Wastewater Treatment by Combination of Advanced Oxidation Processes and Conventional Biological Systems

One of the most challenging issues of the last decades is the presence of recalcitrant compounds in the effluents of wastewater treatment plants, due to their toxicity on both human health and environment. Although conventional biological processes are usually efficient for the degradation of pollutants occurring in wastewaters, most of these compounds are not effectively removed. In this context, Advanced Oxidation Processes (AOPs), which are oxidation methods relying on the action of highly reactive species such as hydroxyl radicals, are raising great interest for the removal of those organic pollutants not treatable by conventional techniques due to their high chemical stability and/or low biodegradability. As several studies pointed out the effectiveness of AOPs in the degradation of a wide spectrum of both organic and inorganic pollutants, they are considered a highly competitive wastewater treatment technology. However, in order to reduce operating costs associated to the application of AOPs, their proper combination with conventional biological processes should be considered. This work aims to discuss the most common AOPs used as pretreatment of wastewater for its biological processing, in order to highlight the enhancement of wastewater biological treatability supplied by different advanced oxidation methods. To this end, main standard tests and parameters for wastewater biodegradability assessment are also pointed out, thus providing an overview of the most reliable ones.