Boron removal from wastewater in a vertical flow constructed wetlands

Abstract

in this study, we investigated the performance of a Vertical flow constructed wetland (VFCW) to boron removal.A VFCW bed (0.70 m × 0.24 m2) planted with Vetiveria zizanioides were used. The bed was filled with light expanded clay aggregates (Leca®NR 3/8, 10 < Ø < 20 mm). A bottom slope of 2% was applied in order to enable the hydraulic collection of the influent continuously distributed by equidistant sprinklers on the top of the bed. A layer of gravel (diameter 10-50 mm) was placed around the outlet valve to prevent clogging with fine particles. A feeding tank (125L), equipped with a submersible pump (Eheim- 1250) was used. The flooding level was maintained at 14% by a siphon on the outlet. Inlet and outlet flow were measured. Wastewater samples were collected daily for immediate characterization or frozen at -20oC. Air and bed temperatures were monitored daily. Rainfall was excluded by covering the beds with a tunnel of 21 transparent fine plastic. A synthetic wastewater was prepared using boric acid as boron source and micronutrients dissolved with tap water according to the operating conditions under study. Each new condition has been in operation up to pseudo- stationary state. It was used two different and increasing boron concentrations (15 ± 1 and 30 ± 1 mgL-1 B) and the flow rate to the VFCW was kept constant, with an -2 -1 hydraulic load (HL) of 191 ± 10 Lm d.