Feasibility study for the implementation and operation of different types of constructed wetlands for a decentralized wastewater treatment system

Abstract

The design of sewage treatment plants involving constructed wetland (CW) systems is a growing and complex demand, given the scarcity of data for supported decision-making. Therefore, this study aimed to assess the feasibility of implementing and operating various types of CWs for decentralized collective sewage treatment, utilizing an analytic hierarchy process (AHP). The evaluated CW modalities were: horizontal flow-constructed wetland (HFCW), vertical flow-constructed wetland (VFCW), and French system-constructed wetland (FSCW). The adopted methodology consisted of designing the three proposed typologies for a subdivision with an estimated population of 868 people; quantification of materials and labor required for implementation and operation over a 15-year lifespan, with the aid of the National System of Costs Survey and Indexes of Construction and Table of Compositions and Prices for Budgets compositions, and decision-making through an AHP, based on basic sustainability criteria: environmental, social, and economic. HFCW had the lowest implementation and operating costs, followed by FSCW and VFCW. Based on the AHP decision-making process, the economic criterion was attributed the greatest importance, 61%. The other criteria, environmental and social, had 27% and 12% of preference, respectively. The alternative that demonstrated greater feasibility due to its low cost of implementation and operation was the HFCW. However, due to the necessity of removing ammoniacal nitrogen to meet Brazil’s environmental regulations (20 mg L−1), the FSCW and VFCW modalities are the most indicated, as they allow nitrification. Furthermore, FSCW offers advantages over VFCW, due to less area demand, and has no need for primary-level treatment and a lower lifespan cost.