BOD-DO Modelling and Water Quality Analysis to Sewage Effluent in Guaratuba Bay, Southern Brazil

Trog -Ferreira, A; Cun h a, C.L.N.; Sant'Ana, D.O.; Gon çalves, J.E., 2024. BOD-DO modelling and water quality analysis to sewage effluent in Guaratuba Bay, southern Brazil. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 1104-1108. Charlotte (North Carolina), ISSN 0749-0208. This study aims to evaluate the effects of sewage discharge into the Guaratuba Bay, located in the southern region of Brazil, using an environmental modeling tool. The cities of Matinhos and Guaratuba, municipalities located in the Guaratuba Bay region, attract thousands of tourists during the summer, causing an increase in the local population, reaching more than one million people throughout the region, causing several environmental problems. The main issue is the increase in sanitary sewage load reaching the bay, with high concentrations of organic matter; the accumulation and persistence of effluents constitute a threat to life, and severely degrades the environment. Correct characterization of hydrodynamic circulation is the first step in studying pollutant dispersion in bays. In this regard, hydrodynamic and water quality models developed to simulate long-term transport and evaluate sewage effluent pollution in the Guaratuba Bay are presented in this study. The hydrodynamic a nd water qu ality mod els used in this study are part of the Hydrodynamic Environmental System known as SisBAHIA® (Base System of Environmental Hydrodynamics). One of the wastewater discharge consequences in the environment is the oxygen deficit, which is caused by the consumption of oxygen by bacteria to oxidize the organic matter, indicated by biochemical oxygen demand (BOD), present in sewage. For the analysis, simulations consider variations in sewage load (low and high) and seasonality (summer and winter), taking into account the implications for pollutant loads on the resident population and a projected population with tourists during the summer; for both scenarios, a 60% removal of BOD load was assumed. The results showed that the sewage discharged in the channels reaches the bay, accumulates along the regions near the estuaries and compromises water quali ty. The outer Bay is less compromised by the discharges.