Water Pollution and Control: Tertiary Methods

 Water Pollution and Control:

Membrane Separation:

Membrane separation is a process that uses thin, semi-permeable membranes to separate molecules based on their size, charge, and other characteristics. 

Working

·            Membranes are made from materials like polymers, ceramics, and metals. 

·         The pressure difference across the membrane determines which substances can pass through. 

·         The process can be used to separate dissolved solutes from water. 

      Membrane separation uses a pressure difference across a membrane to separate molecules. The type of membrane separation process depends on the size of the molecules being separated, the desired separation efficiency, and other factors. 

1.      High pressure is applied to one side of the membrane.

2.      Smaller molecules pass through the membrane's pores, while larger molecules are blocked.

3.      The separated molecules are collected on the other side of the membrane.

Construction

Membrane

The membrane is made of a material that allows some molecules to pass through while blocking others. 

Module

The membrane is often wrapped around a central tube to form a spiral wound membrane module. 

Applications 

·         Wastewater treatment: A critical part of wastewater treatment in many industrial settings

·         Water purification: Removes microorganisms and suspended particles from water

·         Desalination: Removes dissolved ions and solutes from water

·         Food and beverage: Separates components in liquids

·         Pharmaceuticals: Separates components in liquids

·         Chemical processing: Separates components in liquids

 

      Ultrafiltration

Ultrafiltration (UF) is a process that separates substances by size using a semipermeable membrane. It's used in water treatment, food and beverage production, and in dialysis to remove excess fluid from the blood. 

Uses pressure to remove colloidal substances, high molecular organic matter, and microorganisms from water 

      Nanofiltration

Nanofiltration (NF) is a membrane-based process that uses nanometer-sized pores to separate dissolved solutes from water. It's used in many industries, including water treatment, pharmaceuticals, and food and beverage. 

Uses nanometer-sized pores to remove ions, viruses, bacteria, and other contaminants from water 

   Microfiltration:

Microfiltration is a process that uses a membrane filter to separate particles from a fluid or gas. It's often used to remove bacteria, yeast, and other microorganisms from water and other liquids. 

Reverse Osmosis:

                                The process of movement of solvent through a semipermeable membrane from the solution to the pure solvent by applying excess pressure on the solution side is called reverse osmosis.

Reverse osmosis is a membrane treatment process primarily used to separate dissolved solutes from water. Reverse osmosis is most commonly known for its use in drinking water purification, particularly with regard to removing salt and other effluent materials from water molecules.

Osmotic pressure is the minimum pressure required to stop solvent flow through the semipermeable membrane. Therefore, when the solution side (the side where the solute concentration is high) is subjected to a pressure greater than the osmotic pressure, the solvent particles on the solution side move through the semipermeable membrane to the region where the solute concentration is low. Such inverse solvent movement through the semipermeable membrane is called reverse osmosis.

It is important to note that the pressure applied to the solution side must be higher than the osmotic pressure for the reverse osmosis process to proceed. Osmotic pressure is a colligative property, which depends on the concentration of the solution. In water purification, the reverse osmosis process is very important. Many water purifiers used today use reverse osmosis in the purification process as one of the steps.

  Working:

                                An easy experiment can be conducted by taking some freshwater and a concentrated aqueous solution. The solutions should be kept on opposite sides with a semipermeable membrane placed in between to separate the two solutions. Pressure should be applied on the side with the concentrated solution. Now this will result in water molecules moving through the membrane to the freshwater side. This basically sums up the process of reverse osmosis.

Benefits of Reverse Osmosis

Some of the benefits of reverse osmosis are discussed below.

• This process can be used to effectively remove many types of dissolved and suspended chemical particles as well as biological entities (like bacteria) from the water.
• This technique has a wide application in treating liquid wastes or discharges.
• It is used in purifying water to prevent diseases.
• It helps in desalinating seawater.
• It is beneficial in the medical field.

Advantages of Reverse Osmosis

Reverse Osmosis has several advantages, including the following:

• Bacteria, viruses and pyrogen materials are rejected by the intact membrane. In this respect, RO water approaches distilled water in quality.
• Available units are relatively compact and require little space. They are well suited to home dialysis.
• In average use, the membrane has a life of a little more than one to two years before replacement is necessary.
• Periodic complete sterilization of the RO system with formalin or other sterilant is practical.

Disadvantages of Reverse Osmosis

            The disadvantages of RO systems include the following;

• Cellulose acetate membranes have limited pH tolerance. They degrade at temperatures greater than 35^oC. They are vulnerable to bacteria. They eventually hydrolyze.
• Polyamide membranes are intolerant of temperatures greater than 35oC. They have poor tolerance for free chlorine.
• Thin-film composites are intolerant of chlorine. High flux polysulfones require softening or deionization of feed water to function properly.