Metal etching industry wastewater pretreatment by coagulation and ion exchange resins

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.