Pulsatile Jet Cleaning of Filter Cloths Contaminated with Yeast Cells The cleaning of filter cloths is necessary to avoid prolonged system downtime and strong fouling. Reliable cleaning concepts are central to the removal of residues from the complex surface of filter cloths. Particle residues, in particular, play a de- cisive role in the sufficiency of the cleaning performance. Consequently, enhanced particle-removal cleaning concepts based on pulsatile jets for filter cloths have been developed. By varying the cleaning parameters, it has been demonstrated that increased pulse numbers and velocities improve the cleaning performance. Furthermore, this promising cleaning concept cleaned more effectively than con- ventional methods. The reduction in the amount of detergent needed is an ecolog- ical and economic advantage of pulsatile cleaning. Keywords: Cleaning, Filter cloths, Particle residues, Pulsatile jets, Yeast Received: January 18, 2016; revised: May 11, 2016; accepted: November 21, 2016 DOI: 10.1002/ceat.201600049 1 Introduction The cleanability and hygienic design of process plants and their components are essential in most applications in beverage, food, or pharmaceutical processing. However, these concepts are still unknown for filter cloths. The prevention of cross-con- tamination and the guarantee of consistent filtration perform- ances require the removal or cleaning of the filter. Often the exchange of the filter cloth is associated with cross-contamina- tion risks or high costs (new filter, longer downtime of the sys- tem) [1]. Thus, the cleaning of the filter media is preferred in many operations. Filter cloths are particularly widespread in the beverage and food industry, e.g., in filter presses (mash, wine, juices, etc.) [2–4]. After a successful filtration, separated substances remain on the filter cloth’s surface or in its pores. This condition is de- fined as fouling and occurs in filtration processes repeatedly [5–7]. Fouling on filter cloths or membranes can be categorized into inorganic, organic, bio-, and particle fouling [1, 8]. Pre- dominantly, the removal of particle residues is crucial for the cleaning of woven filters. Particles adhere on or in the filter cloth as a result of adhesive forces like van der Waals forces [6, 9]. Another important point in the field of cleaning is the behavior of the dirt towards the cleaning water. This behavior can be classified as soluble, swellable, emulsive, or suspendable [10]. The last category, the suspendable dirt, mainly consists of insoluble particles, which are therefore difficult to remove with water or chemical detergents [11]. Small particles are especially hard to remove if they are in the deeper layers of the filter cloth. These problem zones are rarely reached by standard cleaning concepts due to stream shades or dead ranges [12–14]. Ripperger et al. compared the attractive and lift forces of differently sized particles during cross-flow filtration. The results show that particles below an average size of 30 mm are not removed by lift forces due to the high surface attraction [15]. Microorganisms, which often have to be separated in the beverage or food industry, are even smaller. As mentioned above, particle residues are one of the most decisive factors in filter cloth cleaning, which is well confirmed by literature [1, 16, 17]. Thus, filter cleaning concepts must be designed for sufficient particle removal. Previously developed methods for cleaning filter cloths were based on overflowing (forward flush) or backwashing (back flush) [1, 18]. These principles can be combined with different detergents, the type and concentration of which have to be adapted to the filter material. However, from an ecological and economical aspect, the utilization of fewer detergents is desir- able. According to Sinner’s Circle and its cleaning influences, other cleaning parameters have to be increased to decrease the extensive utilization of cleaning chemicals [10]. However, an increase of the cleaning temperature can result in damage because of the material’s sensitivity to heat. Furthermore, the use of enlarged cleaning intervals leads to higher costs. Conse- quently, the mechanical cleaning parameter remains. One possible mechanical option is cleaning by jets, which are streamed with a defined velocity toward the filter surface. Therefore, the streaming impact has to be modified to increase the mechanical influence. A potential approach is the utiliza- tion of pulsatile jets. It had already been shown that a change from continuous to pulsed cleaning results in higher cleaning rates in pipes or surfaces from particles or other types of foul- ing [19–24]. The filtration performance of membranes or filter cloths, in particular, is enhanced by using pulsatile flows, which Chem. Eng. Technol. 2017, 40, No. 3, 450–458 ª 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.cet-journal.com Roman Werner Bernadette Bollwein Roman Petersen Johannes Tippmann* Thomas Becker – Roman Werner, Bernadette Bollwein, Roman Petersen, Dr.-Ing. Johannes Tippmann, Prof. Dr.-Ing. Thomas Becker j.tippmann@tum.de Technische Universita¨t Mu¨ nchen, Institute of Brewing and Beverage Technology, Weihenstephaner Steig20, 85354 Freising, Germany. Research Article 450