Journal of Membrane Science 367 (2011) 306–313 Contents lists available at ScienceDirect Journal of Membrane Science journal homepage: www.elsevier.com/locate/memsci Use of fluorescent silica particles for checking the integrity of microfiltration membranes Soo Hoon Choi, Juhee Yang, Changwon Suh, Jinwoo Cho ∗ Water Environment Center, Environmental Division, Korea Institute of Science and Technology, 39-1, Hawolgok-dong, Wolsong-gil 5, Seoungbuk-gu, Seoul 136-791, Republic of Korea article info Article history: Received 9 March 2010 Received in revised form 4 November 2010 Accepted 5 November 2010 Available online 12 November 2010 Keywords: Membrane Integrity test Fluorescent silica particles Surrogate Dimensional analysis Image analysis abstract 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 m and used to test the integrity of microfiltration membranes with nominal pore sizes of 0.25 m. The fluorescent particles only flowed through the dam- aged 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 func- tional 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. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Membrane processes are being increasingly applied in the treat- ment of drinking and wastewater, and water reuse [1], in addition for use in the food, pharmaceutical, and biotechnology industries [2]. These applications aim to separate particles, macromolecules, microorganisms, and viruses from mixtures to obtain clean water or pure solutions. However, due to immoderate operations, factory defects, and improper shipping and maintenance, the integrity of such mem- branes can be compromised, leading to feedwater leakage. The damaged membranes result in high turbidity; even filtrates with low turbidity (<0.1 NTU) can have significant bacterial contami- nation [3]. Thus, the integrity of the membrane must be checked regularly during operation to confirm reliable filtration perfor- mance. Compromised membranes can be caused by chemical oxidation of the membrane materials, installation and mainte- nance faults, excessive stress or strain on the membrane induced by backwashing or vigorous aeration, and physical damage by sharp objects [1]. Polymeric membranes can also be damaged by microor- ganism attack in the bio-fouled cake layer [4]. Many researchers propose various available testing methods [5–8] on lab- or full- ∗ Corresponding author. Tel.: +82 2 958 5838; fax: +82 2 958 6854. E-mail address: cogito1@kist.re.kr (J. Cho). scale systems [9,10]. The characteristics of these various methods are comprehensively reviewed in previous studies [1,5]. However, these studies indicate that the existing methods are neither simple nor sufficiently effective to detect the occurrence and magnitude of damage to membranes. Therefore, for practical applications, some of these methods are combined to have synergistic effects, such as in Memsure TM [11] in which a pressure decay test (PDT) and a sonic sensor are applied to check any breach in the membrane as well as the position of any leak. However, this method is time consuming and demands a series of different tests that need to be conducted by experienced professionals. In addition, direct meth- ods such as the PDT, and bubble point and vacuum hold tests can only indicate whether a membrane module is compromised. On the other hand, indirect methods, such as particle counting, turbid- ity monitoring, and the microbial challenge test using surrogates, are proven to be highly sensitive; in many cases a direct relation- ship exists between the measured data and removal efficiency [5]. However, such indirect tests only provide information on the possi- ble breakthrough of particles, pathogens, or viruses [12]. The sonic sensor test can reveal the location of leak and quantify the magni- tude of damage [13]; however, its application is very limited due to noise interference, which results in low sensitivity and poor relia- bility [14]. This in turn may lead to situations where the operator must access the damaged membrane due to unacceptable perme- ate quality. Consequently, there is a need to develop a method capable of assessing the level of membrane integrity in addition 0376-7388/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2010.11.015