Scaling reduction in carbon nanotube-immobilized membrane during membrane distillation

Membrane distillation (MD) is fast evolving as a desalination technology for high-salinity waters where scaling remains a major challenge. This paper reports the scaling reduction in carbon nanotube-immobilized membranes (CNIMs) and by the use of the antiscalant polyacrylic acid. High concentrations of CaSO₄, CaCO₃, and BaSO₄ were deliberately used to initiate scaling on the membranes. It was observed that after ten hours of operation in a highly scaling CaSO₄4 environment, the CNIM showed 127% higher flux than what was observed on a membrane without the CNTs. The trends were similar with CaCO₃ and BaSO₄, where the CNIM showed significantly improved antiscaling behavior. The normalized flux declination for CNIM was found to be 45%, 30%, and 53% lower compared to the pristine membrane with CaSO₄4, CaCO₃, and BaSO₄ solutions, respectively. The use of antiscalant in the feed solution was also found to be effective in improving antiscaling behavior, which reduced salt deposition up to 28%, and the water vapor flux was 100% and 18% higher for the pristine polypropylene and CNIM, respectively. Results also showed that the presence of CNTs facilitated the removal of deposited salts by washing, and the CNIM regained 97% of its initial water flux, whereas the polypropylene only regained 85% of the original value.