The removal of high Se(IV) and Cd(II) concentrations in sulfur autotrophic reactor based on the “hibernation-like microbial survival strategy”

The removal of selenite (Se(IV)) and cadmium (Cd(II)) from low-carbon wastewater presents significant challenges. However, the addition of external organic carbon sources is limited in application due to the high cost and potential for secondary pollution. This study introduced a “hibernation-like microbial survival strategy”, enabling efficient removal of Se(IV) and Cd(II) in sulfur autotrophic reactor, with S⁰ acting as the electron donor. The removal efficiencies of 5–120 mg/L Se(IV) and 50 mg/L Cd(II) were higher than 99 % in phase I–IV, and the nanoparticles formed in sulfur autotrophic reactor were available for recycling. The analysis of X-ray photoelectron spectroscopy confirmed that the removal pathways of Se(IV) and Cd(II) were biological reduction, adsorption, and biosynthesis. The decreased ratio of actual to theoretical sulfate concentrations indicated the weakened sulfur disproportionation trend in sulfur autotrophic reactor. The formation of autotrophic-heterotrophic symbiont was beneficial for promoting electron transfer, material exchange, and information flow. Microorganisms strategically decreased metabolic activity to reduce extra energy consumption under Se(IV) and Cd(II) stress, which was manifested in the decreased extracellular DNA, extracellular polymeric substances, and electron transfer system activity. Furthermore, microorganisms reduced the secretion of nicotinamide adenine dinucleotide, cytochrome c, and cyt-c oxidase on the premise of ensuring the required electron flux. The “hibernation-like microbial survival strategy” was proposed to explain the removal of Se(IV) and Cd(II) in sulfur autotrophic reactor, expanding the potential application of sulfur autotrophy in environmental engineering.