Post on 28-Jan-2022
transcript
Strategies for Wastewater
Treatment: Physico-Chemical
ApproachConventional Approach and Recent Trends
Purnendu Bose
Department of Civil Engineering
IIT Kanpur
Strategies for Wastewater Treatment: Physico-Chemical Approach
Introduction
What does Wastewater Contain ??
> 98% water (by weight) approx. 1 – 2 % Contaminants
Wastewater Treatment involves removing the contaminants from water
Cost of removal of contaminants: from Rs. 10/kL to Rs. 400/ kL
Secondary Treatment of DomesticSewage before disposal into rivers
Tertiary Treatment of Industrial Effluent for Recycling
Origin of Wastewater: Domestic/Commercial or Industrial
Strategies for Wastewater Treatment: Physico-Chemical Approach
Introduction
Types of Contaminants in Wastewater
Inorganic: 1) Particulate; 2) Colloidal; 3) Dissolved
Organic: 1) Large Floating Material; 2) Particulate;
3) Colloidal ; 4) Dissolved;
Biodegradable Non-Biodegradable
Biological Treatment Physico-Chemical Treatment
Strategies for Wastewater Treatment: Physico-Chemical Approach
Introduction
Objective of Wastewater Treatment:
Removal of Organic and Inorganic Contaminants
How is it Done?
UO-1 UO-2 UO-3 UO-4 UO-nRaw
Wastewater
Treated
Wastewater
Chemical Addition
Mixing
+
Bacterial Action
Heating / Pressure
Catalyst
Aeration
By Designing a Wastewater Treatment Process Train
UO – Unit Operation
Strategies for Wastewater Treatment: Physico-Chemical Approach
Introduction
‘Unit Processes’ in Wastewater Treatment:
Say, a wastewater treatment train consists of ‘n’ unit operations, UO(1) – UO(n)
The first ‘i’ unit operations, i.e., UO(1) – UO(i) constitute an ‘unit process’ called,
‘Preliminary Treatment’
The unit operations from ‘i + 1’ to j, i.e., UO(i+1) – UO(j) constitute an ‘unit process’ called
‘Primary Treatment’.
The unit operations from ‘j + 1’ to ‘k’, i.e., UO(j+1) - UO(k) constitute an ‘unit process’
called Secondary Treatment’.
The unit operations from ‘k + 1’ to ‘n’, i.e., UO(k+1) – UO(n) constitute an ‘unit process’
called ‘Tertiary Treatment’.
Each ‘Unit Process’ performs a particular function in wastewater treatment
Strategies for Wastewater Treatment: Physico-Chemical Approach
Introduction
Functions of ‘Unit Processes’ in Wastewater Treatment:
Preliminary Treatment: Physical Processes
Unit Operations in Preliminary Treatment removes, 1) large organic floating material and
2) inorganic particulate and matter from wastewater
Primary Treatment: Physical/Chemical Processes
Unit Operations in Primary Treatment removes, 1) organic particulate matter and
inorganic colloidal matter from wastewater and 2) also help (if required) in transforming
non-biodegradable dissolved organic matter in wastewater to a more biodegradable form
Secondary Treatment: Biological/Physical Processes
Unit operations in Secondary Treatment remove colloidal and dissolved organic matter
from wastewater
Tertiary Treatment: Biological/Chemical Physical Processes
Unit operations in Tertiary Treatment remove, 1) residual dissolved organic matter from
wastewater, 2) residual organic/inorganic particulate matter from wastewater, 3) dissolved
inorganic matter from wastewater
Treated wastewater may be disposed, reused or recycled
Domestic sewage after ‘Secondary Treatment’ is generally suitable for disposal into natural surface
water bodies
Industrial effluent may require some ‘Tertiary Treatment’ before being suitable for disposal into
natural water bodies.
Both domestic sewage and industrial effluent can generally be reused for various beneficial purposes
after adequate ‘Tertiary Treatment’.
Industrial effluent can be recycled, generally after adequate ‘Tertiary Treatment’
Disposal, Reuse and Recycling
Treated wastewater may be discharged to natural water bodies provided the relevant discharge
standards are attained through wastewater treatment. This is known as wastewater disposal.
Alternatively, the treated wastewater may be used for certain other beneficial purpose, provided
adequate treatment is given to the wastewater to meet the water quality standards for that
beneficial use. This procedure of using water for multiple beneficial uses is known as reuse.
Alternatively, the treated wastewater may be used for the same beneficial purpose as before,
provided adequate treatment is given to the wastewater such that it meets the standards for the
original beneficial use. This procedure for using water for the same beneficial use is known as
recycling.
Strategies for Wastewater Treatment: Physico-Chemical Approach
Introduction
Grit ChamberProportional Weir
Grit Collection
Sewer
Rectangular Open Channel
Bar Rack / Screens
Front View
Top View
Strategies for Wastewater Treatment: Physico-Chemical Approach
Conventional Unit Operations
Name of UO: Bar Rack / Screen
Type: Physical Process
Unit Process: Preliminary Treatment
Purpose: Removal of Large Floating Material (up to 1 mm size) from Wastewater
Large floating materials are caught inthe screen and removed
Three screens with progressivelysmaller openings are provided in seriesto remove all floating material > 1 mmsize
Sewer
Rectangular Open Channel
Bar Rack / Screens
Front View
Top View
Strategies for Wastewater Treatment: Physico-Chemical Approach
Conventional Unit Operations
Name of UO: Grit Chamber
Type: Physical Process
Unit Process: Preliminary Treatment
Purpose: Removal of Inorganic Particles (up to 1 mm size) from Wastewater
Placed immediately after bar rack /screen
The channel is suddenly widened, sothat horizontal flow velocity is reducedin grit chamber. Particles settle in thechamber and are removed.
Proportional Weir
Grit ChamberProportional Weir
Grit CollectionFront View
Top View
Strategies for Wastewater Treatment: Physico-Chemical Approach
Conventional Unit Operations
Name of UO: Equilization Tank
Type: Physical Process
Unit Process: Preliminary Treatment
Purpose: Flow Equilization
Equalization Tank (Flow Equalization)
Variable Flow(from Grit Chamber)
EqualizationTank Constant Flow
In- Line Equalization
EqualizationTank
Variable Flow Constant Flow
Inflow Outflow
Off - Line Equalization
Placed immediately after GritChamber
Inflow into Equilization tank isvariable, but the outflow isconstant.
Equilization tank is required forefficient operation of thedownstream unit operations.
Two types of Equilization tanksare possible, off-line and on-lineequilization.
Strategies for Wastewater Treatment: Physico-Chemical Approach
Conventional Unit Operations
SC-1 SC-2 SC-3 GC EQTo Primary Treatment
From Sewer
The wastewater after preliminary treatment has,
1) No floating matter2) No inorganic particles of size > 0.2 mm3) Equalized Flow
The First Unit Process: Preliminary Treatment
Rapid Mix Tank: Vertical Shaft Impeller
Plan
Elevation
Inflow
outflow
Coagulant
Strategies for Wastewater Treatment: Physico-Chemical Approach
Conventional Unit Operations
Name of UO: Rapid Mix Tank
Type: Physical Process
Unit Process: Primary Treatment
Purpose: Dispersal of Coagulant
Coagulant addition is mostlyrequired for industrialwastewater treatment.
This unit is generally notrequired for domesticwastewater treatment.
The objective of the rapid mixtank is to quickly disperse theadded coagulant into the bulkwastewater
Flocculation Tank:Horizontal Shaft Paddle
Plan
Elevation
Strategies for Wastewater Treatment: Physico-Chemical Approach
Conventional Unit Operations
Name of UO: Flocculation Tank
Type: Physical Process
Unit Process: Primary Treatment
Purpose: Flocculation of destabilized particles
Flocculation tank provided immediatedownstream of the rapid-mix tank. It ismostly required for industrialwastewater treatment.
This unit is generally not required fordomestic wastewater treatment.
The objective of the flocculation tank isto facilitate the agglomeration ofparticles destabilized by coagulantaddition.
The larger particles thus formed areremoved in the settling tank providedimmediate downstream of theflocculation tank.
Sludge
Scum RemoverEffluent Launder
Inlet Channel
Elevation of Sedimentation Tank
Baffle
Settling Zone
L
D
Strategies for Wastewater Treatment: Physico-Chemical Approach
Conventional Unit Operations
Name of UO: Primary Sedimentation Tank
Type: Physical Process
Unit Process: Primary Treatment
Purpose: Sedimentation of organic particles up to 60 mm size
Organic particles up to60 mm size areremoved in thesedimentation tank
Strategies for Wastewater Treatment: Physico-Chemical Approach
Conventional Unit Operations
FT PSTTo Secondary Treatment
From Preliminary Treatment
The wastewater after Primary treatment has,
1) No floating matter2) No inorganic particles of size > 0.2 mm3) Equalized Flow
1) All organic and inorganic particles up to 60 mm size removed
The Second Unit Process: Primary Treatment
RMT
Coagulant
Optional
Preliminary Treatment
Primary Treatment
After Primary Treatmentwastewater mainly has colloidal and dissolved organic and inorganic matter
Strategies for Wastewater Treatment: Physico-Chemical Approach
Conventional Unit Operations
Name of UO: Biological Treatment - Secondary Sedimentation
Type: Biological – Physical Process
Unit Process: Secondary Treatment
Purpose: Removal of colloidal organic and inorganic and dissolved organic matter
SSTTo Tertiary Treatment or Disposal
From Primary
Treatment
The wastewater after Secondary treatment may have,1) Non-Biodegradable organic matter (may impart color)2) Small concentrations of colloidal organic matter (mostly biomass)3) Dissolved inorganic matter (cations and anions)
Domestic wastewater after secondary treatment looks clean
The Third Unit Process: Secondary Treatment
Bioreactor
Dissolved organic matter(assuming biodegradable) isalmost completely removed.Colloidal organic matter ispartially removed.
Colloidal organic and inorganic matter, along with biomass effluent from the bioreactor is removed.
Strategies for Wastewater Treatment: Physico-Chemical Approach
Recent Trends
SC-1 SC-2 SC-3 GC EQTo Primary Treatment
From Sewer
The First Unit Process: Preliminary Treatment
FT PSTTo Secondary
Treatment
From Preliminary Treatment
RMT
Coagulant
Optional
The Second Unit Process: Primary Treatment
SSTTo Tertiary Treatment or Disposal
From Primary
Treatment
The Third Unit Process: Secondary Treatment
Bioreactor
Summary
Biological Process
Large floating organic matter and inorganic particle up to 0.2 mm size is removedFlow is equalized.
Inorganic and organic particle up to 60 mm size is removed.
Dissolved organic matter and colloidal organic and inorganic matter is removed.
Strategies for Wastewater Treatment: Physico-Chemical Approach
Recent Trends
Recent Trends:
Conversion of Non-Biodegradable organic matter to a more biodegradable form during
primary treatment using physico-chemical methods. This helps more efficient organic
matter removal during secondary treatment.
This is mostly applicable for industrial effluents with large non-biodegradable organic
content.
Physico-Chemical Tertiary Treatment Processes:
1. Chemical precipitation of specific inorganic cations and anions (phosphate, heavy
metals, etc.) followed by removal of residual particulate matter and precipitates by
sand and membrane filtration (micro-, nano-filtration).
2. Removal of residual dissolved organic matter (non-biodegradable, micro-pollutants) by
a) activated carbon adsorption, b) nanofiltration, and c) post-ozonation.
3. Removal of residual inorganic cations/anions by, a) ion exchange, b) reverse osmosis
Tertiary treatment makes the treated wastewater more suitable for recycle/reuse. Degree
of tertiary treatment provided depends on the end-use of the treated effluent.
Aliphatic Compounds are easily biodegradable
Compounds with Aromatic rings and Cross linkages are difficult to Degrade
Biodegradability
Strategies for Wastewater Treatment: Physico-Chemical Approach
Recent Trends
Strong Oxidizing Agents: Advanced Oxidation Processes (AOPs)
Only Ozone (O3):
Ozone (O3) is a strong oxidizing agent. In aqueous solutions O3 often directly reacts with
the target contaminant.
O3 may combine with OH- in water and through a series of reactions form hydroxyl
radical. Hydroxyl radical is also a strong oxidizing agent.
O3/UV:
H2O2/UV:
H2O2/O3:
Fe2+/H2O2 (Fenton’s Reaction):
Strategies for Wastewater Treatment: Physico-Chemical Approach
Recent Trends
2h
23 OOH2OHO
OH2OHh
22
2232
32222
OOOHOHO
OHHOOHOH
]OH[
OHOHFeFeOH 3222
Mechanism of AOP:
Strong oxidizing agents attack electron-rich sites in complex organic molecules, i.e., aromatic
rings and double bonds. This breaks up the molecules into more aliphatic components, which
are more amenable to subsequent biodegradation.
Strategies for Wastewater Treatment: Physico-Chemical Approach
Recent Trends
Name of UO: Pre-Oxidation (AOP)
Type: Chemical Process
Unit Process: Primary Treatment
Purpose: Enhancing Biodegradability of Non-Biodegradable Organic Matter
FT PST
To Secondary Treatment
From Preliminary Treatment
RMT
Coagulant
Optional
PO
Optional
Pre-Oxidation (PO) will enhance the biodegradability ofnon-biodegradable organic matter often found inindustrial effluents. This is beneficial for the subsequentbiological treatment
The Second Unit Process: Primary Treatment
Removal of Specific Inorganic Cations/Anions: Chemical Precipitation
Addition of chemicals to promote precipitation of specific cations/anions in secondary treated
effluent.
Strategies for Wastewater Treatment: Physico-Chemical Approach
Recent Trends
Name of UO: Chemical Precipitation
Type: Chemical Process
Unit Process: Tertiary Treatment
Purpose: Removal of specific dissolved inorganic cations/anions
FT
From SecondaryTreatment
RMT
Chemical
Used mainly for removal of phosphate from domestic effluent or in thetreatment of industrial effluent. Chemical Precipitation will precipitatespecific dissolved inorganic cations/anions present in secondary treatedeffluent.
BackwashTank
BackwashTank
Pump
Backwash Rapid Sand Filter Schematic
Plan
Front Sectional View
Strategies for Wastewater Treatment: Physico-Chemical Approach
Recent Trends
Filtration: Removal of Residual Particulates and Precipitates
Filtration can be done either using sand filters, i.e., rapid sand filters or pressure filters,
followed by membrane filters, i.e., micro- or ultra-filtration.
Name of UO: Filtration
Type: Physical Process
Unit Process: Tertiary Treatment
Purpose: Removal of residual particulates and precipitates
Pressure Filtration
Operating principle is the same as in a rapid sand filter
Due to higher pressure application, throughput in pressure filters are higher
Compact systems, which can be purchased off the shelf and installed quickly
Strategies for Wastewater Treatment: Physico-Chemical Approach
Recent Trends
Membrane FiltrationWater is passed through membranes of various pore sizes. Depending on the pore-size of the membrane, some impurities in water are ‘rejected’ by the membrane.
Inlet
Outlet
Reject
Hollow Fiber Membranes
Outlet
Membrane Reactor Schematic
Strategies for Wastewater Treatment: Physico-Chemical Approach
Recent Trends
FT
From SecondaryTreatment
RMT
Chemical
After filtration, the treated effluent will have no particulate or dissolved solids.Hence the turbidity of the effluent should be below 1 NTU.
However, the effluent may still contain residual non-biodegradable organicmatter and salts.
RSF/PF M/U Filt
Chemical Precipitation Residual Solids Removal
Strategies for Wastewater Treatment: Physico-Chemical Approach
Recent Trends
Name of UO: Adsorption
Type: Chemical Process
Unit Process: Tertiary Treatment
Purpose: Removal of residual dissolved organic matter
Activated Carbon Adsorption
Treated effluent is passed throughcolumns containing activated carbon.Dissolved organic molecules areattached to the activated carbon surfaceand thus removed from the effluent
Strategies for Wastewater Treatment: Physico-Chemical Approach
Recent Trends
Name of UO: Post-Ozonation
Type: Physical Process
Unit Process: Tertiary Treatment
Purpose: Removal of residual dissolved organic matter (Color, odor)
Name of UO: Nano-filtration
Type: Physical Process
Unit Process: Tertiary Treatment
Purpose: Removal of residual dissolved organic matter
NFFiltered Effluent AC
PostOzonation
Removal of Residual Organic Matter
Removal of Residual Organic Matter. Color and Odor removal.
Sparkling Water.
Strategies for Wastewater Treatment: Physico-Chemical Approach
Recent Trends
Name of UO: Ion Exchange
Type: Chemical Process
Unit Process: Tertiary Treatment
Purpose: Removal of residual dissolved inorganic matter
Name of UO: Reverse Osmosis
Type: Physical Process
Unit Process: Tertiary Treatment
Purpose: Removal of residual dissolved inorganic matter
Filtered Effluent IE/RO
Removal of Residual Inorganic Ions
Recyclable Effluent
SC-1 SC-2 SC-3 GC EQTo Primary Treatment
From Sewer
The First Unit Process: Preliminary Treatment
FT PSTTo Secondary
Treatment
From Preliminary Treatment
RMT
Coagulant
Optional
PO
Optional
The Second Unit Process: Primary Treatment
SSTTo Tertiary Treatment or Disposal
From Primary
Treatment
The Third Unit Process: Secondary Treatment
Bioreactor
Summary
Biological Process
Large floating organic matter and inorganic particle up to 0.2 mm size is removedFlow is equalized.
Inorganic and organic particle up to 60 mm size is removed. Non-biodegradable organic matter is made biodegradable
Dissolved organic matter and colloidal organic and inorganic matter is removed.
Summary: Tertiary Treatment
FT
From SecondaryTreatment
RMT
Chemical
NF/DF
Biological ProcessAmmonia/Nitrate
Removal RSF/PF M/U Filt
NFFiltered Effluent AC
PostOzonation IE/RO
Phosphate, heavy metals precipitation and residualcolloidal matter and precipitate removal
Residual dissolved non-biodegradable organicmatter, organic micro-pollutants, color, odorremoval
Residual Inorganiccations and anions,i.e., salt removal