Redox potential and pH behavior effect on arsenic removal from water in a constructed wetland mesocosm

Abstract

Arsenic retention in constructed wetlands is highly influenced by environmental conditions, physicochemical and biological interactions, particularly in the rhizosphere (pH, redox potential, and temperature). The present research investigated the effects of redox potential and pH behavior on arsenic retention in the constructed wetland mesocosm. The study was conducted in three prototypes. Two planted (HA and HB) with Eleocharis macrostachya and Schoenoplectus americanus, respectively; a third one (HC) remained unplanted as control. The system was in continuous operation during 343 days, fed by groundwater with arsenic concentration at 90.66 ± 14.95 µg L−1, and a hydraulic retention time of 2 days. Monitored parameters were: redox potential, pH, dissolved oxygen, water and environmental temperature, arsenic concentration inlet and outlet. Oxidizing conditions (87–516 mV) were reported during most of the hot and warm season (84–90%); while reducing conditions (up to −539 mV) where reported the rest of the time. On cold season, only oxidizing conditions were detected. A pH from 7.0 to 8.0 was preserved for HA and HB, whereas HC preserved higher pH values (8.0 to 8.5). HA and HB behavior was observed similar among them, reporting higher arsenic retention than HC. This means that plants play an important role on arsenic retention in the constructed wetlands mesocosm. © 2013 American Institute of Chemical Engineers Environ Prog, 33: 1332–1339, 2014