SEMINAR REPORT

A Dissertation submitted in partial fulfilment of the requirements for the award of the degree of

BACHELOR OF ENGINEERING
in
CIVIL ENGINEERING
by
MD MUDASSER
HT.NO.160922732303
Under the Guidance of
G. SRIKANTH
Assistant Professor

DEPARTMENT OF CIVIL ENGINEERING

LORDS INSTITUE OF ENGINEERING AND TECHNOLOGY
(An Autonomous Institution)
(AFFILIATED TO OSMANIA UNIVERSITY, HYDERABAD)
HIMAYAT SAGAR, HYDERABAD – 500091
A.Y:-2024-2025
 LORDS INSTITUTE OF ENGINEERING AND TECHNOLOGY
(An Autonomous Institution)
(Affiliated to Osmania University & Approved by AICTE, Accredited
by NBA, Accredited by NAAC “A” Grade).

CERTIFICATE

This is to certify that the dissertation titled “ADVANCED WASTE WATER TREATMENT” submitted

by MD MUDASSER bearing the Roll No: 160922732303 in partial fulfilment of the requirements for the

award of Degree of BACHELOR OF ENGINEERING in CIVIL Engineering is a Bonafide record of

the work carried out by him under the supervision of G. SRIKANTH, Assistant Professor, Department

of CIVIL, Lords Institute of Engineering and Technology during the academic year 2024-2025.

Date of submission of report: 02-05-2025

Guide HoD-CE

G. Srikanth Dr. Khaja Fareed Uddin

Assistant professor Professor

Dept. of Civil Engineering. Dept. of Civil Engineering

TABLE OF CONTENT
S.NO TOPIC’S PAGE.NO
CHAPTER-1
1.Introduction To Advanced Wastewater Treatment
1.1 Overview of Conventional Wastewater Treatment
1.2 Purpose and Scope of Advanced Wastewater Treatment
1.3 Technologies in Advanced Wastewater Treatment
1.4 Preliminary Treatment

1 1.5 Primary Treatment 2-9

1.6 Secondary Treatment (Biological Treatment)
1.7 Tertiary or Advanced Treatment
1.8 Sludge Treatment and Disposal
1.9 Final Effluent Discharge or Reuse
2.0 Advanced Wastewater Treatment Processes

CHAPTER-2
2.Preliminary Treatment in Wastewater Management
2.1 Overview
2.2 Objectives of Preliminary Treatment
2.3 Major Units of Preliminary Treatment
2.3.1 Screening
2.3.2 Comminution
2 10-14
2.3.3 Grit Removal
2.3.4. Pre-Aeration
2.3.5 Oil and Grease Removal
2.4 Flow Scheme of Preliminary Treatment
2.5 Advantages Of Preliminary Treatment
2.6 Challenges in Preliminary Treatment

CHAPTER-3

3.PRIMARY TREATMENT IN WASTEWATER MANAGEMENT

3.1 Overview
3.2 Objectives of Primary Treatment
3.3 Major Components of Primary Treatment
3.3.1 Sedimentation Tanks (Primary Clarifiers)
3.3.2 Skimming Devices
3 15-19
3.3.3 Use of Coagulants (Optional)
3.4 Working Principle of Primary Treatment
`
 ABSTRACT
TITLE: Advanced waste water treatment.

As urbanization and industrial activities increase, the demand for cleaner and more sustainable water
resources intensifies. Conventional wastewater treatment methods, while effective at removing large
contaminants and organic matter, are often insufficient for addressing emerging pollutants such as
pharmaceuticals, microplastics, nutrients, and pathogens. Advanced wastewater treatment (AWT)
represents a critical evolution in treatment processes designed to achieve higher water quality
standards. AWT involves the application of innovative physical, chemical, and biological techniques,
including membrane filtration (e.g., reverse osmosis, ultrafiltration), advanced oxidation processes
(AOPs), nutrient removal technologies, and bioaugmentation. These methods aim to remove residual
suspended solids, dissolved contaminants, and micropollutants that escape primary and secondary
treatments.

Key AWT technologies include membrane bioreactors (MBRs), which combine biological treatment with
membrane filtration for superior contaminant removal, and AOPs like ozonation and UV/H₂O₂, which
degrade complex organic molecules into harmless end-products. Additionally, nutrient recovery
processes such as biological nitrogen and phosphorus removal help mitigate eutrophication risks in
receiving water bodies. Recent advancements have also introduced sustainable practices like energy
recovery and resource recycling within wastewater plants, transforming them into water resource
recovery facilities (WRRFs).

Challenges in AWT implementation include high operational costs, energy intensity, membrane fouling,
and the management of concentrated waste streams. However, ongoing research in nanomaterials,
automation, and process optimization offers promising solutions to enhance efficiency and reduce costs.
Ultimately, advanced wastewater treatment is pivotal in safeguarding public health, protecting
ecosystems, and ensuring a resilient water supply in the face of global environmental pressures.

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2|Page
 CHAPTER 1
1.INTRODUCTION TO ADVANCED WASTEWATER TREATMENT
Water is an essential resource for all forms of life, and its contamination poses serious risks to public health
and the environment. With increasing urbanization, industrial growth, and climate change, traditional
wastewater treatment processes are often insufficient to meet stringent environmental standards. This has
led to the development and implementation of advanced wastewater treatment (AWT) technologies, which
go beyond conventional methods to remove nutrients, pathogens, micropollutants, and emerging
contaminants. These technologies are pivotal in ensuring sustainable water management, especially in
regions facing water scarcity or dealing with heavily polluted water sources.

1.1 Overview of Conventional Wastewater Treatment

To understand the need for advanced treatment, it's important to first consider the limitations of
conventional systems. Traditional wastewater treatment typically involves primary and secondary
processes. Primary treatment focuses on the removal of large solids and suspended particles through
screening and sedimentation. Secondary treatment, usually biological, employs microbial activity to
degrade organic matter. Activated sludge systems, trickling filters, and oxidation ponds are common
biological processes that reduce biochemical oxygen demand (BOD) and suspended solids.

However, while effective at reducing organic loads and pathogens, these conventional methods are not
designed to address nutrient overloads (nitrogen and phosphorus) or trace contaminants like
pharmaceuticals, personal care products, endocrine disruptors, and heavy metals. As environmental
regulations become more stringent and the need for water reuse grows, conventional treatment alone is no
longer sufficient.

1.2 Purpose and Scope of Advanced Wastewater Treatment

Advanced wastewater treatment, often referred to as tertiary treatment, is implemented after secondary
treatment to further purify effluent and make it suitable for discharge into sensitive ecosystems or for reuse
in agricultural, industrial, or even potable applications. The main objectives of AWT include:

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 Nutrient Removal: Excess nitrogen and phosphorus contribute to eutrophication in receiving water
bodies. Advanced processes such as biological nutrient removal (BNR) and chemical precipitation are
used to achieve strict nutrient limits.

 Pathogen Reduction: To ensure public health safety, especially for water reuse, AWT systems often
incorporate disinfection methods like ultraviolet (UV) radiation, chlorination, or ozonation.

 Micropollutant Removal: Substances like hormones, antibiotics, and synthetic chemicals are increasingly
found in wastewater. Techniques like activated carbon adsorption, membrane filtration (e.g.,
nanofiltration and reverse osmosis), and advanced oxidation processes (AOPs) help in degrading or
removing these contaminants.

 Water Reclamation and Reuse: One of the most pressing applications of AWT is the production of high-
quality reclaimed water for various non-potable and potable uses. In some cases, such as in Singapore
and parts of California, AWT is integrated into direct or indirect potable reuse systems.

1.3 Technologies in Advanced Wastewater Treatment

A wide array of physical, chemical, and biological technologies are employed in AWT, either alone or in
combination:

a. Membrane Technologies: Ultrafiltration, nanofiltration, and reverse osmosis are highly effective for
removing particles, bacteria, viruses, and dissolved salts. These technologies are central to membrane
bioreactors (MBRs), which combine biological treatment and membrane filtration in a compact system.

b. Activated Carbon: Both powdered and granular activated carbon can adsorb a broad spectrum of
organic compounds and micropollutants, making it suitable for polishing effluent before discharge or
reuse.

c. Advanced Oxidation Processes (AOPs): These involve the generation of highly reactive hydroxyl radicals
through methods such as UV/H₂O₂ or ozone/UV, capable of breaking down even persistent organic
pollutants.

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d. Ion Exchange and Chemical Precipitation: These are commonly used for removing specific contaminants
such as heavy metals and nutrients like ammonia and phosphate.

e. Constructed Wetlands and Natural Systems: Though often considered low-tech, constructed wetlands
can be part of AWT, offering sustainable and low-energy options for polishing effluent and removing
specific pollutants through natural processes.

1.4 Preliminary Treatment

Outcome: Remove large objects that can damage equipment or hinder further treatment.

 Screening: Large debris like plastics, sticks, and rags are removed using metal screens.

 Grit Removal: Sand, gravel, and other heavy particles settle out in grit chambers.

 Flow Equalization (optional): Balances flow and pollutant load variations before primary treatment.

1.5 Primary Treatment

Purpose: Remove settleable solids and floating materials (about 50–60% of suspended solids and 30–
40% of BOD).

 Sedimentation (Primary Clarifier): Wastewater flows slowly through large tanks so that heavy solids
settle to the bottom (forming sludge) and lighter materials float to the surface (scum).

 Both sludge and scum are removed for further treatment.

1.6 Secondary Treatment (Biological Treatment)

Purpose: Degrade dissolved and suspended organic matter using microorganisms.

 Activated Sludge Process: Air is pumped into aeration tanks where bacteria consume organic pollutants.
The mixture then flows to a secondary clarifier where biomass (sludge) settles out.

 Trickling Filters: Wastewater trickles over a bed of stones or plastic media covered with microbial
biofilm.

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 Oxidation Ponds or Lagoons: Large shallow ponds where natural biological processes treat the
wastewater over time.

1.7 Tertiary or Advanced Treatment

Purpose: Further purify effluent by removing nutrients (nitrogen, phosphorus), pathogens, and trace
contaminants.

 Filtration: Sand or membrane filters remove remaining solids.

 Nutrient Removal: Biological or chemical processes remove nitrogen and phosphorus.

 Disinfection: Chlorine, ozone, or UV light is used to kill pathogens.

 Advanced Processes: May include reverse osmosis, activated carbon, or advanced oxidation to remove
micropollutants.

1.8 Sludge Treatment and Disposal

Purpose: Stabilize and reduce the volume of sludge from primary and secondary treatment.

 Thickening: Reduces water content.

 Digestion: Anaerobic or aerobic processes break down organic matter, producing biogas.

 Dewatering: Sludge is dried using centrifuges or drying beds.

 Disposal or Use: Treated sludge may be incinerated, landfilled, or used as fertilizer if safe.

1.9 Final Effluent Discharge or Reuse

 Treated water is either discharged into rivers, lakes, or oceans or reused for agriculture, industry, or even
drinking after further treatment (in advanced systems).

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2.0 Advanced Wastewater Treatment Processes

These processes come after primary and secondary treatment and aim to remove:

 Nutrients (nitrogen, phosphorus)

 Pathogens (bacteria, viruses)

 Micropollutants (pharmaceuticals, chemicals)

 Dissolved solids, heavy metals, and toxins

1. Nutrient Removal

Nitrogen Removal

 Nitrification: Ammonia (NH₃) is converted to nitrate (NO₃⁻) by aerobic bacteria.

 Denitrification: Nitrate is reduced to nitrogen gas (N₂) by anaerobic bacteria.

 Used in: Sequencing batch reactors (SBR), oxidation ditches, or MBRs.

Phosphorus Removal

 Chemical Precipitation: Chemicals like alum or ferric chloride are added to form insoluble phosphates
that are removed as sludge.

 Enhanced Biological Phosphorus Removal (EBPR): Special bacteria accumulate phosphorus and are
removed with sludge.

a. Filtration Processes

Sand or Media Filtration

 Removes fine particles and some pathogens by passing water through layers of sand or granular media.
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 Membrane Filtration

 Ultrafiltration (UF): Removes bacteria and viruses.

 Nanofiltration (NF) & Reverse Osmosis (RO): Removes salts, micropollutants, and even some
pharmaceuticals.

 Common in water reuse and desalination systems.

b. Disinfection Methods

Ultraviolet (UV) Disinfection

 UV light damages microbial DNA, making pathogens inactive.

 No chemical residues; effective against bacteria and viruses.

Chlorination

 Chlorine or chlorine compounds kill pathogens.

 May produce disinfection byproducts (DBPs), so often followed by dichlorination.

Ozonation

 Powerful oxidant that destroys microorganisms and oxidizes organic compounds.

 Also helps with taste, odor, and color control.

c. Micropollutant & Emerging Contaminant Removal

Activated Carbon Adsorption

 Powdered Activated Carbon (PAC) or Granular Activated Carbon (GAC) traps organic pollutants like
pharmaceuticals, pesticides, and hormones.

Advanced Oxidation Processes (AOPs)

 Combines ozone, hydrogen peroxide, and/or UV to produce hydroxyl radicals.

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d. Specialized Techniques

Membrane Bioreactor (MBR)

 Integrates biological treatment with membrane filtration.

 Produces high-quality effluent suitable for reuse.

Ion Exchange

 Removes specific ions (like ammonia, nitrate, or heavy metals) using resin beds.

Constructed Wetlands

 Natural treatment using plants and microbial action.

 Polishes effluent and removes nutrients in eco-friendly systems.

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 CHAPTER 2

2.PRELIMINARY TREATMENT IN WASTEWATER MANAGEMENT

2.1 Overview

Preliminary treatment is the first major step in the process of wastewater treatment. Its main goal is to
remove large solids, grit, oils, and floating materials that can cause damage or reduce the efficiency of
subsequent treatment stages. By doing so, it protects pumps, pipes, and other mechanical equipment
from clogging and abrasion, and ensures smoother operation of secondary treatment processes.

This stage doesn't involve biological treatment or chemical changes; instead, it focuses on physical
separation methods. Although it may seem basic, it is absolutely essential for the overall success and
longevity of the treatment plant.

2.2 Objectives of Preliminary Treatment

The primary objectives of preliminary treatment are:

 Protection of Equipment: Prevent clogging, fouling, and excessive wear of downstream equipment.

 Reduction of Suspended Solids: Remove larger floating and settleable materials.

 Improvement of Overall Efficiency: Increase the efficiency of biological and chemical treatment by
minimizing the load.

 Odor Control: Early removal of organic matter that could decay and produce foul smells.

 Prevent Environmental Damage: Avoid the release of harmful solids into receiving waters or
environments.

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 2.3 Major Units of Preliminary Treatment

Preliminary treatment typically involves several key processes, each designed for specific types of
materials:

2.3.1 Screening

Purpose: To remove large objects such as rags, plastics, sticks, cans, and other debris.

Types of Screens:

 Bar Screens: Heavy-duty metal bars placed at regular intervals. Debris is trapped and manually or
mechanically removed.

 Fine Screens: Finer openings (less than 6mm) to capture smaller particles.

 Micro-screens: Very fine mesh used in specialized cases to remove very small particles.

Cleaning Methods:

 Manual Cleaning: In smaller plants or during emergencies.

 Mechanical Cleaning: In larger plants, automatic raking systems remove trapped materials.

Importance: Prevents blockages in pumps and pipes downstream.

2.3.2 Comminution

Purpose: Instead of removing large solids, comminutors grind or shred them into smaller pieces,
allowing them to continue through the treatment process.

How it Works:

 Solids are directed into grinders equipped with rotating cutting blades.

 The materials are cut into smaller sizes without being physically removed.

Importance: Reduces the risk of clogging downstream equipment without the need for manual removal
of solids.

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 2.3.3 Grit Removal

Purpose: To remove dense inorganic materials like sand, gravel, cinders, and broken glass.

Why it’s Important:

 Grit can cause excessive wear on pumps.

 It settles in channels and tanks, reducing flow capacity.

Methods:

 Horizontal Flow Grit Chambers: Water velocity is controlled so that heavier grit settles out while lighter
organic matter remains in suspension.

 Aerated Grit Chambers: Air is pumped into the chamber, allowing lighter organic particles to remain
suspended while heavier grit settles.

 Vortex Grit Chambers: Circular flow causes grit to move to the center and settle at the bottom.

2.3.4. Pre-Aeration

Purpose: To add air to the wastewater before further treatment.

Functions:

 Helps in the removal of oil and grease by flotation.

 Reduces odors by providing oxygen to aerobic bacteria.

 Aids in grit removal by promoting settling.

Implementation:

 Wastewater is passed through tanks where air is bubbled through diffusers.

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 2.3.5 Oil and Grease Removal

Purpose: To remove floating oil and grease which can interfere with biological treatment.

Methods:

 Skimming Tanks: Special tanks where oil rises to the surface and is skimmed off.

 Air Flotation Units: Fine bubbles attach to oil particles and bring them to the surface for removal.

Importance: Prevents scum formation and protects biological reactors.

2.4 Flow Scheme of Preliminary Treatment

The typical sequence of preliminary treatment units is:

1. BAR SCREENING

2. FINE SCREENING/COMMINUTION

3. GRIT REMOVAL

4. PRE-AERATION

5. OIL AND GREASE REMOVAL

Each step prepares the wastewater for the more sensitive primary and secondary treatment phases.

2.5 Advantages Of Preliminary Treatment

 Protects downstream processes from damage and inefficiency.

 Minimizes operational costs by reducing wear and tear on equipment.

 Improves overall plant efficiency by reducing the solid load early on.

 Reduces odors and environmental nuisance early in the treatment process.

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 2.6 Challenges in Preliminary Treatment

 Handling and Disposal of Collected Materials: Screenings and grit must be properly disposed of, often at
landfills.

 Equipment Maintenance: Screens, grinders, and grit removal systems require regular cleaning and
servicing.

 Odor Control: Even preliminary units can be sources of bad odors if not properly managed.

 Energy Consumption: Mechanical cleaning and aeration systems add to the plant’s energy demands.

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 CHAPTER 3

3.PRIMARY TREATMENT IN WASTEWATER MANAGEMENT

3.1 Overview

Primary treatment is the second major stage in the wastewater treatment process, following preliminary
treatment. Its primary purpose is to remove settleable organic and inorganic solids by sedimentation and
to remove materials that will float (such as grease and oil) by skimming. Unlike preliminary treatment,
primary treatment deals with finer particles and partially reduces the organic load before the water
enters the secondary (biological) treatment.

Primary treatment focuses mainly on physical separation rather than chemical or biological processes.
Even though it does not remove all contaminants, it significantly reduces the pollutant load, making the
next treatment steps much more efficient.

3.2 Objectives of Primary Treatment

The main objectives are:

 Removal of Suspended Solids: Settleable solids are separated from the liquid by gravity.

 Reduction of Organic Load: Partially reduces Biochemical Oxygen Demand (BOD) by removing organic
solids.

 Improvement of Downstream Efficiency: Eases the burden on secondary treatment units.

 Oil and Grease Removal: Skimming helps remove floating materials such as fats and oils.

 Protection of the Environment: Reduces the amount of solids and pollutants discharged into water
bodies.

Typically, 30-40% of BOD and 50-60% of suspended solids are removed during primary treatment.

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 3.3 Major Components of Primary Treatment

Primary treatment usually involves sedimentation tanks or clarifiers, skimming devices, and sometimes
chemical aids to improve the process.

3.3.1 Sedimentation Tanks (Primary Clarifiers)

Purpose: To allow heavy solids to settle at the bottom and lighter materials to rise to the top.

Design Features:

 Inlet Zone: Distributes incoming wastewater evenly across the tank to avoid turbulence.

 Settling Zone: The calm area where solids can settle by gravity.

 Sludge Zone: Where settled solids accumulate at the bottom.

 Outlet Zone: Clarified water exits the tank through weirs.

 Scum Removal Equipment: Skimming mechanisms collect floating oils and debris.

Types of Sedimentation Tanks:

 Rectangular Tanks: Long and narrow, with sludge scrapers moving the settled material to hoppers.

 Circular Tanks: Water enters at the center and flows outward; a rotating scraper collects sludge.

Operational Factors:

 Detention Time: Typically, 1.5 to 3 hours.

 Surface Overflow Rate: About 800-1200 gallons per day per square foot (gpd/ft²).

 Sludge Removal: Sludge is continuously or periodically removed and sent for further treatment.

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 3.3.2 Skimming Devices

Purpose: To remove floating materials such as oil, grease, and lighter organic solids.

How It Works:

 Surface scum is collected by rotating arms or mechanical skimmers.

 Skimmed materials are sent to separate sludge treatment units or disposal systems.

Importance:

 Prevents the buildup of fats and oils in the downstream biological treatment processes.

3.3.3 Use of Coagulants (Optional)

Sometimes, chemicals like alum, ferric chloride, or polyelectrolytes are added to the influent to enhance
the settling of finer particles. This process is called chemically enhanced primary treatment (CEPT).

Benefits:

 Increases the removal efficiency of BOD and suspended solids.

 Reduces the load on secondary treatment.

Downsides:

 Additional operational costs.

 Production of more chemical sludge that needs further handling.

3.4 Working Principle of Primary Treatment

The primary treatment works on simple principles of physics:

a) Gravity Separation:

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o Solids heavier than water settle under gravity.

o Light materials (oil, grease) rise to the surface.

b) Flow Velocity Control:

o The speed of the wastewater through tanks is controlled to promote settling without resuspension.

c) Collection and Removal:

o Settled solids are collected at the bottom and pumped to sludge treatment.

o Floating materials are skimmed off the top.

The result is primary effluent, which is much clearer and ready for biological treatment, and primary
sludge, which is thickened and processed separately.

3.5 Performance of Primary Treatment

Typical Removal Efficiencies:

o Suspended Solids: 50-60%

o BOD: 30-40%

o Oil and Grease: 60-90%

Factors Influencing Performance:

o Temperature (warmer water improves settling).

o Flow rates (too fast reduces efficiency).

o Characteristics of incoming wastewater (density, particle size).

3.6 Advantages of Primary Treatment

o Simple and Reliable: Requires minimal energy compared to biological or chemical processes.

o Cost-Effective: Lower operational costs.

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o Reduces Load on Secondary Treatment: Smaller biological units needed.

o Reduces Environmental Impact: Lower solids content in discharged effluent.

3.7 Challenges in Primary Treatment

o Sludge Management: Sludge produced needs separate treatment (thickening, digestion, dewatering).

o Odor Control: Organic sludge can produce unpleasant odors if not promptly removed.

o Incomplete Treatment: Primary treatment alone cannot remove dissolved pollutants or nutrients like
nitrogen and phosphorus.

o Space Requirements: Sedimentation tanks need considerable space.

3.8 Applications of Primary Treatment

o Municipal Wastewater Treatment Plants: Almost universally included.

o Industrial Effluent Treatment: Where large quantities of settleable solids are generated.

o Combined Sewer Systems: Handling both sewage and stormwater.

o Pretreatment Before Advanced Treatment Systems: Like membrane bioreactors (MBR) and tertiary
treatment units.

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 CHAPTER 4

4.SECONDARY TREATMENT IN WASTEWATER TREATMENT

4.1 Overview

Wastewater treatment is a crucial process for maintaining public health and environmental integrity. It is
generally divided into three stages: primary, secondary, and tertiary treatment. After the physical
removal of large particles during primary treatment, secondary treatment plays a key role by biologically
removing dissolved and suspended organic matter. This step uses microbial processes to degrade organic
contaminants and substantially improves water quality before it is discharged into the environment or
sent for further purification.

4.2 Purpose of Secondary Treatment

The primary goal of secondary treatment is to significantly reduce the biological oxygen demand (BOD)
and suspended solids content of the wastewater. BOD is a measure of the amount of oxygen required by
aerobic microorganisms to break down organic material. If untreated, high BOD levels in discharged
water can lead to oxygen depletion in receiving water bodies, harming aquatic life.

Secondary treatment also helps in:

o Reducing pathogenic microorganisms.

o Preparing wastewater for potential nutrient removal (in tertiary treatment).

o Stabilizing organic waste to prevent foul odors.

4.3 Biological Processes Used in Secondary Treatment

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 Secondary treatment relies on microbial communities, mainly bacteria, to digest organic pollutants.
There are several types of systems used:

4.3.1 Activated Sludge Process

This is the most common method in modern wastewater treatment plants.

o Process: Wastewater is mixed with a small amount of sludge (containing microorganisms) in an aeration
tank. Air (or pure oxygen) is pumped into the tank to keep the microorganisms active and to supply
oxygen for aerobic digestion.

o Flocculation: Microorganisms and solids clump together to form flocs.

o Sedimentation: After sufficient aeration, the mixture flows to a secondary clarifier where the flocs settle
out as sludge.

o Sludge Recycling: Some of the sludge is recycled back to the aeration tank to maintain an active
microbial population.

4.3.2 Trickling Filters

This method uses a bed of stones, plastic media, or other materials.

o Process: Wastewater is sprayed over the filter media where a biofilm (microbial layer) grows.

o Degradation: As wastewater trickles over the media, the biofilm consumes organic material.

o Sloughing: As the biofilm grows thicker, parts of it slough off and are collected for removal.

4.3.3 Rotating Biological Contactors (RBCs)

These are mechanical systems that rotate large discs partially submerged in wastewater.

o Process: As the discs rotate, they alternately expose the biofilm growing on them to wastewater and air,
promoting aerobic digestion.

o Advantages: RBCs are energy-efficient and require less maintenance than activated sludge systems.

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 4.3.4 Sequencing Batch Reactors (SBRs)

A batch process that combines aeration and settling in a single tank.

o Cycle: Fill → React → Settle → Draw → Idle.

o Benefits: Flexible and capable of handling variable flow rates.

4.4 Key Parameters and Conditions

For secondary treatment to be effective, several conditions must be carefully controlled:

o Dissolved Oxygen (DO): Adequate oxygen levels must be maintained to support aerobic microbes.

o Temperature: Microbial activity depends on temperature, typically optimized between 20–35°C.

o pH: Most microbial communities thrive in neutral pH (around 6.5–8.5).

o Retention Time: Sufficient time must be given for microbial degradation.

o Sludge Age: In activated sludge processes, maintaining an optimal sludge age (time biomass stays in the
system) is critical.

4.5 Challenges in Secondary Treatment

Despite its effectiveness, secondary treatment faces several challenges:

o Shock Loads: Sudden increases in pollutant concentration can disrupt microbial populations.

o Toxic Substances: Industrial waste can contain substances toxic to microorganisms.

o Foaming and Bulking: In activated sludge processes, certain filamentous bacteria can cause foaming or
poor sludge settling.

o Energy Consumption: Aeration requires significant energy input, making the process costly.

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 4.6 Outcomes of Secondary Treatment

After secondary treatment, wastewater typically achieves:

o 85-95% reduction in BOD and suspended solids.

o Significant reduction in pathogens, although disinfection (tertiary treatment) may still be necessary.

o Production of secondary sludge, which must be treated and disposed of separately.

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 CHAPTER 5

5. TERTIARY (ADVANCED) WATER TREATMENT

5.1 Overview

Tertiary treatment, also called advanced water treatment, is the third stage of water and wastewater
treatment. It comes after primary treatment (which removes solids) and secondary treatment (which
removes biodegradable organic matter). Tertiary treatment is designed to further polish the water,
removing remaining contaminants to produce high-quality effluent suitable for discharge into sensitive
environments or for reuse.

Tertiary treatment focuses on removing:

o Remaining suspended solids,

o Nutrients (such as nitrogen and phosphorus),

o Pathogens (like bacteria and viruses),

o Dissolved inorganic and organic substances (such as heavy metals, pesticides, and pharmaceuticals).

With the increasing demand for water reuse and environmental protection, tertiary treatment is
becoming an essential part of modern water treatment plants.

5.2 Objectives of Tertiary Treatment

o Achieve very high-quality effluent suitable for reuse or safe environmental discharge.

o Remove nutrients (nitrogen and phosphorus) that cause eutrophication in receiving waters.

o Eliminate pathogens to protect public health.

o Remove fine suspended solids and residual organics.

o Address emerging contaminants like microplastics, pharmaceuticals, and endocrine-disrupting chemicals.

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 Tertiary treatment ensures compliance with strict environmental standards and supports sustainable
water management through water recycling and resource recovery.

5.3 Major Processes in Tertiary (Advanced) Treatment

Tertiary treatment can involve a variety of physical, chemical, and biological processes depending on the
goals of the treatment plant.

5.3.1 Filtration

Filtration is used to remove any remaining suspended solids from the secondary-treated effluent.

5.3.1.1 Types of Filtration:

o Sand Filters: Water passes through layers of sand and gravel.

o Dual Media Filters: Use layers of different materials (like sand and anthracite) for better performance.

o Membrane Filtration:

o Microfiltration (MF): Removes bacteria and fine particles.

o Ultrafiltration (UF): Removes viruses and smaller organic molecules.

Advantages:

o Simple operation.

o High removal efficiency for solids.

5.3.2 Nutrient Removal

a. Nitrogen Removal:

o Nitrification: Ammonia (NH₃) is converted to nitrate (NO₃⁻) by nitrifying bacteria.

o Denitrification: Nitrate is reduced to nitrogen gas (N₂) by denitrifying bacteria under anoxic conditions.

b. Phosphorus Removal:

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o Chemical Precipitation: Adding chemicals like alum or ferric chloride forms insoluble phosphates that are
settled out.

o Biological Phosphorus Removal: Special bacteria accumulate phosphorus within their cells.

Importance:

o Prevents algal blooms and oxygen depletion in lakes, rivers, and coastal waters (eutrophication).

5.3.3 Advanced Oxidation Processes (AOPs)

These involve generating highly reactive species like hydroxyl radicals (•OH) that can oxidize and break
down complex organic pollutants.

Examples:

o Ozonation (O₃): Ozone gas oxidizes organics, pathogens, and odors.

o UV/H₂O₂ Treatment: Ultraviolet light combined with hydrogen peroxide produces radicals that degrade
micropollutants.

o Fenton Reaction: Use of iron and hydrogen peroxide to produce hydroxyl radicals.

Applications:

o Treating pharmaceuticals, pesticides, and resistant organic compounds.

5.3.4 Activated Carbon Adsorption

How It Works:

o Water passes through activated carbon (powdered or granular).

o Organic compounds, chlorine, taste, and odor-causing compounds are adsorbed onto the carbon surface.

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 Advantages:

o High efficiency in removing micropollutants.

o Polishes water for reuse applications.

Types:

o Granular Activated Carbon (GAC): Used in fixed-bed filters.

o Powdered Activated Carbon (PAC): Added to the water and later separated.

5.3.5 Disinfection

The final step to ensure pathogens are destroyed before water discharge or reuse.

Methods:

o Chlorination: Traditional, but can form harmful disinfection byproducts.

o Ultraviolet (UV) Irradiation: Effective against bacteria, viruses, and protozoa without chemical residuals.

o Ozonation: Strong oxidizer, but requires complex equipment.

Considerations:

o Balance between effective pathogen removal and minimizing harmful byproducts.

5.4 Emerging Technologies in Tertiary Treatment

1. Membrane Bioreactors (MBRs)

o Combine biological treatment and membrane filtration in one system.

o Produce very high-quality effluent.

o Compact footprint compared to conventional systems.

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 Challenges:

o Higher energy requirements.

o Membrane fouling management.

2. Reverse Osmosis (RO)

o Forces water through semi-permeable membranes under high pressure.

o Removes dissolved salts, heavy metals, viruses, and organic compounds.

Application:

o Especially important for producing potable reuse water and desalination.

Limitations:

o Expensive.

o Requires brine management.

3. Electrocoagulation

o Uses electric current to generate coagulants from sacrificial metal electrodes.

o Removes suspended solids, heavy metals, and some organic compounds.

Benefits:

o Chemical-free.

o Produces less sludge.

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 5.5 Advantages of Tertiary Treatment

o Produces very high-quality water for discharge or reuse.

o Protects aquatic ecosystems by removing nutrients and pathogens.

o Enables water recycling and supports sustainable resource management.

o Reduces public health risks associated with waterborne diseases.

5.6 Challenges of Tertiary Treatment

o High Capital and Operational Costs: Advanced systems are expensive to build and maintain.

o Energy Intensive: Some processes (like RO and MBR) consume a lot of energy.

o Skilled Operation Required: Needs trained operators and strict monitoring.

o Complex Sludge and Waste Management: Advanced processes generate different waste streams (e.g.,
RO brine, chemical sludges).

o Potential Formation of Disinfection Byproducts: Especially in chlorination and ozonation.

5.7 Applications of Tertiary (Advanced) Water Treatment

o Municipal Wastewater Plants: For discharge into rivers, lakes, or oceans with strict standards.

o Water Reuse Projects:

o Agricultural irrigation.

o Industrial cooling or process water.

o Groundwater recharge.

o Indirect and direct potable reuse (e.g., "toilet-to-tap" projects).

o Industrial Wastewater: Oil refineries, textile industries, food processing industries.

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o Stormwater Management: Polishing stormwater runoff before reuse.

5.8 Examples of Tertiary Treatment in Practice

o Orange County Water District, California: Produces drinking water from treated wastewater using
microfiltration, reverse osmosis, and UV disinfection.

o Singapore’s NEWater: Recycles treated wastewater to produce high-quality drinking water.

o Australia’s Perth Groundwater Replenishment Scheme: Uses advanced treatment for sustainable
groundwater recharge.

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 CHAPTER 6

6. SLUDGE TREATMENT AND DISPOSAL

6.1 Overview

Sludge is the byproduct generated from water and wastewater treatment processes. It consists mainly of
water (about 95–99%) along with organic and inorganic solids, microorganisms, and sometimes toxic
substances.

Effective sludge treatment and disposal are essential because untreated sludge can:

 Cause environmental pollution,

 Create public health risks,

 Emit foul odors,

 Increase treatment plant costs.

Thus, managing sludge safely and efficiently is a crucial part of the overall wastewater treatment process.

6.2 Sources of Sludge

Sludge is produced at different stages of water and wastewater treatment:

 Primary Sludge: From primary sedimentation tanks; mainly settled solids.

 Secondary Sludge (Waste Activated Sludge): From biological treatment processes (e.g., aeration tanks).

 Chemical Sludge: Produced when chemicals are used (like in coagulation and precipitation).

Each type of sludge has different characteristics that affect its treatment and disposal methods.

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 6.3 Objectives of Sludge Treatment

The main goals of sludge treatment are:

 Volume Reduction: Minimize the amount of sludge to handle and dispose.

 Stabilization: Reduce the potential for odor, putrefaction, and pathogens.

 Pathogen Reduction: Protect public health.

 Resource Recovery: Recover energy or useful materials (like biogas or compost).

 Safe and Sustainable Disposal: Ensure minimal environmental impact.

6.4 Steps of Sludge Treatment

Sludge treatment is generally divided into several key stages:

6.4.1 Sludge Thickening

Purpose:

 Increase the solids concentration by removing some of the water.

 Reduces volume and prepares sludge for further treatment.

6.4.2 Methods:

 Gravity Thickening: Sludge settles in a thickening tank.

 Flotation Thickening: Air bubbles carry sludge particles to the surface (common for lighter biological
sludge).

 Centrifugal Thickening: High-speed centrifuges separate solids and water.

 Gravity Belt Thickening: Sludge is squeezed between moving belts.

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 6.4.2.1 Typical Solids Content After Thickening:

 4–6% solids for primary sludge.

 2–5% solids for secondary sludge.

6.5 Sludge Stabilization

Purpose:

 Reduce biological activity to prevent odor and pathogen regrowth.

 Stabilized sludge is safer to handle and can sometimes be reused.

Methods:

a. Aerobic Digestion

 Uses oxygen to break down organic matter.

 Suitable for small plants.

 Produces stable, non-odorous sludge.

 Higher energy consumption due to aeration.

b. Anaerobic Digestion

 Decomposition of sludge in the absence of oxygen.

 Produces biogas (methane + carbon dioxide), which can be captured for energy.

 Common in medium to large plants.

 Lower energy input compared to aerobic digestion.

c. Composting

 Sludge is mixed with bulking agents (like wood chips) and composted aerobically.

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 Produces a soil-like product (biosolids) usable as fertilizer.

d. Lime Stabilization

 Adding lime raises the pH and inhibits microbial growth.

 Simple and cost-effective, but adds to sludge volume.

6.6 Sludge Dewatering

Purpose:

 Further remove water to reduce sludge volume and weight for easier handling and disposal.

Methods:

 Belt Filter Press: Sludge is pressed between moving belts.

 Plate and Frame Filter Press: Sludge is compressed between plates.

 Centrifuges: High-speed spinning separates water.

 Drying Beds: Sludge dries naturally under the sun (low-tech, land-intensive).

Typical Solids Content After Dewatering:

 20–30% solids for mechanical dewatering.

 60–70% solids for drying beds.

6.7 Sludge Drying and Heat Treatment (optional)

Purpose:

 Further reduce moisture and sometimes sterilize sludge.

Methods:

 Thermal Drying: Heats sludge to evaporate water.

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 Thermal Hydrolysis: High-temperature, high-pressure treatment before digestion improves biogas
production and dewatering.

 Incineration: Burns sludge to ash, recovering energy but at high operational cost.

6.8 Sludge Disposal Methods

Once treated, sludge must be safely disposed of or reused.

1. Land Application

 Treated sludge (biosolids) can be used as fertilizer or soil conditioner.

 Rich in nutrients like nitrogen and phosphorus.

 Must meet strict regulations for pathogens and heavy metals.

Advantages:

 Recycles nutrients.

 Reduces chemical fertilizer usage.

Challenges:

 Public acceptance issues.

 Risk of contaminant buildup in soils.

2. Landfilling

 Dewatered or dried sludge is placed in engineered landfills.

Advantages:

 Easy to manage.

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 Suitable for sludge not meeting land application standards.

Challenges:

 Landfill space is limited.

 Potential for leachate generation.

3. Incineration

 Sludge is burned at high temperatures (~850°C).

 Reduces volume drastically (~90% volume reduction).

 Energy can be recovered.

Advantages:

 Highly effective volume reduction.

 Destroys organic contaminants and pathogens.

Challenges:

 High capital and operational costs.

 Air pollution control needed (e.g., scrubbers).

4. Ocean Disposal (now rare)

 Dumping sludge into the ocean was once common but is now banned in many countries due to marine
pollution concerns.

Energy and Resource Recovery from Sludge

Modern wastewater plants increasingly view sludge as a resource, not just a waste.

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 Biogas from anaerobic digestion can be used for:

o Electricity generation.

o Heating.

o Vehicle fuel (biomethane).

 Phosphorus Recovery:

o Technologies like struvite crystallization can recover phosphorus for use as fertilizer.

 Biosolids can be used for land reclamation or landscaping.

6.9 Challenges in Sludge Treatment and Disposal

 High Costs: Equipment, energy, and labor.

 Volume Management: Even treated sludge can be bulky.

 Public Perception: Concerns about odors, pathogens, and pollutants.

 Environmental Regulations: Stricter limits on land application and landfill disposal.

 Contaminants of Emerging Concern: Microplastics, pharmaceuticals, heavy metals in sludge pose new
challenges.

6.91 Recent Trends in Sludge Management

 Energy-Positive Plants: Facilities that generate more energy from biogas than they consume.

 Integrated Resource Recovery: Extracting energy, nutrients, and even water from sludge.

 Decentralized Treatment Systems: For smaller communities, using modular, efficient sludge treatment.

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 Sludge-to-Energy Plants: Thermal processing like pyrolysis and gasification turning sludge into biochar or
syngas.

Conclusion:
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Advanced wastewater treatment plays a vital role in addressing the growing environmental and public
health challenges associated with water pollution. While traditional treatment processes are effective at
removing large solids and biodegradable organic matter, they often fall short in dealing with emerging
contaminants such as pharmaceuticals, heavy metals, microplastics, and nutrient overloads. Advanced
technologies like membrane filtration, advanced oxidation processes, and enhanced biological nutrient
removal provide critical solutions to these limitations, enabling the production of high-quality effluent
suitable for reuse and safe discharge into sensitive environments.

The integration of energy-efficient systems, resource recovery methods, and automation is gradually
transforming wastewater treatment plants into sustainable water resource recovery facilities. This shift
not only improves the ecological footprint of wastewater management but also contributes to circular
economy principles by recovering valuable resources such as clean water, biogas, and nutrients.
However, challenges remain, including high capital and operating costs, the need for skilled operation,
and managing waste by-products.

Continued innovation and investment in research are essential to overcome these barriers and make
advanced treatment technologies more accessible and economically viable. With increasing regulatory
pressures and the urgency posed by climate change, the adoption of advanced wastewater treatment is
no longer optional but a necessity for building resilient, sustainable communities. Through a combination
of technological advancement, policy support, and public engagement, advanced wastewater treatment
can ensure a cleaner, healthier future for all.

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