Goethite-enriched biochar mitigates soil emissions of CO2 during arsenic passivation: Effect and mechanisms

Iron-enriched biochar has excellent adsorption capacity for contaminants, which is a sustainable multifunctional potential material to mitigate environmental pollution. Both biochar and Fe (hydr)oxides are important materials for accumulating and preserving soil organic carbon. However, it is unclear that the potential of iron-enriched biochar for mitigating CO2 emission from contaminated soil. In this study, soil incubation and extraction experiments were conducted to determine the effects and mechanisms of goethite-enriched wheat straw biochars (GWBs) prepared at two pyrolysis temperatures (GWB450 and GWB600) on mitigation of CO2 emissions in arsenic (As) contaminated soil. The results showed that compared to the control, GWBs significantly reduced the soil available arsenic (As), decreased soil Eh, and promoted the water stability of soil aggregates (<1mm). GWBs also regulated bacterial community structures, and efficiently improved microbial carbon use efficiency (CUE) in contaminated soil, thereby significantly reducing CO2 emission by 37.2 %−40.9 % in 37 days. Spectroscopic and microscopic analysis indicated that microbial colonization widely occurred on the surfaces of the goethite-enriched biochar, and promoted the formation of organo-mineral layers, which resulted in the significant decrease in the CO2 emission. These findings enhance the understanding of the mechanisms of soil carbon sequestration induced by metal-enriched biochar and indicate a new strategy of biochar-based multifunctional soil amendment that can mitigate heavy metal pollution and reduce CO2 emission simultaneously in contaminated soils.