The effect of substrates on the removal of low-level vanadium, chromium and cadmium from polluted river water by ecological floating beds.

Ecological floating beds (EFBs) is one of the effective methods lately used to remove heavy metals pollutions in water. However, the role of substrate in EFBs was mainly focused on the study of microorganisms, and the effect of substrates on plants enrichment of heavy metals was rarely investigated. This study aimed to investigate the promotion of different substrates (green zeolite, sepiolite, absorbent paper, and ceramsite) on the removal of multi-heavy metals (V, Cr, and Cd) by Acorus calamus L. It also investigated the plant growth status. Results showed that the relative increase rate of Acorus calamus L. fresh weight increased the most in EFBs with green zeolite group (EFB-GZ), which was 60.50%, higher than 38.17% in EFBs with Acorus calamus L. (EFB-A). The enrichment ability of multi-metals in Acorus calamus L. was stronger in EFBs with substrates than in EFB-A, and green zeolite was the best. After 34 days, the total removal efficiency of V, Cr and Cd in EFB-GZ were 79.91%, 95.24% and 91.80%, respectively. Heavy metals translocation from root to shoot influenced by the kinds of substrates. In EFB-GZ, the translocation factor (TF) of V, Cr and Cd were 0.081, 0.263 and 0.180, respectively (0.024, 0.608 and 0.032 in EFB-A). The ability of Acorus calamus L. to resist multi-metals stress was significantly higher in EFBs with substrates than that in EFB-A and the activity of SOD, POD and CAT were increased by heavy metals stress. Our results acquired that green zeolite was the best substrate to promote multi-metals uptake by Acorus calamus L., which could effectively maintain the pH of water, provide a stable environment and nutriment for Acorus calamus L. Green zeolite can promote the translocation of V and Cd from root to shoot in Acorus calamus L., but is not conducive to Cr.