Wastewater Treatment

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Chapter 4A
Wastewater Treatment:
Characteristics and Systems Characteristics and Systems
Learning Outcomes
At the end of this learning session
students should be able to;
1. Understand what causes water pollution 1. Understand what causes water pollution
2. Recognize the sources of wastewater
3. State the characteristics of wastewater
4. Appreciate the importance of w/w treatment
5. Apply systems used to treat the wastewater
What is water pollution?
• Water pollution is any chemical, physical
or biological change in the quality of water
that has a harmful effect on any living
thing that drinks or uses or lives (in) it. thing that drinks or uses or lives (in) it.
• When humans drink polluted water it often
has serious effects on their health. Water
pollution can also make water unsuited for
the desired use.
The Sources of Pollution
Water pollution occurs when a
body of water is adversely
affected due to the addition of affected due to the addition of
large amounts of materials to the
water. When it is unfit for its
intended use, water is considered
Domestic and Industrial Sewage, which
contains decomposable organic matter and
pathogenic agents.
Industrial and trade wastes, which contain
Sources of Water Pollution
Industrial and trade wastes, which contain
toxic agents ranging from metal salts to
complex synthetic organic chemicals.
Agricultural pollutants, which comprise
fertilizers and pesticides. Physical pollutants,
such as thermal pollution and radioactive
A heavily polluted stream in Guiyu, China. Along side domestic
rubbish the water is badly polluted with toxic waste from the e-
waste recycling yards in the town.
Example of water pollution
Citarum River (Central Java)
– Most polluted in the world
Polluted River in India
Kyoto River
Clean river and
drainage channels in
Kyoto (Aug 2008)
A River in Seoul, Korea
What is Wastewater?
• Wastewater is any water that
has been adversely affected
in quality by anthropogenic
• It comprises liquid waste
discharged by domestic
residences, commercial
properties, industry, and/or properties, industry, and/or
agriculture and can
encompass a wide range of
potential contaminants and
• In the most common usage, it refers to the municipal
wastewater that contains a broad spectrum of contaminants
resulting from the mixing of wastewaters from different
Significance of Wastewater
• Suspended solids – can cause
sludge deposits and anaerobic
conditions in the environment
• Biodegradable organics – can
cause anaerobic conditions in
the environment
• Pathogens – transmit disease • Pathogens – transmit disease
• Nutrients – can cause
• Heavy metals – toxicity to biota
and humans
• Refractory organics – toxicity to
biota and humans
• Dissolved solids – interfere with
Characteristics of Wastewater
• Physical
– The physical characteristics of waste water
include its solid content--suspended organic
matter, floating matter and dissolved matter,
its temperature, color, odor/smell, density, its temperature, color, odor/smell, density,
conductivity, specific gravity, transmittance
and specific weight.
– Septic sewage is black (due to precipitation of
iron sulfide)
• Chemical
– Municipal wastewater also contains a variety of inorganic
substances from domestic and industrial sources, including a
number of potentially toxic elements such as arsenic,
cadmium, chromium, copper, lead, mercury, zinc, etc.
– Among the organic substances present in sewage are
Characteristics of Wastewater
– Among the organic substances present in sewage are
carbohydrates, lignin, fats, soaps, synthetic detergents,
proteins and their decomposition products, as well as various
natural and synthetic organic chemicals from the process
– Number of chemicals found in w/w is limitless
– Measure of w/w strength often use COD and BOD
• COD – Chemical Oxygen Demand
• BOD – Biological Oxygen Demand
Characteristics of Wastewater
• Biological
– Pathogenic bacteria will be present in
wastewater at much lower levels than the
coliform group of bacteria, which are much
easier to identify and enumerate (as total easier to identify and enumerate (as total
coliforms/100ml). Escherichia coli are the
most widely adopted indicator of faecal
pollution and they can also be isolated and
identified fairly simply, with their numbers
usually being given in the form of faecal
coliforms (FC)/100 ml of wastewater.
Characteristics of Domestic
Municipal Wastewater
Treatment Systems
• Pretreatment – removes materials
that can cause operational
problems, equalization optional
• Primary treatment – remove ~60% • Primary treatment – remove ~60%
of solids and ~35% of BOD
• Secondary treatment – remove
~85% of BOD and solids
• Advanced treatment – varies: 95+
% of BOD and solids, N, P
Treatment Plant
Pretreatment of Industrial
• Industrial wastewaters must be pretreated
prior to being discharged to municipal
sewer system
• Approach is to remove materials that will
not be treated by municipal system
• Local authority must monitor and regulate
industrial discharges
• Pretreatment requirements set by the law
• Coarse screens
– Function to remove
large objects such
as pieces of wood,
plastic bottles, plastic bottles,
rags, textile etc
– Size of opening up
to 75-100 mm
– Cleaned either
manually or
• Fine Screens
– Function is to
remove fine
debris, plastics that
are not hang on are not hang on
coarse rack screen.
– Opening size small
up to only 13 mm
– Most fine screens
are mechanically
Grit Chambers
• Purpose: remove inert
dense material, such as
sand, broken glass, silt
and pebbles. These
materials is called “grit”
• Grit will cause abrasion • Grit will cause abrasion
of pumps and other
mechanical devices if
not removed
• Grit chambers can be of
rectangular or circular
shape (vortex)
Note : All design and calculation are the
same as water supply grit chamber
Vortex Grit Chamber
• A Vortex Grit Chamber usually
follows screening equipment. The
screened influent enters tangentially
and flows around the upper chamber
• Adjustable, rotating paddles augment
the spiraling flow to create a
mechanically induced vortex which mechanically induced vortex which
settles the grit, transports it to the
center opening of the fixed floor plate
for collection in the lower chamber,
and lifts and returns the lighter
organic particles to the main flow.
• The grit solids are removed from the
lower chamber by an air lift or
recessed impeller pump for further
washing and dewatering.
End of Chapter 4A

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