Jardins flutuantes: uma ecotecnologia no tratamento de esgotos domésticos no Semiárido Brasileiro.

Abstract

Large volumes of untreated wastewater are discharged daily into water bodies, mainly in underdeveloped and developing countries with limited or insufficient sanitary infrastructure in the provision of basic sanitation services. In Brazil, it is common to use stabilization ponds in wastewater treatment, however, although efficient in reducing organic matter and pathogens in the effluent, these systems do not present the same result for pollutants such as phosphorus and nitrogen, which cause eutrophication. Faced with the need to preserve natural waters and reduce the environmental impact, strategies have been sought to optimize this treatment in recent decades. In this sense, nature-based solutions, such as the floating treatment wetlands, have emerged as an alternative for the treatment of effluents or improvement of the treatment carried out by ponds, with no need to expand the Wastewater Treatment Plant (WWTP) becoming a an efficient, low-cost treatment, easy adaptation and ornamental function. Thus, seeking to expand field-scale studies, this work aims to build, install and evaluate a floating treatment wetland (FTW) in the anaerobic lagoon of WWTP do Glória, located in the municipality of Campina Grande - Paraíba (Brazil). Each of the gardens of the FTW was built with an expanded polystyrene (EPS) structure, organic substrates (coconut fiber and sugarcane bagasse) and inorganic substrates (gravel and crushed EPS) and different species of plants (Cyperus papyrus, Tradescantia zebrina, Callisia fragrans, Canna x generalis and Xanthosoma sagittifolium), totaling a surface coverage area of 4.0% of the lagoon. The monitored water quality parameters were temperature, pH, turbidity, electrical conductivity, total dissolved solids, dissolved oxygen, biochemical oxygen demand, chemical oxygen demand, total phosphorus, soluble orthophosphate, total Kjeldahl nitrogen, ammonia nitrogen and chlorophyll a. The study was divided into two phases: the first with distribution in 6 rows of 7 gardens each and monitoring from May/2019 to March/2020 at 8 collection points; and the second with distribution in the form of a single barrier and monitoring from February to August/2021 at 4 collection points. The EPS structure showed good stability, buoyancy and strength throughout the experiment. The organic substrates, sugarcane bagasse and coconut fiber, performed well in the initial support function of the plants, however they may have added organic matter to the effluent. Among the plant species tested in the gardens, C. papyrus was effluent tolerant, Canna x generalis and T. zebrina were partially tolerant, X. sagittifolium and C. fragrans were sensitive. Other spontaneous plant species were also identified in the SJF. In the first phase, the reduction of turbidity, electrical conductivity, BOD5, total phosphorus and soluble orthophosphate was greater before the installation of row gardens. However, these results were promising in the second phase, with a reduction in organic matter and total phosphorus, but an important increase in the influent of BOD5 and COD in the configuration of gardens in a single barrier. In this phase, an increase in chlorophyll a in the water mass was recorded, thus contributing to natural oxygenation and better effluent quality without increasing maintenance costs. In general, the use of floating gardens was effective in optimizing the ecotreatment carried out by stabilization ponds, with the potential to reduce organic matter and nutrients through phytoremediation. The SJF showed health and environmental potential and qualities that should be studied in future