Arsenic Removal from As-Hyperaccumulator Pteris Vittata Biomass with Potential to Methane Production.

Proper disposal of As-hyperaccumulator Pteris vittata biomass (Chinese brake fern) enhances its application in phytoremediation. This study was to optimize As removal from P. vittata (PV) biomass by testing different particle sizes, extractants, extraction times and solid-to-liquid ratios. Besides, methane index potential was also assessed in PV biomass. Dry PV biomass was first extracted using different extractants followed by different Mg-salts to recover soluble As via precipitation while methane production was tested in pre and post extracted biomass. Water-soluble As varied from 6.8% to 61% of As pending on extraction time with 99% of As being arsenate (AsV). Extraction with 2.1% HCl, 2.1% H₃PO₄, 1 M NaOH and 35% ethanol recovered 81, 78, 47 and 14% of As from PV biomass. Second extraction using HCl recovered 27-32% with ethanol recovering only 5%. Though ethanol showed the lowest extractable As, residual As in the biomass was also the lowest. Among the extractants, ethanol was the best extractor to remove As from PV biomass. Approximately ~90% As was removed from PV biomass using particle size < 1 mm at solid: liquid at 1:50 and pH 6 for 2 h. Adding MgCl₂ at As:Mg ratio of 1:400 with pH 9.5 was effective to precipitate soluble As. Methane production was 10% greater in pre-extracted biomass compared to ethanol extracted biomass. After 30 days, all As in solution was present as arsenite and carbon content decreased ~76%. Total arsenic remaining in no treated biomass was ~10 times greater than in treated biomass. Ethanol extraction combined with anaerobic digestion removed ~96% of total As from PV biomass. Effective As removal from PV biomass was achieved combining extraction, anaerobic biomass degradation and precipitation enhancing phytoremediation application.