Quick Removal of Suspended Cadmium from Irrigation Water Using Water Hyacinth ( Eichhornia crassipes )-Phosphoric Fertilizer

The rapid decontamination of farmland irrigation water polluted with heavy metals has attracted a great deal of attention. This paper addressed the removal of trace suspended cadmium (Cd) from irrigation water by using the water hyacinth ( Eichhornia crassipes ) and the phosphate fertilizer (WH-PF). Compared with control samples, Cd removal rate was 12 times higher in the presence of Eichhornia crassipes ; furthermore, removal rate rose 36 times after application of WH-PF. A 40 μg/L Cd in irrigation water was reduced to less than 3.5 μg/L within two treatment hours, with the removal efficiency of 91%. Both the root exudates of Eichhornia crassipes and phosphate fertilizers decreased the zeta potential of suspended substance (SS) and increased its size, resulting in accelerating sedimentation. The gas chromatography-mass spectrometer (GC–MS) revealed the presence of large volumes of amino-containing organic matter in the root exudates, such as 2,7-diamino-5-((3-(1-amino-1-carboxypropan-2-yl)-1,4-dihydroquinolin-7-yl)methyl)-6-methyl-7-oxoheptanoi acid, 1H-Indole-3-carboxaldehyde, which played important role in neutralizing charges of the SS. Additionally, phosphate fertilizers can decrease the zeta potential of SS by increasing the Fe 3+ /Fe 2+ value. And then the phosphate-iron-hydroxyl-formed multinuclear polymer with network structure can rapidly flocculate the suspended Cd. Our study demonstrated that a WH-PF technology can quickly and effectively remove suspended Cd from farmland irrigation water.