A Lab Scale Study to Investigate the Monochloramine Demand and Decay in the Tarrant Regional Water District’s Large Diameter Pipelines in the Presence of Biofilm

Biofilm growth in the Tarrant Regional Water District (TRWD) pipelines increases their operational costs and affects the life of their pipes. TRWD has been treating the raw water by adding monochloramine for the biofilm control, but it has difficulties in maintaining the residual monochloramine over the full lengths of the pipelines. In this study, experiments were conducted in the UTA Environmental Engineering Laboratory in the presence and absence of biofilm to simulate the initial monochloramine demand and decay rates in the Cedar Creek (CC) and Richland Chambers (RC) pipeline systems. Biofilms were grown and harvested from pilot plants at the CC and RC pump stations and added to the reactors as TSS. From this study, it is found that the presence of biofilm increased the initial demand and decay over 48 h of total chlorine and monochloramine. Also, demand over 48 h for total chlorine and monochloramine increased significantly with temperature. For the better biofilm control, a year-round application of chloramine at a dosage of 5 mg/L formed above pH 8.0 is recommended.