Catalytic oxidation of industrial wastewaters - a comparison study using different analyzing methods Anne Heponiemi 1 *, Laura Rahikka 1,2 , Ulla Lassi 1,2 and Toivo Kuokkanen 1 1 Department of Chemistry, University of Oulu, P.O.Box 3000, FIN-90014 Oulu, Finland 2 Kokkola University Consortium Chydenius, P.O.Box 569, FIN-67101 Kokkola, Finland. *email for corresponding author: anne.heponiemi@oulu.fi Catalytic and non-catalytic wet air oxidation of industrial wastewaters was studied. Wastewaters originating from Finnish food industry were oxidized in a stainless steel autoclave at temperature of 150 ºC and at pressure of 3.5 bar (air partial pressure). Ruthenium supported on Ce-Zr-mixed oxide was used as an oxidation catalyst. The progress of the oxidation processes were followed by sampling and analyzing water samples during the reactions. The changes in the composition of wastewaters (DOC, COD and manometric respirometric BOD) were determined as a function of time. 1. Introduction The increased consumption of water, and therefore, the growing amounts of wastewaters force to find out more ecological and cost-efficient solutions to the wastewater treatment. Further, the legislation concerning the wastewater treatment and quality continuously become more restrictive. The composition of wastewaters depends on the water source. Therefore, in the selection of the most suitable method for the specific effluent both the economics of the treatment as well as the feasibility of the process need to be considered. There are a number of different kinds of techniques available for the wastewater treatment such as chemical, physical and biological treatments and their combinations. All these technologies have their own application ranges depending on the composition and quantity of wastewaters produced. One available technique is wet air oxidation (WAO). WAO is a destructive wastewater treatment process where pollutants of the wastewater are oxidized with oxygen containing gas (typically air or oxygen) at elevated temperatures (125 ºC - 300 ºC) and pressures (0.5 - 20 MPa ) to CO 2 , water and also to intermediates which are usually carboxylic acids (Mishra et al. 1995). The enhanced solubility of oxygen in water at elevated temperatures and pressures provides a strong driving force for oxidation reaction (Kolaczkowski et al. 1999). However, the energy- intensive WAO process may be quite too expensive for industrial use. The severe conditions (high temperature and pressure) of WAO can be reduced and the efficiency