Abstract
In this work, an innovative arrangement of a vertical subsurface flow wastewater infiltration system (SWIS) was studied. The principal objective of this study was to evaluate the oxygen transfer rate (OTR) in two different pilot-scale arrangements of an SWIS. The two pilot plants were composed of four filter beds in series, one with a vertical arrangement of the beds (one over the other) and the other with a horizontal arrangement of the beds (one next to the other). Furthermore, two kinetic models were applied for correlating the COD and NH4+-N concentrations at the inlet and outlet of each treatment step in both pilot plants. The fitting of experimental data to the models allowed the calculation of the areal rate constants. The OTR values obtained were 54.69 g m−2 h−1 and 28.84 g m−2 h−1 for horizontal and vertical arrangement, respectively. These values were considerably higher than those obtained by other authors. The plug flow model describes the behaviour of these SWISs better, and the best fits were achieved for the vertical arrangement. The areal rate constant values obtained in this study were higher than those reported in the bibliography, which indicates a great removal efficiency and therefore lower surface area needed for the treatment.
Highlights
Conventional wastewater treatment technologies present some disadvantages, such as high cost and operational difficulties, thanks to changes in wastewater flowrate and contaminant loads [1].Considering the necessity to hunt alternative options to standard systems, the technologies that have a minimum or null energy cost have had preference, with easy operational and maintenance procedures, and which guarantee efficacy and great versatility in the face of both large flow and load fluctuations, simplifying sludge treatment and disposal management
Nitrite concentration was always very low. This fact is produced in other similar systems in such vertical subsurface constructed wetlands, as is reported by Arias et al, (2001) [28] and Prochaska et al, (2007) [29]. As it can be seen, NH4 + -N and organic nitrogen concentrations considerably diminished in the two pilot plants, and the higher removal happened in the plant with the horizontal arrangement
This can be due to the longer retention time of the water within the bed, which is directly related to the greater depth of the gravel bed
Summary
Considering the necessity to hunt alternative options to standard systems, the technologies that have a minimum or null energy cost have had preference, with easy operational and maintenance procedures, and which guarantee efficacy and great versatility in the face of both large flow and load fluctuations, simplifying sludge treatment and disposal management. The large land requirement area of these technologies is a major limitation of their application. They can require up to ten times more land area (0.5–20 m2 pe−1 ) than conventional systems, such as activated sludge (0.2–0.3 m2 pe−1 ). Vertical subsurface flow constructed wetlands are among the non-conventional technologies that require less area, between 0.8 and 5.5 m2 pe−1 [4]
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