Influence of salinity on partial nitrification in a submerged biofilter

Partial nitrification under various concentrations of NaCl (0–40 g/l) at a constant operational condition was investigated in a submerged biofilter reactor. The highest NO2–N/NOx–N ratio (0.76) was achieved at the NLR of 830 g NH4–N/m3 day with salt free wastewater. Small increase the salt content led to higher activities and the NH4–N removal efficiency increased from 92% to 95% at 1 g/l NaCl concentration. Over this concentration, each NaCl addition provoked the NH4–N oxidation and a sharp increase of inhibition was observed. The total oxidized NH4–N was achieved at the nitrogen loading rate (NLR) and surface loading rate (SLR) of 0.754 kg/m3 day and 3.23 g/m2 day, respectively without salt in the feed wastewater and it was decreased to 0.322 kg/m3 day and 1.38 g/m2 day at the salinity of 40 g/l in the PNBR.