The impact of the phosphorus limitation on denitrification efficiency and specific sludge production in industrial wastewater treatment

ABSTRACT Heterotrophic denitrification is applied to the treatment of industrial wastewater from nitrated products with high concentrations of residual nitric and sulphuric acids and without organic matter. Wastewater with a concentration of nitrate nitrogen of 100–400 mg/L needs to be neutralized, methanol is used as an organic substrate, and phosphoric acid is used as a nutrient supplement. The pilot model of continuous denitrification was constructed with real wastewater influent. Experiments with different dosages of phosphorus 0–16.8 mg/g P/N-NOx were carried out to determine the effect of phosphorus limitation on the efficiency of denitrification. The minimum phosphorus concentration of 0.24 mg/L, representing a specific dose of P to remove oxidized nitrogen of 1.8 mg/g for sufficient denitrification efficiency was found after a sufficient time of adaptation of 70 days of the denitrification culture to low phosphorus concentrations in the reactor. Long-term successive reduction of phosphorus supply led to an increased proportion of organisms within the denitrifying sludge with lower phosphorus requirements. The results indicated that potential savings could be achieved by reducing phosphoric acid demand although limited phosphorus supply did not reduce specific sludge production.