Fate and Transport of Combined Residual Chlorine in Small Stream

Abstract

Concentration profiles of combined residual chlorine (CRC) are measured in a small stream just below a municipal wastewater outfall. Loss of CRC is found to be due primarily to volatilization. Vertical and longitudinal concentration profiles are successfully modeled with a 2‐dimensional diffusive transport model, not incorporating a stagnant film. To calibrate this model, a Henry's Law constant for CRC is determined in the laboratory. The model proves superior in the case studied to the classical two‐film model for the prediction of depth‐integrated combined residual chlorine. The diffusive transport model is nearly identical to the two‐film model under conditions of imposed gas‐phase limitation. However, the two‐film theory predicts liquid‐phase limitation for the data in this study, and as a result, significant differences exist between the two sets of model predictions. Field data clearly indicates gas‐phase limitation, which was predicted by the 2‐dimensional diffusive transport model.