Spectroscopic sensing of membrane fouling potential in a long-term running anaerobic membrane bioreactor

The application of anaerobic membrane bioreactors (AnMBRs) for wastewater treatment is seriously challenged by membrane fouling. Online monitoring of the fouling potential would promisingly support smart control of fouling. The monitoring is most likely achievable using spectroscopic methods, but the spectroscopic indicators are yet to be qualified. In this study, 11 ultraviolet (UV) indicators, 19 fluorescence excitation-emission matrix indicators and 2 infrared scattering indicators were screened during 151-day operation of a lab-scale AnMBR. The critical filtration volume for flux declining to 50% or 25% (V0.5 or V0.25) and the specific resistance (Kcf) were employed as benchmarks of fouling potential for initial pore blocking and subsequent gel/cake layer growth. The 254 and 280 nm UV absorbances (UV254 and UV280) displayed significant correlation coefficients of 0.57-0.77 with the fouling indexes, while the Peak 1 and Peak 2 fluorescence intensities (FIP1 and FIP2) displayed 0.84-0.92. Statistical variance partitioning and Fourier transform infrared analyses showed that polysaccharidelike solutes were mostly responsible for fouling and were UV/fluorescence-sensitive due to the chromophoric/ fluorophoric segments they carried. X-ray photoelectron spectra revealed a correlation of fouling and fluorescence with the O=C-(R N O) content. Ultrahigh-performance liquid chromatography-mass spectrometry substantiated the direct connection of sugar units with chromophoric/fluorophoric groups. Regression models were then established to predict the fouling potential during AnMBR operation. The combined use of FIP1 and UV280 achieved the best prediction of V0.5, V0.25 and Kcf with R2 = 0.763, 0.891 and 0.845, respectively, showing the viability of spectroscopic sensing in membrane bioreactor applications.