Influência da variação da profundidade do leito em wetlands construídos de fluxo vertical ascendente no tratamento de águas de córrego urbano

Abstract

In this study, the behavior of a set of constructed wetlands (WC) with vertical upward flow was evaluated, concerning the influence of the depth of the filtering mass, composed of construction waste, in the removal of organic matter in terms of COD, operated in a continuous form, with hydraulic detention time of 24 and 48 hours. The system consists of three WC’s with a surface area of 0,22m² and the following depths of filtering mass: 1, 56 m in WCVA 1, 0.70 m in WCVA 2, and P2 in WCVA 3. The filtering mass consists of fragments of ceramic blocks that have Si, O, Al, Ca, C, and other elements in their composition, in addition to having roughness and porosity that provide a favorable environment for fixing colonies of bacteria and microorganisms that favor treatment of low organic concentration effluents. On its surface, each WCVA has Chrysopogon zizanioides seedlings (Vetiver grass) planted directly in the filtering mass, developed with an average depth of 40 cm at a density of 23 seedlings per m². For each WCVA, parameters of temperature (T), pH, dissolved oxygen (OD), turbidity (UNT), Total Kjeldahl Nitrogen (NTK), Ammoniacal Nitrogen (N-Amon), nitrite (NO2-), nitrate (NO3-) and total phosphorus (PT) were evaluated. Evaluating the removal of organic matter in terms of COD at different depths of the substrate, WCVA 1 (1.56 m) presented the best performance results, suggesting that the depth of the filling and its type have a direct influence on the efficiency of the treatment. The system showed removal efficiency for Steps 1and 2 (24 and 48 hours, TDH) of 67% and 58%, respectively. 35.2% and 39.7% for efficiency in the removal of total Phosphorus analyzing parameters of incoming effluent and outgoing effluent. As for the evaluation of the nitrogen series, it can be observed that WCVA 1 obtained better results for NNTK and N-Amon, the removal efficiencies reached 24% and 12% and 2% and 10% for both Stages 1 and 2. WCVA 1, in relation to nitrite in Stage 1, obtained better results when reaching 39%. In Stage 2, WCVA 2 obtained greater removal efficiency for nitrite (28%). WCVA 1 obtained greater removal efficiency for nitrate (50% and 59%), as well as for Total Phosphorus (35% and 40%) in both stages, using 24-hour TDH (Stage 1) and 48 hours (Stage 2).