Nitrate removal from a nitrate-rich reverse osmosis concentrate: Superior efficiency using the bioaugmentation of an Acinetobacter biofilm

Highly effective nitrate removal from a nitrate-rich reverse osmosis (RO) concentrate was achieved by the bioaugmentation of a new Acinetobacter isolate. The anoxic denitrifying capabilities of the isolate were studied in a real RO concentrate solution (containing 230 mg/L nitrate, 14,120 mg/L total dissolved solids, and 18 mg/L biological oxygen demand) obtained from a brackish, nitrate-rich groundwater desalination facility. The treatment of the real RO concentrate with a biofilm afforded a nitrate removal efficiency up to four times greater than that of a bioaugmented bacterial suspension of the Acinetobacter isolate in both batch and continuous bioreactors (nitrate removal rates: 1.34 and 1.37 kg-N/m³•d, respectively). These values are the highest rates of groundwater and groundwater RO concentrate denitrification ever reported. Additionally, the developed method provides the highest denitrification ratio (C:N = 3:1) between biological nitrate assimilation and denitrification. Lastly, both the isolate suspension and the biofilm cultures were able to consume all the organic matter supplemented to the concentrate, which is important since that the organic matter must be removed prior to chlorination and release. This bacterium, therefore, has great potential for successful nitrate removal during RO concentrate treatment.