Usability of rice straw biochar for remediation and amelioration of vanadium contaminated soils in areas under acid rain leaching

Environmental context Biochar produced by agricultural wastes can be used for vanadium treatment, soil fertility improvement, and agricultural waste disposal, whereas acid rain leaching may decrease its remediating efficiency of the metal contaminated soil. Therefore, vanadium behaviour in soil and soil quality change after biochar application were analysed under simulated acid rain leaching. Findings provide insights into acid rain leaching effects on soil quality, vanadium release from soil, and biochar remediating efficiency. Rationale Considering the effects of acid rain on the leaching of metals and nutrients in soil, rice straw biochar, with the potential to remediate and improve the quality of vanadium contaminated soil, was further evaluated for its remediating and ameliorating performance of soil under acid rain. Methodology The adsorption capacity and isotherm of vanadium by rice straw biochar were investigated. Simulated acid rain leaching experiments were performed to study the influence of acid rain on vanadium behaviour in soil and nutrients and on the structure of the soil. Results Isotherm adsorption studies indicated a preference for a monolayer process without transmigrations of the adsorbed vanadium onto the biochar surface. After leaching with simulated acid rain, compared with the untreated soil, the available vanadium (129.63 ± 3.75–76.10 ± 3.24 mg kg−1) in the soil decreased notably by adding 2–3 wt% biochar (P < 0.05). The organic matter content (1.71 ± 0.25–4.31 ± 0.42%) and available P content (15.13 ± 0.56–29.88 ± 0.28 mg kg−1) in the soil increased with the biochar application ratio increasing from 0 to 3 wt%. Whereas the available N concentration in the soil amended with 3 wt% biochar (27.70 ± 4.35 mg kg−1) was significantly lower than that without biochar addition (41.28 ± 1.62 mg kg−1) (P < 0.05). In addition, an increased proportion of macro-aggregates and decreased proportion of micro-aggregates of the soil after application of 2–3 wt% biochar was also observed. Discussion The application of rice straw biochar at the addition level of 3 wt% has potential for remediating and ameliorating vanadium contaminated soil under acid rain. Appropriate modification of the biochar should be undertaken in future to achieve an effective remediation and amelioration of soil under a long-term influence of acid rain. It is also of interest to study the capacity of the biochar to amend soils with high N load.