Synthesis, characterization, and application of gravity-driven ceramic microfiltration membranes for surface water treatment

Abstract

Gravity-driven ceramic microfiltration (MF) disk-shaped membranes were synthesized using kaolin and different alumina contents (0 % wt, 25 % wt, and 50 % wt). The pure water flux, mean pore size, porosity and contact angle of membranes were measured. Their structure and composition were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The effect of alumina content was evaluated for long-term river water filtration in terms of permeate flux, turbidity, dissolved organic carbon (DOC), UV254, pH, and alkalinity removal. The physical characteristics of the biofouling layer, such as thickness and roughness, were studied using optical coherence tomography (OCT) imaging and the concentration of active microorganisms in the biofilm. The results showed acceptable turbidity removal after the flux stabilization period and relatively high performance for DOC, UV, and alkalinity removal during the first three days of filtration. Flux stabilized at 2.5–3 LMH on day 24 of filtration, indicating that the alumina content does not considerably affect the stable flux. As the flux modeling data showed, prior to the flux stabilization time, the fouling was controlled by the pore blocking mechanism. This was confirmed by OCT imaging that showed a very outspread biofilm layer with a low relative roughness; the layer became more compact with a higher relative roughness over time, showing that the cake layer is dominant after the flux stabilization period. Increasing the alumina content of the membranes increased the number of active microorganisms in the biofilm layer; possibly because of an increased adsorption of nutrients in the biofouling layer.