Efficient recovery of heavy metals and selenium from wastewater using granular sludge: The crucial role of glutathione (GSH)

Abstract

Microbial technology offers an effective method for treating heavy metals and selenium (Se) in wastewater, yet the recovery of these valuable elements is often overlooked. This study introduces a glutathione (GSH)-enhanced granular sludge technology for the removal and recovery of heavy metals and Se from wastewater. Using the new technology, the removal rates of copper (Cu), cadmium (Cd), and Se from wastewater reached 99.4-99.99%, while the recovery rates reached 73.2-87.9%. Both long-term reactor operation and short-term stimulation experiments indicated that GSH substantially increased the residual fraction of Cu, Cd, and Se in the sludge. This residual fraction was identified as metal selenides (MSe), composed of Cu_1.08Se (75.4 ± 1.8%) and CdSe (15.4 ± 1.0%). The increased abundance and significant upregulation of GSH-related genes, including gshA, gshB, and gor, as well as the indispensable roles of GSH, glutathione reductase (GorA), and NADPH in the in vitro synthesis of MSe, demonstrated that the GSH-mediated Painter-type reaction was the primary pathway for MSe synthesis in the sludge. The biosynthesized MSe was efficiently extracted and recovered from the final sludge, and the extract showed high catalytic activity in pollutant degradation. Given the widespread presence of GSH in diverse microorganisms, the GSH-mediated mechanism for MSe synthesis is likely to occur in various environments contaminated with heavy metals and Se.

Keywords: Bio-mineralization; Elemental recovery; Heavy metals; Painter-type reaction; Selenium reduction.