Dynamic monitoring and proactive fouling management in a pilot scale gas-sparged anaerobic membrane bioreactor

Abstract

This study examines membrane performance data of a pilot-scale gas-sparged anaerobic membrane bioreactor (AnMBR) over its 472 day operational period and characterizes the foulant cake constituents through a membrane autopsy. The average permeability of 336 ± 81 LMH per bar during the first 40 days of operation decreased by 92% by the study's conclusion. While maintenance cleaning was effective initially, its ability to restore permeability decreased with time. Wasting bioreactor solids appeared to be effective in restoring permeability where chemical cleans were unable to. The restoration mechanism appears to be a decrease in colloidal material, measured by semi-soluble chemical oxygen demand (ssCOD), rather than bioreactor total solids concentration. This is further supported through the use of fluorometry during AnMBR operation, which showed an increase in tyrosine-like compounds during heavy fouling conditions, suggesting that proteinaceous materials have a large influence on fouling. This was corroborated during membrane autopsy using Fourier transform infrared spectroscopy (FTIR). FTIR, scanning electron microscopy with energy dispersive X-ray spectroscopy, and transmission electron microscopy were used to characterize inorganic scalants and predominantly found phosphate salts and calcium sulfate. Fundamentally characterizing foulants and introducing novel and dynamic monitoring parameters during AnMBR operation such as ssCOD and fluorometry can enable more targeted fouling control.