Oxygen Consumption in Two Subsurface Wastewater Infiltration Systems under Continuous Operation Mode

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.