4.16.24 21st Century Movements for Black Lives.pptx
Waster water treatment
1. Module- IV
Unit Operations for
Waste Water
Treatment
Bibhabasu Mohanty
Asst. Prof.
Dept. of civil Engineering
SALITER, Ahmedabad
2. Course Content
Physical unit operation-Screening,
flow equalization, mixing, flocculation,
sedimentation. Chemical unit
processes-Chemical precipitation.
Biological unit processes: Aerobic
attached growth and aerobic
suspended growth treatment
processes, anaerobic suspended
growth treatment process. Low Cost
Sanitation System: septic tanks, soak
3. INTRODUCTION
We will start with an overview of treatment
processes
1) Why do we treat water and wastewater?
The main objectives of the conventional
wastewater treatment processes are the
reduction in biochemical oxygen demand,
suspended solids and pathogenic organisms.
4. Also necessary to remove nutrients such as N
and P, toxic components, non-biologically
degradable compounds and dissolved solids.
Removal of these materials are necessary for the
simple reason that discharge to the environment
will result in “damage” of some sort.
5. 2) What are the materials in water and wastewater that
we must remove?
There are a wide range of these pollutants
(contaminants) ranging from municipal sewage
to highly specific industrial wastes. The usual
approach in discussing treatment schemes is to
categorize pollutants into general classes so that
a general class of treatment methods can be
applied.
6. Note that many pollutants fall into several
categories.
For example, some biodegradable organic matter
(one category) is in the form of suspended solids
(another category).
So removal of SS sometimes results in the
removal of organic matter.
7. 3) To what level do we need to remove contaminants?
The degree to which drinking water must be
treated depends on the raw water quality and
the desired quality of the finished water.
Similarly the degree of treatment of a
wastewater depends on the quality of the raw
waste and the required effluent quality.
8. BOD5 = 30 mg/L monthly average
Suspended Solids = 30 mg/L monthly average
pH (if there is industrial input) = 6 – 9
continuous
For drinking water treatment the requirements
are, of course, much more stringent with many
more categories and lower contaminant limits.
9. Turbidity (a measure of suspended solids): less
than 0.5 NTU in at least 95% of samples taken
each month.
Lead: 0.005 mg/L
Copper: 1.3 mg/L
Total Coliform: no coliform detection in more
than 5% of samples collected each month.
10. 4) How are these contaminants removed from
water and wastewater?
Contaminant removal is accomplished by a series of
unit processes or unit operations.
Unit operation is a physical ,chemical or biological
treatment process.
The system of integrated unit processes or unit
processes used to treat a water or wastewater is
called a treatment train.
11.
12.
13.
14. General overview of plant components
Raw Wastewater Influent
PRELIMINARY
Preliminary Residuals PRIMARY
A (i.e., grit, rags, etc.)
Clarifier
SECONDARY
Biological (e.g., attached-grwoth
B Primary Sludge Treatment
Usually to Landfill Suspended-Growth,
System Constructed Wetland, etc.)
Wastewater
Clarifier
Clarifier
Treatment
Residuals
DISINFECTION
C Secondary Sludge
Biosolids
Processing
and Disposal Clean Wastewater Effluent
Discharge to Receiving Waters
15. Figure Location of physical unit operations in a wastewater-treatment plant flow diagram
16. Physical Chemical Biological
Processes Processes Processes
Screening Precipitation Aerobic
Sedimentation Chlorination Anaerobic
Filtration Disinfection
Different unit operation process
18. 1. damage subsequent process equipment
Coarse screen
2. reduce overall treatment process
is to remove
3. contaminate waterways
materials
1. protect process equipment
Fine screen 2. eliminate materials that may
is used to inhibit the beneficial reuse of
biosolids
19. A. Bar Racks
Typical design information for mechanically cleaned bar racks
U.S. customary units SI units
Cleaning method Cleaning
method
Parameter Unit Manual Mechanical Unit Manual
Mechanical
Bar size
Width in 0.2 – 0.6 0.2 – 0.6 mm 5 -15 5 -15
Depth in 1.0 – 1.5 1.0 – 1.5 mm 25- 38 25 – 38
Clear spacing between In 1.0 – 2.0 0.6 – 3.0 mm 25 – 50 15 – 75
bars
Slope from vertical ° 30 – 45 0 – 30 30 – 45 0 – 30
Approach velocity
Maximum ft/s 1.0 – 2.0 2.0 – 3.25 m/s 0.3 – 0.6 0.6 – 1.0
Minimum ft/s 1.0 – 1.6 m/s 0.3 – 0.5
Allowable headloss in 6 6 - 24 mm 150 150 - 600
21. B. Fine screens
Description of fine screen
Type of Screening surface
Screening Size Size range Screen
device classification in mma medium Application
Stainless-steel
inclined
Medium 0.01 – 0.1 0.25 – 2.5 wedgewire Primary treatment
(fixed) screen
Drum Stainless-steel
Coarse 0.1 – 0.2 2.5 – 5 wedgewire Preliminary treatment
(rotary)
Stainless-steel wedgewire
Medium 0.01 – 0.1 0.25 – 2.5 screen Primary treatment
Removal of residual
Stainless-steel and
Fine 6 – 35㎛ secondary
polyester
suspended solids
screen cloths
Horizontal Combined sewer
reciprocati Medium 0.06 – 0.17 1.6 – 4 Stainless-steel overflows/
ng bars stormwater
Combined sewer
Tangential Fine 0.0475 1200㎛ Stainless-steel
overflows
mesh
22. Fine screens for Combined Sewer Overflows(CSO)
horizontal
drum type
type
23. flow equalization
Description/ Application
(1) dry – weather flows to reduce peak flows and loads
(2) wet – weather flows in collection system :
inflow/infiltration
(3) Combined stormwater and sanitary system flows
Benefits and Disadvantages
Benefits · shock loading, pH, inhibiting substance
· improved consistency in solid loading
· reduce filtration surface area/ process
reliability
Disadvantages · large land areas
· have to be covered for odor control
· capital cost is increased
25. Volume Requirements for Equalization Basin
Schematic mass diagrams for the volume of Equalization Basin
26. Mixing
Important unit operation in wastewater
treatment including
1. Mixing of one substance completely with
another
2. blending of miscible liquids
3. flocculation of waste particles
4. continuous mixing of liquid suspensions
5. heat transfer
27. Mixing operations classified as continuous rapid
(< 30 s)
continuous (i.e. ongoing)
Continuous rapid mixing
Most often used when one substance is to be
mixed with another.
Mainly used for blending of chemicals with
waste water (addition of alum & addition of
disinfectants)
Blending of miscible liquids
Addition of chemicals to sludge.
28. Continuous mixing
Used where the contents of a reactor or holding
tank or basin must be kept in suspension such as
in equalization basins, flocculation basins,
aerated lagoons, suspended growth biological
treatment process, and aerobic digester.
29. Types of mixers used for rapid mixing
Static mixers
High-speed induction mixers
Pressurized water jets
Turbine and propeller mixers
33. Objectives of Sedimentation
To separate solids from liquid using the force
of gravity. In sedimentation, only suspended
solids (SS) are removed.
Use
Sedimentation is used in water and
wastewater treatment plants
34.
35. Types of Settling
Type I settling (free settling)
Type II settling (settling of flocculated
particles)
Type III settling (zone or hindered
settling)
Type IV settling (compression settling)
36. Particle Settling Theory
where : gravitational force, MLT-2
: density of particle, ML-3
: density of water, ML-3
: acceleration due to gravity, LT-2
: volume of particle, M3
: frictional drag force, MLT-2
where
: drag coefficient
: cross-sectional area, L2
: particle settling velocity, LT-1
37. Type I (Discrete sedimentation)
Occurs in dilute suspensions, particles
which have very little interaction with each
other as they settle.
Particles settle according to Stoke’s law
Design parameter is surface overflow rate
(Q/As)
38. Discrete Particle Settling
The rate at which clarified water is produced is equal to
where ; : flowrate, ㎥/sec
: surface of the sedimentation basin
: particle settling velocity
Rearranging upper Eq
: Q/A = overflow rate “ critical velocity "
39. Type II (flocculent sedimentation)
Particles flocculate as they settle
Floc particle velocity increase with time
Design parameters:
1. Surface overflow rate
2. Depth of tank
or,
3. Hydraulic retention time
40. 2. Flocculent Particle Settling
Figure Definition for the analysis of flocculent settling
41. The settling velocity in flocculent
settling
where : height of the settling column
: time reguired for a given degree of removal to be
achieved, T
The fraction of particles removed is given by
where
: total height of settling column
: distance between curves of equal percent removal
: TSS removal
42. Type III settling (zone or hindered settling)
Is the settling of an intermediate
concentration of particles
The particles are close to each other
Interparticle forces hinder settling of
neighbouring particles
Particles remain in fixed position relative to
each other
Mass of particles settle as a zone
43. 3. Hindered (zone) settling and compression
where
: area required for
sludge thickening
: flowrate into tank
: initial height of interface
in column
: time to reach desired
underflow
Figure Graphical analysis of hindered concentration
interface settling curve
44. Type IV settling (compression settling)
Settling of particles that are of high
concentration
Particles touch each other
Settling occurs by compression of the
compacting mass
It occurs in the lower depths of final
clarifiers of activated sludge
45.
46. Chemical unit processes-precipitation
Widely used, technology for the removal of metals and
other inorganics, suspended solids, fats, oils, greases,
and some other organic substances from wastewater.
Precipitation is a method of causing contaminants that
are either dissolved or suspended in solution to settle
out of solution as a solid precipitate, which can then be
filtered, centrifuged, or otherwise separated from the
liquid portion.
47. It can be used on a small or large scale.
A beaker full of waste, a 50,000 tank, a 1,000,000
gallon lagoon or a lake can be batch treated with
chemicals.
Chemical precipitation can be used in a continuous
treatment system on flows ranging from a trickle to 1
gallon/minute, 1,000 gallons/minute and more.
Precipitation is assisted through the use of a coagulant,
an agent which causes smaller particles suspended in
solution to gather into larger aggregates.
Frequently, polymers are used as coagulants.
48. When colloidal matter such as emulsified oil or metal
bearing particles are treated with metal salts and lime
or NaOH, the metal salts act as primary coagulants.
The positively charged metal ions combine with the
negative colloid particles and neutralize their charge.
The particles then repel each other less strongly and
tend to coagulate or collect into larger particles.
49. Chemicals for precipitation
Lime – Calcium Oxide, CaO
Ferrous Sulfate – Fe(SO4)3
Alum or Filter Alum – Al2(SO4)3.14H2O
Ferric Chloride – FeCl3
Polymer
50. Advantages
Chemical precipitation is a well-established technology
with ready availability of equipment and many
chemicals.
Some treatment chemicals, especially lime, are very
inexpensive.
Completely enclosed systems are often conveniently
self-operating and low maintenance.
51. Disadvantages
Competing reactions, varying levels of alkalinity and
other factors typically make calculation of proper
chemical dosages impossible.
Chemical precipitation may require working with
corrosive chemicals, increasing operator safety
concerns.
The addition of treatment chemicals, especially lime,
may increase the volume of waste sludge up to 50
percent.
Large amounts of chemicals may need to be
transported to the treatment location.
Polymers can be expensive.
52. APPLICATION OF DIFF. CHEMICALS
Lime – Calcium Oxide, CaO
Produces calcium carbonate in wastewater
which acts as a coagulant for hardness and
particulate matter. Often used in conjunction
with other coagulants, since:
(1) by itself, large quantities of lime are required
for effectiveness, and
(2) lime typically generates more sludge than
other coagulants.
53. Ferrous Sulphate – Fe(SO4)3
Typically used with lime to soften water. The
chemical combination forms calcium sulfate
and ferric hydroxide. Wastewater must contain
dissolved oxygen for reaction to proceed
successfully.
Ferric Chloride – FeCl3
Reacts with alkalinity or phosphates to form
insoluble iron salts.
54. Alum or Filter Alum – Al2(SO4)3.14H2O
Used for water softening and phosphate removal.
Reacts with available alkalinity (carbonate, bicarbonate
and hydroxide) or phosphate to form insoluble
aluminium salts.
Polymer
High molecular weight compounds (usually synthetic)
which can be anionic, cationic, or non-ionic. When
added to wastewater, can be used for charge
neutralization for emulsion-breaking, or as bridge-
making coagulants, or both. Can also be used as filter
aids and sludge conditioners.
55. Biological unit processes
In the case of domestic wastewater treatment, the
objective of biological treatment is:
– To stabilize the organic content
– To remove nutrients such as nitrogen and phosphorus
Types:
Attached Growth
Aerobic Processes
Suspended Growth
Anoxic Processes
Combined Systems
Anaerobic Processes
Combined Aerobic-Anoxic-
Anaerobic Processes
Aerobic
Pond Processes Maturation
Facultative
Anaerobic
56. Attached Growth Process
What can this process do?
1. Remove Nutrient
2. Remove dissolved organic solids
3. Remove suspended organic solids
4. Remove suspended solids
57. Cross-section of an attached growth
biomass film
Oxygen (the natural or forced draft)
Wastewater
Organic/ nutrient
Biomass : viscous, jelly-like substance containing bacteria
filter media
58. Major Aerobic Biological Processes
Type of Common Name Use
Growth
Suspended Activated Sludge (AS) Carbonaceous BOD removal (nitrification)
Growth Aerated Lagoons Carbonaceous BOD removal (nitrification)
Attached Trickling Filters Carbonaceous BOD removal. nitrification
Growth Roughing Filters (trickling Carbonaceous BOD removal
filters with high hydraulic
loading rates)
Rotating Biological Carbonaceous BOD removal (nitrification)
Contactors
Packed-bed reactors Carbonaceous BOD removal (nitrification)
Combined Activated Biofilter Process Carbonaceous BOD removal (nitrification)
Suspended & Trickling filter-solids
Attached contact process
Growth Biofilter-AS process
Series trickling filter-AS
process
59. Activated Sludge Process
The aeration tank contains a suspension of the wastewater and
microorganisms, the mixed liquor. The liquor is mixed by aeration devices
(supplying also oxygen)
A portion of the biological sludge separated from the secondary effluent
by sedimentation is recycled to the aeration tank
Types of AS Systems: Conventional, Complete-Mix, Sequencing Batch
Reactor, Extended Aeration, Deep Tank, Deep Shaft
60. Advantages/Disadvantages
Advantages Disadvantages
Flexible, can adapt to High operating costs
minor pH, organic and (skilled labor, electricity,
temperature changes etc.)
Small area required Generates solids requiring
Degree of nitrification is sludge disposal
controllable Some process alternatives
Relatively minor odor are sensitive to shock
problems loads and metallic or
other poisons
Requires continuous air
supply
61. Trickling Filters
• The trickling filter or biofilter consists of a bed of permeable
medium of either rock or plastic
• Microorganisms become attached to the media and form a
biological layer or fixed film. Organic matter in the wastewater
diffuses into the film, where it is metabolized. Periodically,
portions of the film slough off the media
62. Flow Diagram for Trickling Filters
Recirculation= A portion of the TF effluent recycled through the filter
Recirculation ratio (R) = returned flow (Qr)/ influent flow (Q)
Qr
Recycle
Final
clarifier
Q
Influent
Primary Wast
clarifier sludg
Trickling
filter
63. Advantages/Disadvantages
Advantages Disadvantages
Good quality (80-90% High capital costs
BOD5 removal) for 2- Clogging of distributors or
stage efficiency could beds
reach 95% Snail, mosquito and
Moderate operating costs insect problems
(lower than activated
sludge)
Withstands shock loads
better than other
biological processes
64. Rotating Biological Contactors
It consists of a series of circular disks of polystyrene or
polyvinyl chloride that are submerged in wastewater and
rotated slowly through it
The disk rotation alternately contacts the biomass with the
organic material and then with atmosphere for adsorption of
oxygen
Excess solids are removed by shearing forces created by the
rotation mechanism
65. Advantages/Disadvantages
Advantages Disadvantages
Short contact periods Need for covering units
Handles a wide range of installed in cold climate to
flows protect against freezing
Easily separates biomass
from waste stream Shaft bearings and
Low operating costs mechanical drive units
Short retention time require frequent
maintenance
Low sludge production
Excellent process control
66. Major Anaerobic Biological Processes
Type of Common Name Use
Growth
Suspended Anaerobic Contact Process Carbonaceous BOD
Growth removal
Upflow Anaerobic Sludge- Carbonaceous BOD
Blanket (UASB) removal
Attached Anaerobic Filter Process Carbonaceous BOD
Growth removal, waste stabilization
(denitrification)
Expanded Bed Carbonaceous BOD
removal, waste stabilization
67. Anaerobic Contact Process
Untreated wastewater is mixed with recycled
sludge solids and then digested in a sealed
reactor
The mixture is separated in a clarifier
The supernatant is discharged as effluent, and
settled sludge is recycled
68. Advantages/Disadvantages
Advantages Disadvantages
Methane recovery Heat required
Small area required Effluent in reduced
Volatile solids chemical form
destruction requires further
treatment
Requires skilled
operation
Sludge to be disposed
off is minimal
69. Upflow Anaerobic Sludge Blanket
Wastewater flows upward
through a sludge blanket
composed of biological
granules that decompose
organic matter
Some of the generated
gas attaches to granules
that rise and strike
degassing baffles
releasing the gas
Free gas is collected by
special domes
The effluent passes into a
settling chamber
70. ACTIVATED SLUDGE
Advantages/Disadvantages
Advantages Disadvantages
Low energy demand Long start-up period
Low land requirement Requires sufficient
Low sludge production amount of granular seed
Less expensive than other sludge for faster start-up
anaerobic processes Significant wash out of
High organic removal sludge during initial
efficiency phase of process
Lower gas yield than
other anaerobic
processes
76. Septic tank
All household wastewater systems will have
a septic tank
Microbial action digests solid wastes
Liquids flow through tank to disposal area
Tank size
-1000 gallon liquid capacity (4-BR house or less)
-Add 250 gallons per additional bedroom
77. System Components
Source
Well
Tank Drainfield
Treatment in Soil
Groundwater
79. Role of the septic tank
Anaerobic fermentation of solids
Reduce the load of pathogens in the effluent
Hold the effluent for 2-3 days for improved
safety
Retain solid material to prevent blockage of
further disposal system
80. The soak-away
Absorption field treatment of septic tank effluent
Absorption trench system
Distribution box
septic
tank
81. The field requires periodic
maintenance.
Diversion of the flow at distribution
box and repacking of the rock fill,
removal of plant roots etc.
82. Connection to a sewage system: what are
the alternatives?
Conventional sewage connection…expensive
Small bore sewage system: less expensive
Use road-side drains, and hope for the best….
Unfortunately this is the common outcome
83. Where do we go from here:
The effluent must be disposed of in a sanitary
manner
The system should be inexpensive and easy to
manage
Tropical areas do have long hours of sunlight,
why not exploit this.
We can by using oxidation ponds…
84. Soak pit
Soak Pit, also known as a soak away or leach pit, is
a covered, porous-walled chamber that allows
water to slowly soak into the ground.
Pre-settled effluent from a Collection and
Storage/Treatment technology is discharged to
the underground chamber from where it
infiltrates into the surrounding soil.
85. The Soak Pit can be left empty and lined with a
porous material (to provide support and prevent
collapse), or left unlined and filled with coarse
rocks and gravel.
The rocks and gravel will prevent the walls from
collapsing, but will still provide adequate space for
the wastewater.
In both cases, a layer of sand and fine gravel
should be spread across the bottom to help
disperse the flow.
The soak pit should be between 1.5 and 4m deep,
but never less than 1.5m above the ground water
table.
86. As wastewater (pre-treated grey water or
black water) percolates through the soil
from the Soak Pit, small particles are
filtered out by the soil matrix and organics
are digested by micro-organisms.
Thus, Soak Pits are best suited to soils with
good absorptive properties; clay, hard
packed or rocky soils are not appropriate.
87. Advantages/Disadvantages
Advantages Disadvantages
Can be built and repaired Pre-treatment is required to
with locally available prevent clogging, although
materials. eventual clogging is
Small land area required. inevitable.
Low capital cost; low May negatively affect soil and
operating cost. groundwater properties.
Can be built and maintained
with locally available
materials.
Simple technique for all
users.
88.
89.
90.
91. Health Aspects
Soak Pit is not used for raw sewage, and as long as
the previous Collection and Storage/Treatment
technology is functioning well, health concerns are
minimal.
The technology is located underground and thus,
humans and animals should have no contact with
the effluent.
It is important however, that the Soak Pit is located
a safe distance from a drinking water source (ideally
30m).
Since the Soak Pit is odourless and not visible, it
should be accepted by even the most sensitive
communities.
92. Maintenance
A well-sized Soak Pit should last between 3 and 5
years without maintenance.
To extend the life of a Soak Pit, care should be
taken to ensure that the effluent has been clarified
and/or filtered well to prevent excessive build up of
solids.
The Soak Pit should be kept away from high-traffic
areas so that the soil above and around it is not
compacted.
93. When the performance of the Soak Pit
deteriorates, the material inside the soak pit can be
excavated and refilled.
To allow for future access, a removable (preferably
concrete) lid should be used to seal the pit until it
needs to be maintained.
Particles and biomass will eventually clog the pit
and it will need to be cleaned or moved.
94. Stabilization ponds
One of the most ancient wastewater treatment
methods known to humans are waste stabilization
ponds, also known as oxidation ponds or lagoons.
They're often found in small rural areas where land is
available and cheap.
Such ponds tend to be only a meter to a meter and a
half deep, but vary in size and depth, and may be three
or more meters deep.
95. Consist of shallow man-made basins comprising a single
or several series of anaerobic, facultative or maturation
ponds.
The primary treatment takes place in the anaerobic
pond, which is mainly designed for removing suspended
solids, and some of the soluble element of organic
matter (BOD).
Secondary stage in the facultative pond most of the
remaining BOD is removed through the coordinated
activity of algae and heterotrophic bacteria.
The main function of the tertiary treatment in
the maturation pond is the removal of pathogens and
nutrients (especially nitrogen).
96. New
Light
cells
Algae
CO2
O2
nutrients
Bacteria
Organic New
matter cells
97. Three processes of stabilization:
anaerobic
Anaerobic Facultative Maturation
Suspended
Settleable &
solids Sludge layer Soluble
solids
98. The second process is facultative
Anaerobic Facultative Maturation
Suspended &
Settleable Soluble
solids solids
Sludge layer
99. In the maturation pond, pathogens are reduced:
the water an be released to a river
Anaerobic Facultative Maturation
Organic matter
Pathogenic
organisms
100. Application and suitability
Stabilization ponds are particularly well suited for
tropical and subtropical countries because the intensity
of the sunlight and temperature are key factors for the
efficiency of the removal processes.
It is also recommended by the WHO for the
treatment of wastewater for reuse in agriculture and
aquaculture, especially because of its effectiveness in
removing nematodes (worms) and helminth eggs.
101. Septic systems can be a
permanent solution to
wastewater
management
if homeowners
understand and
maintain their systems.