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In the present work, four oxidation techniques were investigated (O3, O3/UV, H2O2/O3, O3/H2O2/UV) to pre-treat reverse osmosis (RO) concentrate before treatment in a moving-bed biofilm reactor (MBBR) system. Without previous oxidation, the MBBR was able to remove a small fraction of the chemical oxygen demand (COD) (5-20%) and dissolved organic carbon (DOC) (2-15%). When the concentrate was previously submitted to oxidation, DOC removal efficiencies in the MBBR increased to 40-55%. All the tested oxidation techniques improved concentrate biodegradability. The concentrate treated by the combined process (oxidation and MBBR) presented residual DOC and COD in the ranges of 6-12 and 25-41 mg L(-1), respectively. Nitrification of the RO concentrate, pre-treated by oxidation, was observed in the MBBR. Ammonium removal was comprised between 54 and 79%. The results indicate that the MBBR was effective for the treatment of the RO concentrate, previously submitted to oxidation, generating water with an improved quality.

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BACKGROUND: The persistence of microcontaminants through conventional wastewater treatments is a matter of concern and it suggests the implementation of advanced treatment steps. Although there is evidence that reverse osmosis (RO) is the most efficient treatment for the the removal of these compounds, it has the drawback of producing significant amounts of highly polluted brine. In this work, chemical analyses and toxicity bioassays were combined to evaluate the removal of different pharmaceuticals and of dioxin-like compounds from RO brine through oxidative processes such as ozone, UV and UV/H 2 O 2 . RESULTS: The removal of the selected pharmaceuticals required a relatively high oxidative capacity, either by ozonation or by the combination of UV radiation and H 2 O 2 . Bioassays showed a significant dioxin-like activity in brine samples, whereas antibacterial or estrogenic activities were negligible. UV by itself was the least efficient in removing this dioxin-like activity.Ozonation appeared as the most competent treatment. CONCLUSIONS:The results of this work indicate the usefulness of advanced oxidation methods, especially ozonation, to remove biologically active micropollutants from brine samples. They also show that only the combination of chemical analyses and bioassays allows complete characterization of the efficiency of advanced water treatment processes to remove recalcitrant pollutants.