Scalable ceramic membrane process for one-step removal of cells and proteins in industrial off-gas fermentation

Syngas fermentation using CO-rich industrial off-gases offers a sustainable route for large-scale bioethanol production. However, the resulting fermentation broths typically contain both high concentrations of suspended microbial cells and soluble proteins, posing major challenges for efficient downstream processing. In this study, commercially available ceramic membranes with nominal pore sizes spanning the microfiltration to nanofiltration range (100, 15, 5, and 2 nm) were systematically evaluated for the one-step simultaneous removal of cells and proteins from both simulated and real bioethanol fermentation broths. All membranes exhibited defect-free surfaces and narrow pore size distributions. Results show that microbial cells were completely retained by all membranes, while soluble proteins were effectively removed with increasing rejection as pore size decreased. Among them, the 15 nm ceramic membrane (CM-15) exhibited the best overall performance, delivering a favorable balance between permeation flux and protein rejection (>98%). Fouling analysis revealed that flux decline was dominated by protein gel layer formation rather than pore blocking, and membrane fouling was largely reversible, with full flux recovery achieved through sequential alkaline and acid cleaning. Importantly, pilot- and engineering-scale operation confirmed the long-term stability of the ceramic membrane process, maintaining stable fluxes of approximately 70 L·m −2 ·h −1 and protein rejection exceeding 99% over 140 h of continuous operation. These results demonstrate that ceramic membranes with moderate pore sizes enable an efficient and scalable one-step clarification strategy, providing a robust and industrially viable solution for downstream processing of syngas-derived bioethanol fermentation broths.