Application of Ozone and Advanced Oxidation Processes to the Treatment of Lye-Wastewaters from the Table Olives Industry

An important fraction of wastewaters generated in the black table olives industry results from the treatment of the olives with sodium hydroxide for debittering and darkening of the fruit. These lye-wastewaters are characterized by a high presence of organic compounds, mainly phenols and polyphenols. The decomposition of that organic content was studied by means of several chemical treatments: ozonation alone and combined with hydrogen peroxide or UV radiation, as well as UV radiation alone and combined with hydrogen peroxide. The degradation levels and the effect of the additional presence of H₂O₂ and UV radiation on the organic matter removal were established for these processes. An approximate kinetic study was conducted, which led to the evaluation of the rate constants for the organic matter reduction. In a second phase, non-pretreated lye-wastewaters and preozonated wastewaters were degraded biologically by means of aerobic microorganisms. The evolution of the organic matter and the biomass were followed. It was demonstrated that the pretreatment with ozone significantly enhances the efficiency of the aerobic process, increasing both the substrate removal level and the degradation rate. This enhancement is probably due to the elimination of most of the toxic phenolic compounds and the increase of the biodegradability in the ozonation pretreatment.