Metal etching industry wastewater pretreatment by coagulation and ion exchange resins

Abstract

The removal of dissolved organic compounds (DOC) in the metal etching industry wastewater was tested by ion-exchange resins (IERs), coagulation and their combination. The appropriate IER was selected by batch and column tests out of Amberlite IR-120, IRA-900 and XAD-4. XAD-4 was the most efficient IER for the DOC removal in addition to removing the added surfactant, showing that the DOC was mostly hydrophobic in nature. The XAD-4 column treated 250 bed volumes. The minimum effluent total organic carbon (TOC) was 30 mg/L during first 50 BV and gradually increased to 90 mg/L at 250 BV. It showed that a column with 0.1 m³ bed volume would be required for the influent flow rate of 24 m³/ day, with daily regeneration. The coagulation with iron salt removed hydrophilic DOC and the minimum and optimum coagulant doses for DOC removal were 2.1 and 15.5 mg Fe(III)/mg TOC, respectively. A combination of coagulation and XAD-4 adsorption decreased minimum effluent TOC to 25 mg/L and 7 mg/L after 2.1 and 15.5 mg Fe(III)/mg TOC pretreatments, respectively. The bed life of XAD-4 was not increased because adsorption capacity is a specific property. Combination process can be used as pretreatment before RO process.

Keywords:

• Metal etching industry
• Wastewater recycle
• Coagulation
• Ion exchange
• Hydrophobicity/hydrophilicity

Acknowledgment

This research was supported by the Yeungnam University research grants in 2012. This research was financially supported by the Ministry of Knowledge Economy (MKE), Korea Institute for Advancement of Technology (KIAT) through the Inter-ER Cooperation Projects.