Interferometric observations and kinetic modeling of the chemical cleaning of humic materials deposited on membranes

In this paper, vertical scanning interferometer (VSI) is used to analyze the decrease in cake layer height of membranes. Nanofiltration membrane was fouled with CaCl2 and humic acid solution for 24 h and then, put into cleaning solution to dissolve the deposits from membrane surface. The height differences between cleaned and uncleaned side of the membranes were measured by interferometry. The cleaning solutions were EDTA (etilendiamin tetraasetikasit), sodium dodecyl sulfate (SDS), H2O2 and NaCl. Concentration, pH and temperature of the cleaning solutions were changed during cleaning experiments. According to experimental results, EDTA was the most efficient chemical to dissolve the Ca and organic matter complexes while NaCl was the inefficient one. UV absorbances of remaining solutions were similar to dissolution rates obtained with interferometry. Additionally, clean water flux recoveries were also the same with dissolution rate of deposits obtained from decrease in cake layer height except H2O2. Kinetic expression based on concentration and time proposed in this study was in agreement with the atomic scale observations obtained with interferometry. UV absorbance data can also be used to estimate the cleaning efficiency in practice.