[Effect of nitrite on aerobic phosphate uptake by phosphate accumulating organisms]

Effect of nitrite at various concentration levels on aerobic phosphate uptake was investigated through a series of batch experiments. Furthermore, the effect of nitrite accumulated in the process of nitrification on aerobic phosphate uptake was studied in saline wastewater treatment. The results show that NO2(-) -N concentration of 4 mg/L inhibits aerobic phosphate uptake by phosphate uptake by phosphate accumulating organisms (PAO) and phosphate uptake rate decreases 8%. Exposure to higher nitrite concentration levels inhibits aerobic phosphate uptake severely. At NO2(-) -N concentration of 15 mg/L, phosphate uptake rate decreases 61%. The toxic effect of nitrite is presumed to be linked with free nitrous acid (FNA). Significant inhibition on aerobic phosphate uptake appeared at 0.000 2 mg/L of FNA concentration. The inhibiting effect of nitrite is found to occur only when nitrite is present. The ability of accumulating phosphate resumes afternitrite is no longer present. During the process of nitrification of nitrification of saline wastewater, the inhibition of nitrite on aerobic phosphate uptake is slight at the initial 1 - 2 h due to low nitrite accumulation. With the build-up of NO2(-) -N(up to about 8 to 9 mg/L), the inhibiting effect of nitrite increases gradually. It is found that higher ammonium concentration causes lower pH value and higher FNA concentration, which could decrease the amount of phosphate uptake.