A systematic study of soluble microbial products and their fouling impacts in membrane bioreactors

A series of stirred dead-end filtration tests were conducted to investigate the fouling potential of BAP (biomass-associated products) and UAP (utilization-associated products), showing that UAP had higher modified fouling index with a value of 1.63 × 104 s/L2. Proteins were mainly accumulated in UAP and accounted for 45.3%, while the proportion of proteins in BAP was only 12.1%. Due to the membrane interception, the permeate concentrations of UAP and BAP decreased largely: proteins decreased to near zero and polysaccharides were effectively retained ranging from 26.6% to 46.8%. Excitation–emission matrix analysis showed that humic-like and fulvic-like compounds had lower retention than proteins. The observation of fouled membrane by Fourier transform infrared spectroscopy demonstrated that membrane foulants were dominated by proteins and polysaccharides. Modeling work well indicated that the main fouling mechanisms for BAP and UAP filtration were cake filtration and complete blockage, respectively, further confirming that UAP had higher fouling potential than BAP.