Journal of Membrane Science 616 (2020) 118561 Available online 11 August 2020 0376-7388/© 2020 Elsevier B.V. All rights reserved. Evaluating the impacts of a high concentration of powdered activated carbon in a ceramic membrane bioreactor: Mixed liquor properties, hydraulic performance and fouling mechanism Muhammad Bilal Asif a, b, c, 1 , Baoyu Ren a, b, c, 1 , Chengyue Li a, b, c , Tahir Maqbool a, b, c , Xihui Zhang a, b, c , Zhenghua Zhang a, b, c, * a Institute of Environmental Engineering & Nano-Technology, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen, 518055, Guangdong, China b Guangdong Provincial Engineering Research Center for Urban Water Recycling and Environmental Safety, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen, 518055, Guangdong, China c School of Environment, Tsinghua University, Beijing, 100084, China A R T I C L E INFO Keywords: Membrane bioreactor (MBR) Powdered activated carbon (PAC) Mixed liquor properties Membrane fouling Fouling models ABSTRACT Owing to the lack of comprehensive studies on the impacts of a high concentration of powdered activated carbon (PAC) in a ceramic membrane bioreactor (MBR), its performance (at 20 g/L) in terms of mixed liquor properties, hydraulic performance and fouling mechanism was elucidated in this study. In addition to the increase in foc size by 29%, zeta potential of the mixed liquor in PAC-MBR increased (from 19 ± 2 mV to 11 ± 2 mV), which was due to the sorption of soluble microbial products on PAC. Importantly, even at a high dose of 20 g/L, membrane fouling was reduced by 33% in PAC-MBR and was attributed to the membrane scouring by PAC and reduced SMP and EPS concentration in the mixed liquor. The viability of the four single and fve combined fouling models was assessed to explain the membrane fouling mechanisms in ceramic MBRs for the frst time. The intermediate-standard and cake-intermediate models well explained the fouling mechanism in the ‘control’ and PAC-MBR, respectively, and the intermediate fouling was the major component of the combined models. This study clarifes that MBR could be operated at a high PAC concentration without compromising the effuent quality, mixed liquor properties and membrane hydraulic performance. 1. Introduction Membrane bioreactor (MBR), which is basically an integration of a microfltration or ultrafltration membrane with an activated sludge- based bioreactor, has become a preferred technology, particularly for municipal wastewater treatment. This is because it provides excellent quality effuent with a compact footprint and low sludge production [1, 2]. Despite the steady growth in the global MBR market (USD $1.2 billion in 2016 to USD $3 billion in 2019), membrane fouling issue should be addressed for wide-scale applications of MBR, particularly in developing countries [3,4]. Membrane fouling can increase the oper- ating cost of MBR due to frequent chemical cleanings, and may reduce the useful life of the membrane [4]. Membrane fouling generally occurs due to: the adhesion/deposition of foulants [5,6]; and the formation of gel layer on the membrane sur- face during the fltration of mixed liquor [7,8]. It is important to note that extracellular polymeric substances (EPS) and/or soluble microbial products (SMP) have been widely recognised as one of the main fou- lants, and their concentration needs to be kept in control for the pro- longed operation of MBR without physical and chemical cleanings [9–11]. In this context, addition of powdered activated carbon (PAC) in MBR has been assessed for membrane fouling control [12,13]. Since PAC may adsorb SMP, membrane fouling propensity in PAC-MBR has been reported to reduce signifcantly as compared to that in ‘control’ MBR [14,15]. Improvement in the properties of mixed liquor suspended solids (MLSS) could be favourable for the membrane hydraulic performance in * Corresponding author. Institute of Environmental Engineering & Nano-Technology, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen, 518055, Guangdong, China. E-mail address: zhenghua.zhang@sz.tsinghua.edu.cn (Z. Zhang). 1 Co-frst authors. Contents lists available at ScienceDirect Journal of Membrane Science journal homepage: http://www.elsevier.com/locate/memsci https://doi.org/10.1016/j.memsci.2020.118561 Received 10 July 2020; Received in revised form 29 July 2020; Accepted 31 July 2020