Use of fluorescent silica particles for checking the integrity of microfiltration membranes

In this study, a new approach utilizing silica-based fluorescent particles as a surrogate for checking the integrity of microfiltration membranes was systematically investigated. The fluorescent particles were synthesized as spheres with diameters of 0.5–0.7 μm and used to test the integrity of microfiltration membranes with nominal pore sizes of 0.25 μm. The fluorescent particles only flowed through the damaged parts of membranes. The permeates were then collected and filtered through a GF/C filter to collect the outflow particles. The collected particles were placed under a UV lamp, and the fluorescence was photographed with a digital camera. The mass of the outflow particles was estimated by analyzing the images of the fluorescence pictures. To estimate the size of damage on the membrane surface, the functional relationship between the damaged area of the membrane and the mass of fluorescent outflow particles was established using a dimensional analysis. In addition, the dead-end filtration results show that at particle concentrations >10 mg/L, the flux decline was approximately 10% even then the particle concentration was increased to 100 mg/L. The cake resistance caused by particle deposition increased the total membrane resistance only by 10% in long-term filtration. Therefore, the synthesized fluorescent silica particles are a suitable surrogate for membrane integrity tests.

Research highlights▶ A novel idea is proposed to check a membrane surface integrity. ▶ Fluorescent silica particles are applied as a feasible surrogate. ▶ The outflow mass of fluorescent particles depend linearly on the size of damage. ▶ The mathematical function is established to predict the size of damaged part.