terms of electrons Loss of electron Gain of electron
Natural sequence of redox reactions in aqueous
environment
Redox couples in natural environments
? O2/H2O
? NO3-/N2
? MnO2/Mn2+
? Fe(OH)3/Fe2+
? SO42-/HS-
? CO2/CH4
Decreasing
redox potential
Study questions
1,What determines the maximum amount of oxygen
that can be dissolved in water?
2,What consumes oxygen in water?
3,What happens after oxygen is exhausted in a water
body?
4,List the major redox pairs in the natural
environments in the order of decreasing redox
potential.
Wastes
General types of water pollutants
? Disease-causing agents (Pathogens)
? Oxygen-consuming agents
? Plant nutrients
? Toxic substances
– Heavy metals
– Pesticides
? Dissolved solids
? Acids
? Suspended solids and sediments
? Oil
? Radioactive substances (Radionuclides)
? Heat (thermal pollution)
Oxygen and aquatic life
? Animals and plants living in an aquatic habitat
depend on oxygen dissolved in the water for their
survival.
? The availability of O2 in water sets the boundary
between aerobic and anaerobic life,This has
implications on:
– Water quality
– Health of ecosystem
? Oxygen in water comes from dissolution of
atmospheric O2.
Dissolved oxygen
The amount of dissolved
oxygen (DO) depends on
the temperature and the
altitude of the water.
Relates to atmospheric
pressure
Biological oxygen demand
? Energy is acquired by oxidation of organic material,In
this process,oxygen is required.
CH2O + O2 = CO2 + H2O
12 mgC 32mg
1mgC 2.7mg O2
? At 20oC,DO=9 mg/l,therefore,only ~3.4mg of CH2O
can be oxidized by the O2 in a liter of water.
? When the concentration of organic material is high,
water can be easily depleted of DO.
? Biological oxygen demand (BOD) is the amount of O2
(in milligram) required by microorganisms to carry out
the oxidation of organic carbon in one liter of water.
– BOD5,the oxygen consumed by microorganisms in five days.
BOD,example problem
What is the BOD of water in which 10 mg of sugar
is dissolved in a liter? How does this compare with
the O2 solubility at 20oC?
Oxygen-consuming wastes
? Organic waste materials released into the water can
rapidly deplete dissolved oxygen.
? When water is overloaded with organic materials,
oxygen-consuming (aerobic) bacteria proliferate,
? As a result,DO is consumed more rapidly than it can be
replaced from the atmosphere.
? When DO<5ppm,fish start to die.
? If DO drops further,invertebrates and aerobic bacteria
will be unable to survive.
? In the absence of DO,anaerobic bacteria take over to
decompose organic material ? The water begins to
smell unpleasant.
DO variation with the distance from organic waste charge
point
Sources for organic wastes
? Human and animal sewage
? Industrial waste from paper mills,tanneries,
and food-processing plants
Typical BODs for wastes from various processes
Type of discharge BOD
(mg O2/liter waste water)
Domestic sewage 165
All manufacturing 200
Chemicals and allied
products
314
Paper 372
Food 747
Metals 13
Decomposition products of organic compounds
Element in org,
compound End products of decomposition
Aerobic conditions Anaerobic conditions
Carbon CO2 CH4
Nitrogen NO3- NH3 and amines
Sulfur SO42- H2S
phosphorus PO43- PH3 and other P
cmpds
Three definitions of oxidation and reduction
oxidation Reduction
In terms of oxygen Gain of oxygen Loss of oxygen
In terms of hydrogen Loss of hydrogen Gain of hydrogen
In terms of electrons Loss of electron Gain of electron
Natural sequence of redox reactions in aqueous
environment
Redox couples in natural environments
? O2/H2O
? NO3-/N2
? MnO2/Mn2+
? Fe(OH)3/Fe2+
? SO42-/HS-
? CO2/CH4
Decreasing
redox potential
Study questions
1,What determines the maximum amount of oxygen
that can be dissolved in water?
2,What consumes oxygen in water?
3,What happens after oxygen is exhausted in a water
body?
4,List the major redox pairs in the natural
environments in the order of decreasing redox
potential.
