The investigations were carried out in the Tisza Oil
Refinery Plant (TIFO) and the Nyirbogda´ny Petrochemical
Plant (NYKV). The Tisza Petrochemical Plant was established
in the 1980s, where mixtures of freshwater and oil
waste and salt water and oil waste are purified separately
in a biological treatment system with activated sludge. The
water from the unit I of the purification system is used as
recirculating cooling water. Unit II of the system is a twostepped
biological unit from where the filtered, purified
saline water is led into a post-treatment constructed
wetland pond-units system and after several months into
the recipient, River Tisza. This combined system has been
studied more than 13 years. The raw sewage water is
transferred from the homogenising tanks through an oil
trap to a flotator and then to an aeration basin. Biogenic
materials are supplied before the aeration basin based on
chemical analysis. In the aeration basin the absorption of
oxygen is promoted by aerators in a vertical spindle. The
filtered water of purification unit II flows into the posttreatment
constructed wetland system which consists of
algal, fish and reed pond units.