Remediation of sulfonamide antibiotic-containing wastewater by constructed wetlands: Importance and action mechanism of plants

Constructed wetlands (CWs) have been proved to be effective in treating sulfonamide antibiotics (SAs) wastewater. Nevertheless, as an essential element in CWs, the significance of plants, continues to be a topic of controversy. In this study, CWs with two different plant species were taken as the research object to investigate their treatment performance, in order to understand the impact of plants on the treatment of SAs wastewater in CWs and to discover the underlying action mechanisms. Experiment results showed that plants played an important role in the CWs, and significantly improved the efficiency of wastewater treatment, with average removal rates for conventional nutrients (COD, NH₄⁺-N, NO₃⁻-N and TP) ranging from 73.69 % to 98.92 %, surpassing the non-plant control group (52.16 %–80.70 %). Similarly, for SAs, the removal efficiency in the plant-treated group was 74.15 %–83.67 %, higher than that in the non-plant control group (65.42 %–70.14 %). Although, as time passed, the efficacy of CWs had slightly decreased, but the rate of pollutant removal remained consistently over 60 %. Further analysis showed that plants promoted the removal of SAs through various mechanisms such as plant uptake, microbial degradation and substrate adsorption. Plants had the ability to absorb SAs from wastewater and eliminated them through metabolism or accumulation. Additionally, plants can improve soil enzyme activity to facilitate microbial degradation, indirectly promoting SAs removal. It's worth noting that most SAs can be degraded through plant metabolism after being absorbed by plants, while only a minority of SAs accumulated in plants in the form of parent compounds. Furthermore, the efficacy of CWs in treating wastewater differed between selected plant species. Specifically, Iris pseudacorus showed a higher purifing potential than Scirpus validus. These results revealed the effect of plants on the treatment of SAs wastewater in CWs, and provided a reference for the practical application of antibiotic wastewater removal by CWs.