Relação de benefício - custo ambiental dos sistemas de água e esgoto sanitário: estudo de caso, Canoas RS

Abstract

This case study was carried out at Canoas a city in the State of Rio Grande do Sul - Brazil, involving sanitation problems, mainly those related to the sanitary sewer thrown directly in the rivers and streams without any previous treatment. The sanitary service in Canoas is made by CORSAN (Companhia Riograndense de Saneamento). The company has a contract ending in 2025. However, the company is not accomplishing the goals, as was accorded between CORSAN and the City Hall. The objective of this study is to analyze the relation benefit-cost of the sanitary system in Canoas, with respect to the environmental and economic-financial aspects. Canoas has an important position in respect to the ambient because is geographically located downstream of hydrographic basins of the rivers Sinos, Gravataí and Jacuí. This last one having in its estuary the State Park of the Delta of the Jacuí, that is part of the Hydrographic Region of the Guaíba. More than 90% of the population has no access to the sanitary sewerage system. The residents do their own sanitary sewer connections directly into the pluvial drain that drives the water to the macro drainage system to the rivers and streams, impact and contaminating the environment. A station of sewerage treatment (ETE) is installed in the city and should have the capacity to treat 1.300 liters of sewer per second, however only one of the six projected modules is actually working, with less than 20% of its capacity. Practically collection nets don't exist, though the net of water has more than 795 km of extension. Regarding to the water supply, CORSAN capture water in two places, one at the city of Esteio. The main point of impounding of water is located in the Arroio das Garças (Stream of the Herons), downstream of the tributaries that lead the sewer, without treatment, through the macro-drain system until the stream. Between they, the estuary of the Arroio Araçá (Stream of the Araçá), launching greater of sewer without treatment, it is the 650 meters of distance of the capitation. In the economic-financial aspect the profit of approximately 24 million of Reais per year that Corsan earns in Canoas is drained to supply administrative expenses itself of the company and to cover the systems deficit of other cities by the method called Crossed Subsidy. Being thus, the population, paid for a precarious attention, inefficient and it supports the operation of the CORSAN in other cities. It has, in the Region Metropolitan of Porto Alegre, a process of pollution of the aquatic resources that must be eliminated, in short time; therefore they are aggravated and they grown, daily, the problems of the public health and the deterioration of the environment cam be come irreversible.