Wastewater recycling: Application of ozone based treatments to secondary effluents

A secondary effluent from a municipal wastewater plant has been treated by means of several processes based on the use of ozone. Application of O3 as the only oxidising reagent is capable of halving the initial COD (35 ppm at a flowrate of 40 L h−1) with a roughly 40% of mineralization degree. The system O3/H2O2 slightly enhances COD removal albeit it is capable of significantly increasing the mineralization level up to 70% (35 ppm of O3 at a flowrate of 40 L h−1 in the presence of 0.01 M of H2O2). The combination of two commercial activated carbons and ozone did not improve the results obtained in the single ozonation process. However, the simultaneous application of ozone and UV radiation showed beneficial effects both in the COD removal rate and TOC conversion if compared to ozonation alone. The systems applied in this work can be acceptably modelled by empirical mathematical expressions based on the inlet ozone concentration, hydrogen peroxide concentration, COD, etc.