Effect of PAC dosage in a pilot-scale PAC–MBR treating micro-polluted surface water Jingyi Hu a,⇑ , Ran Shang a , Huiping Deng b , Sebastiaan G.J. Heijman a , Luuk C. Rietveld a a Delft University of Technology, P. O. Box 5048, 2600 GA Delft, The Netherlands b Key Laboratory of Yangtze River Water Environment, Ministry of Education, Tongji University, 200092 Shanghai, China highlights  Pilot-scale MBR amended with PAC was operated to treat micro-polluted surface water.  Higher pollutant removal and sustained membrane flux were obtained in 2 g/L PAC–MBR.  Small molecular weight organic matter is refractory to 2 g/L PAC–MBR treatment.  PAC needs to be renewed in 2 g/L PAC–MBR after 21 days continuous operation. article info Article history: Received 9 October 2013 Received in revised form 6 December 2013 Accepted 11 December 2013 Available online 22 December 2013 Keywords: MBR Micro-polluted surface water Optimal dosage PAC abstract To address the water scarcity issue and advance the traditional drinking water treatment technique, a powdered activated carbon-amended membrane bioreactor (PAC–MBR) is proposed for micro-polluted surface water treatment. A pilot-scale study was carried out by initially dosing different amounts of PAC into the MBR. Comparative results showed that 2 g/L performed the best among 0, 1, 2 and 3 g/L PAC–MBR regarding organic matter and ammonia removal as well as membrane flux sustainability. 1 g/L PAC–MBR exhibited a marginal improvement in pollutant removal compared to the non-PAC sys- tem. The accumulation of organic matter in the bulk mixture of 3 g/L PAC–MBR led to poorer organic removal and severer membrane fouling. Molecular weight distribution of the bulk liquid in 2 g/L PAC– MBR revealed the synergistic effects of PAC adsorption/biodegradation and membrane rejection on organic matter removal. Additionally, a lower amount of soluble extracellular polymer substances in the bulk can be secured in 21 days operation. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Owing to the rapid industrial development in the past few dec- ades, a growing number of pollutants were discharged into the receiving surface water without adequate treatment, which caused a huge threat to the quality of potable water sources as a conse- quence. This contaminated surface water is referred to as micro- polluted surface water (MPSW). Generally, it contains chemical oxygen demand COD Mn below 10 mg/L, with organic carbon and ammonia being the major pollutants (Sagbo et al., 2008). Most re- cently, membrane bioreactor (MBR) as an advanced technology has been receiving widespread popularity for MPSW treatment (Ma et al., 2012, 2013; Tian et al., 2008), based on the following aspects: (1) biodegradation is favorable for the removal of primary pollu- tants in MPSW, such as ammonia (Li et al., 2006; Xu et al., 2007); (2) membrane rejection in the MBR system provides a barrier against microbes leakage into the product water (Oh et al., 2007; Tian et al., 2009), which offers biologically stable water with a desirable quality. However, due to the oligotrophic condition associated with MPSW, extra material is preferred to enrich the pollutants and used as a carrier for better microbial community formation. Pow- dered activated carbon (PAC) is a commercial porous adsorbent with a significant surface area, which appears to be the most appropriate material for the aforementioned purpose. In a PAC- amended MBR (PAC–MBR) system, the bio-refractory substances could be eliminated by PAC adsorption (Liu et al., 2005). Therefore, simultaneous adsorption and biodegradation rather than a single biological process reflect the advantage of PAC–MBR system (Ng et al., 2013). Moreover, PAC addition has been proven to be bene- ficial for improving membrane filterability, by altering the floc characteristics in the bulk mixture and lowering the foulant con- centrations (Le-Clech et al., 2006). Although PAC–MBR hybrid technology has been well studied for MPSW treatment (Ma et al., 2012, 2013; Tian et al., 2008), these experiments were mostly designed on a laboratory scale using synthetic or simulated surface water, which might not properly 0960-8524/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.biortech.2013.12.075 ⇑ Corresponding author. Tel.: +31 0152785457. E-mail address: j.hu-1@tudelft.nl (J. Hu). Bioresource Technology 154 (2014) 290–296 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech