Effect of biogas slurry and sucrose addition on electrokinetic removal of arsenic from paddy soil

Electrokinetic remediation is a promising technology for removal of heavy metals from soil, but its effect on arsenic remains poorly understood. Biogas slurry (10%, 25%, and 50% by mass) and sucrose (2%, 5%, and 10% by mass) were added to soil contaminated by mine drainage to enhance arsenic migration ability. Chemical sequential extraction, flame atomic absorption spectrometry, hydride generation atomic fluorescence spectrometry, and high-throughput sequencing were used to determine the iron and arsenic speciation, arsenic removal rate, and microbial community structure. Electroosmotic flow was found to play the main role in the treatment. The electroosmotic flow rate of the sucrose treatment was lower than that of the biogas slurry treatment. The sucrose could maintain a lower pH in soil compared with biogas slurry. It could also form a stronger reducing environment (redox potential, - 274 mV) and increase the abundance of iron oxide reducing bacteria. The amorphous iron oxide content increased at the end of the experiment. The removed arsenic was mainly from the residual fraction. The 25% biogas slurry and 5% sucrose treatments, could quickly remove 13.7% and 13.4% of the arsenic in one week, respectively. The highest removal rate was 14.3% in the 5% sucrose treatment at the end of the experiment and was about three times higher than the untreated control. Moreover, sucrose addition was more helpful than the biogas slurry treatment to stabilize the current and reduce energy consumption. These findings provide theoretical support to enhance microbial activity to improve this technology for removal of soil arsenic.

Automated summary

Electrokinetic remediation coupled with the addition of sucrose or biogas slurry was used to enhance arsenic migration ability in contaminated soil. Sucrose treatment led to lower electroosmotic flow rate and maintained a lower pH in soil, while also creating a stronger reducing environment and increasing the abundance of iron oxide reducing bacteria. The addition of sucrose was more effective in stabilizing the current and reducing energy consumption. These findings provide theoretical support for improving the technology for removal of soil arsenic.