Process for removal of suspended solids, colloidal solids and organic and inorganic dissolved solids

The removal of suspended solids, colloidal solids, and organic and inorganic dissolved solids from industrial waste involves several treatment processes. Each process targets specific types of contaminants and can be employed in various combinations to achieve the desired level of waste treatment. 

Removal of Suspended Solids

1. Screening:

   • Description: Physical process that removes large solids using screens with various mesh sizes.
   • Applications: Typically the first step in wastewater treatment to prevent damage to subsequent equipment.

2. Sedimentation:

   • Description: Gravity-based process where heavier suspended solids settle to the bottom of a sedimentation tank or clarifier.
   • Applications: Used in primary and secondary treatment stages.

3. Flotation:

   • Description: Air bubbles are introduced into the water, causing suspended particles to float to the surface where they can be skimmed off.
   • Applications: Effective for removing oil and grease, and fine suspended solids.

4. Filtration:

   • Description: Passing wastewater through porous media (sand, gravel, or membranes) to trap suspended solids.
   • Applications: Often used after sedimentation or flotation to further reduce suspended solids.

Removal of Colloidal Solids

1. Coagulation:

   • Description: Adding chemicals (coagulants) such as alum, ferric chloride, or polymers to destabilize colloidal particles, allowing them to agglomerate.
   • Applications: Essential for removing fine particles that cannot settle naturally.

2. Flocculation:

   • Description: Gentle mixing that encourages agglomerated particles (flocs) formed during coagulation to grow larger.
   • Applications: Typically follows coagulation and precedes sedimentation or flotation.

3. Ultrafiltration:

   • Description: Membrane filtration process that removes colloidal particles and macromolecules.
   • Applications: Used in advanced wastewater treatment for high-quality effluent.

Removal of Organic and Inorganic Dissolved Solids

1. Biological Treatment:

   • Activated Sludge Process:
     • Description: Aerobic microorganisms degrade organic matter in aeration tanks.
     • Applications: Widely used in municipal and industrial wastewater treatment.
   • Trickling Filters:
     • Description: Wastewater is distributed over a bed of media where microorganisms degrade organic matter.
     • Applications: Suitable for smaller plants or as secondary treatment.

2. Advanced Oxidation Processes (AOPs):

   • Description: Using strong oxidants (ozone, hydrogen peroxide) or UV light to break down organic pollutants.
   • Applications: Effective for removing persistent organic pollutants and achieving high levels of purification.

3. Chemical Precipitation:

   • Description: Adding chemicals to form insoluble compounds that can be removed by sedimentation or filtration.
   • Applications: Commonly used for removing heavy metals and phosphates.

4. Ion Exchange:

   • Description: Replacing undesirable ions in wastewater with more benign ions using ion exchange resins.
   • Applications: Used for softening water and removing specific inorganic dissolved solids like heavy metals.

5. Reverse Osmosis (RO):

   • Description: Applying pressure to force water through a semipermeable membrane, leaving dissolved solids behind.
   • Applications: Producing high-purity water, often used in the final treatment stage.

6. Electrodialysis:

   • Description: Using electrical potential to move dissolved ions through ion-selective membranes.
   • Applications: Suitable for desalination and removing certain inorganic dissolved solids.

Detailed Steps and Examples:

Screening

• Step: Wastewater passes through bar screens or mesh screens to remove large debris.
• Example: Removing sticks, leaves, and plastic particles.

Sedimentation

• Step: Wastewater flows into a sedimentation tank; heavy solids settle to the bottom.
• Example: Primary treatment in municipal wastewater plants to remove grit and sand.

Flotation

• Step: Air is diffused into the water, creating bubbles that attach to suspended solids.
• Example: Dissolved air flotation (DAF) units in food processing plants to remove fats and oils.

Filtration

• Step: Water passes through filter media (sand, gravel) or membranes.
• Example: Sand filters in drinking water treatment plants.

Coagulation and Flocculation

• Step: Coagulants are added to destabilize particles, followed by gentle mixing.
• Example: Alum addition in water treatment plants to remove turbidity.

Biological Treatment

• Activated Sludge: Aeration tanks where microbes digest organic matter.
  • Example: Municipal wastewater plants treating sewage.
• Trickling Filters: Wastewater trickles over a media bed where biofilms degrade organics.
  • Example: Small town sewage treatment plants.

Advanced Oxidation Processes

• Step: Combination of UV light, ozone, and hydrogen peroxide to oxidize contaminants.
• Example: Treatment of pharmaceutical residues in wastewater.

Chemical Precipitation

• Step: Addition of lime to precipitate out heavy metals as insoluble hydroxides.
• Example: Treatment of industrial effluents from plating factories.

Ion Exchange

• Step: Water passes through resin beds exchanging unwanted ions for benign ones.
• Example: Removing calcium and magnesium to soften water in industrial boilers.

Reverse Osmosis

• Step: Pressurizing water to move through a semipermeable membrane.
• Example: Desalination plants producing potable water from seawater.

Electrodialysis

• Step: Applying electric current to move ions through selective membranes.
• Example: Desalination of brackish water.

These processes are often used in combination, tailored to the specific waste characteristics and treatment goals, ensuring effective removal of all types of contaminants.