Wastewater treatment by membrane ultrafiltration enhanced with ultrasound: Effect of membrane flux and ultrasonic frequency Laura Borea a , Vincenzo Naddeo a,⇑ , Marwa S. Shalaby b , Tiziano Zarra a , Vincenzo Belgiorno a , Heba Abdalla b , Ahmed M. Shaban c a Sanitary Environmental Engineering Division (SEED), Department of Civil Engineering, University of Salerno, Via Giovanni Paolo II 132, 84084 Fisciano, SA, Italy b Chemical Engineering and Pilot Plant Department, Engineering Research Division, National Research Centre, 33 El Bohouth Street (Former El Tahrir Street), P.O. Box 12622, Dokki, Giza, Egypt c Water Pollution Research Department, National Research Centre, 33 El Bohouth Street (Former El Tahrir Street), P.O. Box 12622, Dokki, Giza, Egypt article info Article history: Received 14 February 2017 Received in revised form 13 June 2017 Accepted 19 June 2017 Available online xxxx Keywords: Fouling Membrane flux Sonication Ultrasound Wastewater reclaim abstract Membrane ultrafiltration is increasingly applied for wastewater treatment and reuse, even though mem- brane fouling still represents one of the main drawbacks of this technology. In the last years, innovative strategies for membrane fouling control have been developed, such as the combination of membrane pro- cesses with ultrasound (US). In present work, the application of membrane ultrafiltration and its combi- nation with US were studied, evaluating the influence on the performance of the treatment and membrane fouling formation of two membrane fluxes, 75 and 150 L/m 2 h, along with two US frequencies, 35 and 150 kHz. The results observed showed that the combination of membrane ultrafiltration with US, respect to the filtration process alone, reduced membrane fouling rates to a greater extent at the higher membrane flux and lower US frequency applied, reaching a reduction of 57.33% at 150 L/m 2 h and 35 kHz. Furthermore, higher organic matter and turbidity removals were observed at higher frequency (130 kHz). The results obtained highlights the applicability of this combined process for the upgrading of membrane ultrafiltration and as an alternative option to conventional tertiary wastewater treatments. Ó 2017 Elsevier B.V. All rights reserved. 1. Introduction Water scarcity along with its increasing demand have focused the attention on the development of best practices for its reuse through the application of advanced wastewater treatments, such as membrane filtration [1–3], adsorption [4–6], ultrasound (US) [7], electrochemical [8,9] and advanced oxidation processes [10,11], in order to reach high effluent quality. Among these treat- ments, membrane filtration represents a promising alternative to the existing technologies, since it increases the removal efficiencies through the physical separation of particulate and colloidal matter from wastewater [12]. However, membrane fouling still represents the main drawback for the widespread application of this technology. Fouling reduces the permeability of a membrane due to the accumulation of col- loids, particles, macromolecules and salts on the membrane sur- face, which consequently decreases the flux, shortens membrane life, due to frequent chemical and physical cleaning, and raises the treatment costs [13–15]. Research studies have focused the attention on membrane foul- ing control through the combination of the membrane filtration with different processes such as adsorption [16,17], electrochemi- cal [18–20] and advanced oxidation processes [21,22]. Further- more, several studies in the last decades have been carried out on the application of US for the enhancement of membrane perme- ability and the overcome of membrane flux decline [23–25]. US is, indeed, widely used as a surface cleaning technique and is a promising method for membrane fouling control since no chemical cleaning reagent is needed, the permeate flux can be maintained during the filtration process, not only after cleaning, and filtration is not interrupted to perform cleaning [26,27]. When US is intro- duced into water, it is subjected to a series of compression and rar- efaction cycles, which lead to the formation of cavitation bubbles [26,28–30]. Under compression cycle, the bubbles collapse and generate different physical and chemical phenomena including localized hot spots with high temperature (up to 5000 K) and pres- sure (up to 105 kPa), high-velocity fluid movement and the forma- http://dx.doi.org/10.1016/j.ultras.2017.06.013 0041-624X/Ó 2017 Elsevier B.V. All rights reserved. ⇑ Corresponding author. E-mail address: vnaddeo@unisa.it (V. Naddeo). Ultrasonics xxx (2017) xxx–xxx Contents lists available at ScienceDirect Ultrasonics journal homepage: www.elsevier.com/locate/ultras Please cite this article in press as: L. Borea et al., Wastewater treatment by membrane ultrafiltration enhanced with ultrasound: Effect of membrane flux and ultrasonic frequency, Ultrasonics (2017), http://dx.doi.org/10.1016/j.ultras.2017.06.013