Full Scale Application of Ozone for Color Removal and Biosolids Reduction in a Textile Plant

An ozonation process was adopted for use in the full scale decolorization of the effluent from a High purity oxygen (HPO) activated sludge biological industrial textile wastewater treatment process. Prior to the adoption of the ozonation process, about 40% color removal was achieved through the biological process while the rest of the color removal was obtained through a tertiary, physical–chemical flocculation and coagulation process. Although the process was effective in removing color, large quantities of inert sludge were generated, making up as much as 60% of the total sludge from the plant. The cost for handling this sludge and for the purchase of the chemicals required for the Flocculation & Coagulation process was significant. The ozone based decolorization process has been effective in meeting effluent targets of 200 mg/l Pt-Co color and 50 NTU. The residual gas stream from the ozonation process comprising about 3.5% ozone (w/w) and about 2.5 metric tons/day of recovered oxygen is recycled back to the biological basin. The reuse of the vent gas stream from the contactor provides about 70% of the oxygenation demand at the facility. This type of recycle scheme which leverages the O2 content in the vent gas stream for supplementing the O2 demand in the biological basin has been implemented at a number of SAWM operated wastewater facilities, and is an effective tool for ensuring cost effective operations when ozone is used as an oxidizing agent in biological wastewater treatment systems.