Modelagem da poluição fecal das águas do Canal do Prado, Campina Grande-PB.

Abstract

The use of drainage systems in urban areas for the transport of sanitary sewage in natura, based on the irregular discharge of domestic effluents, has been one of the primary causes of degradation of water resources in cities. This has serious consequences for the environment, through the large amount of pollutants that reach the springs. Being fecal pollution one of the main threats to urban ecosystems. Thus, the objective of this research is to analyze the process of fecal pollution in the waters of the macrodrainage system of the Riacho do Prado Watershed - Campina Grande/PB, through the computational model Storm Water Management Model - SWMM. For this, five sample points were monitored in the coated extension of the drainage channel, with the analysis of organic matter indicators and microbiological indicator. As well as the hydrological and qualitative modeling of the waters of the basin, with calibration, validation and sensitivity analysis of the SWMM model for the study area. Still, with the intention of understanding the most efficient ways to reduce the fecal pollution discharged in the Prado channel, and how the water quality variables react in function of the implementation of different interventions in the system, among them the application of LIDs techniques, simulations were carried out with different scenarios. Through the analysis of pollutant concentrations, it was found that the highest concentrations are found during dry periods. It was also verified that the quality of the water transported by the channel has a typical characteristic of sanitary sewage, ranging from concentrations considered weak to strong, manifesting a critical situation of quality in two tributaries of the main channel. As for the calibration and validation of the SWMM model, the results obtained for the simulations of the surface runoff in the channel and for the concentrations of the pollutants were consistent with the values observed in loco and in the laboratory analyses, confirming the efficiency of using this model to the simulations of the proposed scenarios. Through the local sensitivity analysis carried out to identify the most influential parameters of the model, it was concluded that the percentage of impermeable area had the greatest effect on the output data of the model, verifying for this parameter rates of change in the output data of up to 65%. In addition, the results of this research showed that despite the ability to simulate the Thermotolerant Coliforms and having obtained good performances for the Biochemical Oxygen Demand and Chemical Oxygen Demand variables, the model did not present a good representation for the bacteria, since it was not satisfactory for return times bigger. A limit return time equal to 3.28 years was observed when considering the continuity error equal to 10%. Finally, through the simulations of the proposed scenarios with interventions in the SWMM model, it was verified that the scenario that presented a greater percentage of reduction in the concentrations of pollutants consisted of the one that proposed interceptions of the points of release of domestic sewage. With values reaching 52% for Biochemical Oxygen Demand, 54% for Chemical Oxygen Demand and 69% for Thermotolerant Coliforms. In view of this, it was exposed that the irregular release of sewage into the drainage network is the main contributor to the degradation of water quality in the macro drainage system of the Prado channel. Therefore, there is a need to adopt management systems that can help reduce the impacts generated by urbanization, especially in faecal pollution of surface water.