ENVE 420 Industrial Pollution Control NEUTRALIZATION Dr. Aslıhan Kerç

Many industrial wastes contain: - Acidic - Alkaline materials Neutralization is required prior to: - discharge to receiving waters - chemical or biological treatment Need for neutralization

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 m 3 /min m 2 Maximum H 2 SO 4 concentration 0.6%  To avoid coating of limestone with non- reactive CaSO 4  To avoid excessive CO 2 evolution which limits complete neutralization

Neutralization of Acid Wastes Through Limestone Beds v f = 2 – 2.4 m 3 /m 2 hr Up –flow beds  higher hydraulic loading rates can be used v f = m 3 /m 2 hr (~10)

Mixing Acid Wastes with Lime Slurries Lime Slaked lime NaOH Na 2 CO 3 NH 4 OH 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% CO 2 can be used Bubbled through the waste CO 2  H 2 CO 3 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