Synergistic effect of up-flow constructed wetland and microbial fuel cell for simultaneous wastewater treatment and energy recovery Yoong-Ling Oon a , Soon-An Ong a,⇑ , Li-Ngee Ho b , Yee-Shian Wong a , Farrah Aini Dahalan a , Yoong-Sin Oon a , Harvinder Kaur Lehl a , Wei-Eng Thung a a School of Environmental Engineering, Universiti Malaysia Perlis, 02600 Arau, Perlis, Malaysia b School of Materials Engineering, Universiti Malaysia Perlis, 02600 Arau, Perlis, Malaysia highlights  Novel multiple anodes to study the effect of electrode spacing.  Organic loading influenced the voltage output despite electrode spacing.  Over 99% of COD removal was achieved by UFCW–MFC.  UFCW–MFC has great potential in removing high strength organic wastewater.  UFCW–MFC can remove organic matter, nutrient and merits with energy recovery. graphical abstract article info Article history: Received 26 September 2015 Received in revised form 5 December 2015 Accepted 9 December 2015 Available online 15 December 2015 Keywords: Up-flow constructed wetland Microbial fuel cell Membrane-less Activated carbon as electrodes Bioelectricity abstract This study demonstrated a successful operation of up-flow constructed wetland–microbial fuel cell (UFCW–MFC) in wastewater treatment and energy recovery. The goals of this study were to investigate the effect of circuit connection, organic loading rates, and electrode spacing on the performance of wastewater treatment and bioelectricity generation. The average influent of COD, NO 3  and NH 4 + were 624 mg/L, 142 mg/L, 40 mg/L, respectively and their removal efficiencies (1 day HRT) were 99%, 46%, and 96%, respectively. NO 3  removal was relatively higher in the closed circuit system due to lower dissolved oxygen in the system. Despite larger electrode spacing, the voltage outputs from Anode 2 (A2) (30 cm) and Anode 3 (A3) (45 cm) were higher than from Anode 1 (A1) (15 cm) as a result of insufficient fuel supply to A1. The maximum power density and Coulombic efficiency were obtained at A2, which were 93 mW/m 3 and 1.42%, respectively. Ó 2015 Elsevier Ltd. All rights reserved. 1. Introduction Constructed wetlands (CWs) are engineered systems, which use natural processes together with a series of treatment mechanisms, including physical, chemical as well as a variety of microbial inter- action processes to mitigate wastewater (Vymazal, 2007). CWs are already in field-level use for wastewater treatment and have been increasingly used worldwide since CWs are simple in construction, minimal or low energy requirement, low operation and mainte- nance cost, as well as good landscape integration (Tanner, 1996; Fang et al., 2013). The roles of plants were frequently reported in CW studies. Some of the important roles of plants in CWs are aesthetic, recreational and ecological function (Tanner, 1996). According to Bezbaruah and Zhang (2004), plants play a significant role in releasing oxygen in the wastewater environment. http://dx.doi.org/10.1016/j.biortech.2015.12.011 0960-8524/Ó 2015 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. Tel./fax: +60 4 9798986. E-mail address: ongsoonan@yahoo.com (S.-A. Ong). Bioresource Technology 203 (2016) 190–197 Contents lists available at ScienceDirect Bioresource Technology journal homepage: www.elsevier.com/locate/biortech