Enhancement of iron-loaded sludge biochar on Cr accumulation in Leersia hexandra swartz: Hydroponic test

In this study, the effect of iron-loaded sludge biochar (ISBC) on the Cr enrichment capacity of Leersia hexandra swartz (L. hexandra) in hydroponic tests was investigated at different Cr treatment levels (5 mg/L, 10 mg/L and 20 mg/L). The results showed that the plant height and biomass of L. hexandra were significantly increased with the rise of ISBC dose (p < 0.01), while the Cr content in L. hexandra showed a significant downward trend (p < 0.01). However, the Cr accumulation capacity of L. hexandra was significantly increased as ISBC dose was raised (p < 0.01), which was attributed to the significant improvement of its biomass. According to Cr accumulation capacity, the appropriate ISBC dose was recommended to be 50 g/L for all Cr treatment levels. Compared to the control (no ISBC; 0.105 mg, 0.167 mg and 0.193 mg), the Cr accumulation capacity of L. hexandra at different Cr treatment levels were increased by 77.40%, 59.72% and 88.41%, respectively. The comparative analysis throughout the test cycle indicated that the addition of ISBC could convert more Cr(VI) to Cr(III), which was beneficial to the biomass and the Cr accumulation capacity of L. hexandra. Meanwhile, the relationship between changes in the concentrations of NH4+, PO43- and K+ and the incremental biomass of L. hexandra was well described by the Logistic model, while the relationship between changes in their concentrations and the Cr accumulation capacity of L. hexandra also followed this model well. Moreover, their effects were found throughout the test, while the contribution of Ca2+ was mainly at the beginning and end of the test. In summary, the enhancement of ISBC on Cr accumulation capacity of L. hexandra was attributed to detoxification and fertilizer supply.