Disappearance of Monochloramine and Production of Residual Oxidant in Seawater

Abstract

Monochloramine (NH₂Cl) is the strongest toxic substance resulting from chlorinated sewage effluent. To estimate of NH₂Cl on the growth of organisms in coastal region, disappearance of NH₂Cl in seawater was investigated.
Changes concentration of NH₂Cl and total oxidant in artificial seawater were determined. The concentration of NH₂Cl decreased with time and reached to 20% of the initial concentration after 6 hour at 30°C. On the other hand, 90% of the initial concentration of total oxidant was detected after disappearance of NH₂Cl. The rate constant of NH₂Cl disappearance was not concerned in the initial concentration at constant temperature. Disappearance of NH₂Cl depended on water temperature, and the rate constant followed the Arrhenius equation. The rate constant and half-life value at 20°C for NH₂Cl in seawater were 0.031 h^-1 and 10 h. These results suggested that the effluent contained NH₂Cl would be enough to effect on coastal organism until its disappearance. NH₂Cl disappearance depended on salinity. However, NH₂Cl in artificial seawater without KBr was stable even in the same condition. It was clear that the disappearance factor of NH₂Cl was in existence of Br^-. NH₂Cl changed to the other oxidant with Br^-, therefore, the product which may act on organisms still remained in seawater after disappearance of NH₂Cl.