Decoupling EPS functionality from quantity for sustained performance in solid biological treatment systems using biochar as a tuning agent

Excessive accumulation of extracellular polymeric substances (EPS) in solid biological treatment systems often causes pore clogging and mass transfer limitation, compromising long-term performance in pollutant transformation. Whether EPS functionality can be decoupled from its quantity, and how such decoupling might be achieved, remain poorly understood. In a 300-day column experiment using landfill cover soil with active methanotrophic communities, five types of biochar were applied as soil amendments to create distinct EPS secretion scenarios and methane removal performance profiles. It demonstrates that EPS functionalitycan be decoupled from its quantity through three distinct microbial investment strategies: functional minimization, achieving the most stable communities and highest methane removal efficiency (98 %) with minimal EPS (0.74mg g-1); active construction, sustaining high performance (91 %) despite high EPS accumulation (3.51mg g-1); and passive defense, exhibiting high EPS (3.29mg g-1) but progressive functional decline (from 92 % to 62 %). These strategies are governed by two critical biochar properties; one is carbon stability, shaping soil dissolved organic carbon dynamics, and the other is salt ion content, determining osmotic stress intensity. Iron modification validated this framework by reducing labile carbon and enhancing carbon stability, redirecting an otherwise inefficient biochar toward a successful decoupling pathway. Collectively, these findings reveal that the EPS quantity-function relationship is context-dependent rather than monolithic, providing a basis for optimizing long-term performance in solid biological treatment systems through EPS functionality management.