Leachate treatment by the combination of photochemical oxidation with biological process

Leachates are well known as a particular sort of problematic wastewater, both from the viewpoint of ecotoxicity and the treatment technique. Leachates from municipal waste deposits, biologically pre-cleaned, were treated subsequently by photochemical oxidation using three different UV sources. The reactor concept was based on a ‘continuous circuit reactor’ with back-mixing and thin film. The power was 84 kW/m3 for the low pressure mercury lamp, 100 kW/m3 for the middle pressure mercury lamp, and 30 kW/m3 for the vacuum mercury lamp. The ratio of chemical oxygen demand (COD) and BOD5 was reduced from ca. 230 to 3–4 (in the case of low pressure and vacuum mercury lamp) and to 6 (middle pressure mercury lamp). After the photochemical oxidation stage, the leachate was treated in an additional step using an activated sludge plant. After this biological stage, the values of COD, BOD, and AOX decreased further below the threshold values defined in the legislative regulation. The Ames-, umu-, and alkaline filter elution-tests were applied at all treatment stages. The treated water, independent on treatment stage, proved to be free of mutagens. The luminescent bacteria—green algae—as well as Daphnia-test were applied for each of the individual treatment stages.