Break through the trade-off between membrane fouling and pathogen removal in ultrafiltration process by poly(amino acid)s modified biochar

The fluctuation of pathogen removal in ultrafiltration (UF) systems and its dependence on irreversible fouling necessitates frequent chemical cleaning/disinfection, raising concerns about leakage of conditioned pathogens. An additional barrier utilizing carbon materials with notable adsorption and antimicrobial properties offers a promising and practical solution. This study achieved complete retention of nano-sized viruses (∼6 log reduction value (LRV)) and micron-sized bacteria (∼7 LRV) by introducing ε-polylysine (EPL)-modified biochar (BC) into UF feeds. During the UF process, biochar with superior adsorption capacities and conformational flexibility, significantly enhanced the entrapments of natural organic matter (NOM), viruses, and bacteria. Specially, EPL exhibited conformational transitions that adapted to different NOM (macromolecule proteins and linear polysaccharides), greatly facilitating the formation of reversible biochar-NOM cake layers and the transfer of pathogens from the irreversible fouling layer to the biochar surface and reversible fouling layer. The random coil structures of EPL promoted electrostatic attraction for virus particles, while bend or sheet-like structures created barriers for both bacteria and viruses through a refined NOM-biochar network. The trapping of viruses was attributed to the combined effects of electrostatic attraction, bonding forces, and the complex cake layers. And size exclusion by the biochar-NOM complex fouling layer played a prominent role in the retention of bacteria. This breakthrough in addressing the trade-off between irreversible fouling and pathogen removal inspires promising applications of EPL-modified biochar for UF systems to consolidate barriers for water and process biosafety. Future efforts should focus on EPL′s conformational response to protein-like NOM with significant steric hindrance, which pose challenges for fouling alleviation and bacteria capture.