Characterization and fenton treatment of hazardous organic substances in Para rubber industrial wastewater in Southern Thailand

Abstract

This study focuses on the characterization and treatment of the hazardous organic substances in rubber latex (Hevea brasiliensis) wastewater. In the characterization part, the organic substances in wastewater were extracted by liquid-liquid extraction (LLE) and solid-phase extraction (SPE) their separation and identification by size exclusion chromatography (SEC) and GC-MS, respectively. The variations of the raw and treated wastewater quality were monitored for 6 months, covering the cropping and leave shedding season. According to the monitoring results, there are 7 organic groups contained in the raw wastewater such as acids, indoles, phthalates, alcohols and phenols, thiazoles, thiocarbamates and the others. Two dominant species in the raw wastewater were 3-methylindole (3MI) and diisobutyl phthalate (DIBP). The first compound, 3MI, belongs to the category of bad smelling property, while the second is recalcitrant to biodegrade. Both cause the problems the para rubber industry suffers frequently, including the malodor and the effluent COD exceeding the standard value. Because of this, Fenton's treatment was proposed in this study. The synthetic wastewater of each compound was prepared and treated by Fenton's reagent. The optimum operating conditions were determined. The results show that the optimal molar ratio of [H[subscript 2]O[subscript 2]]:[Fe[superscript 2+]]:[DIBP or 3MI] is 5:5:1 for DIBP, and 1:1.5:1 for 3MI, given the pH of 3. With such information available, the optimum conditions were applied to the industrial wastewater, and the results of which were compared with those of the synthetic wastewater. According to the experimental results, there were significant differences in %degradation between the synthetic and the real wastewater. Consequently, the operating condition of both industrial raw and treated wastewater were re-optimized. The results show that the optimum condition for the raw wastewater was 20:10:1 for 3MI at pH 3, while the optimum values for treated wastewater were 617 mg H[subscript 2]O[subscript 2] L[superscript -1] and 70 mg Fe[superscript 2+] L[superscript -1] at pH 3. Under these conditions, the 3MI in the raw wastewater could be removed nearly 100% in 180 min, and the biodegradability index was increased by 0.1, approximately. Therefore, the Fenton's oxidation is recommended as pretreatment system for the subsequent industrial biological treatment. The DIBP and COD in the treated wastewater could be removed by 90% and 48%, respectively under the optimum condition. These are enough to meet the discharge. In addition, the empirical kinetic equations with respect to Fenton treatment were also determined for further application.