ENVE 420
Industrial Pollution Control
NEUTRALIZATION
Dr. Aslıhan Kerç
Need for neutralization
• Many industrial wastes contain:
- Acidic
- Alkaline materials
Neutralization is required prior to:
- discharge to receiving waters
- chemical or biological treatment
Neutralization requirement for
biological treatment
• For biological treatment pH ?
6.5 – 8.5
Biological process itself provides a neutralization
and buffer capacity due to carbon dioxide
production.
Requirement for pre-neutralization
Types of Neutralization Processes
• Mixing acidic and alkaline waste streams
Requires sufficient equalization capacity
• Neutralization using chemicals
Neutralization of Acid Wastes Through
Limestone Beds
• Can be designed as upflow or downflow
• Max hydraulic rate for downflow (unit ?)
4 x 10-2 m3/min m2
Maximum H2SO4 concentration 0.6%
To avoid coating of limestone with nonreactive CaSO4
To avoid excessive CO2 evolution which limits
complete neutralization
Neutralization of Acid Wastes Through
Limestone Beds
Up –flow beds  higher hydraulic loading
rates can be used
vf = 2 – 2.4
m3/m2 hr
vf = 3 - 40 m3/m2 hr
(~10)
Mixing Acid Wastes with Lime Slurries
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Lime
Slaked lime
NaOH
Na2CO3
NH4OH
Mg(OH)2
This method is useful below pH 4.2
Mixing Acid Wastes with Lime Slurries
• In lime slaking reaction is accelerated by heat
and agitation
• Neutralization can be defined by basicity
factor.
• Titration of 1 g sample with excess HCl, boiling
15 minutes followed by back titration with
0.5N NaOH to phenol phtalein end point
Neutralization of Basic (Alkaline) Wastes
• Any strong acid can be used for neutralization
Sulfuric acid, Hydrochloric acid
• Using flue gas for neutralization?
Flue gas that contain 14% CO2 can be used
Bubbled through the waste
CO2  H2CO3 reacts with waste
Slow reaction. May be sufficient for pH
adjustment ~ pH 7-8
• Can also be applied in spray towers
• Stepwise addition of chemicals
• Selection criteria for neutralization agents:
- Reaction rate
- Sludge production and disposal
- Safety
- Ease of handling
- Cost, Equipment cost
- Side reeactions (dissolved salts, scale
formation, heat produced)
- Effect of overdosage