Available online at www.sciencedirect.com Chemical Engineering and Processing 47 (2008) 1647–1655 Mechanism of centrifugal filtration for separation of microbe/protein bio-suspension Kuo-Jen Hwang ∗ , Yiang-Chen Chou Department of Chemical and Materials Engineering, Tamkang University, Tamsui, Taipei Hsien 25137, Taiwan Received 14 February 2007; received in revised form 7 August 2007; accepted 5 September 2007 Available online 15 September 2007 Abstract The mechanism of centrifugal filtration of microbe/protein bio-suspension is studied. The bio-suspension is prepared by adding baker yeast and albumin bovine serum (BSA) into a buffer solution at pH 7.0; and the BSA molecules are purified from the mixture in a swing-arm centrifuge under rotational speeds ranging from 500 to 4000 rpm. A numerical program is established for estimating the concentration profiles of yeast cells in the filter chamber, the cake growth rate, the cake properties and filtration rate. The variations of the average specific filtration resistance and average porosity of cake are estimated based on a Voigt-in-series compression model. The simulated results of cake properties and filtrate rate agree fairly well with the available experimental data. In addition, the separation efficiency of BSA can be predicted accurately under various conditions once the BSA permeation through the cake and the filter septum is analyzed. To compare the separation efficiency of BSA in the centrifugal and cross-flow microfiltration systems, use of centrifugal filtration with a centrifugal effect just over the critical value is an optimum on the viewpoint of operating time, separation efficiency, and energy-saving. © 2007 Elsevier B.V. All rights reserved. Keywords: Centrifugal filtration; Protein purification; Bio-separation; Cake properties 1. Introduction Centrifugal filtration is one of the most efficient and eco- nomic methods for solid–liquid separation. Since the centrifugal field can generate a huge pressure drop through the filter cake, it has many advantages, such as high filtration rate, low cake moisture, etc. Therefore, it has been widely used in many chemical, food, environmental, and biochemical engineering processes. In these processes, the raw suspensions frequently contain multi-components, e.g., proteins, enzymes, microbial cells, and the other impurities co-existing in the cultivation prod- ucts in fermentation. How to purify those mixtures is increasing its importance in the fine chemical and biochemical industries in recent years. However, rare researchers have paid their attentions on the separation mechanism of centrifugal filtration, especially for the purification of bio-mixtures. This fact causes process engineers to spend too much time and costs for searching the optimum operating conditions or efficient equipments. ∗ Corresponding author. Tel.: +886 2 26215656x2726; fax: +886 2 26209887. E-mail address: kjhwang@mail.tku.edu.tw (K.-J. Hwang). The performance of a centrifugal filtration has been studied in the past years by correlating the suspension concentration or filtration resistance to the applied pressure or rotational speed [1,2]. Tiller et al. [3] indicated that neglecting the sedimentation effect in a centrifugal filtration would lead to an underestima- tion in the cake growth rate and an overestimate in the specific filtration resistance. Recently, the particle concentration profile in the filter chamber and the cake growth rate were simulated by analyzing the particle migration velocities under various con- ditions in swing-arm and basket centrifugal filtration systems [4,5]. The hindered settling factor, a function of local volume fraction of particles, was introduced into their models to take the sedimentation effect into consideration. Their results indicated that the effect of particle sedimentation caused a quicker cake formation and a more heterogeneous cake. Hence, the filtration resistance could be estimated once the cake formation and the particle size distribution in the cake were known. Besides the particle size distribution, the cake compress- ibility is also an important factor in determining the filtration resistance, especially for deformable particles or microbial cells. The deformable particles may exhibit a time-dependent viscoelastic mechanical behavior during filtration [6–8]. This 0255-2701/$ – see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cep.2007.09.007