Toxicity and Biodegradability Behavior of Xenobiotic Chemicals Before and After Ozonation: A Case Study with Commercial Textile Tannins

Abstract

Ozonation of a natural tannin (NT; COD_o = 1195 mg/L; TOC_o = 342 mg/L; BOD_5,o = 86 mg/L) and a synthetic tannin ST; COD_o = 465 mg/L; TOC_o = 55 mg/L; BOD_5,o = 6 mg/L) being frequently applied in the polyamide dyeing process was investigated. Synthetic wastewater samples containing these tannins individually were prepared and subjected to ozonation at varying ozone doses (625– 1250 mgO₃/L wastewater), at pH = 3.5 (the application pH of tannins) and pH = 7.0 at an ozone dose of 1125 mgO₃/L wastewater. The collective environmental parameters COD, TOC, BOD₅, UV₂₅₄ and UV₂₈₀ (UV absorbance at 254 nm and 280 nm, representing aromatic and unsaturated moieties, respectively) were followed during ozonation. Changes in the biodegradability of the tannins were evaluated in terms of BOD₅ measurements conducted before and after ozonation. In addition, activated sludge inhibition tests employing heterotrophic biomass were run to elucidate the inhibitory effect of raw and ozonated textile tannins towards activated sludge biomass. Partial oxidation (45% COD removal at an ozone dose of 750 mg O₃/L wastewater and pH = 3.5) of ST was sufficient to achieve elimination of its inhibitory effect towards heterotrophic biomass and acceptable biodegradability improvement, whereas the inhibitory effect and biodegradability of NT could not be reduced via ozonation under the same reaction conditions.

Keywords:

• Ozone
• Textile Industry Wastewater
• Xenobiotic Pollutants
• Polyamide Dyeing Process
• Biodegradability
• Activated Sludge Inhibition

ACKNOWLEDGMENTS

The authors are thankful to Mr. Izzet Alaton for his courtesy of supplying the textile tannins and the Turkish Academy of Sciences for the TUBA-GEBIP scholarship.

Notes

ISO 6060:1989, Water Quality—Determination of the Chemical Oxygen Demand TC 147/SC 2, Geneva (1986).

ISO 8192:2007, Water Quality—Test for Inhibition of Oxygen Consumption by Activated Sludge for carbonaceous and ammonium oxidation. TC 147/SC 5, Geneva (2007).