Bioreactors for brine denitrification produced during polluted groundwater desalination in fertigation areas of SE Spain: batch assays for substrate selection

Increasing knowledge of nitrate removal using denitrifying bioreactors has illustrated the usefulness of this management practice for treating discharge water from agricultural land uses. The objective of this study was to assess the viability of almond shell, chopped carob, olive bone, and citrus woodchip as carbon media for denitrification of brine with high nitrate load (EC approximate to 20 dS m(-1), NO3--N concentration approximate to 65-80 mg NO3--N L-1) in bioreactors. To the authors' knowledge, this is the first test of denitrifying brine using organic wastes as the carbon substrate, and the first use of these carbon media for that purpose. Nitrate removal efficiency and efficiency:cost ratio were considered. The results indicated that the best removal efficiency and cheapest cost were provided by citrus woodchip (3.02 +/- 0.15 mg NO3--N m(-3)d(-1)) at a cost of approximate to 6euro m(-3), followed by almond shell (1.54 +/- 0.20 mg NO3--N m(-3)d(-1)) at a cost of approximate to 19euro m(-3). Chopped carob and olive bone showed negligible nitrate removal in the brine; chopped carob generated acidic leachate with extremely high dissolved organic carbon, and olive bone resulted in a highly saline leachate. Of the four media tested, the results of this study indicated that citrus woodchip was the most suitable media for denitrification of the brine.