Prediction and uncertainty analysis of bacteria concentrations from deep marine wastewater discharges in case of submerged wastefield formation

Wastewater discharges to marine environment by marine outfall systems are the most commonly used method of wastewater disposal in coastal regions. The aim of this study is to predict concentrations of the bacteria in marine environment originated from marine discharges in case of submerged wastefield formation and to analyse the uncertainties originated from dynamic nature of the marine environment and wastewater treatment system. The study has been realized using data collected from Antalya Bay, Antalya Hurma Wastewater Treatment Plant and Marine Outfall System. In scope of the study, diurnal wastewater flow rate fluctuations and variations of effluent bacteria concentration have been investigated for one year. Daily flow rates of the discharged effluent were obtained from Antalya Hurma Wastewater Treatment Plant for the years 2008 and 2009. Additionally, total coliform (TC) and faecal coliform (FC) concentrations of influent and effluent of the wastewater treatment plant were weekly sampled and analysed for one year to determine temporal variations of the indicator bacteria. Ambient current speed and directions are the major sources of uncertainty in the marine environment. Seasonal measurements of current velocities have been carried out near the discharge point to obtain current data needed for both dilution modelling and uncertainty analysis. Intensive in-situ sampling and analysis of wastewater borne indicator bacteria in the marine environment have also been conducted seasonally for one year to achieve the indicator bacteria concentrations for model calibration. During the seasonal sampling studies, salinity and temperature values along the water column have been measured to evaluate the seasonal mixing and stratification conditions. In addition to the in-situ sampling and measurement studies, bacteriological inactivation experiments have been carried out in the laboratory to achieve bacterial inactivation rates under different environmental conditions and to evaluate the uncertainties of the bacterial inactivation process. In the experiments, bacterial inactivation rates have been studied under separate and combined effects of salinity, temperature and solar radiation. All the results of the studies conducted in-situ and at the laboratory have been used as input data for HIDROTAM-3 hydrodynamic model and Visual Plumes discharge model, to model wastewater plume behaviour and dilution processes. Bacteria concentrations obtained from in-situ sampling studies have been used to calibrate the utilized models. Following model calibration, the wastewater plume behaviour and bacteria concentrations at different point of interests have been studied and evaluated for different management scenarios. Uncertainty analysis have been carried out to determine probability distributions of the indicator bacteria at the nearest recreational beach to the discharge point. Additionally, health risk analysis for wastewater borne Enteropathogenic E.coli have also been carried out using the probability distributions of the bacteria concentrations to evaluate infection risk at the selected recreational area close to the discharge point.