Desenvolvimento da ecotecnologia dos wetlands construídos aplicados para o tratamento descentralizado de efluentes nos últimos 30 anos

Abstract

The different active elements in the process of treatment on wetlands ecotechnology, such as the sizing and operating criteria (organic load, add rate, hydraulic loading rate, among others), the wetland mode, the filter media composition and the macrophytes used, present particular characteristics subject to the location of the project and/or its application. The significant variability in the parameters data mentioned above makes it difficult to compare and standardize. Because of that, in Brazil there are no regulatory standards for construction, operation and maintenance for this technology. This paper compiles the compilation of 274 scientific articles from indexed journals (impact factor > 1.0), in order to map and discuss the advances of this treatment model, with the general aim of evaluating the performance of the application of different constructed wetland types (WC) under the context of decentralized sewage over a period of 30 years (1980 to 2018). Therefore, a systematic review was carried out with stratified analysis of scientific articles in indexed journals, two international platforms: Scopus and Science Direct, because they contain the largest number of studies addressing wetlands. From this, the keyword "wetlands" was determined to select the articles and the downloads of 391 scientific articles (Scopus) and 694 scientific articles (Science Direct) were carried out. After that, a stratified sampling was performed by means of which the analysis of 25 % was determined, resulting in 100 (Scopus) and 174 (Science Direct) articles, totalizing in 274 scientific articles. Subsequently, the topics were established to the systematic review, being these: reference; data base; country; technological arrangement; WC mode; filter material; macrophyte; hydraulic system; volume; treated effluent; applied organic load (in terms of COD and BOD); hydraulic application rate; total nitrogen load; affluent C/N ratio; removal of pollutants; general objective of the research; and analytical technique employed (ATE). From the analysis of these parameters it was possible to explain the main agents in order to evaluate the performance of the different WC modalities in the period from 1980 to 2018 under the context of decentralized sewage. The results showed that during the three decades, the evolution of the application of different modalities of wetlands presented a tendency to decrease the use of WN (natural wetlands) and greater use of WC. From the mid-1990s onwards, a trend towards demand for WC evolution of surface flow (WCFS) and subsurface (WCFSS). There was a gradual increase of studies with the use of horizontal WC (WCH), vertical descendent WC (WCVD), vertical ascendent WC (WCVA), hybrid system (WCVD - WCH) and saturated vertical WC (WCV - FS). The WCH as post-treatment of wastewater was the most used technological arrangement over the evaluated period, making a total of 97 studies, followed by WCFS (70 articles), WCVD (58 articles), WC (42 articles) and WN (36 articles), with respective numbers of scientific articles. The most studied types of effluents addressed in the studies were: household or sanitary effluents (105 articles), effluents from agroindustry activities (61 articles), industrial sewage (59 articles), surface water (41 articles) and synthetic effluent (25 articles). The most used macrophytes in the different WC modalities were those of the genus Phragmites spp. (110 articles), Typha spp. (86 articles), Scirpus spp. (24 articles), Cyperus spp. (22 articles), Juncus spp. (19 articles), Schoenoplectus spp. (15 articles), Carex spp. (13 articles), Pontederia spp. (10 articles), Iris spp. (10 articles) e Canna spp. (10 articles). The types of filtering masses most used were: gravel (130 articles), sand (76 articles), clay (18 articles), soil (14 articles) and organic compounds (11 articles). The pollutants treated in the studies corresponded to nitrogen compounds (136 articles), organic matter (66 articles), phosphorus compounds (62 articles), metals (43 articles), solids series (42 articles) and agrochemicals (26 articles). It was also verified that most of the values adopted in the studies attributed the organic load in terms of biochemical oxygen demand (BOD) and chemical oxygen demand (COD) ranging from 0.05 g BOD m-2 d-1 to 70,200 g BOD m-2 d-1 and from 0.07 g COD D m-2 d-1 to 50,000,000 g COD m-2 d-1. In relation to total nitrogen (TN) applied the values vary from 0.00196 g TN m-2 d-1 to 685,800 g TN m-2 d-1. The values of affluent hydraulic rate ranged from 0.003 mm d-1 to 25,920,000 mm d-1. In the case of the concentration of BOD, COD and TN the values varied from 0.483 mg BOD L-1 to 68,163.00 mg BOD L-1, from 0.0000207 mg COD L-1 to 57,934.80 mg COD L-1 and from 0.01 mg TN L-1 to 116912 mg TT L-1. These constituent elements and operational conditions were considered as promising alternatives for the maximization of performances of the different WC modalities in the treatment of different effluents.