A comprehensive guide to chemical dosing systems – design, operation, and common applications.

Common Chemicals Used

pH Adjustment

• Acids: Sulfuric acid, hydrochloric acid
• Bases: Sodium hydroxide (caustic soda), lime

Coagulation/Flocculation

• Coagulants: Alum, ferric chloride, PAC
• Flocculants: Cationic, anionic, non-ionic polymers

Disinfection

• Chlorine: Sodium hypochlorite, chlorine gas
• Other: Ozone, hydrogen peroxide

Dosing System Components

Storage Tank

• Material: HDPE, FRP, SS316
• Capacity: 7-30 days supply
• Features: Level indicator, overflow drain

Dosing Pump

• Types: Diaphragm, piston, peristaltic
• Capacity: 0.1-1000 L/hr
• Control: Manual, timed, flow-paced

Mixing System

• Static mixers for in-line
• Mechanical mixers for tanks
• Proper mixing time critical

Design Considerations

Sizing Criteria

• Maximum dosing rate
• Daily chemical consumption
• Storage requirements
• Backup capacity needs

Safety Features

• Secondary containment
• Emergency shutdown
• Leak detection
• Safety showers/eyewash

Control Systems

Manual Control

• Fixed stroke/adjustment
• Operator monitoring
• Simple but labor-intensive

Automatic Control

• Flow-paced: Dosing proportional to flow
• pH-controlled: Maintains setpoint
• PID control: Optimized response

Common Applications

• Coagulant dosing for filtration
• pH adjustment for discharge
• Chlorine disinfection
• Polymer preparation and dosing

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