Light-driven biodegradation of azo dyes by Shewanella decolorationis-CdS biohybrid in wastewater lacking electron donors.

Abstract

The lack of electron donors prevents the effective degradation of azo dyes by bacteria, which severely limits the practical application of conventional biological treatment. Herein, we innovatively designed a bio-photoelectric reduction degradation system composed of CdS and Shewanella decolorationis, which could effectively degrade amaranth in anaerobic conditions driven by light when electron donors were unavailable. Compared with bare S. decolorationis and S. decolorationis (heat-killed)-CdS biohybrid, S. decolorationis-CdS biohybrid had 39.36-fold and 3.82-fold higher first-order kinetic constants, respectively. The morphology, particle size, elemental composition, crystalline type, photovoltaic properties, and band structure of the nanoparticles synthesized by S. decolorationis were carefully examined and analyzed. Light-driven biodegradation experiments showed that amaranth was degraded by the synergy of CdS and S. decolorationis. Reductive degradation of amaranth by electrons was demonstrated by electron and hole trapping. The effect of potential coexisting contaminants, which might serve as hole scavengers, on the degradation of amaranth was evaluated. Membrane protein inhibition experiments also suggested that NADH dehydrogenase, menaquinone, and cytochrome P450 played an important role in electron transfer between CdS and Shewanella decolorationis. The cyclic conversion of NAD+/NADH was probably the most critical rate-limiting step. Electrochemical measurements suggested that faster electron transfer might facilitate the degradation of amaranth. Our findings might contribute to the degradation of azo dyes in wastewater lacking electron donors and deepen our recognition of the microbe-material interface. KEY POINTS: • A BPRDS was constructed with Shewanella decolorationis and CdS. • Amaranth was effectively degraded by BPRDS in anaerobic conditions driven by light. • NDH, MQ, and CYP450 were involved in electron transfer.