Does an unknown mechanism accelerate chemical chloramine decay in nitrifying waters?

Abstract

Accelerated chloramine decay has been observed after the onset of nitrification in water utilities. The reason for such rapid loss is not known. To investigate the role of chemical parameters in accelerated chloramine decay, mildly and severely nitrified bulk water samples were collected from laboratory‐scale reactors. After samples were filtered through a 0.2‐pm polycarbonate membrane filter, chloramine decay tests were conducted by adjusting similar initial chloramine residuals. Accelerated chloramine decay and significant nitrite and total ammoniacal nitrogen loss were observed in severely nitrified water. To discern whether increased nitrite levels and pH were responsible, chemical decay coefficients were determined by adjusting initial chloramine residual, nitrite, pH, and temperature in the mildly nitrified sample. The chemical decay coefficient determined in a severely nitrified sample was three to four times higher than that in a mildly nitrified sample, indicating that changes in adjusted parameters that occurred during nitrification could not explain the rapid chemical chloramine loss in severely nitrified water.