BAC filtration to mitigate micropollutants and EfOM content in reclamation reverse osmosis brines

•BAC filtration alone only improved some water quality parameters of the RO brine.•The highest EfOM removals were achieved by the combination of ozone and BAC.•To ensure the total removal of pharmaceuticals was necessary the integration of an AOP with BAC.•ATP analyses and FISH technique allow the assessment of the BAC filters biomass.•β-Proteobacteria was the main bacteria phylum identified in the three biofilters.

The effluent organic matter (EfOM) including micropollutants present in the concentrate streams generated from reverse osmosis (RO) based municipal wastewater reclamation processes entails environmental and health risks on its disposal to the receiving environment. The suitability of a biological activated carbon (BAC) process to treat municipal wastewater RO concentrate was evaluated at lab scale during 320 days of operation. BAC alone and combined UV/H2O2–BAC and ozone–BAC were performed. The combination of both advanced oxidation processes with the BAC filter improved considerably the water quality parameters. Overall eliminations for dissolved organic carbon, chemical oxygen demand and ultraviolet absorbance at 254 nm ranged between 50–66%, 48–66% and 73–87%, respectively, improving considerably the removals obtained without pretreatment step (28%, 19% and 37%, respectively). Moreover, although some pharmaceuticals were partially removed by the BAC filter, the integration of the UV/H2O2 or the ozone step was necessary to achieve the total removal of those micropollutants. Finally, biomass assessment techniques allowed determining the diversity of different BAC filter scenarios.