Arsenic removal and biomass reduction of As-hyperaccumulator Pteris vittata: Coupling ethanol extraction with anaerobic digestion

Highlights: • A novel treatment method was used to remove arsenic from Pteris vittata biomass. • Ethanol extraction removed 93% As in P. vittata biomass, reducing As to 197 mg kg⁻¹. • Anaerobic digestion further reduced As in P. vittata biomass by 89% to 60 mg kg⁻¹. • Coupling ethanol extraction with anaerobic digestion removed 98% As in total. • Anaerobic digestion also reduced biomass of arsenic-rich P. vittata by 64%. -- Abstract: Improper disposal of arsenic-rich biomass and the lack of efficient methods to treat it may cause contamination in the environment. We developed an efficient method for arsenic (As) removal and biomass reduction of As-rich biomass of the As-hyperaccumulator Pteris vittata by coupling ethanol extraction with anaerobic digestion. This study assessed As partitioning among the three phases (gas, liquid and solid) after anaerobic digestion of P. vittata biomass. Biomass with and without As was first extracted with ethanol. Ethanol extraction removed ~93% As, with remaining As concentration at 197 mg kg⁻¹. The extracted biomass was then digested at 35 °C under anaerobic conditions for 35 d. Arsenic in the digested biomass was reduced by 89%, with remaining As concentration at 60 mg kg⁻¹. In addition, anaerobic digestion reduced the biomass by 64–71% and decreased the volatile solids content from 94 to 15–18%. Methane production was 145 and 160 L_NCH₄/kgVS after 35 d for As-rich and control biomass, respectively. As a final step, As concentration in anaerobic digestate supernatant was reduced to 0.26 mg L⁻¹ by As-Mg precipitation. Overall, coupling ethanol extraction with anaerobic digestion decreased As concentration in P. vittata biomass from 2665 to 60 mg kg⁻¹, or by 98%. At this level ( < 100 mg As kg⁻¹), P. vittata biomass can be considered a safe material based on USEPA regulations. Effective As removal from P. vittata biomass prior to disposal improves the phytoremediation process and lowers biomass transport and landfill disposal costs.