Analysis of fouling control strategies in ceramic nanofiltration membranes: CaCO₃ precoating versus continuous dosing

Ceramic membrane filtration is increasingly applied in water reclamation and purification, demonstrating particular efficacy in treating challenging industrial wastewater streams and non-potable water sources. During precoating, a removable filtration layer can be deposited on the membranes to enhance particle retention and reduce fouling, although it requires periodic renewal. The continuous dosing strategy is implemented by premixing calcium carbonate (CaCO₃) with the feed solution at the onset of each cycle, prior to the start of filtration. Both methods address membrane fouling but differ fundamentally in longevity and modification mechanisms. In this study, dead-end filtration was employed to deposit a CaCO₃ coating, with particular focus on fouling mitigation using citric acid treatment. Compared to the precoating method, the continuous dosing method enabled the addition of CaCO₃ throughout the fouling experiment, followed by citric acid cleaning. Experimental results demonstrated that, although the continuous dosing method also showed good permeability recovery, the precoated membrane exhibited better permeability recovery than the continuous dosing method, with consistent observations across both model wastewater and surface water. This performance difference likely results from the protective CaCO₃ layer on the membrane, while the continuous dosing method allowed for partial foulant deposition before sufficient CaCO₃ coverage was achieved. The precoated membrane exhibited the lowest irreversible fouling (3 × 10 10 m −1 after the second cycle, versus 21 × 10 10 m −1 for continuous dosing and 72 × 10 10 m −1 for the uncoated membrane). The precoated membrane also performed better in treating Schie Canal water. The treatment system showed better performance in bulk water quality improvement, achieving a 94% removal of dissolved organic carbon and a 65% reduction in electrical conductivity. The process exhibited high ion selectivity, rejecting divalent cations (Ca 2+ , Mg 2+ > 68%) and specific anions, with particularly high removal rates for fluoride and phosphate (F − , PO₄ 3− > 98%).