Inorganic and Organic Silicon Fouling of Nanofiltration Membranes during Pilot-Scale Direct Potable Reuse

Fouled nanofiltration membranes from lead and lag positionsofa 2-stage pilot-scale direct potable reuse plant treating secondarymunicipal wastewater effluent in El Paso, Texas were thoroughly characterizedafter 9 months of operation to elucidate the role of silicon moietieson fouling. X-ray photoelectron (XPS), energy dispersive X-ray (EDS),and Fourier transform infrared (FTIR) spectroscopies identified siliconoxides/silica as dominant foulants, especially on the lag element.Gas chromatography/mass spectroscopy also identified organosiliconmoieties such as linear- and cyclosiloxanes on the lead element. Extensivesiliceous fouling was accompanied by calcium, aluminum, and magnesiumscaling as well as deposition of bioorganic materials thereby modifyingmembrane surfaces that resulted in irreversible productivity loss.None of the three selected cleaning agents (sodium dodecyl sulfateand NaOH, EDTA and NaOH, and HCl), either singly or in combinationsatisfactorily restored water permeability of the membrane. EDTA performedbetter in the lead element (where bioorganic fouling prevailed), andHCl was more effective in the lag element (where mineral scaling accompaniedsilicon oxides). This suggests the express need for novel antiscalantsto reduce organosilicon/silicon oxide deposition and the necessityof harsher cleaning agents/regimens specifically targeting silicon(e.g., hydrofluoric acid or ammonium bifluoride).

Automated summary

This study thoroughly characterized fouled nanofiltration membranes from a 2-stage pilot-scale direct potable reuse plant in El Paso, Texas. It identified silicon oxides/silica as dominant foulants, especially on the lag element, and organosilicon moieties on the lead element. The study also found that fouling led to irreversible productivity loss and traditional cleaning agents were not effective in restoring water permeability.