Biomass reduction and arsenic transformation during composting of arsenic-rich hyperaccumulator Pteris vittata L

Composting is being proposed as a pretreatment step before disposal of metal-rich biomass after phytoextraction process. This study determined the biomass reduction and arsenic transformation during composting As-rich biomass of hyperaccumulator Chinese brake fern (Pteris vittata L.).

High-As fern biomass containing approximately 4,600 mg As kg(-1) was composted for 120 days in a laboratory-scale composter under aerated condition. Solid As speciation was determined using X-ray diffraction (XRD) and scanning electron microscopy equipped with X-ray energy dispersive elemental spectroscopy (SEM-EDS), while liquid As speciation was evaluated by high-performance liquid chromatography coupled with inductively coupled plasma mass spectrometry.

Composting reduced the fern biomass by 38%, comparable to 35% reduction of the low-As fern biomass containing approximately 12 mg As kg(-1), indicating that the high As concentration in P. vittata had little detrimental effect on microorganisms involved in composting. Total As on a per composter basis and water-soluble As in composted biomass were lowered by 25% and 32%, respectively. Arsenic loss from the biomass resulted mainly from generation of compost leachate, with less from the As volatilization; whereas As immobilization was due to oxidation of As(III) to As(V), followed by precipitation of hoernesite [Mg(3)(AsO(4))(2).8H(2)O] which was evidenced by XRD and SEM-EDS analysis.

Results from this study indicate that composting As-rich fern significantly reduced its biomass, As content, and water-soluble As. It seems that composting can be an effective step for treating As-rich biomass before disposal in landfill.