AWWA WQTC71494

The Long Beach Water Department (LBWD) is engaged in significant testing for reducing the costs associated with operating desalting membranes, including using nanofiltration membranes arranged in a two-pass configuration, and mitigating the effects attributed to biofouling. The primary objective for this research is to safely add chlorine dioxide as a chemical disinfectant prior to the reverse osmosis (RO)/nanofiltration (NF) membrane process. In order to do this it is important to establish a reliable and practical way to analyze residual chlorine dioxide in seawater. Methods tested included DPD method, Amperometric titration II, and Lissamine Green B method. Initial tests conducted with ClO₂ applied at a residual of 1 mg/L to flat sheet membranes showed rapid membrane degradation (measured as function of increased permeate flux and salt passage). Because the ClO₂ was generated using free chlorine as a reagent, it was questioned whether the ClO₂ or free chlorine caused the membrane degradation. Significant difficulties were encountered when analyzing ClO₂ and free chlorine in seawater, not only due to the high ionic strength but the byproducts which were created when the disinfectants were added. In the end, this investigation resulted in a more reliable technique. This paper details the step-by-step process used to modify the Amperometric Titration II method to develop a reliable method for measuring ClO₂ and chlorine in seawater. Includes 4 references, table, figures.