Purification and recycling of selenium in wastewater using polyacrylamide capsule containing selenate-reducing bacterium

BACKGROUND: Rare metals are often used in high-technology industries and, as a result, their demand has increased in present years. The shortage of some kinds the metals is concerning for the industries in question. The development of technologies to recover metals from wastewater and wastes is necessary for securing a stable supply of these metals. The present physicochemical treatments cannot easily recover metals from wastewater and wastes when they are present in low concentrations. In contrast, biochemical treatments, such as biomineralization, are expected to recover these metals efficiently. Selenium (Se) is one of the indispensable metals used in various products, such as electronics, glass manufacturing, pigments, metallurgical additives, and so on. A selenium reducing bacterium, Pseudomonas stutzeri NT-I, was isolated previously. This bacterium reduces soluble seleno-oxyanions to solid elemental selenium efficiently via a bioprocess called biomineralization. RESULTS: A polyacrylamide capsule (PAC) containing selenate-reducing bacterium, Pseudomonas stutzeri NT-I, was prepared by double-capsulation to recover selenium from wastewater simply and efficiently. The double-capsulation is inclusion of alginate beads (AB) containing NT-I by polyacrylamide composed of N-isopropylacrylamide (NIPAM), N-(2-hydroxyethyl)acrylamide (HEAA), N-[3-(dimethylamino)propyl]acrylamide (DMAPAA), or (3-acrylamidopropyl)trimethylammonium chloride (APTAC) cross linked by N,N′-methylenebisacrylamide (MBAA). CONCLUSION: The PACs had good stability in NaCl aq. and basic water in comparison with non-capsulated AB. HEAA-PAC and APTAC-PAC showed relatively high water-retaining capacity under the wet conditions. Selenate reduction tests were conducted in selenate, Se(VI) aq. at 37 °C in the presence of PACs, and APTAC-PAC was effective in reducing and capturing Se.