Decolorization and Biodegradability Enhancement of Synthetic Batik Wastewater Containing Reactive Black 5 and Reactive Orange 16 by Ozonation

Abstract

The batik industry generates large amounts of highly colored wastewater. Azo dyes in batik wastewater can cause environmental pollution. In this study, synthetic batik wastewater containing 32 mg/L Reactive Black 5 (RB5) and 32 mg/L Reactive Orange 16 (RO16) was treated by ozonation in a 2 L batch reactor. The wastewater color unit was reduced from 4240 to 70 after 10 min ozonation and to below 50 after 15 min ozonation (7.3 g O3/m3, 4 L/min). The first-order decay constant for 5 min ozonation was determined to be 1.11 min−1 for RB5 and 0.82 min−1 for RO16. Biodegradation tests using activated-sludge microorganisms showed the toxicity of RB5 and RO16 for microbial respiration and revealed the detoxification of the dyes by ozonation. Three-dimensional fluorescence spectroscopy analysis indicated the temporal accumulation of ozonolysis products of RO16 and RB5. The chemical oxygen demand concentration of the wastewater was reduced from 86 mg/L to 73 mg/L by biodegradation alone, 63 mg/L by ozonation alone, and 54 mg/L by ozonation followed by biodegradation. Existing wastewater treatment plants using conventional bioprocesses can be upgraded to achieve robust dye treatment by installing the ozonation process as a pretreatment.