Dynamics of biofouling development on the conditioned membrane and its relationship with membrane performance

• Biofouling of conditioned membrane caused a more severe membrane performance loss.
• Conditioning layer promoted the initial adhesion of dead bacteria and biofilm maturation.
• Salt rejection and permeate flux behaviors were closely related to biofilm dynamics.
• The dominant mechanism of biofouling effects changed with biofilm formation.
• Polysaccharides played a more important role than proteins in the dense biofilm structure.

In this study, the impacts of a conditioning layer on the dynamics of biofouling development were investigated through batch biofouling experiments under the RO cross-flow filtration process. Fouled RO membranes extracted over the course of biofouling were prepared for measurements of extracellular polymeric substances (EPS) and total organic carbon (TOC) and confocal laser scanning microscopy (CLSM) observations. A close relationship between the biofilm dynamics and permeate flux and salt rejection were delineated. The patterns of membrane performance change demonstrated that the dominant mechanism governing the biofouling effects varied with the biofouling stage: concentration polarization dominated the early stage of biofouling, while fouling resistance was the dominant mechanism at the later stage. In addition, compared with the virgin membrane, the conditioning layer led to a severe deterioration in permeate flux and salt rejection. The results of biofilm dynamics showed the enhancement of bacterial initial attachment and biofilm maturation by the conditioning layer. Finally, there were increased biomass accumulation measured by TOC and the ratio of live to dead cells is higher on the bottom than that on the top of the biofilm on the conditioned membrane. In conclusion, conditioning layer had great influence on the counts of attached cells in the early stage of biofouling, but on the EPS concentration in the later stage of biofouling.