Upscale of a laboratory rotating disk biofilm reactor and evaluation of its performance over a half-year operation period in outdoor conditions Petra Sebestyén a , Ward Blanken b , István Bacsa c , Gábor Tóth c , Alfredo Martin d , Tasneem Bhaiji e , Ágnes Dergez a , Péter Kesserű a, ⁎, Ákos Koós a , István Kiss a a Division for Biotechnology (BAY-BIO), Bay Zoltán Nonprofit Ltd. for Applied Research, Derkovits fasor 2, H-6726 Szeged, Hungary b Bioprocess Engineering, AlgaePARC, Wageningen University, PO Box 16, 6700 AA Wageningen, The Netherlands, c ATEKNEA Solutions Hungary, Tétényi út 84-86, HU-1119 Budapest, Hungary d Biogas Fuel Cell S.A., Parque Científico Tecnológico C/Ada Byron, n°107, 1°izq., 33203 Gijon, Spain e Manufacturing and Materials Department, School of Applied Sciences, Cranfield University, College Rd, MK43 0AL Cranfield, United Kindgom abstract article info Article history: Received 16 March 2016 Received in revised form 20 June 2016 Accepted 23 June 2016 Available online xxxx Biofilm-based microalgae cultivation techniques are promising technologies to overcome several issues of suspended cultivations, although only a few large-scale systems have been examined so far. In this study, a rotat- ing biological contactor-based laboratory-scale Algadisk reactor of 0.39 m 2 was tested under low light intensity, and then scaled up to 15.9 m 2 and operated for 6 months in outdoor conditions in order to test its stability and biomass production efficiency with Chlorella sorokiniana. The highest biomass productivity observed in the lab- scale reactor on disk surface base was 3.2 g (m 2 day) -1 with a 0.9 g mol -1 biomass yield on light and 208 g kg -1 dry weight content in biofilm. Due to pH crashes, extreme temperature variations, CO 2 limitation, and fail- ure of disk rotation, the Algadisk pilot system showed varying biomass productivity from 0.5 to 8.4 g (m 2 day) -1 on reactor footprint area. Also, biomass yield on light and biomass density remained lower than at labo- ratory scale. Nonetheless, a total of 7.4 kg CO 2 was fixed in the biofilm during the operating time. Despite the dif- ficulties and the complexity of the system, over 20 weeks of continuous operation was achieved without the need of reinoculation. © 2016 Elsevier B.V. All rights reserved. Keywords: Pilot scale Microalga Flue gas Sunlight Attached cultivation 1. Introduction More and more research focuses worldwide on the biotechnological and carbon capturing potential of microalgae. Microalgae play a huge role in CO 2 sequestration from the atmosphere in nature. This character- istic feature is also applied to capture CO 2 from industrial sources, for example, flue gases of combustion engines of power plants and biogas plants, thus reducing its effect on climate change while producing O 2 and biomass [1,2]. Due to their high diversity, applications of algae bio- mass vary from food and feed additives, pharmaceutical compounds, biofertilizers [3], biofuel production, including biodiesel, bioethanol, and biohydrogen production, [4], to wastewater treatment [5]. Addi- tionally, microalgae production does not require arable land therefore it is not competitive with food and feed production [6]. Numerous cultivation systems have been developed and optimized for a more efficient biomass and/or compounds production, e.g., open pond systems, tubular photobioreactors, flat plate reactors, and biofilm-based cultivation. Suspended systems are widely used tech- niques for large-scale algae cultivation; however, they entail several dif- ficulties such as high water demand, surface attachment of algae, high cost of downstream biomass concentration, and large occupied area [7,8]. On the other hand, researches on biofilm-based algal cultivation techniques show promising results to overcome these drawbacks of suspended cultivation methods and could provide solution for econom- ically feasible alga biomass production systems [9,10]. A wide range of biofilm reactors have been developed so far, for in- stance, vertical twin layer sheets and twin layer like systems [11–16], vertical rotating belts [17], algal turf scrubber [18], rotating algal biofilm reactor with spool harvester [19], and rotating disks [20]. Besides all the differences in the concept of their structure and operation, they all have one important quality in common: the high biomass content of the bio- film. The dry weight content of the growing biofilm is reported often around 100–175 g dry weight kg -1 wet biofilm [9,19–23], in some cases it can reach up to 200 g kg -1 [12,21]. These values are comparable with the solid content of centrifuged biomass from suspended cultures [24,25], albeit without the expenses of dewatering processes like centri- fugation and/or additional chemical compounds for flocculation, which can reach up to 20% of the total cost of biomass production [26]. Algal Research 18 (2016) 266–272 ⁎ Corresponding author. E-mail address: peter.kesseru@bayzoltan.hu (P. Kesserű). http://dx.doi.org/10.1016/j.algal.2016.06.024 2211-9264/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Algal Research journal homepage: www.elsevier.com/locate/algal