Effect of physical and chemical co-application of biochar and sulfidated nano scale zero valent iron on the NB degradation in soil: Key roles of biochar

Sulfidated nano zero-valent iron (S-nZVI) can efficiently degrade nitrobenzene (NB) in water. However, its practical application in soil remediation is constrained by limited contact with soil-sorbed NB, leading to sparse research. Herein, Biochar (BC), with its notable adsorption capacity, was coupled with S-nZVI to assess the role of physical (S-nZVI + BC) and chemical (S-nZVI@BC) co-application of BC and S-nZVI, respectively, on enhancing NB degradation in soil. Regardless of the physical or chemical co-application, there was a remarkable advantage after addition of BC relative to S-nZVI alone. In physical co-application, the NB degradation rate of S-nZVI + BC increased as the increasing BC concentration from 0 to 3.5 g·L−1, attributed to enhanced NB desorption via the solubilization effect of BC, facilitating interaction with S-nZVI. Beyond this concentration, no significant improvement was observed, possibly due to BC obstructing reactive sites on S-nZVI surface. In chemical co-application, the S-nZVI@BC (S-nZVI/BC mass ratio of 1:1) exhibited a high NB degradation rate constant (1.097 h−1) during reaction. Apart from solubilization effect, BC in S-nZVI@BC endowed S-nZVI with a higher anti-oxidation property, hydrophobicity, electron transfer capacity, and dispersion effect, accounting for the higher reactivity of S-nZVI@BC over S-nZVI + BC. Besides, the water/soil ratio and initial soil pH significantly affected NB degradation rate, with the optimum water/soil ratio and initial soil pH being 3 and 5, respectively. Our finding broadens the applicability of BC and may offer a highly effective way in soil remediation.