Biochemical Engineering Journal 38 (2008) 226–233 Removal of suspended solids from tuna spleen extract by microfiltration: A batch process design and improvement Zhenyu Li a,c , Aran H-Kittikun a , Wirote Youravong b,c,∗ a Department of Industrial Biotechnology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai 90112, Thailand b Department of Food Technology, Faculty of Agro-Industry, Prince of Songkla University, Hat Yai 90112, Thailand c Membrane Science and Technology Research Center, Prince of Songkla University, Hat Yai 90112, Thailand Received 15 January 2007; received in revised form 30 May 2007; accepted 4 July 2007 Abstract In order to reduce the fouling load during separation of trypsin and chymotrypsin from yellowfin tuna spleen extract by ultrafiltration, a batch concentration microfiltration was designed as a pretreatment process to remove suspended solids from this extract. The design process included both dead-end and crossflow microfiltration (CFMF) to select optimal conditions for operation. The optimal membrane pore size of 0.10 m was selected by a preliminary test using dead-end microfiltration. And then based on total recycle and single-batch concentration CFMF, a continuous-batch concentration CFMF (CBC-CFMF) with 0.10 m hollow fiber membrane, crossflow velocity of 0.2 m s -1 , transmembrane pressure of 0.15 bar and gas injection factor of 0.38 was designed and applied successfully to remove suspended solids from tuna spleen extract while transmissions of about 1 for both trypsin and chymotrypsin were attained in this study. The negative effects of shear stress, high concentration of feed and long holding time in batch operation process were minimized by CBC-CFMF combined with gas bubbling technique. The optimal gas injection factor (r) of 0.38 resulted in a 300% improvement in flux comparing to the process without gas injection. Higher gas injection factor caused damage on both transmission and activity of expected enzymes. A clear permeate with slight yellow colour was obtained after CBC-CFMF. © 2007 Published by Elsevier B.V. Keywords: Enzyme production; Pretreatment; Suspended particles; Filtration; Microporous membranes; Optimization 1. Introduction The demand of fishery product has increased significantly in recent years. As one of the largest exporters of canned tuna in the world, Thailand produces more than 311,070 t canned tuna annually [1]. Since the major part of aquatic animal for fishery processing is only meat, a large amount of wastes has been generated from the fishery industry. In the tuna canning process, there are 23–25% solid waste (e.g. head, skin, viscera) and about 35% liquid waste (e.g. blood, tuna condensate, oil) [2]. The utilization of fishery waste has caught more attention. The pressure driven membrane processes, e.g. mcirofiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmo- sis (RO) have successfully been implemented in many fishery ∗ Corresponding author at: Department of Food Technology, Faculty of Agro- Industry, Prince of Songkla University, Hat Yai 90112, Thailand. Tel.: +66 7428 6321; fax: +66 7421 2889. E-mail address: wirote.y@psu.ac.th (W. Youravong). industrial cases [3–6]. In previous studies, the proteases was recovered from yellowfin tuna spleen by UF [7]. However the wastes from fishery processing contain many impurities, such as fat, meat debris and blood. After extraction, the extract is normally turbid and contains a lot of suspended solids which may limit the function of UF process. A suitable pretreatment method is required. According to its separation range in solute size varying from approximately 0.02–10 m and operational advantages, MF may serve as a simple, low cost and continuous operation to substitute for other methods such as centrifugation as pretreatment process to remove suspended solids from tuna spleen extract and provide a clear permeate as feed bulk for further recovery of valuable compound by UF process. It is well known that concentration polarization and fouling including reversible and irreversible types are major problems causing functional decay of MF process and low permeate flux to far below the theoretical capacity of the membrane. The total avoidance of these two problems is not possible, but their impact could be limited by a variety of techniques, such as pretreat- ment of feed bulk, modification of membrane material and flow 1369-703X/$ – see front matter © 2007 Published by Elsevier B.V. doi:10.1016/j.bej.2007.07.005