Use of ATR/FTIR spectrometry to study fouling of microfiltration membranes by natural waters

Attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectrometry provided insight into the chemical nature of deposits on polypropylene microfiltration membranes after filtration of two North American surface waters. The spectra of the foulants were easy to distinguish from the spectra of the membrane material. The results did not show strong evidence for the presence of carboxylic acid, carboxylate, phenolic, or hydroxyl functional groups in the foulants, although these functional groups are common in natural waters. ATR/FTIR also indicated the presence of inorganic foulants; the ratio of inorganic to organic foulants varied between the two water sources. The spectra of the foulants were significantly more distinct than spectra of other natural waters, suggesting that relatively few components present in Medina River and Beaver Lake surface waters may adsorb to this membrane material. ATR/FTIR appears to be a valuable tool for studying membrane fouling by natural waters.

Two natural surface waters were filtered through 0.2-µm polypropylene membranes and examined by ATR/FTIR spectrometry. The vibrational bands associated with the foulants could be clearly distinguished from those of the membrane material. The foulants on these membranes produced relatively sharp absorption bands; in contrast to the broad bands natural waters typically produce. There was no strong evidence for the presence of carboxylic acid, carboxylate, phenolic, or hydroxyl functional groups, although these are common components in DOM. These results suggest that a substantial portion of DOM did not adsorb to the membranes in these experiments, a conclusion that was corroborated by DOC measurements. Carboxylate and hydroxyl groups impart significant solubility to molecules, so it is reasonable to expect that DOM molecules rich in these functional groups would not partition onto the membrane surface. The chemical compositions of the foulants in the two sources were different from each other. Both inorganic and organic compounds appeared to be present, although the proportion of inorganic and organic foulants varied between the sources. This conclusion was corroborated by elemental analysis of the membrane surfaces. The inorganic foulants appeared to contain aluminum silicates and the organic foulants may have contained carbonyl or amide functional groups. The functional chemistry of the deposited material did not appear to change significantly when the pH of the feed water was varied between values of 4.0 and 9.0. Acknowledgments This research was funded by the American Water Works Association Research Foundation.