Immobile Iron-Rich Particles Promote Arsenic Retention and Regulate Arsenic Biotransformation in Treatment Wetlands

Abstract

Remediation of arsenic (As)-contaminated wastewater by treatment wetlands (TWs) remains a technological challenge due to the low As adsorption capacity of wetland substrates and the release of adsorbed As to pore water. This study investigated the feasibility of using immobile iron-rich particles (IIRP) to promote As retention and to regulate As biotransformation in TWs. Iron-rich particles prepared were immobilized in the interspace of a gravel substrate. TWs with IIRP amendment (IIRP-TWs) achieved a stable As removal efficiency of 63 ± 4% over 300 days, while no As removal or release was observed in TWs without IIRP after 180 days of continuous operation. IIRP amendment provided additional adsorption sites and increased the stability of adsorbed As due to the strong binding affinity between As and Fe oxides. Microbially mediated As(III) oxidation was intensified by iron-rich particles in the anaerobic bottom layer of IIRP-TWs. Myxococcus and Fimbriimonadaceae were identified as As(III) oxidizers. Further, metagenomic binning suggested that these two bacterial taxa may have the capability for anaerobic As(III) oxidation. Overall, this study demonstrated that abiotic and biotic effects of IIRP contribute to As retention in TWs and provided insights into the role of IIRP for the remediation of As contamination.

Field and Laboratory Evidence for Manganese Redox Cycling Controlling Iron and Arsenic Retention in Household Sand Filters

“…Under such conditions, Mn oxides might complement the heterogeneous oxidation of As­(III) and Fe­(II) by O 2 (eqs and ) to enhance As and Fe retention in SFs. Indeed, under O 2 -depleted conditions, Mn­(IV) oxides (either as abiotic or biogenic birnessite) prevented As mobilization in soil and sand columns. − However, until now, there is no direct evidence that under O 2 -depleted conditions the presence of Mn­(IV) oxides can control the immobilization of As and Fe in household SFs. One of the issues is that most studies have examined As, Fe, and Mn removal by sampling at specific time points to confirm the high removal efficiency.…”