Ozonation of Biologically Refractory Pollutants

Abstract

Advanced oxidation processes (AOPs) are an effective emerging technology for removal and enhancement of biodegradability of biologically resistant and toxic pollutants of wastewater. One of these AOPs is ozonation carried out at higher pH values. Ozone is a powerful oxidizing agent available for the treatment of industrial wastewaters. The ozonation reactions are accomplished into two pathways: direct ozone oxidation and indirect free hydroxyl radical oxidation. The industrialization of human society has grown also the risk of environmental problems caused by a diversity of anthropogenic chemicals and substances in wastewater from industry. Wide group of these substances are able to enter into the organism and interrupt with their endocrine systems. They are resistant and bioactive, thus they are able to pass conventional treatment systems, wide-spread with surface and underground water and enter into organisms. We have studied removal of 2-mercaptobenzothiazole (MBT) contained in synthetic wastewater. This xenobiotic compound is used mainly in the manufacture of rubber additive chemicals but also has other uses, notably as a corrosion inhibitor in cooling water and in antifreeze for automobiles. It is known as a widespread, toxic and poorly biodegradable pollutant. Biological treatment of the wastewaters of rubber chemicals production often seems to be problematic, most probably due to presence of MBT. In fact, MBT is used due to its fungicidal properties, or its antimicrobial effects. Data concerning the biodegradation of MBT are inconclusive. Some authors have suggested it is recalcitrant to biodegradation. MBT was not metabolised by microorganisms, which were non adapted to activated sludge to this pollutant. The feasibility of utilisation of ozonation process for reduction of concentration of MBT was investigated in laboratory scale equipment. The system was operated in batch mode. Synthetic wastewater with MBT was added into ozonation reactor at the beginning of trials. Continuous flow of oxygen 30 l h-1 was applied for generation of ozone. Ozonation trials were carried out at different performance of ozone generator in the range from 30 to 90% of the power maximum. Initial concentration of MBT in synthetic wastewater was about 50 mg l-1. Significant decrease of MBT content was observed after four minutes of ozonation. Correspondent efficiency values for COD and TOC removal were 55 and 16%. Higher removal rates were achieved in the sample with lower initial content of MBT. The highest removal rate values were observed during the first 10 minutes of the process for both COD as well as TOC content. The first order reaction kinetics follows for COD removal. Positive influence of power of ozone generator on COD removal resulted from the work.