The Mechanism of Arsenic-Contaminated Soil Remediation by Immobilized Achromobacter sp. HC3

The potential of immobilized microbial technology as a solution to arsenic (As) soil contamination is underexplored, despite its promising prospects. This research employed sodium alginate-silkworm excrement biochar (SB) as a carrier for immobilizing Achromobacter sp. HC3, thereby creating an immobilized As-oxidizing bacterium. Subsequent soil incubation experiments were conducted to assess the remediation effects of this sodium alginate-silkworm excrement biochar immobilized HC3 (SB-HC3), HC3 suspension (FB), and blank immobilized carrier without HC3 (BIC) on As in soil. Compared to the control group, both the SB-HC3 and FB exhibited a significant decrease in soil As(III) content, with the SB-HC3 demonstrating the most substantial reduction at 57.79%. Analysis of soil As fractions revealed that SB-HC3 effectively immobilized As in soil, transitioning it from unstable non-specifically-sorbed, specifically-sorbed, and amorphous poorly-crystalline hydrous oxides of Fe and Al to more stable well-crystallized hydrous oxides of Fe and Al and residual phases. The soil pH in the SB-HC3 initially increased and then decreased, eventually stabilizing between 6.63 and 6.59. At the end of the incubation (28 d), the soil redox potential (279.3) was significantly lower than the control group. Additionally, the soil dehydrogenase enzyme activity (24.601 TTC µg/g/d) and the soil fluorescein diacetate enzyme activity (67.338 µg/g/h) were significantly higher than those of the control group. This study underscores the efficacy of SB-HC3 in not only removing soil As(III) but also reducing toxicity, mobility, and bioavailability of As in soil. These findings could serve as a valuable reference for applying Immobilization technology in treating As-contaminated soil.