Quantifying defects in ceramic tight ultra- and nanofiltration membranes and investigating their robustness

One of the perceived benefits of ceramic membranes is their robustness, which makes them suitable for treating high organic load waste streams. In particular, ceramic tight ultrafiltration (tUF) and nanofiltration (NF) form an important barrier against small colloids and organic molecules. In order to achieve this barrier, the quality of the membranes should be uncompromised. An extension on a commonly used size exclusion method was developed in order to quantify defects in membranes and calculate the MWCO accurately excluding the defects. This approach gives a better representation of the membrane quality than the original method. The quality of a broad range of commercial ceramic membranes was investigated by determining the (i) hydraulic permeability, (ii) molecular weight cut-off, and (iii) quantitative defects. Several membranes – both tubular and disc membranes, selected from various suppliers – were tested to investigate their variability. Furthermore, the robustness of tubular NF membranes was studied by monitoring the effect of long-term exposure to sodium hypochlorite, which is commonly used to mitigate organic fouling. The results showed that batches of both tubular and disc membranes of different pore size and suppliers included membranes with defects. Furthermore, the long-term treatment of tubular ceramic membranes with sodium hypochlorite negatively affected, beyond expectation, the quality of the membranes. The separation layer in these membranes was not notably compromised by sodium hypochlorite exposure, but the end seal layer was damaged.