Application of green and red local soils as a catalyst for catalytic ozonation of fulvic acid: experimental parameters and kinetic

The chlorination of surface waters leads to the formation of thrihalomethans (THMs) and haloaceticacids (HAAs) due to the presence of natural organic matters. Thus, the removal of fulvic acid (FA) as one of the most prominent natural organic matters in water is necessary. Therefore, this study was aimed to evaluate the efficiency of catalytic ozonation of FA in the presence of the local montmorillonite (Mnt). The soils were collected from the Ardabil Sarcham area and used as a catalyst, after the required preparation. The variables in this study including initial solution pH, catalyst dosage, reaction time, and initial pollutant concentration were examined. For the ozonation of the samples, an ozone generator with a capacity of 5 g/h was used. It was found that, with increasing contact time, pH, and catalysts dosage, as well as decreasing initial FA concentration, the performance of the catalytic ozonation process increased significantly. The results demonstrated that radical scavengers like nitrate, chloride, sulfate, and carbonate a high concentration had very low effect on the efficiency of this process compared to conventional ozonation. The kinetic data was found to fit into the pseudo-first-order kinetic model (R-2 = 0.98) than the zero and pseudo-second-order model. The Green Mnt was more effectual than the Red Mnt at pH: pH = 7, FA concentration = 25 mg/L, time = 30 min, catalyst dosage = 1.25 g/L, inlet ozone concentration = 2.2 mg/L-min; which gave COD removals of 84.68 and 78.25%, respectively. As a whole, green and red soils increase highly the efficiency of FA removal in the catalytic ozonation process, because of low costs and availability of these soils.