Edinburgh Napier University

  The protection of aquatic ecosystems from artificial or natural pollutants of industrial origin is of paramount importance and technology to reduce or eliminate these from waste streams is urgently needed. Chlorophenols represent a particular group of priority toxic pollutants listed by the US EPA in the Clean Water Act and by the European Decision 2455/2001 EC. They are ubiquitous aquatic contaminants and originate from both anthropogenic and natural sources. The combined use of UV radiation and strong chemical oxidizing agents constitutes one type of advanced oxidation processes (AOPs) that has embraced modern technologies for removal of toxic organic pollutants from water and wastewater. This report presents original results on alternative technologies for the reduction of contaminants that may result in environmental burden. 2-chlorophenol (2-CP), 4-chlorophenol (4-CP) and 2,4-dichlorophenol (2,4-DCP) were degraded in water by direct UV photolysis using UV microwave lamps (254 nm) and XeBr excilamp (283 nm) in a flow-through photoreactor. The pseudo-first-order rate constants were highest and half-life times were shortest for 4-CP photolysis by both types of UV lamps. The rates of photolysis under these experimental conditions increased in the order: 2-CP < 2,4-DCP < 4-CP (excilamp) and 2,4-DCP < 2-CP < 4-CP (microwave lamps). The narrow band UV irradiation for CPs photolysis at 283 nm appeared to be more effective in comparison with broad spectrum UV irradiation and long-wavelength UVA spectral range earlier reported in the literature. The considerable improvement in the levels of 2-CP, 4-CP and 2,4-DCP degradation was also attained by microwave-assisted photolysis using UV microwave lamps. In this case, the effect of microwave thermal treatment becomes significant. The evolution of hydroquinone and p-benzoquinone as major intermediates of 4-CP photolysis was also monitored as were intermediates of photolysis identified by GC–MS and HPLC. Products of degradation were found to accumulate in the media as a result of preliminary UV treatment. A method of coupled UV-biological degradation is proposed to remove chlorophenols as well as their degradation products. It is based on the pretreatment of chlorophenols by XeBr excilamp in a flow photoreactor with subsequent biodegradation of photolysis products by the bacterium Bacillus cereus, isolated from an aeration-pond of Baikalsk pulp and paper mill (Siberia, Russia). The highest efficiency of coupled method was observed for 2-CP (95%). The results illustrate the high potential of the combination of UV irradiation from excilamp as a pre-treatment step, followed by biological treatment. This coupled treatment scheme can be associated with low investment costs and high removal capacity.