Critical evaluation of procedures fundamental to reverse osmosis membrane autopsy

Membrane autopsies are destructive investigations performed to identify the cause of membrane failure or of loss of membrane performance. Procedures important for the outcome of autopsy studies were critically evaluated in this work, including foulant removal, sample drying at 100 degrees C and loss-on-ignition at 550 degrees C. Colorimetric assays for silica and iron in fouling samples were investigated as surrogates for field analytical procedures. Homogenization in a blender worked best for foulant removal, followed by gentle scraping, whilst sonication was ineffective. A thin fouling film was left on the membrane surface even after application of the best removal techniques. A time of 3 h was sufficient to allow for sample drying at 105 degrees C. Loss-on-ignition at 550 degrees C was completed after 20 min, but significant reductions of FeCl3 (50%), ammonium chloride and ammonium sulfate (both 100%) demonstrate that loss-on-ignition weight loss may not be an accurate measure of organic matter content in foulant samples with a high proportion of inorganics. Calibration curves for quantification of iron and silica in kitchen blender foulant homogenates with the colorimetric phenanthroline and ammonium molybdate assays, respectively, had to be established by standard addition directly to the sample. Fouling removal with a kitchen blender produced homogeneous extracts suitable for chemical analysis with field kits.