The aim of the investigation described in this work is to gain a better understanding of the processes involved in the oxidation of organic compounds by photolytic ozonation in a laboratory scale reactor. The results and discussions are presented in Chapter III. This chapter contains four parts. In the first part, mass transfer efficiency and the calculation of the mass transfer coefficient, KLa, as well as the ozone decomposition rate constant, KD, are presented and compared with those obtained by other investigators. The second part deals with the kinetics of the photolysis of 2,2',4,4',6,6'-hexachlorobiphenyl both in purified and natural lake water. Mathematical expressions and a discussion of the possible reaction processes involved are given. Kinetic models of ozonation and photolytic ozonation in purified and natural lake water are developed and discussed in part three. Rate constants are calculated from experimental data and used to predict values of substrate destruction with a mathematical model. The fourth part of this chapter deals with the identification of products from the photolysis, ozonation and photolytic ozonation of 2,2'4,4',6,6'-hexachlorobiphenyl. The products are isolated and identified using combined gas chromatography and mass spectroscopy, and reaction mechanisms are suggested.