Date:29/12/2021 Name:Advanced Wastewater Treatment Technologies

1. Membrane Sheet:

• Comprised of a semi-permeable material.
• Usually made of polymers like polyamide (PA), polysulfone (PS), or cellulose acetate.

2. Permeate Collection:

• The membrane sheet is wound around a permeate collection tube, which acts as a central core.
• This tube collects the treated water (permeate) that passes through the membrane.

3. Feed Spacer:

• A mesh-like structure placed between membrane layers.
• Facilitates fluid flow and prevents blockages caused by fouling or deposits.

4. Feed Channel:

• The space between the membrane layers where the untreated water (feed) flows.

The construction creates a spiral structure where feedwater flows along the membrane surface in a spiral motion. As water passes through the membrane, contaminants are retained, and purified water (permeate) is collected in the central tube.

1. Track-Etched Membranes:

These membranes are produced by chemically etching a polymer film with high-energy particles, creating cylindrical pores. They have precisely controlled pore sizes and distributions.

2. Phase Inversion Membranes:

These are made by precipitating a polymer from a solution. The method alters the phase of the polymer from a solution to a solid, creating a porous structure. They offer various pore sizes and structures.

3. Ceramic Membranes:

These membranes are made from inorganic materials like alumina, titania, or zirconia. They are highly stable, with good chemical and thermal resistance. Ceramic membranes can have narrow pore size distributions.

4. Polymeric Membranes:

These membranes are constructed from synthetic polymers like polysulfone, polyethersulfone, or polyvinylidene fluoride (PVDF). They are versatile, offering different pore sizes and chemical resistances.

Membrane Fouling:

Membrane fouling refers to the accumulation of unwanted materials on the surface or within the pores of a membrane. This accumulation can comprise various substances like organic matter, minerals, microbes, or other particulates. Fouling reduces membrane efficiency, decreases permeate quality, and increases operating costs.

Membrane Cleaning by Reverse Flow:

Reverse flow cleaning, also known as backwashing, involves altering the direction of fluid flow through the membrane. By reversing the flow, accumulated materials are dislodged from the membrane surface, allowing them to be flushed out and removed. This method is effective for removing loosely attached particles and restoring some level of membrane performance.

Membrane Cleaning by Chemicals:

Chemical cleaning involves using specific cleaning agents to dissolve or disperse fouling materials. Acidic or alkaline solutions, surfactants, chelating agents, and oxidizing agents are commonly employed chemicals. These agents break down different types of fouling. For instance, acids can dissolve mineral scales, while surfactants help remove organic matter. The chemicals are circulated through the membrane system to dissolve and remove fouling substances, restoring membrane performance.

Advanced Treatment:

Advanced treatment for wastewater involves processes that go beyond primary and secondary treatment methods. It focuses on removing specific contaminants that might not be effectively addressed by conventional treatment processes. This includes the reduction of nutrients like nitrogen and phosphorus, the removal of micropollutants, and the disinfection of residual pathogens. Processes such as membrane filtration, activated carbon adsorption, and advanced oxidation techniques are common in advanced treatment.

Tertiary Treatment:

Tertiary treatment is a specific subset of advanced treatment and is often considered the final stage in the wastewater treatment process. It further improves the quality of effluent from secondary treatment by removing remaining contaminants and solids. Tertiary treatment methods usually involve additional filtration, disinfection (often using chlorination or UV treatment), and sometimes advanced chemical processes to meet specific water quality standards before discharge or reuse.

Type of Microorganisms:

The microorganisms primarily involved in phosphorus removal through biological processes are phosphorus-accumulating organisms (PAOs) and polyphosphate-accumulating organisms (PAOs). These include certain types of bacteria within the classes of Proteobacteria and Actinobacteria.

Role of Microorganisms in Phosphorus Removal:

PAOs and PAOs play a crucial role in phosphorus removal by utilizing biological mechanisms to store excess phosphorus within their cells in the form of polyphosphate. This process occurs under specific environmental conditions, such as alternating aerobic and anaerobic conditions in the treatment system.

During the aerobic phase, these microorganisms take up organic compounds and use them as an energy source while storing excess phosphorus. In the subsequent anaerobic phase, they release stored phosphorus as orthophosphate, which precipitates as insoluble compounds. These insoluble phosphorus compounds are then removed from the system through sedimentation or filtration processes, effectively reducing phosphorus levels in the treated water.

Nitrification:

Nitrification is a two-step biological process involving specific bacteria:

1. Ammonia-Oxidizing Bacteria (AOB):
   • Bacteria like Nitrosomonas and Nitrosospira convert ammonia (NH3) to nitrite (NO2-) by oxidation.
   • Chemical equation: NH3 + O2 → NO2- + 3H+ + 2e-
2. Nitrite-Oxidizing Bacteria (NOB):
   • Bacteria such as Nitrobacter and Nitrospira further oxidize nitrite (NO2-) to nitrate (NO3-).
   • Chemical equation: NO2- + 0.5O2 → NO3-

De-nitrification:

De-nitrification involves a series of steps where specific bacteria are crucial:

1. De-nitrifying Bacteria:
   • Bacteria like Paracoccus, Pseudomonas, and Bacillus facilitate the reduction of nitrates to nitrogen gas.

Chemical steps in de-nitrification:

1. Conversion of nitrate to nitrite: NO3- → NO2-
2. Reduction of nitrite to nitric oxide: 2NO2- → 2NO + 2e- + 2H+
3. Reduction of nitric oxide to nitrous oxide: 2NO + 2H+ → N2O + H2O
4. Reduction of nitrous oxide to nitrogen gas: 2N2O → N2 + 2O2

Chemicals Used in Phosphorus Removal:

1. Aluminum Salts (Alum or Aluminum Sulfate - Al₂(SO₄)₃):

   Equation for phosphorus precipitation:

   Al³⁺ + H₂PO₄^- → AlPO₄(s) + 2H⁺

2. Iron Salts (Iron Chloride or Iron Sulfate):

   Equation for phosphorus precipitation:

   Fe³⁺ + H₂PO₄^- → FePO₄(s) + 2H⁺

3. Calcium Salts (Calcium Hydroxide or Calcium Chloride):

   Equation for phosphorus precipitation:

   Ca²⁺ + 2HPO₄^2- → CaHPO₄(s) + 2OH^-

Sketch of Wastewater Treatment Plant:

Chemical Addition Points for Phosphorus Removal:

• At the influent stage, where wastewater enters the treatment plant:
• Chemicals (Aluminum, iron, or calcium salts) are added at the primary treatment stage for phosphorus precipitation.
• Highlighted points:
• Mixing chambers or dosing units for chemical addition.
• Schematic representation of the primary treatment stage where chemicals are added to facilitate phosphorus removal.

i) Adsorbate:

Adsorbate refers to the substance or molecules that are attracted to and accumulate on the surface of a solid or liquid material through the process of adsorption. These molecules adhere to the surface due to various intermolecular forces, creating a layer or film of the adsorbate on the adsorbent material.

ii) Adsorption Capacity:

Adsorption capacity is the maximum amount of adsorbate that a given adsorbent material can hold or adsorb under specific conditions, such as a particular temperature, pressure, or concentration of the adsorbate in the surrounding environment. It is typically measured in terms of mass or volume of adsorbate per unit mass or volume of the adsorbent.

iii) Chemisorption:

Chemisorption is a type of adsorption process wherein the adsorbate molecules form chemical bonds with the atoms or molecules of the adsorbent surface. Unlike physisorption (physical adsorption), which involves weak van der Waals forces, chemisorption results in stronger and more specific interactions, often involving electron sharing or transfer between the adsorbate and the adsorbent surface.

Mass Transfer Zone in Activated Carbon Contactor:

The mass transfer zone in an activated carbon contactor is the region within the contactor where the primary adsorption process occurs. It represents the area where contaminants from the water being treated come into contact with the activated carbon surface, leading to the adsorption of these contaminants onto the carbon particles.

Sketch Description:

1. Activated Carbon Contactor: A vessel or column containing activated carbon particles.
2. Inlet: Represents the entry point for the water containing contaminants.
3. Mass Transfer Zone: The section of the activated carbon bed where the adsorption of contaminants onto the carbon surface predominantly occurs.
4. Outlet: Where treated water exits the contactor after the adsorption process.

The mass transfer zone is critical for efficient adsorption. The longer the contact time between the contaminated water and the activated carbon within this zone, the more effective the adsorption process becomes.

Visualizing this concept involves a columnar structure with an inlet for contaminated water, a defined zone where adsorption predominantly occurs (the mass transfer zone), and an outlet for treated water.

Characteristics of a Good Adsorbent:

1. Porous Structure: A good adsorbent should possess a high surface area with a well-developed porous structure. This facilitates more sites available for adsorption.
2. High Surface Area: Increased surface area allows for more interaction between the adsorbate molecules and the adsorbent surface, enhancing adsorption capacity.
3. Chemical Stability: Stability under varying chemical conditions ensures the adsorbent's durability and performance in diverse environments.
4. Specific Surface Chemistry: Tailored surface chemistry allows for affinity towards specific contaminants, improving selectivity in adsorption.
5. Regenerability: The ability to be regenerated or reused after adsorption by desorbing the adsorbed substances.
6. Low Cost and Availability: Cost-effectiveness and availability in sufficient quantities are essential for practical and economical applications.
7. Mechanical Strength: Adequate mechanical strength prevents breakdown or pulverization during usage, ensuring long-term effectiveness.
8. Environmental Compatibility: Minimal environmental impact during production, usage, and disposal is a desirable characteristic for sustainable applications.

Factors Affecting Ion-Exchange Process:

1. Nature of Ion-Exchange Resin: Properties such as resin type, functional groups, and porosity impact ion-exchange efficiency.
2. pH of the Solution: The acidity or alkalinity of the solution influences ion-exchange capacity and selectivity.
3. Temperature: Heat affects the rate of ion exchange and the equilibrium between ions.
4. Ion Concentration: Higher ion concentrations generally lead to faster exchange rates.
5. Particle Size: Smaller particle sizes of the resin increase the surface area available for exchange.

Explanation of Factors:

1. Nature of Ion-Exchange Resin:
The properties of the ion-exchange resin, such as its type (e.g., cationic or anionic), specific functional groups attached to the resin, and porosity significantly impact the effectiveness of ion exchange. The nature of the resin determines the types of ions it can attract and exchange, as well as the capacity and selectivity for specific ions.

2. pH of the Solution:
pH influences the ionization of functional groups on the resin. For example, in acidic conditions, cation-exchange resins with weak acidic groups are more effective, while anionic resins with weak basic groups perform better in alkaline conditions. The pH also affects the solubility and dissociation of ions, thereby impacting ion-exchange capacity and efficiency.

External MBR:

In an external MBR system, the membrane modules are located outside the biological reactor tank. The mixed liquor containing microorganisms and suspended solids is circulated from the bioreactor tank to the membrane modules by a pump.

The membrane modules, usually in the form of flat sheets or hollow fibers, are arranged outside the tank in a separate unit. They function to separate the treated effluent from the mixed liquor, retaining solids and allowing only purified water to pass through the membrane.

Submerged MBR:

In a submerged MBR system, the membrane modules are submerged directly within the biological reactor tank. The membrane elements, typically immersed in the mixed liquor, separate the treated water from the activated sludge.

The mixed liquor flows across the membrane surface, and the pressure gradient or suction forces the purified water through the membrane while retaining the biomass and suspended solids within the tank.

Chemical Coagulation:

Process: Chemical coagulation involves the addition of coagulants (such as aluminum sulfate, ferric chloride) to the water. These coagulants neutralize the charges of suspended particles, causing them to aggregate and form larger flocs that can be easily removed.

Operation: It is a well-established process used in conventional water treatment plants and wastewater treatment facilities.

Advantages:

• Proven effectiveness in removing turbidity, suspended solids, and some dissolved substances.
• Relatively simple operation and widely accepted in treatment plants.

Electrocoagulation:

Process: Electrocoagulation involves the use of electric current to destabilize and aggregate suspended particles and contaminants. The current generates metal ions from sacrificial electrodes, which neutralize charges and cause coagulation.

Operation: It is an emerging technology that uses electricity to treat various types of water and wastewater.

Advantages:

• Efficient in removing contaminants, heavy metals, and certain organic compounds.
• Potential for reduced chemical usage and lower sludge production compared to chemical coagulation.
• Ability to target specific pollutants in water streams.

Considerations: Electrocoagulation systems might require careful monitoring to manage energy costs and electrode maintenance.

Membrane Materials:

Membranes used in various separation processes are constructed from diverse materials, each with specific properties tailored for particular applications. Common membrane materials include:

• Polymers: Materials like polysulfone (PS), polyethersulfone (PES), polyvinylidene fluoride (PVDF), and polyethylene (PE) are widely used due to their chemical resistance, flexibility, and ease of manufacturing.
• Ceramics: Inorganic materials such as alumina, titania, and zirconia offer high thermal and chemical stability, making them suitable for harsh conditions and high-temperature applications.
• Composites: These membranes combine different materials to achieve specific properties, for instance, blending polymers with ceramic nanoparticles to enhance both strength and selectivity.
• Metal Membranes: Metals like stainless steel or alloys provide robustness but are less common due to cost and challenges in fabrication.

The choice of membrane material depends on factors like desired separation efficiency, chemical compatibility, operating conditions (temperature, pH), and cost-effectiveness for a particular application.

Membrane Materials:

Membranes used in various separation processes are constructed from diverse materials, each with specific properties tailored for particular applications. Common membrane materials include:

• Polymers: Materials like polysulfone (PS), polyethersulfone (PES), polyvinylidene fluoride (PVDF), and polyethylene (PE) are widely used due to their chemical resistance, flexibility, and ease of manufacturing.
• Ceramics: Inorganic materials such as alumina, titania, and zirconia offer high thermal and chemical stability, making them suitable for harsh conditions and high-temperature applications.
• Composites: These membranes combine different materials to achieve specific properties, for instance, blending polymers with ceramic nanoparticles to enhance both strength and selectivity.
• Metal Membranes: Metals like stainless steel or alloys provide robustness but are less common due to cost and challenges in fabrication.

The choice of membrane material depends on factors like desired separation efficiency, chemical compatibility, operating conditions (temperature, pH), and cost-effectiveness for a particular application.

Differentiation between Electrocoagulation and Electro-Oxidation

	Electrocoagulation	Electro-Oxidation
Process	Uses electric current to destabilize and aggregate suspended particles by generating metal ions from sacrificial electrodes.	Involves the direct application of an electric current to oxidize or break down contaminants, transforming them into less harmful substances or gases.
Objective	Destabilizes and aggregates suspended solids, colloids, and some dissolved substances for easier removal.	Targets the degradation or conversion of organic pollutants, pathogens, and refractory compounds into simpler and less harmful forms.
Mechanism	Metal ions from electrodes neutralize charges, leading to coagulation and flocculation of contaminants.	Oxidation occurs at the anode, generating reactive species like hydroxyl radicals that break down pollutants.
Contaminant Removal	Effective in removing turbidity, suspended solids, heavy metals, and certain ions through coagulation and precipitation.	Efficiently degrades organic pollutants, pathogens, and refractory compounds through oxidation reactions.
Applicability	Widely used for pretreatment in wastewater prior to conventional treatment or for specific contaminant removal.	Suitable for treating complex organic compounds, dyes, pesticides, and persistent pollutants, offering higher efficiency in targeted degradation.
Byproducts	Produces sludge or precipitates that require subsequent separation.	May generate byproducts or intermediate compounds that need monitoring or further treatment for complete removal.
Energy Consumption	Moderate energy consumption, generally lower compared to some other advanced treatment methods.	Consumption might vary but can be higher due to the need for sustained oxidation reactions.

List of Photochemical Processes:

• Photolysis
• Photocatalysis
• Photooxidation
• Photoreduction
• Photodegradation

Catalytic Photochemical Process for Wastewater Treatment:

Catalytic photochemical processes involve the use of catalysts to accelerate or enhance the degradation of contaminants in wastewater under the influence of light.

Key Elements:

• Catalyst: Utilizes semiconducting materials such as titanium dioxide (TiO₂) as a catalyst.
• Light Source: UV or visible light initiates the activation of the catalyst.
• Mechanism: Photogenerated electron-hole pairs on the catalyst's surface induce redox reactions, leading to the breakdown of organic pollutants.
• Reaction: Reactive oxygen species (ROS) like hydroxyl radicals (•OH) formed during the process attack and degrade organic pollutants into harmless byproducts.
• Advantages: Increased efficiency in treating recalcitrant organic compounds, pesticides, dyes, and pharmaceuticals compared to traditional methods.
• Considerations: Optimal catalyst concentration, light intensity, and contact time are crucial for effective pollutant removal.

Working Principle of Electrodialysis:

Electrodialysis is a membrane-based separation process used for the selective separation of ions from a solution by employing an electric field.

Key Components:

• Ion-Exchange Membranes: These selectively allow the passage of either cations (positively charged ions) or anions (negatively charged ions) based on their charge.
• Electrodes: Placed on either side of the ion-exchange membranes, electrodes create an electric field across the membrane stack.
• Feed Solution: The solution containing mixed ions to be separated is introduced into the electrodialysis cell.
• Process:

When an electric potential is applied across the stack of alternating anion and cation exchange membranes, it results in the migration of ions towards their respective electrodes. Positively charged ions (cations) move towards the negatively charged electrode (cathode), while negatively charged ions (anions) migrate towards the positively charged electrode (anode).

As a result of this migration, cations are selectively transported through the cation-exchange membranes, and anions through the anion-exchange membranes, effectively separating the ions present in the feed solution into different compartments or channels within the electrodialysis cell.

Application:

Electrodialysis finds extensive use in various industries for desalination, purification of brackish water, selective removal of ions from solutions, and in the production of ultrapure water for industrial applications.

Electroflotation Process:

Electroflotation is a method used for the removal of suspended particles, oils, and other contaminants from water or wastewater by using electrolysis and gas flotation.

Key Components:

• Electrodes: An anode and a cathode are placed in the treatment chamber.
• Power Supply: Provides the necessary electric potential between the electrodes.
• Process:

The electrolysis process involves the following reactions at the electrodes:

Anode Reaction: At the anode (positive electrode), typically made of iron or other materials, water undergoes oxidation:

2H₂O → O₂ + 4H⁺ + 4e^-

This reaction generates oxygen gas and protons (H⁺) while releasing electrons.

Cathode Reaction: At the cathode (negative electrode), hydrogen ions combine with electrons to produce hydrogen gas:

4H⁺ + 4e^- → 2H₂

Hydrogen gas bubbles rise to the surface, carrying suspended particles and oils attached to them. The process creates a froth or foam layer at the surface, which can be easily removed to separate the contaminants from the water.

Application:

Electroflotation is commonly used in wastewater treatment plants, oil-water separation processes, and various industries to efficiently remove suspended solids, oils, and other pollutants from water streams.

Working Principle of Electrooxidation Process:

Electrooxidation is a technique used in wastewater treatment to oxidize organic and inorganic pollutants by applying an electric current.

Key Components:

• Anode: It serves as the positive electrode.
• Cathode: It functions as the negative electrode.
• Electrolyte: Conductive solution or wastewater being treated.
• Process:

The electrooxidation process involves redox reactions at the electrodes:

Anode Reaction (Oxidation): At the anode, typically made of materials like titanium or platinum, oxidation occurs:

2H₂O → O₂ + 4H⁺ + 4e^-

This reaction generates oxygen gas, protons (H⁺), and releases electrons.

Cathode Reaction (Reduction): At the cathode, hydrogen ions and water interact to produce hydrogen gas:

4H⁺ + 4e^- → 2H₂

Hydrogen gas bubbles form and rise to the surface, helping to neutralize the pH in the vicinity of the cathode.

Electrochemical Oxidation: The released oxygen gas (O₂) and reactive oxygen species (ROS) like hydroxyl radicals (•OH) generated at the anode attack and oxidize organic pollutants into simpler and less harmful compounds through complex oxidation reactions:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O

This represents the oxidation of glucose into carbon dioxide and water, showcasing the breakdown of organic compounds into benign substances.

Application:

Electrooxidation is utilized in wastewater treatment to efficiently degrade various organic pollutants, industrial dyes, pesticides, and pharmaceuticals, leading to the reduction of environmental contaminants.