Synergistic removal of sulfamethoxazole and dimethyl phthalate by five constructed wetland substrates

Frequent detection and joint toxicity of sulfonamides (SAs) and phthalate acid esters (PAEs) in water environment have caused serious health and safety problems that can be reduced by vertical flow constructed wetland (VFCW). However, it remains unclear what kind of substrate used in VFCW can synergistically remove SAs and PAEs. In this study, it was determined if biochar, zeolite, vermiculite, peat and sand synergistically removed sulfamethoxazole (SMX) and dimethyl phthalate (DMP) as representatives of SAs and PAEs by using batch and column experiments. The batch experiments showed that pseudo-second-order and intraparticle diffusion kinetics and Freundlich isotherm could better describe the synergistic adsorption of SMX and DMP on each substrate. SMX promoted hydrophobic interaction between DMP and each substrate so that low concentration DMP almost was adsorbed completely at neutral pH. Both neutral and alkaline pH conditions were favorable for synergistic adsorption of SMX and DMP on each substrate. The column experiments showed that removal of SMX or DMP in VFCW by substrate adsorption alone was limited with run time increasing, but SMX and DMP were effectively removed with run time increasing when loaded with simulated wastewater, SMX and DMP. The VFCW not only removed 94.7% SMX and 91.8% DMP after running 50 d, but also improved total nitrogen removal. In conclusion, these results strongly suggest that biochar, zeolite, vermiculite, peat and sand filled in VFCW can synergistically remove SMX and DMP.