Selective Removal of As(V) from Water by Polymeric Ligand Exchange and Engineered Treatment of Spent Regenerant
Type of DegreeThesis
MetadataShow full item record
Arsenic introduced by natural or human activities into drinking water sources has been a challenging issue around the world. In the western United States, high arsenic concentrations in drinking water have caused serious health threats. The U.S. Environmental Protection Agency (U.S. EPA) has recently implemented a Maximum Contaminant Level (MCL) for arsenic of 10 µg/L. To comply with the MCL, development of new technologies or modification of conventional treatment is needed. This study developed a new technology, polymeric ligand exchange (PLE) for selective removal of arsenic from drinking water in the presence of strong competing anions (e.g. sulfate). Compared to Strong Base Anion Exchanges (SBA), which is currently recommended by the U.S. EPA, PLE resins exhibited much improved arsenic selectivity. Equilibrium isotherm tests also demonstrate 60 ~ 120 times orders of magnitude greater selectivity for arsenic by the PLE. The relative affinity of the anions observed for the PLE and IRA 900 (SBA) resins are shown respectively: HAsO42- >> HCO3- > SO42- > Cl-; and SO42- > HAsO42- > Cl-. The arsenic selectivity of two best PLE resins, XUS 3N-Cu and DOW 3N-Cu, is 12 and 17 times greater, respectively than that of SBA. Although the PLE has a strong affinity for arsenic, 96% of sorbed arsenic could be removed during regeneration using 4% NaCl at pH 9.1 within 20 BV. Furthermore, it can be reused for four consecutive runs with only pH adjustment. It has been reported that millions of tons As-bearing sludge are annually produced as waste residuals from water treatment process. It is imperative to reduce waste volume and to yield the most stable process waste residuals. Aluminum chloride (AlCl3) was investigated to treat the spent regenerant brine containing concentrated arsenic. At an Al/As molar ratio of 5 or greater and at pH 5-8, nearly 100% of As in the spent brine can be removed The U.S. EPA TCLP and California WET leaching tests, both with a limit of 5 mg/L as arsenic, were followed to determine the leachability of arsenic from the brine treatment residuals. When the Al/As molar ratio was increased from 5 to 20, the arsenic leachability was reduced from 200 mg/L to 50 mg/L according to the WET test. In the pH range 5 – 10, the extractable arsenic was at a minimum at pH 5. Also, the extracted arsenic concentration increased by 30% as the dry aging time increased from 20 to 40 days.