Immobilization of arsenic in wastewater from regeneration of fixed-bed adsorbent by co-precipitation with zirconium nano-sludge for disposal in landfills

Abstract

Arsenic is a toxic and carcinogenic element that must be removed from water in many parts of the world. However, arsenic removal techniques also generate arsenic waste, which requires appropriate handling and/or stabilization prior to disposal. In this study, we proposed co-precipitation with Zr(IV) nano-sludge as a solution for management of arsenic-laden waste created from regeneration of exhausted adsorbents. California’s Waste Extraction Test (WET) and the Toxicity Characteristic Leaching Procedure (TCLP) were used to test this Zr nano-sludge against co-precipitaiton with conventional iron salt, using experimental variations that assessed stability over short- and long-term durations under a range of pH and oxidation-reduction (ORP) conditions, which are commonly found in landfills. The study found that the Zr(IV) nano-sludge had similar affinity for inactivating arsenate (i.e., As(V)) in regenerant wastewater as compared to the conventional iron salt. The Zr(IV) nano-sludge, however, was comparatively more stable at normal ORP conditions (200 mV), at reducing (−150 mV) conditions, and at acidic pH ranges (1−7). The maximum concentration of soluble arsenic detected in leachate from the iron salt (986.8 µg/L) and Zr(IV) nano-sludge (761.6 µg/L) co-precipitaiton sludges occurred after 45 days under reducing conditions, which was lower than the relevant regulatory limit for arsenic toxicity (5000 μg/L). Overall, under reducing conditions, the percentage of As that leached from Zr and Fe nano-sludges were 0.19% and 0.28%, respectively. The results suggested that Zr may be used to stabilize arsenic in adsorbent regenerant wastewater prior to disposal in landfill, thus supporting the global effort to protect vulnerable populations from arsenic in drinking water.