Análise da viabilidade econômica do aproveitamento de água de chuva para edificações verticais do tipo residencial na cidade de João Pessoa-PB.

Abstract

The systems for the use of rainwater emerge as measures aimed at the conservation and reduction of water waste and represent one of the most prominent contemporary alternatives with regard to water sustainability in urban areas. These rainwater catchment systems make it possible to reduce the consumption of drinking water, saving the use of good quality water that has undergone several processes to reach potability, provide the minimization of floods in urban areas and is an alternative that can be cheaper than the water supply, since do not require advanced technologies for its implementation and operation. Thus, the general objective of this work was analyzed the economic feasibility of implementing a system to use rainwater to meet non-potable uses in vertical residential buildings in the city of João Pessoa-PB. The analysis included assessing the possibility of using the water collected by the system for use in flushing sanitary basins. Based on the characteristics of the base enterprise, some hypotheses were created for further analysis of different scenarios, as well as an analysis of the economic viability corresponding to each scenario. The first hypothesis considers a variation in the number of floors, ranging from 5 to 30. The second hypothesis considers a variation in the volume of the reservoir. The volumes considered and tested were 15m³, 25m³, 45m³ and 65m³, thus, 104 scenarios were created, in addition to the reservoirs dimensioned by the Rippl method. Were collected data on the consumption of non-potable water by the company and the rainfall in the city of João Pessoa in order to describe the volumetric balance of the reservoirs that determine the calculation of the volumes used in each system. The survey of water supply and demand, volumes used, construction costs, implementation and maintenance were necessary for the calculation of economic indicators: net present value (NPV), benefit-cost ratio (B/C) and return period to over the 30 years of the project's useful life. In the financial analysis, an average interest rate of 6.42% was considered, based on the Selic rate. In the general panorama of the different scenarios analyzed, 79.8% of the scenarios have B/C greater than 1 and 20.2% less than 1. Restricting this analysis to the 15m³ reservoir, 92.31% of the scenarios presented B / C greater than 1, in contrast, the 65m³ reservoir presented 65.38% of the B / C values greater than 1. The best performance achieved was for the scenario of 21 floors and a 15m³ reservoir, with a B / C of 1.96, NPV of R $ 24.446,92 and payback period of 9,3 years.