pH Neutralization System

Overview

• Fully automated system with automatic controls and alarm.
• Controls the pH of wastewater before discharge.

Understanding pH

• pH is a measure of acidity or alkalinity of water.
• Scale: 0 to 14
  • <7: Acidic

  • 7: Basic (Alkaline)

• Bases neutralize acids; acids neutralize bases.
• Byproducts are usually soluble or insoluble salts and water.

System Functionality

• Adjusts pH of process stream to an acceptable discharge range.
• Common chemicals used:
  • Acid: 98% sulfuric acid
  • Base: 50% sodium hydroxide (NaOH)
• Chemical selection considerations:
  • Health and safety
  • Cost and convenience
  • Storage environment and location

Chemical Neutralization Process

• Neutralization involves adding hydroxide ions (OH-) or hydrogen ions (H+).
• Acid Neutralization: Caustic (NaOH) is used.
  • Process: Solution transferred to primary pH neutralization tank.
  • pH electrode senses and displays pH.
  • Chemical metering pump dispenses caustic to adjust pH.
  • If pH > 9.0, acid is dispensed to decrease pH to 7.5.

System Stages

1. Stage 1:
   • pH adjusted from 3.0 to 6.0 units.
   • Mixer agitates solution.
   • Caustic dispensed if needed.
2. Stage 2:
   • Further agitation in tank 2.
   • pH adjusted from 6.0 to 7.5 units.
   • Acid dispensed if pH > 9.0.

Final Monitoring

• Treated wastewater flows to final pH monitoring device and flow meter.
• Final pH meter is for monitoring only (no chemical control).
• Continuous recording of pH and flow rate on a digital chart recorder.
• Effluent flows to sewer via gravity.