Uncertainty and sensitivity analysis of dilution processes for marine discharges

Sea outfall systems are cost-effective solutions for final disposal of the wastewaters generated in coastal areas. Main design parameters of an outfall system are flow rate, initial bacteria concentration of the effluent, time required for 90% reduction of bacteria (T
₉₀
), ambient currents, discharge depth and outfall length. Discharge depth and outfall length are certain parameters whereas the other parameters are usually uncertain due to their dynamic features. These parameters could be described using probabilistic approaches. In this study, uncertainty analysis has been carried out using Monte Carlo Simulation for Antalya Sea Outfall System to obtain probabilistic bacteria concentrations at recreational areas. Additionally, sensitivity analysis has also been performed to evaluate correlations of input parameters. The estimated total coliform concentrations were below 565 and 844 cfu/100 ml with 95% probability in winter and summer seasons respectively, with dominant currents and 2500 meters away from the diffuser. The most sensitive parameter on coliform concentration was current velocity for winter and initial coliform concentration of the effluent for summer season. The obtained results are evaluated for their compliance with the recreational water quality standards.