Estudo de viabilidade de implantação e operação de diferentes tipos de wetlands construídos para sistema descentralizado coletivo

Abstract

The search for new technologies for the domestic wastewater treatment has been increasingly discussed in academia, and even more so by public entities. The lack of sewage treatment in Brazil is a public health problem, since many diseases are caused by the lack of treatment or the inefficiency of the systems in operation. Much has been researched on more efficient viable alternatives, and this is where Constructed Wetlands (CW) systems appear. Another important reason to be highlighted is the urban territorial expansion through subdivisions, condominiums or other types of land subdivision, a trend that can be visibly verified in the municipality of Frederico Westphalen/RS in recent years, whith several projects being built. In this context, this research aimed to carry out a cost analysis for the implementation of a CW as a form of decentralized treatment of domestic wastewater applied to subdivisions in that municipality. The investigation included the comparison of three distinct typologies of Wetlands, namely the Constructed Wetlands with horizontal flow (HFW), the vertical flow Constructed Wetlands (VFW) and the French vertical flow Constructed Wetlands (FVFW), aiming to carry out an analysis of cost of implementation and operation over a 15-year lifespan. Based on a decision-making methodology through an analytic hierarchical process called AHP, the best implementation alternative was chosen by evaluating basic sustainability criteria such as the environmental, social and economic scopes. For this, it was necessary to measure the three proposed typologies, to then quantify the materials and labor of each one, and with the assistance of SINAPI and TCPO compositions, as well as inputs from the SINAPI table, it was possible to price each quantified item and then obtain the implementation cost of each technology .An implantation cost of R$ 291,971.79 was obtained for the HFW, for the VFW the operating cost was R$ 465,192.71, obtaining the highest cost among the three evaluated systems, and finally the FVFW obtained the operating cost of R$ 317,779.78. The monthly operating costs for the HFW, VFW and FVFW systems were also evaluated, which respectively obtained R$ 910.08, R$ 1,820.16 and R$ 1,365.12 of monthly cost necessary for the maintenance of the systems. This resulted in a lifetime cost of R$ 163,814.40 for the HFW, R$ 327,628.80 for the VFW and R$ 245,721.60 for the French system. Applying the AHP methodology for data analysis, in addition to the defined sustainability criteria, three more variables were adopted for each criterion, making it possible to elaborate the preference matrices and finally obtain the priority vector for each set of variables of each criterion, as well as a global priority vector for the sustainability criteria. As an example, it was verified through the AHP method that the economic criterion had the greatest importance, totaling the percentage of 61%, followed by the environmental criterion with 27% and finally the social criterion with 12% of preference. From this analyses, it was concluded that the best Constructed Wetland system to be applied in the subdivisions is firstly the HFW system due to its low cost of implantation and operation, and secondly the FVFW, which is a system that requires less implementation area, it does not require primary sewage treatment and the difference in cost was not so different from the HFW.