Recycling of wastewater is regulated (amongst other parameters)
by COD content. This parameter can be easily obtained without
the need of a specific and expensive apparatus as it is the case
for TOC analysis. Additionally, in oxidation processes even when no
appreciable TOC changes have been observed, low COD values indicate
the formation of small carboxylic acids (acetic, oxalic, maleic,
etc.) of non-toxic nature, i.e. contamination reduction is more correlated
to COD depletion than to TOC elimination. Consequently,
COD was adopted as the parameter to indicate the wastewater
contamination level, and therefore, it was used in the modelling
process. As stated previously, the presence of dissolved ozone
immediately after the start of experiments suggests that the process
is chemically controlled, i.e. slow reactions develop in the
aqueous bulk and/or with the solid COD. A simple power kinetic
law was proposed of the form