Effects of advanced oxidation pretreatment on residual aluminum control inhigh humic acid water purification

Due to the formation of disinfection by-products and high concentrations of Al residue in drinking water purification, humicsubstances are a major component of organic matter in natural waters and have therefore received a great deal of attention in recentyears. We investigated the effects of advanced oxidation pretreatment methods usually applied for removing dissolved organic matterson residual Al control. Results showed that the presence of humic acid increased residual Al concentration notably. With 15 mg/L ofhumic acid in raw water, the concentrations of soluble aluminum and total aluminum in the treated water were close to the quantityof Al addition. After increasing coagulant dosage from 12 to 120 mg/L, the total-Al in the treated water was controlled to below 0.2mg/L. Purification systems with ozonation, chlorination, or potassium permanganate oxidation pretreatment units had little effects onresidual Al control; while UV radiation decreased Al concentration notably. Combined with ozonation, the effects of UV radiation wereenhanced. Optimal dosages were 0.5 mg O3/mg C and 3 hr for raw water with 15 mg/L of humic acid. Under UV light radiation, thecombined forces or bonds that existed among humic acid molecules were destroyed; adsorption sites increased positively with radiationtime, which promoted adsorption of humic acid onto polymeric aluminum and Al(OH)3(s). This work provides a new solution forhumic acid coagulation and residual Al control for raw water with humic acid purification.