Removal of nitrates from simulated ion-exchange brines with Paracoccus denitrificans encapsulated in Lentikats Biocatalyst

A series of batch tests was carried out in order to optimize denitrification of brines from the regeneration of ion-exchange columns (12.14 g.L− 1 Cl−, 1.35 g.L− 1 SO42−, up to 2.86 g.L− 1 N-NO3−) using Paracoccus denitrificans encapsulated in polyvinylalcohol matrix (Lentikats Biocatalyst, further LB). The elimination of nitrates followed zero-order kinetics, while the concentration of nitrite-intermediates peaked. Higher initial concentrations of nitrates resulted in faster denitrification. Higher tested concentrations of salts did not affect the denitrification rate. They did however cause significant advancing of the nitrite peaks to nitrates minimum. Maximum obtained activity of 1 kg of LB was > 1000 mg of N-NO3− removed per hour and the efficiency of nitrates removal exceeded 99%. Denitrification activity of the LB systematically decreased during the course of repetitive experiments due to a lack of nutrients within the brines, disabling any proliferation of the encapsulated microorganisms. Integration of nutrient-rich cultivation steps into the process enabled restoration of the initial denitrification activity and repetitive long-term applicability of the Biocatalyst. The results show that P. denitrificans encapsulated in Lentikats is applicable for the removal of high concentrations of nitrates from such types of ion-exchange brine.

Research Highlights
► Simulated brines were denitrified by P. denitrificans encapsulated in Lentikats Biocatalyst.
► Up to 2.27 g.L− 1 N-NO3− was eliminated with efficiency > 99%.
► No inhibition by salts (12.14 g.L− 1 Cl−, 1.35 g.L− 1 SO42−) was observed.
► Denitrification rate decreased with time from cultivation.
► Regular cultivation ensured repetitive long-term usage of encapsulated bacteria.