Biofilm management via loach predation: An eco-friendly approach to enhance membrane performance in wastewater treatment

The dense biofilm structure developing on membrane surfaces in gravity-driven membrane bioreactors (GDMBR) reduces the membrane permeate and efficiency, limiting its practical application in wastewater treatment. Biological predation, as an environmentally friendly approach, synergistically improves biofilm structure and membrane performance. However, the regulatory mechanism of biological predation efficiency through predator numbers and membrane packing densities remains to be elucidated. This study found that loach (Misgurnus anguillicaudatus) predation effectively enhanced the stable flux of GDMBR, especially in combination with the lower membrane packing density, which was 73.80 % higher than that of GDMBR without predation. In addition, loach predation significantly modulated the thickness and porosity of the biofilm and effectively reduced extracellular polymeric substances and the adenosine triphosphate attached to the membrane surface. This expanded the abundance ratio of dominant bacteria in the biofilm while decreasing bacteria diversity and increasing removal rates of chemical oxygen demand and ammonia nitrogen by over 80 % and 60 %. Furthermore, the implemented loach predation extended the eukaryotic food chain while suppressing Rotifera abundance in the community. These findings provide a theoretical foundation for optimising biofilm regulation strategies to enhance the operational stability and antifouling performance of GDMBR systems in wastewater treatment.