Abstract

The effect of sodium chloride concentration (0.47-100 g l-1) on the rates of nitrate and nitrite reduction was studied at 37°C and pH 7.5 in a batch reactor fed with a mixture (v/v) of salmon bloodwater and synthetic substrate and inoculated with biomass adapted to saline conditions (24 g NaCl per litre). NaCl inhibited the nitrate and nitrite reduction rates; the rates were increasingly inhibited at increasing NaCl concentrations in the studied concentration range. An empiric non-competitive model adequately quantified the effect of NaCl on the rates of nitrate and nitrite reduction. The maximum reduction rate (RD,max) in a low salt medium and the inhibition constant (KI) were determined for each reductive step. The calculated kinetic parameters were RD,max = 25.5 ± 0.74 mg N (g VSS h)-1 and KI = 34.9 ± 2.34 10-3 g l-1 for nitrate reduction and RD,max = 18.7 ± 1.05 mg N (g VSS h)-1 and KI = 62.5 ± 3.32 × 10-3 g l-1 for nitrite reduction. NaCl has a greater effect on nitrite reduction rate than on the nitrate reduction rate. © Taylor & Francis, 2008.