Scaled-up wastewater semiconductor-biohybrids for stable solar-driven biosynthesis

Semiconductor-biohybrids provide a sustainable platform for efficient solar-driven biosynthesis, yet high costs hinder scalability. Utilizing wastewater as low-cost feedstock offers transformative potential via waste-to-wealth conversion, but large-scale implementations remain unexplored. This study is the first to demonstrate a scaled-up (50 L) biohybrid system operating with actual wastewater. We employed genetically engineered Vibrio natriegens to concurrently utilize wastewater pollutants (e.g., heavy metals, sulfate and organics) for in situ biosynthesis of either CdS or PbS semiconductor nanoparticles on microbial cell surfaces. This enabled semiconductor-biohybrids assembly, thereby enhancing high-value 2,3-butanediol (BDO) production. Optimal salinity (40 g L⁻¹ NaCl), heavy metal supplementation (0.1 mM Cd²⁺/Pb²⁺), and bioaugmentation significantly stabilized the system, suppressing wastewater indigenous microbes and enabling robust biohybrid formation. The lab-scale preliminary experiments showed that biohybrids achieved >99 % heavy metal removal while increasing peak biomass by ∼30 % (550 to 717 mg L⁻¹) and peak BDO production by 111 % (5.7 to 12 g L⁻¹) compared to V. natriegens alone during 20 days operation. Bioaugmentation on day 20 by supplementing the bioreactor with freshly cultured V. natriegens further enhanced biohybrid biomass by 51 % (276 to 416 mg L⁻¹) and BDO production by 19 % (7.0 to 8.3 g L⁻¹). In the scaled-up reactor, the biohybrids achieved significantly higher performance than that in the lab-scale system, with peak biomass reaching 1338–1536 mg L⁻¹ and peak BDO yields of 15.1–20.8 g L⁻¹. CdS-based biohybrids outperformed PbS counterparts, attributable to their photophysical properties. Light-driven increases in intracellular NADH and ATP corroborated the semiconductor-to-cell electron transfer mechanism underlying enhanced BDO production. This work demonstrates the practical feasibility of engineered biohybrids for scalable, continuous conversion of non-sterile wastewater into valuable chemicals.