Mitigation of membrane biofouling by a novel Pseudomonas knackmussii HITSZ-Q1 immobilized in biochar-reinforced beads: Quenching mechanism and MBR performance

The application of quorum quenching (QQ) bacteria for fouling control in membrane bioreactors (MBRs) is often hampered by the gradual loss of biological activity during operation. Here, this limitation is overcome by combining a newly isolated QQ bacterium (Pseudomonas knackmussii HITSZ-Q1) with a low-cost biochar-reinforced polyvinyl alcohol/sodium alginate (PVA/SA/BC) immobilization matrix. The strain completely degraded N-octanoyl-l-homoserine lactone (C₈-HSL) and N-(3-oxododecanoyl)-l-homoserine lactone (3-oxo-C₁₂-HSL) within 2 h via intracellular acylase, maintained stable QQ activity at 30–40 °C and pH 6–8, and inhibited Pseudomonas aeruginosa biofilm formation by approximately 30%. Biochar incorporation enhanced the hydrogen-bonding network, compressive strength, and adsorption capacity of the matrix, providing a protective microenvironment for strain Q1. In flask tests, the PVA/SA/BC QQ beads maintained integrity over six reuse cycles and retained >40% degradation activity for both AHLs after 90 days of storage at 4 °C. When applied in lab-scale MBRs, the QQ beads delayed membrane fouling by 69% without compromising effluent quality, which correlated with a 50% reduction in C₈-HSL, decreased polysaccharide and protein contents in extracellular polymeric substances, and an altered microbial community. Notably, after 34 days of continuous operation, the recovered PVA/SA/BC QQ beads showed increased quenching activity, with degradation rates for C₈-HSL and 3-oxo-C₁₂-HSL rising by a further 13% and 4%, respectively, a phenomenon rarely reported in QQ systems. This work offers a practical and durable QQ strategy that turns the activity decay problem into sustained, and even slightly enhanced, biofouling control.