Influência do tempo de cheia em um sistema de wetland construído tidal flow tratando água de córrego antropizado na remoção de poluentes e na comunidade bacteriana

Abstract

In this study, the behavior of a Tidal flow Constructed Wetland (TFCW) under variation of the flood time in the removal of carbonaceous, nitrogenous and phosphorous matter and its influence on microbial community structure when treating anthropized stream water was evaluated. The WCTF (117 L) was filled with fragments of red ceramic blocks (44% porosity) and vegetated with the macrophyte Althernanthera philoxeroides (32 plants m-2). After 94 days of system stabilization, four operational stages were evaluated with volumetric hydraulic loads of 4,68×10-2, 5,85×10-2, 7,8×10-2 e 1,17×10- 1 m³ d-1 in stages E1 (48 h full / 12 h empty), E2 (36 h full / 12 h empty), E3 (24 h full / 12 h empty) and E4 (12 h full / 12 h empty), respectively. No significant difference was observed (p> 0.05) in the removal efficiencies of raw COD (66 to 94%), filtered COD (57 to 93%), TKN (60 to 86%), N-Amon (58 to 87 %) and TN (53 to 78%) between stages. The average concentrations of nitrite and nitrate in the samples of the effluent from the four stages were lower than 0.016 mg L-1 and 5.76 mg L-1, respectively. High PT removal was obtained in 48 h of the flood, with an average of 79%. The organic loading rate in terms of PT was a limiting factor in the removal of PT, which reduced along with the reduction of flood time and varied from 16 to 84%. The conversion of carbon and nitrogen possibly carried out by bacteria of the phylum Proteobacteria (classes Alpha, Beta and Gamma) in 48 h and 36 h of the flood, may have been performed by bacteria of Proteobacteria and Acidobacteria in 24 h and 12 h, among others identified in smaller percentages like Nistrospira, involved in nitrogen removal. The bacterial community structure was influenced by the time of flood, but the interaction between microorganisms in Stages E1, E2, E3 and E4 provided a similar performance in the removal of organic matter in terms of COD and NT. In the mass balance was observed that A. philoxeroides was responsible for the removal of 2.1% of the TN and 2.7% of the TP from the total removed by the system, and the low performance of macrophyte was attributed to the intermittent feeding. The total removal of TN by was 65.1%, mainly attributed to adsorption in the filtering material and microbial metabolism during bed rest, a period in which atmospheric air filled the pores of the system.