Phosphate removal using zeolite in treatment wetlands under different oxidation-reduction potentials

摘要

The aim of this study was a comparison between PO4-3-P removal from sewage using zeolite as support medium in subsurface flow treatment wetlands (SSF TWs) operated with different oxidation-reduction potentials (ORPs). In addition, the zeolite's phosphate adsorption characteristics were evaluated. For this, Two mesocosm SSF TWs were installed and operated during 504 d for the PO4-3-P adsorption from sewage: a) mesocosm SSF TW with natural zeolite (MTW-Z1) and b) mesocosm SSF TW with gravel (MTW-G1). Two ORPs was used in MTW-Z1 and MTW-G1: a) ORP-A, ORP +50 mV, b) ORP-B, ORP -50 mV. Furthermore, the adsorption characteristics were evaluated in batch assays (zeolite amount and particle size were studied) with different PO4-3-P initial concentrations. Regarding the mesocosm SSF TWs evaluation, the PO4-3-P removed from sewage by MTW-Z1 is between 20% and 50% significantly (p 0.05) higher than the MTW-G1. At the same time, ORP-A, above + 50 mV, significantly improves (p 0.05), by 10% more, the PO4-3-P removal capacity from sewage. Regarding adsorption characteristics, maximum adsorption capacity determined by Langmuir kinetic was 0.03 mg PO4-3-P g(-1) for initial concentrations of 10-15 mg PO4-3-P L-1. In the case of MTW-Z1 with ORPs A ( + 50 mV) and B ( - 50 mV), the zeolite maximum adsorption capacity was 0.3 mg PO4-3-P g(-1). Therefore, the potential maximum adsorption capacity of natural zeolite used as a medium in SSF TWs with ORP conditions below -50 mV and above +50 mV can be increased until 10-fold regarding Langmuir adsorption kinetic.