Removal of humic acid from aqueous media using Sono-Persulphate process: optimization and modelling with response surface methodology (RSM)

Abstract

ABSTRACT The most important effect of humic acid (HA) as a natural organic matter in water is the reaction with disinfectants and the generation of toxic and carcinogenic byproducts. The aim of this study was to investigate the applicability of the sono-persulphate process for the removal of HA from aqueous media by box-Behnken design (BBD) using response surface methodology (RSM). This study was experimental and was performed in a laboratory-scale pilot. The effect of important operational parameters such as solution pH, persulphate concentration, and reaction time at three levels (+α, 0, and -α) was studied using a constant intensity of ultrasonic (US) waves (37 kHz) and the initial HA concentration of 25 mg/L. Optimisation and analysis of the results were performed by Design Expert 10 and the residual-HA was measured using a spectrophotometer. The results showed that the quadratic model was suitable for the data (Pvalue>0.0001) and the proposed model was confirmed with a high correlation coefficient ((R2 = 0.9966) and (R2 Adj = 0.9932)). Under the optimal conditions for the process (pH of 3, optimal persulphate concentration of 0.514 mg/L and reaction time of 39.29 min), the observed removal efficiency was 87.59%. The synergetic degradation of the sono-persulphate process and removal of COD under optimal conditions were 42.63% and 81.2%, respectively. According to the results, the sono-persulphate process was found to be an appropriate process in the degradation of HA, and the BBD was found as a suitable tool for optimising the process conditions in the removal of HA.