Application of photocatalytic procedure combined with ozonation for treatment of industrial wastewater - a case study

Several kinds of industrial wastewaters contain pollutants which cannot be entirely removed by physico-chemical treatments. In this case study wastewaters of a metal-working factory were purified. The results clearly indicated that TiO_2-based heterogeneous photocatalysis combined with ozonation can efficiently decrease the COD value of the effluent from the cleaning plant currently applied, thus a final biological treatment ensures the required new (higher) level of purity. However, for waste­waters of large volume, which are generally mixtures of various process waters of different origins, the application of this heterogeneous photocatalysis at the end of the purification chain is not reasonable because of the high costs of investment. Insertion of the combined method into the middle of the cleaning technology, as a pre-treating stage of a heavily polluted constituent (an emulsion in this case) of the whole mixture before the biological treatment, is more cost effective. In the most economical procedure t he combined method is applied for the emulsion diluted with weakly polluted wash waters. Thus, the subsequent biological treatment of the total mixture decreases the COD to 116 mg dm^-3