Effects of photolytic ozonation on biodegradability and toxicity of industrial wastewater

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/O-3 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/O-3 process. On the basis of the results, a photolytic ozonation unit with conditions of UV light intensity 3.0 mW/cm(2), ozone supply rate 400g/m(3)/hr, and 1 m(3) 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.