Alum

Chemical Identity:

• Chemical Name: Aluminum sulfate
• Chemical Formula: Al₂(SO₄)₃·nH₂O (commonly used as the hydrate, Al₂(SO₄)₃·18H₂O)
• Common Names: Alum, papermaker's alum

Role of Alum in Effluent Treatment Plants

Coagulation and Flocculation:

• Coagulant: Alum is widely used as a coagulant in wastewater treatment. It helps in the aggregation of suspended particles into larger flocs, which can then be removed more easily through sedimentation or filtration.
• Flocculation Aid: By neutralizing the negative charges on particles, alum facilitates their coming together to form flocs.

Phosphate Removal:

• Chemical Precipitation: Alum reacts with phosphate ions in the wastewater to form insoluble aluminum phosphate, which can then be removed through sedimentation or filtration. This helps in reducing the phosphorus load in the effluent.

Turbidity Reduction:

• Clarification: By coagulating suspended solids, alum helps in reducing the turbidity of the wastewater, leading to clearer effluent.

Application of Alum in ETP

Dosage Calculation:

• Based on Influent Characteristics: The dosage of alum is determined by analyzing the characteristics of the influent wastewater, including the concentration of suspended solids, turbidity, and phosphate levels.
• Jar Testing: Laboratory jar tests are commonly conducted to determine the optimal dosage required for effective coagulation and flocculation.

Feeding Method:

• Solution Addition: Alum is typically added to wastewater in the form of an aqueous solution to ensure even distribution and efficient reaction.
• Point of Addition: Alum can be added at various stages of the treatment process, such as the rapid mix tank, flocculation tank, or directly into the wastewater stream before sedimentation.

Mixing and Reaction Time:

• Rapid Mixing: Immediate and thorough mixing after the addition of alum ensures that the coagulant is evenly distributed and reacts quickly with the wastewater constituents.
• Flocculation Time: After rapid mixing, gentle stirring is required to allow the formation and growth of flocs. This process typically takes 15-30 minutes.

Monitoring and Adjustment:

• Regular Monitoring: Monitor the pH, turbidity, and concentration of suspended solids and phosphates to ensure effective treatment.
• Adjust Dosage: Adjust the alum dosage based on monitoring results to maintain optimal treatment conditions and achieve the desired effluent quality.

Handling and Safety

• Storage: Store alum in a cool, dry place, away from moisture to prevent it from caking. Ensure that storage containers are sealed properly.
• Handling: Use personal protective equipment (gloves, masks, goggles) to avoid irritation from dust or contact with skin and eyes. Alum can be mildly corrosive.
• Safety: Although alum is generally safe to handle, it is slightly acidic and can cause skin and eye irritation. Handle with care and follow safety guidelines to prevent accidents.