Contents lists available at ScienceDirect Applied Energy journal homepage: www.elsevier.com/locate/apenergy Optimization of methane bio-hydroxylation using waste activated sludge mixed culture of type I methanotrophs as biocatalyst Ahmed AlSayed a , Ahmed Fergala a , Saif Khattab b , Adham ElSharkawy a , Ahmed Eldyasti a, ⁎ a Department of Civil Engineering, Lassonde School of Engineering, York University, Toronto, Ontario M3J 1P3, Canada b Department of Chemical Engineering, Ryerson University, 350 Victoria Street, Toronto, Ontario M5B 2K3, Canada HIGHLIGHTS • Methanotrophs enriched from waste activated sludge were used to produce methanol. • Multiple methanol dehydrogenase in- hibitors concentrations were screened. • Headspace gas composition were op- timized to promote methanol pro- ductivity. • The attained methanol productivity obtained was comparable to pure cul- tures. • Methanol concentration attained was double the reported using mixed cul- ture. GRAPHICAL ABSTRACT ARTICLE INFO Keywords: Methanotrophs Value-added products Wastewater treatment Methane Mixed culture Methanol ABSTRACT Captured biogas produced within wastewater treatment facilities can be the remedy to offset its increasing energy requirements. Furthermore, the conversion of methane to methanol is quite attractive as it is more transportable and has higher energy yield. Methane can be utilized by methanotrophs in which methanol is produced as a metabolic intermediate. Compared to type II, type I methanotrophs are more advantageous due to its higher growth yields and energy efficiency. This work objective is to optimize methanol bio-production using type I methanotrophs enriched from activated sludge process. This study demonstrates methanol production using mixed culture from wastewater sludge. Optimization of methanol dehydrogenase inhibitors, sodium for- mate, and copper concentrations, as well as, the gaseous headspace composition and biomass density resulted in a significant enhancement in methanol production. The maximum methanol concentration achieved in this study was 485 ± 21 mg/L. Whereas, the highest methanol productivity obtained was equal to 2115 ± 81 mg/L/day. Those findings show the high potential of producing methanol using mixed culture enriched from activated sludge process. 1. Introduction Over the past few decades, our planet has witnessed the augmen- tation of greenhouse gases (GHG) emissions resulting in notable climate and environmental changes. Having the same GHG emissions trend, it is predicted that by 2050 the global warming would increase by 2 °C above the temperature level in 1900 [1]. Wastewater treatment facil- ities (WWTFs) contribute to the global warming phenomena not only by GHG emissions such as methane and carbon dioxide, but also, by con- suming enormous amount of fossil fuel based energy [2]. For instance, https://doi.org/10.1016/j.apenergy.2017.11.090 Received 12 August 2017; Received in revised form 20 November 2017; Accepted 21 November 2017 ⁎ Corresponding author. E-mail address: Ahmed.eldyasti@lassonde.yorku.c (A. Eldyasti). Applied Energy 211 (2018) 755–763 0306-2619/ © 2017 Elsevier Ltd. All rights reserved. T