CEN-105 - PPT - FifthSet (Water & Wastewater Treatment)
CEN-105 - PPT - FifthSet (Water & Wastewater Treatment)
CEN-105 - PPT - FifthSet (Water & Wastewater Treatment)
WASTEWATER
TREATMENT
Surface water
rivers
lakes
reservoirs
Characteristics Groundwater
River
Lake/
Reservoir
Generally safe
Not safe
Better than
river
Composition
Constant
Varying with
season
Relatively
constant
Turbidity/SS
Nil
Present
Very Less
Present
Variable
Variable
Sometimes
Nil
Variable
Safety
(bacteriological)
Minerals
Iron & Manganese
Steps
Surface Water
Hard Groundwater
Screening/Microstrainer
Aeration
Pre-Sedimentation/PreChlorination
Oxidation/Prechlorination
Precipitation
Sedimentation
Sedimentation
Filtration
Recarbonation
Filtration
Disinfection
Disinfection
.
.
.
.
Sedimentatio
n
basin
Sludge
To
Distribution
System
Clariflocculator
Sludge
Storage
To
Distribution
System
Colloids
Small particles (0.001 to 1 m)
Usually negatively charged
Particles repel so suspension is
considered stable
Colloidal particles
(0.001 - 1 m)
+
+ +
+
+
+
+ +
+ ++
++
+
+ +
+
++
+
+ ++ + +
+ +
++ +
++
+
+ +
+
floc
(1 - 100 m)
Coagulant
Non-toxic and relatively inexpensive
Insoluble in neutral pH range - do not want high
concentrations of metals left in treated water.
Alum: Al2(SO4)3.14H2O, Ferric chloride: FeCl3, Ferric
sulfate: FeSO4, Polyelectrolyte
Aquometallic ions
Neutralization of
surface charge on
colloids
Rapid Mixing
Used to blend chemicals and water being
treated
Retention time from 10 - 30 sec.
Mechanical mixing using vertical-shaft impeller
in tank with baffles
Rapid Mixing
Flocculation
Paddle units
rotate slowly,
usually <1 rpm
Velocity of water:
0.5 - 1.5 ft/sec
Detention time of
at least 20 min
Flocculation
Sedimentation/Settling
Following flocculation, the water then
flows into the settling basins
Water is nearly quiescent low flow with
little turbulence
Water resides for at least 3 hours and the
flocs settle out and collect at the bottom.
Circular Clarifiers
where
s = settling velocity
s = density of particle (kg/m3)
g
d
Overflow rate
Q
v
As
where
v = overflow
rate (m/s)
Q = water flow
(m3/s)
As = surface
area (m2)
Vs
The particle will travel vertically from A to B in the same time as it takes to travel
horizontally from A to B
This is the detention time and is given by
H L
td
v s vh
Q
Also, from continuity, vh
BH
H
H Q
Q
Q
v s vh .
L
L BH BL AS
Q
is known as surface loading rate or overflow rate
AS
Coagulation-Rapid Mixing
Used to blend chemicals and water being
treated
Retention time from 10 - 30 sec.
Mechanical mixing using vertical-shaft impeller
in tank with baffles
Flocculation-Slow Mixing
Paddle units rotate slowly, usually <1 rpm
Velocity of water: 15 - 45 cm/sec
Detention time of at least 20 min
Filtration
The final step in removing particles is
filtration.
Removal of those particles that are too
small to be effectively removed during
sedimentation
Multiple removal mechanisms depending
on design
Sedimentation effluent: 1 - 10 NTU
Desired effluent level: <0.3 NTU
Filtration
Filter Design
Q
va
As
where
va = face velocity
(m/day) or loading rate
(m3/daym2)
Q = flow rate (m3/day)
As = filter surface area
(m2)
Head Loss
Groundwater Treatment
Primary objectives are to
1.Remove hardness and other minerals
2.Eliminate Bacteria or Ensure Residual
Disinfectant in water
Treatment technologies largely based on
precipitation
Groundwater Treatment
Sedimentation
basin
Ground water
from wells
Recarbonation
Rapi
Slow
d
Basin
Mix
Disinfection
Storage
CO
Sludge
To Distribution
System
ION EXCHANGE
FOR HARDNESS
REMOVAL
REVERSE OSMOSIS
REVERSE OSMOSIS
Wastewater Treatment:
Characteristics and Systems
OBJECTIVES
WHY ???
Waste
FINAL GOAL
?
?
Significance of Wastewater
Contaminants
Suspended solids can cause sludge deposits
and anaerobic conditions in the environment
Biodegradable organics can cause anaerobic
conditions in the environment
Pathogens transmit disease
Nutrients can cause eutrophication
Heavy metals toxicity to biota and humans
Refractory organics toxicity to biota and humans
Dissolved solids interfere with reuse
Characteristics of Domestic
Wastewater
Septic Systems
Septic Systems
Septic Systems
Municipal Wastewater
Treatment Systems
Pretreatment removes materials
that can cause operational
problems, equalization optional
Primary treatment remove ~60%
of solids and ~35% of BOD
Secondary treatment (Biological
Treatment) remove ~85% of BOD
and solids
Advanced treatment varies: 95+
% of BOD and solids, N, P
Aeration
Tanks
Secondary
Clarifiers
Return Sludge
Pumping Facility
Sludge
Thickeners
Anaerobic
Digestors
Primary
Clarifiers
Pretreatment of Industrial
Wastewaters
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
MoEF ,Govt. of India & U.S. EPA
Bar racks
Purpose
remove larger objects
Grit Chambers
Purpose: remove inert
dense material, such as
sand, broken glass, silt
and pebbles
Avoid abrasion of
pumps and other
mechanical devices
Material is called grit
Primary Settling
Basins
Primary Settling
Secondary Treatment
Provide BOD removal beyond what is
achieved in primary treatment
removal of soluble BOD
additional removal of suspended solids
Microorganisms
separated from water
Microorganism
combined together and
form flocs (X)
Qr Xs
Qw Xs
Basic Ingredients
High density of microorganisms (keep
organisms in system)
Good contact between organisms and
wastes (provide mixing)
Provide high levels of oxygen (aeration)
Favorable temperature, pH, nutrients
(design and operation)
No toxic chemicals present (control
industrial inputs)
Biological Treatment
Aerobic:
Activated Sludge Process (ASP)
Sequencing Batch Reactor (SBR)
Anaerobic Process
Up-flow Anaerobic Sludge Blanket
(UASB) Reactor
Activated Sludge
Process in which a mixture of wastewater and
microorganisms (biological sludge) is agitated
and aerated
Leads to oxidation of dissolved organics
After oxidation, separate sludge from
wastewater
Induce microbial growth
Need food, oxygen
Want Mixed Liquor Suspended Solids (MLSS) of
3,000 to 6,000 mg/L
Activated sludge
Activated Sludge
w/w
Return
Activate
d Sludge
(RAS)
Waste
Activate
d
Sludge
Mixed
Liquor
Air
Treated
Secondary w/w
clarifier
Discharge to
River or Land
Application
Sludge Treatment
Bar screens
Grit chambers
Flotation
Especially effective
on activated sludge
Increases solids
content from 0.5 - 1%
to 3-6%
Primary
Sludge
Secondary
Sludge
Gravity Thickening
Further processing
Flotation
Stabilization
Anaerobic Digestion
Filtration
Apply vacuum to pull
out water
Force out water by
essentially squeezing
water between two
moving filter belts
Low-tech solutions
(Waste Stabilization Pond)
Ponds 1 - 2.5 m
deep
td = 30 - 180 d
not easily subject
to upsets due to
fluctuations in Q,
loading
low capital, O&M
costs
BOD
Non-Settleable
CO2
Final Effluent
No BOD
O2
(During Day)
O2
Algae
N&P
O2
CO2
Bacteria
WASTE STABILIZATION
POND