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Chlorine is used commonly to prevent biofouling in cooling water systems. The addition of chlorine poses environmental risks in natural systems due to its tendency to form chlorination by-products (CBPs) when exposed to naturally-occurring organic matter (NOM). Some of these CBPs can pose toxic risks to aquatic and benthic species in the receiving waters. It is, therefore, important to study the fate of residual chlorine and CBPs to fully understand the potential impacts of chlorination to the environment. The goal of this study was to develop improved predictions of how chlorine and CBP concentrations in seawater vary with time, chlorine dose and temperature. In the present study, chlorination of once-through cooling water at Ras Laffan Industrial City (RLIC), Qatar, was studied by collecting unchlorinated seawater from the RLIC cooling water system intake, treating it with chlorine and measuring time series of chlorine and CBP concentrations. Multiple-rate exponential curves were used to represent fast and slow chlorine decay and CBP formation, and site-specific chlorine kinetic relationships were developed. Through extensive analysis

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A 3-dimensional hydrodynamic model was developed to simulate thermal mixing zones and predict the fate of residual chlorine and chlorination by-products (CBPs) from industrial cooling water discharged to a shallow coastal environment influenced by strong tides and winds (the Arabian Gulf). This model is novel since the individual and cumulative effects of cooling water discharges from several outfalls are estimated in a single simulation instead of requiring separate model runs for each outfall. For thermal discharge, size and configuration of the thermal plume emerging from cooling water outfalls was modeled using the concept of probability plume analysis. For CBP formation, comparatively little is known about their characteristics in saline waters. A comprehensive study was devised that included laboratory experiments to quantify the kinetics of residual chlorine loss and subsequent formation of CBPs in seawater as well as extensive field data collection and testing of Arabian Gulf seawater samples for chlorine and CBPs in the vicinity of the discharges. Equations to describe site-specific chlorine reactions were developed to replicate observations. This empirical approach takes into account the complexity of the reactions between organic precursors and chlorine, which usually involve several parallel pathways leading to a great variety of CBP formation products. Analysis of lab and field data obtained in this study has enabled calibration of a site-specific numerical modeling tool that can be used to study transport and fate of various constituents in the coastal area.