Effects of photolytic ozonation on biodegradability and toxicity of industrial wastewater

Abstract

Two industrial wastewaters containing pesticide, dye‐auxiliary organics, respectively from BASF Co., Taiwan were used as the model wastewater and treated by photolytic ozonation to investigate the potentiality of photolytic ozonation as a pretreatment step by measuring biodegradability (BOD₅/COD), toxicity (EC₅₀), and mineralization efficiency. It was found that as treatment of industrial wastewaters by UV/O₃ process for one hour, COD just reduced 6.2%, 18%, TOC also merely decreased 2.4%, 9.5% for pesticide and dye‐auxiliary wastewater, respectively, resulting in the value of BOD₅/COD enlarged significantly to be an easily biodegradable level, and toxicity declined obviously. At this time, ozone consumption for one gram COD removed was merely 1.375 g, 1.552 g for pesticide and dye‐auxiliary wastewater, respectively, indicating extremely efficient with UV/O₃ process. On the basis of the results, a photolytic ozonation unit with conditions of UV light intensity 3.0 mW/cm², ozone supply rate 400g /m³/hr, and 1 m³ reactor volume is appreciable for allowing wastewaters to have one hour reaction time and then be oxidized to be more biodegradable (BOD₅/COD > 0.4), less toxic (EC₅₀ reduction > 50%), and the most part of mineralization work of wastewater is intended to be done by a following biological unit rather than photolytic ozonation. The combination of photolytic ozonation and biological processes enables process designer to have a good approach to industrial wastewater containing xenobiotic organics.

Key words:

• Photolytic ozonation
• biodegradability
• toxicity
• mineralization