The use of ozonation process in coke wastewater treatment

The paper presents presents the possibility of using the ozonation process in coke wastewater treatment. The wastewater produced during processing of coke was initially pre-treated mechanically in order to remove solid impurities, oils and tar substances. The raw wastewater was characterized by the phenolic odor, brown color and alkaline pH (pH 9.2). The COD value of raw wastewater was 8100 mg/dm(3) and the value of BOD was very low (180mg/dm(3)). A high concentration of total nitrogen (2420 mg/dm(3)) and TOC (2240 mg/dm(3)) was also noted. The study was conducted in three stages. In the first stage, coking wastewater was treated only by ozone, the dose of which varied from 10 mg/dm(3) to 40 mg/dm(3). The effect of pH during ozonation process was determined on TOC removal efficiency. For all of the pH values (pH=3.5, pH=7, pH=8.5 and pH=11.5) the TOC removal rate constant was determined. In the second stage, the rate OH radicals generation was accelerated by the addition of hydrogen peroxide to the reactor. The ratio by weight of COD: H2O2 was 1:2.5, 1:5, 1:10 and 1:20. In the last stage of the study, we attempted to assist the ozonation process with ultrasonic field. The sonication time was 8 minutes and the amplitude was 61.5 mu m. It was found that the ozonation process is the most effective at alkaline pH (8.5). The TOC removal efficiency was 34% (1470 mg/dm(3)) after 60 minutes of zonation. The best results of oxidation of pollutants measured as COD and TOC removal were observed when the dose of ozone was 30 mg/dm(3). The combination of sonication and ozonation has resulted in a reduction of COD and TOC values by 1000 mg/dm(3) and 300 mg/dm(3), respectively, in comparison to ozonation process alone. It was found that the most effective process in coke wastewater treatment is the combination of ozonation with hydrogen peroxide addition (COD:H2O2=1:10). The COD, TOC and BOD value were 54%, 35% and 20% lower, respectively, in comparison to ozonation process conducted alone.