Effect of combined fouling on desalination performance of membrane capacitive deionization (MCDI) during long-term operation

The effect of combined fouling on desalination performance of membrane capacitive deionization (MCDI) process was investigated and bovine serum albumin (BSA) as well CaCl2 were chosen as representative of organic and inorganic matter, respectively. Result showed that when calcium concentration was in the range of 0.5-3 mM, the removal efficiency for CaCl2/BSA mixed solution displayed slower decline compared to the single solution indicating that the presence of BSA mitigated fouling degree. However, after the calcium concentration exceeded to 5 mM, the co-existence of BSA showed negative effect for the ion removal and the efficiency for the mixed solution declined more obviously compared to that in the single solution. Additionally, it was found that calcium concentration had an important effect on BSA absorption onto membrane surface and BSA deposition degree was intuitively distinguished by Scanning electron microscopy (SEM). Based on analysis of size distribution and zeta potential, the result showed that when calcium concentration was in the range of 0.5-3 mM, the adsorption amount for BSA onto the membrane surface decreased from 1.72 to 0.71 mu g/cm(2) accordingly, while it increased to 1.02 mu g/cm(2) when calcium concentration increased to 5 mM. These findings would offer deeper insights into the effect of combined fouling on MCDI performance, which was expected to provide a theoretical basis for further application.