Course TEN-702
Industrial waste management
unit-2
• Lecture -8 & 9
Physical unit operations
Treatment methods in which the application of physical forces
predominates are known as physical unit operations. Because
most of these methods evolved directly from man’s first
observations of nature, they were the first to be used for
wastewater treatment.
Screening,
mixing,
flocculation,
sedimentation,
flotation,
filtration, and
gas transfer are typical unit operations.
Screening
Removal of large floating, suspended and settleable solids
Bar racks and screens of various description
Grit Removal
Removal of inorganic suspended solids
Grit chamber
Chemical Unit Processes
Treatment methods in which the removal or conversion of contaminants
is brought about by the addition of chemicals or by other chemical
reactions are known as chemical unit processes.
 Precipitation,
 adsorption, and
 disinfection are the most common examples used in
wastewater treatment.
In chemical precipitation, treatment is accomplished by
producing a chemical precipitate that will settle. In most cases, the
settled precipitate will contain both the constituents that may have
reacted with the added chemicals and the constituents that were
swept out of the wastewater as the precipitate settled.
Adsorption involves the removal of specific compounds from
the wastewater on solid surfaces using the forces of attraction
between bodies.
Biological Processes
Treatment methods in which the removal of
contaminants is brought about by biological
activity are known as biological unit processes.
Biological treatment is used primarily to remove
the biodegradable organic substances (colloidal
or dissolved) from wastewater. Basically, these
substances are converted into gases that can
escape to the atmosphere and into biological
cell tissue that can be removed by settling.
Biological treatment is also used to remove
nutrients (nitrogen & phosphorus) from
wastewater. With proper environmental control,
wastewater can be treated biologically in most
cases.
Pretreatment
• Goal is to prepare raw influent
wastewater for treatment
• Pretreatment can involve:
– Removal of large solids and rags
– Removal of grit
– Equalization of high flow and
loads (important)
– Odor control
– Chemical Addition
Pretreatment
• Removal of large solids and rags
– Why would this be important?
– Can plug downstream equipment
– Decreases cleaning effort
Pretreatment Program Implementation
• Types of pretreatment include:
– pH neutralization
– Temp regulations
– Solids separation
– Toxic metal removal
– Oil and grease
Pretreatment - Screens
• Screens are used
to remove solids
and rags
• Simplest is
manual, coarse
bar screen
• Used at smaller
plants
• Often outdoors
• Screen opening
of 1” to 2”
Pretreatment - Screens
• Mechanical fine screens are used at larger
plants
• Need to install inside building
• Common screen opening size is ¼” (6 mm)
–
Membrane biological reactors (MBRs) can
require 0.06” openings (1.5 mm)
• Includes motors, controls
• Many types
• Typically includes a washer and compactor
Pretreatment - Screens
• Basket type
mechanical fine
screen, 4.6 MGD
• Compactor is
integral with
screen
• Note manual
coarse bar screen
in background
Pretreatment - Screens
• Large
mechanical fine
screen, 9 MGD
• Influent flow
channel is on
floor below
• Note “plug” of
screenings
going into
green basket
Pretreatment - Screens
• Other screens
– Static screen
on left
– Rotary drum
screen on right
• Compactor in
between
Assignment-1
• Discuss the philosophy behind
industrial wastewater treatment with
reference to wastewater quality
characteristics, standards, unit
processes and process train.
Assignment-2
• Write a short note to clearly bring out
the difference between disposal, reuse
and recycling of industrial wastewater.
In next lecture we will discuss grit removal, equalization, odour control
Thanks!