Sistemas alagados construídos de escoamento horizontal subsuperficial com chicanas: desempenho, cinética, degradação e colmatação

Abstract

Many studies have been engaged in developing effluent treatment systems with low cost of implementation and operation. The horizontal subsurface-flow constructed wetlands (HSSF-CWs) are designed to treat the most diverse effluents. Based in natural wetland systems, performing the same chemical, physical and biological processes in the treatment of effluents. These systems have shown great treatment potential, in addition to low implementation and operation costs, as there is no external energy requirement. As a way to enhance the treatment in these systems, many studies use baffles, or deflector plates, to improve the treatment, without the need for greater investments. In that regard, this study aimed to survey the state of the art and evaluate the removal of pollutants, clogging and degradation kinetics in flooded systems built with horizontal subsurface flow, with different internal configurations, planted with Penninsetum setaceum, in the treatment of university sewage. The CWs were built in fiberglass, differing by the presence of horizontal baffles (CW-B), vertical (CW-C) or the absence of internal partitions, of the conventional type (CW-A), with detention time of 1.36, 1.32, 1.31 days, respectively, with a surface area of 1 m2, filled with gravel. The systems showed significant removal efficiency, however, they did not differ statistically, with values above 47% for COD, 22% for ST, 39% for STV, 10% for STF, 9.7% for NTK. The low efficiencies, as well as the similarity in removals, were caused by the maturation of the systems, evidenced by the formation of a superficial layer, formed due to the initial saturation of the bed, decreasing the hydraulic conductivity, indicating a possible clogging, in addition to facilitating the formation of paths preferential treatment, standardizing the treatment between the systems. A greater accumulation of ST, STV and STF was observed in the initial portion of CWs A and B, in the first 0.45 m, and in the upper layer, 0.15 m below the support material, in relation to the bottom layer (0, 50 m). The kinetic model proposed by Chan and Chu (2003) demonstrated the best fit for the CW-A (conventional) and the model proposed by Brasil et al. (2007) resulted in the best adjustments for SACs with the presence of baffles (CW-B and C). CWs A and B showed similar behavior, with flow tending to complete mixing and full use of the reactor volume, indicating that it is less clogged than CW-C, which showed a tendency to piston flow, with the presence of short circuits and dead zones. CW-C had the highest mass removal rates, highest dry matter productivity, as well as higher nitrogen and phosphorus extraction in the plant, followed by CW-B and finally CW-A, with phosphorus extraction values of 2 g m-2 in section II for CW-B and in sections I, II and IV for CW-C. There was a strong positive correlation between EC and the variables NTK and PT, affluent and effluent to treatment, and a very strong positive correlation between EC and phosphate, for the three systems evaluated, showing high potential in determining nutrient concentrations by means of EC in university sewage and after treatment in HSSF-CWs.