Direct comparison of aerated and vibrated filtration systems for harvesting of Chlorella vulgaris M.R. Bilad a , L. Marbelia a , P. Naik a , C. Laine b , I.F.J. Vankelecom a, ⁎ a Centre for Surface Chemistry and Catalysis, Faculty of Bioscience Engineering, KU Leuven, Kasteelpark Arenberg 23, Box 2461, 3001 Leuven, Belgium b Amer-Sil S.A., Zone Industrielle, L-8287 Kehlen, Luxembourg abstract article info Article history: Received 2 May 2014 Received in revised form 3 August 2014 Accepted 8 September 2014 Available online 16 September 2014 Keywords: Algae harvesting Membrane fouling Magnetically induced membrane vibration C. vulgaris Submerged microfiltration Applying membrane filtration as the primary step in microalgae harvesting has been proven to be effective to re- duce the overall harvesting costs. However, membrane fouling remains a bottleneck to improve the performance. In this study, a direct comparison of an aerated and a vibrated membrane system for the fouling control of a Chlorella vulgaris broth filtration is presented in terms of membrane permeance and permeance recovery, respec- tively, in multiple filtration and cleaning stages. The result shows that the vibrated system offers a significant ad- vantage to maintain high permeance by minimizing the fouling and thus sustaining the filtration operation, especially for membranes with a more open structure. However, both systems were unable to prevent severe pore blocking in the early stage of filtrations, thus diminishing the advantage of using highly permeable mem- branes in microalgae harvesting. Nevertheless, further system and membrane cleaning procedure developments can still be conducted to overcome this problem. © 2014 Elsevier B.V. All rights reserved. 1. Introduction For decades, microalgae have received a lot of attention because of their capability of using inorganic carbon (CO 2 ) as carbon source and nu- trients from wastewater while producing useful biomass. The microalgal biomass can indeed be used as source for a variety of high- and low- value products, including health products, pharma- and nutraceuticals, pigments, animal feeds and biofuel. Harvesting microalgal biomass from cultivation broths is one of the major challenges that limit the widespread and full-scale application of microalgae as raw material for many different end-products, especially for the bulk (low-value) products [1]. A series of harvesting, dewatering, drying and pre- processing steps is required before the biomass can be converted into a desired product [2]. Because of their low concentration in the culture medium (0.5–2 g/l), their density close to that of water and their small size (typically a few micrometres), harvesting microalgal biomass is challenging [3]. In our earlier studies, we proposed the application of a hybrid process to harvest microalgae by combining a submerged membrane filtration (as primary step) with centrifugation (secondary step) [4]. The key advantage of this approach is that the majority of the water (up to 93%) is removed from the stream via the low-cost membrane filtration, while the remaining water is removed via a significantly downscaled centrifugation. However, the degree to which the primary concentration can take place, like in most membrane processes, is limited by the occurrence of membrane fouling. The microalgal biomass accumulates together with algogenic substances in the concentrated retentate and fouls the membrane. The application of membrane technology to harvest microalgae can be done in two ways: (1) as a standalone step to concentrate the broth [5,6] and (2) coupled directly to the cultivation process in a mem- brane photobioreactor (MPBR) [7,8]. Both ways are only efficient up to a certain biomass concentration due to the increasing fouling propensity of the more concentrated broth. Membrane fouling is too severe at high biomass concentrations, which is further worsened by the produc- tion of materials with high fouling properties (i.e. colloidal algogenic matters). However, the MPBR offers two additional main advantages: the biomass is concentrated and the productivity increased. The mem- brane can be directly immersed in the PBR, thus the aeration can be used not only to supply dissolved CO 2 (contained in the air) and mix the broth, but also to scour the membrane for fouling control. In the par- ticular case when water quality and availability is an issue, permeate reuse/recycle (with partial nutrient recycling) is also possible. Two different systems have been proposed to manage membrane fouling in the submerged membrane filtration for microalgae harvest- ing, namely an aerated [4] and a vibrated system (magnetically induced membrane vibration, MMV) [9]. Both have the objective of inducing enhanced shear-rates at the membrane–feed interface. In the aerated system, the shear rate is generally provided by coarse air bubbles, which, in the case of algae cultivation, also acts to supply the required CO 2 and promote mixing. In the vibrated system, shear rate is provided via membrane vibration. Although both systems were recently tested as the primary step of microalgae harvesting, a direct comparison using Algal Research 6 (2014) 32–38 ⁎ Corresponding author. E-mail address: ivo.vankelecom@biw.kuleuven.be (I.F.J. Vankelecom). http://dx.doi.org/10.1016/j.algal.2014.09.001 2211-9264/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Algal Research journal homepage: www.elsevier.com/locate/algal