MONITORING PARTICULATE FOULING IN MEMBRANE SYSTEMS

Deposition of particulates, especially colloids, during membrane filtr ation causes a decline in permeate flux. The existing modified fouling index (MFI) uses a microfilter membrane as a quic test of feedwater q uality. The MFI is based on ca e filtration, and thus a model can be d eveloped for flux decline prediction. However, this MFI is not sensiti ve to the presence of smaller particles. Therefore, more recently the MFI using ultrafiltration membranes (MFI-UF) was developed. This resea rch investigates various criteria of the MFI-UF test for use as a wate r quality indicator; stability of the MFI-UF over time, linearity of t he index with particulate concentration, and reproducibility (1) of th e test (reusability of a UF module) and (2) module manufacture. The pr essure dependency of the MFI-UF was also examined. The aforementioned criteria were examined using a poly acrylonitrile module of 13,000 mol ecular-weight-cut-off for low fouling (tap and process water) and high fouling waters (diluted canal water). The MFI-UF was stable over time and directly related to colloidal concentration. The MFI-UF test was reproducible for one module with repeated testing and reproducible mod ule manufacture was found for 80% of tested modules. Ca e compression occurred at higher applied test pressures and using the compressibilit y factor determined in this research, accurate pressure correction was found.