(167b) Impact of Cool Water Blowdown from District Cooling on Surface Water Using Water Quality Analysis Simulation Program (WASP 8)

Cooling towers are primarily used for heating, air conditioning, ventilation, and other industrial purposes. They are cost-effective and far more efficient than alternative dry systems. However, due to the water loss caused by evaporation, leakage, etc. the concentration of ions increase, which could lead to corrosion and scale formation (e.g. magnesium, calcium, silica, scale inhibitors, and chloride) remain inside the tower. This can have detrimental effects on the tower and lead to corrosion problems. To prevent such operational issues, a relatively great volume of cooling water needs to be discharged regularly as blowdown and replaced with fresh water as make-up to the tower. Despite being a viable solution, the discharge of cooling water blowdown (CWBD) into water bodies must be studied to determine if there are any adverse impact on marine life. In the state of Qatar, district cooling facilities play a major role in providing large-scale cooling needs to business districts, schools, etc. There is a need to find a suitable and practical system for the management of the cool water blowdown discharge. One alternative is to consider discharge to surface water. Doha Bay which is located on the Arabian Gulf, bordering Doha, the capital city of the State of Qatar. Due to water scarcity, Qatar has certain regulations and permissible limits for industrial discharges into surface water outfalls to prevent any negative impacts on the sea. Hence, it is important to conduct a sea outfall study to investigate the fate and transport of the contaminants in the CWBD stream using a water quality modelling tool and to assess the long-term effect of such contaminants on the marine life.

Studies related to sea outfall in the Arabian Gulf are scarce, which mainly aims to investigate the ambient environment of seawater. However, risk assessment of discharging contaminants associated with CWBD in Qatar requires more research. Therefore, this study aims to examine the fate and transport of contaminants associated with CWBD in Doha Bay using the Water Quality Analysis Simulation Program (WASP8). The EPA’s WASP8 is a model that provides the users with the option to interpret and predict water quality responses to natural phenomena and manmade pollution. Two main outfalls in the Bay area are selected to model the daily variations of CWBD constituents in both outfalls. Inputs to the model, such as outfall segmentations, bathymetric data for each segment, a volumetric flow rate of CWBD discharge, inflow concentration of constituents, kinetics, and weather data will be used to develop a WASP8 model. Seawater samples are taken at each segment for both outfalls and are analyzed in the lab to determine the concentration of the main constituents of CWBD and their kinetic processes that govern the fate of the CWBD contaminants. Finally, a sensitivity analysis will be applied to investigate both, the impact of varying the volumetric flow rate and dilution effect on the fate and transport of the modelled variables