Improved anaerobic co-digestion of food waste and domestic wastewater by copper supplementation – Microbial community change and enhanced effluent quality Pak Chuen Chan a , Qihong Lu a,b , Renata Alves de Toledo a , Ji-Dong Gu c , Hojae Shim a, ⁎ a Department of Civil and Environmental Engineering, Faculty of Science and Technology, University of Macau, Macau b School of Environmental Science and Engineering, Sun Yat-Sen University, Guangzhou, China c School of Biological Sciences, The University of Hong Kong, Hong Kong, China HIGHLIGHTS • 10 mg/L Cu 2+ enhanced the cumulative methane yield compared to the control. • Higher concentrations (30–50 mg/L) of Cu 2+ inhibitory to the anaerobic co- digestion • SCFA and LCFA concentrations de- creased substantially after the Cu 2+ supplementation. • A clear shift of microbial community di- versity after microelement supplemen- tation • Significant COD, TN, and NH 3 -N removal by A 2 O reactor treating UASB reactor effluent GRAPHICAL ABSTRACT abstract article info Article history: Received 7 December 2018 Received in revised form 4 March 2019 Accepted 6 March 2019 Available online 08 March 2019 Anaerobic co-digesters are biorefineries for energy recovery from food waste and domestic wastewater via methane production. Nonetheless, the performance of this technology was not always satisfied due to the long chain fatty acids (LCFAs) generation from food waste. Micronutrient supplementation is an effective strategy that could be applied during the anaerobic (co-)digestion to further enhance the diges- tion efficiency while treating food waste. In this study, supplementing copper (as CuSO 4 and CuCl 2 ) at 10, 30, and 50 mg/L Cu 2+ was selected to further enhance the methane production of anaerobic co- digester while treating food waste and domestic wastewater. Overall, with the supplementation of cop- per, the chemical oxygen demand (COD) removal efficiency was over 90%, while higher methane yields (0.260–0.325 L CH 4 /g COD removed ) were obtained compared to the control without supplementation (0.175 L CH 4 /g COD removed ). For the cumulative methane yield, the highest increment of 94.1% was ob- tained when 10 mg/L of Cu 2+ were added. The results showed copper as a cofactor of many microbial enzymes and coenzymes involved in the methane production further improved both methane produc- tion and COD removal efficiency. Meanwhile, the microbial community analysis verified the copper sup- plementation significantly changed the bacterial communities but with the limited effect on the diversity of archaea. Furthermore, since the anaerobic co-digester was not that much efficient on the nutrients re- moval, the effluent from the upflow anaerobic sludge blanket (UASB) reactor was further treated by the Keywords: Anaerobic co-digestion Copper supplementation Methane production Microbial community change UASB reactor Science of the Total Environment 670 (2019) 337–344 ⁎ Corresponding author. E-mail address: hjshim@umac.mo (H. Shim). https://doi.org/10.1016/j.scitotenv.2019.03.081 0048-9697/© 2019 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv