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 degrees 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 noncompetitive model adequately quantified the effect of NaCl on the rates of nitrate and nitrite reduction. The maximum reduction rate (R(D,max)) in a low salt medium and the inhibition constant (K(I)) were determined for each reductive step. The calculated kinetic parameters were R(D,max) = 25.5 +/- 0.74 mg N (g VSS h)(-1) and K(I)= 34.9 +/- 2.34 x 10(-3) g l(-1) for nitrate reduction and R(D,max) = 18.7 +/- 1.05 mg N (g VSS h)(-1) and K(I) = 62.5 +/- 3.32 x 10(-3) g l(-1) for nitrite reduction. NaCl has a greater effect on nitrite reduction rate than on the nitrate reduction rate.
