Paulo Cesar Colonna Rosman

Comparative study of fecal bacterial decay models for the simulation of plumes of submarine sewage outfalls.

In the literature, analytical models have been shown to be extremely useful for estimating the decay rates of coliform as fecal indicator microorganisms, providing reliable predictions of bathing conditions in coastal and continental waters. Although a number of different formulations have been developed in the literature, each one may only be suitable for specific environments, and no comparison between these methods has ever been carried out. In the present article, a comparative analysis of bacterial decay models, calculated by eight different formulations, was performed in coastal outfall plumes, considering identical environmental conditions of solar radiation, temperature and salinity. A statistical approach was applied to identify the differences in means and in behaviors of the results obtained in the various simulations. The results indicate good agreement between bacterial decay rates calculated with at least four methods that were considered more reliable, and at least one of the models was shown to be suitable for estimating bacterial decay rates under night-time conditions, considering only the combined influences of temperature and salinity. Moreover, under daytime conditions, it provides consistent decay rates when compared with measurements taken in the field.

Coupling bacterial decay and hydrodynamic models for sewage outfall simulation

The evaluation of wastewater concentrations in coastal environments has to be accurate for water quality control. The description of the physical process in a comprehensive model is a complex task. Due to the different spatial and temporal scales involved, the use of different numerical models is required: far-field hydrodynamic models; near-field and pollutant transport models. In this paper, a coupled application of these models is described. Capabilities and limitations of modelling techniques applied to wastewater mixing and dispersion from submerged multiport discharges are discussed for environmental impact analysis. The recommended procedure combines a near-field mixing zone model, such as NRFIELD, with the Lagrangian far-field flow and water quality models within SisBaHia® (http://www.sisbahia.coppe.ufrj.br/). The results showed that the model coupling improves the description and analysis of treated wastewater discharges over large scales. This allows a more realistic evaluation of the environmental impact due to domestic sewage discharges in coastal waters.

Using modelling techniques to assess sewage pollution in the Potengi River Estuary, Brazil

The Potengi River Estuary (PRE) is a fragile system governed by the interaction of diverse physical-chemical and biological processes, and its ecological, economic and cultural importance for the State of Rio Grande do Norte, Brazil, is unquestionable. The present paper assesses sanitary sewage pollution in the PRE using a numerical model, thereby contributing to the solution of environmental problems. The water quality model used in this study is part of the Hydrodynamic Environmental System (SisBAHIA ® ). Organic matter is introduced into bodies of water mainly through the discharge of domestic sewage, although it may be present in industrial wastes or it may occur naturally, as part of biogeochemical cycles. Large amounts of organic matter may increase the number of microorganisms and, consequently, cause the excessive consumption of dissolved oxygen (DO). Two indicators of organic matter in water are generally used: biochemical oxygen demand (BOD) and dissolved oxygen (DO). Simulations were performed considering two scenarios: the current one and a projected one, which exhibits a 90% removal of the BOD load. Results from the combined numerical model show that sewage discharged into the Baldo Channel reaches the estuary, accumulates along the regions nearest to it and significantly compromises water quality. However, the model shows that this improvement does not occur uniformly in the PRE.

Modeling of coastal water contamination in Fortaleza (Northeastern Brazil)

An important tool in environmental management projects and studies due to the complexity of environmental systems, environmental modeling makes it possible to integrate many variables and processes, thereby providing a dynamic view of systems. In this study the bacteriological quality of the coastal waters of Fortaleza (a state capital in Northeastern Brazil) was modeled considering multiple contamination sources. Using the software SisBaHiA, the dispersion of thermotolerant coliforms and Escherichia coli from three sources of contamination (local rivers, storm drains and submarine outfall) was analyzed. The models took into account variations in bacterial decay due to solar radiation and other environmental factors. Fecal pollution discharged from rivers and storm drains is transported westward by coastal currents, contaminating strips of beach water to the left of each storm drain or river. Exception to this condition only occurs on beaches protected by the breakwater of the harbor, where counterclockwise vortexes reverse this behavior. The results of the models were consistent with field measurements taken during the dry and the rainy season. Our results show that the submarine outfall plume was over 2 km from the nearest beach. The storm drains and the Maceió stream are the main factors responsible for the poor water quality on the waterfront of Fortaleza. The depollution of these sources would generate considerable social, health and economic gains for the region.