In-situ bioremediation of vanadium contaminated soil using volatile fatty acids obtained from fruit and vegetable waste

Fatty acids (VFAs) that obtained from organic waste are environmentally friendly and readily available soil amendments that could enhance the bioremediation efficiency of vanadium (V)-contaminated soils. This study aimed to clarify the in-situ immobilization mechanisms of VFAs for actual V-contaminated soils in mining areas, and investigated the effects of varying concentrations of VFA application on the valence state, existing forms, bioavailability, and toxicity of V in soils, as well as the changes in plant growth, V uptake, and abundances of microbial species and their metal resistance genes. The findings revealed that the water-extractability, bioavailability, toxicity, and acid-soluble (F1) fractions of V reduced by up to 52.8%, 51.0%, 46.9%, and 81.7%, whereas the oxidizable (F3) and residual (F4) fractions increased by a factor of up to 3.1 and 1.1, following VFA addition. Consequently, the stem height of Setaria viridis increased by a factor of 4.5, and the reduction in V accumulation in shoots and roots were reached up to 95.4% and 67%. The VFA-induced soil pH decrement, along with the enhancement of soil organic matter content and the proliferation of Proteobacteria and its arsenic reduction genes, were the key factors influencing environmental behavior and biochemistry of V in contaminated soils. This work investigated the effects of various concentrations of biomass derived VFAs on the bioavailability, mobility, toxicity and fractionation of V in contaminated soils, and elucidated their immobilization mechanisms. The reduction in soil pH, along with the increase in soil OM and AP content, are the primary abiotic factors influencing the valence state, bioavailability, and toxicity of vanadium in contaminated soils, whereas the enhancement of the abundances of Proteobacteria and their arsenic reduction genes represent the major biotic factors affecting these properties.