Removal of humic acid by fixed-bed electrocoagulation reactor: Studies on modelling, adsorption kinetics and HPSEC analyses

The performance of the fixed-bed electrocoagulation (EC) reactor using aluminium ball anodes has been investigated for the removal of humic acid (HA). Response surface methodology with four factors and three levels (Box-Behnken design) was used to create a set of 29 experimental runs needed for optimizing the operating conditions. Four operational parameters; initial pH (pHi): 4-8, current density (j): 2-10 mA/cm2, EC time (t): 5-25 min and initial humic acid concentration (CHA): 10-50 mg/L, were used as input parameters whereas, percentage dissolved organic carbon (DOC), UV254 and color (VIS436) removals (y1-y3) and the adsorption capacity, qt, (mg DOC/g Al produced or coulomb, y4) were used as responses of the system. Analysis of variance (ANOVA) showed a high R2 correlation coefficients value (R2 = 0.79) and satisfactory prediction for Quadratic regression models. The experimental results showed that under the optimum conditions of pHi = 4, j = 6 A/m2, t = 25 min and CHA = 30 mg/L, the EC process could effectively reduce DOC, UV254, and color as 90.8%, 96.5%, and 99.6%, respectively. Furthermore, the adsorption capacity of HA in the EC process was found to be 1740 mg DOC/g Al or 0.162 mg DOC/C. The results of the SEC showed that the affinity of the EC process is higher for the large molecular size fractions.