Interactions of chlorpyrifos degradation and Cd removal in iron-carbon-based constructed wetlands for treating synthetic farmland wastewater

Abstract

Pesticide and heavy metal contaminants, such as chlorpyrifos (CP) and cadmium (Cd) in farmland drainage had caused the water pollution and attracted extensive concerns around the world. The incorporation of zeolite-based iron-carbon (ZB-IC) into constructed wetlands (CWs) was prepared to simultaneously remove chlorpyrifos (CP) and cadmium (Cd) in farmland drainage, and the interaction of CP degradation and Cd removal was investigated. Laboratory simulated experiments were carried out in this study, and the results presented that the removal efficiencies of CP and Cd by ZB-IC coupled CWs (ZB–IC–CW) were 99.55% and 98.59%, respectively, which were much higher than that of the zeolite-based (ZB) CWs (CP = 92.99%; Cd = 63.54%). The removal mechanism of CP and Cd by ZB-IC substrate was mainly attributed to electron transfer, which occurred from iron corrosion and hydrogen generation process. In addition, CP could act as carbon source to promote denitrification process. Microbial analysis revealed that the relative abundances of CP-resistant bacteria (Firmicutes, Clostridia and Acetobacterium), Cd-resistant bacteria (Bacteroidetes) and denitrifying bacteria (Proteobacteria and Patescibacteria) were dramatically increased due to the addition of ZB-IC. The higher czcA gene and opd gene in ZB–IC–CW demonstrated that the addition of CP played a positive role in Cd removal, while Cd showed slightly affect to CP removal.