Contents lists available at ScienceDirect Journal of Water Process Engineering journal homepage: www.elsevier.com/locate/jwpe Biofouling on RO-membranes used for water recovery in the dairy industry Iuliana Madalina Stoica a, ⁎ , Eirini Vitzilaiou a , Henriette Lyng Røder b , Mette Burmølle b , Dorrit Thaysen c , Susanne Knøchel a , Frans van den Berg a a Department of Food Science, Faculty of Science, University of Copenhagen, Rolighedsvej 26, DK-1958 Frederiksberg C, Denmark b Department of Biology, Faculty of Science, University of Copenhagen, Universitetsparken 15, 2100, Copenhagen Ø, Denmark c Arla Foods Ingredients, Sønderupvej 26, DK-6920 Videbæk, Denmark ARTICLE INFO Keywords: Reverse osmosis (RO) membranes Water recovery Biofouling CIP Confocal laser scanning microscopy (CLSM) ABSTRACT Recovery followed by re-use of process-water obtained from dairy effluents by means of reverse osmosis tech- nology is one route that can provide the dairy industry with the possibility to reach sustainable water regimes. However, membrane fouling is a phenomenon that limits both the efficiency and increases the running costs of such reverse osmosis units and can potentially alter the quality characteristics of permeate water. In this paper, several industrial-scale RO membranes used for recovery of process-water from whey UF permeate have been examined for their fouling tendency. At the end of a complete clean-in-place (CIP) protocol based on alkaline- acid formulations, biofouling appears to be the main issue in the investigated RO-elements. Between 4.19 and 5.69 log 10 (CFU cm -2 ) of viable microorganisms still remained on the membrane retentate surface and, more surprisingly, evidence of significant contamination was found on permeate side of these particular membranes. Microbiological analysis indicate that minor loads of microorganisms do pass into the permeate streams but final UV treatments ensured final process-water with non-detectable levels. There is a need for optimization of cleaning procedures and finding the best compromise for achieving surface disinfection while still preserving membrane integrity and not compromising the water quality. 1. Introduction Climate change responsibilities, fresh water shortage, strict dis- charge regulations and financial gains are all factors that drive in- dustries to seek out more sustainable practices and possibilities of water recovery in order to lower their effluents and water intake. Over the years, reverse osmosis (RO) membrane technology has demonstrated to be an excellent platform for recovery of water with high quality char- acteristics. Acting as a barrier to nearly all pollutants, the RO mem- branes produce water which can fulfill the strict quality regulations for public health and environment protection [1]. The food industries depend upon clean fresh water for a wide range of processes and cleaning operations and the implementation of safe and efficient water recovery strategies has become a major priority for many stakeholders [2]. Several examples of water recycling or reuse within the food sector have been reviewed by Vourch et al. [3] and Casani et al. [4]. Emerging originally as the biggest consumer and wastewater producer within the food area, the dairy industry is be- coming one of the leaders in water reuse practices [5]. This is enabled primarily by their vast experience in applying membrane technology for concentrating or fractionating different liquid streams, but also due to the great potential of recovering water from different process streams such as milk or cheese whey [6,7]. This trend is also stimulated by the large volumes of water required for cleaning [8]. Raw whey was tra- ditionally considered a big biological pollutant. However, using various membrane technologies in series, such as ultrafiltration (UF) followed by RO and possibly a RO-polisher, it can now be valorized by harvesting high nutritional products - whey and lactose powder - and ultimately the liquid can be recovered as water which can qualify for reuse in production steps such as heat exchangers and clean-in-place (CIP) op- erations [9]. RO units primarily use reverse osmosis membrane elements with a spiral wound configuration. The main reason for this is their compact format, advantageous price, high membrane surface area in relation to their volume, and fitness for multiple applications [10]. Unfortunately, when processing a product with increased organic loads, such as permeates from whey separation, organic fouling and more notable biofouling are major risks that need to be minimized. Next to the po- tential safety risks, the biofilm formation can have a serious negative impact on the performance of the filtration system by lowering the trans-membrane flux [11] and cause decreased salt rejection [12]. Most published works conclude that biofouling appears to be an inevitable https://doi.org/10.1016/j.jwpe.2018.05.004 Received 30 January 2018; Received in revised form 1 May 2018; Accepted 3 May 2018 ⁎ Corresponding author. E-mail address: iuliana.stoica@food.ku.dk (I.M. Stoica). Journal of Water Process Engineering 24 (2018) 1–10 2214-7144/ © 2018 Elsevier Ltd. All rights reserved. T