Journal of Environmental Chemical Engineering 11 (2023) 110955 Available online 8 September 2023 2213-3437/© 2023 Elsevier Ltd. All rights reserved. Recycling of catering waste for sequential production of biohydrogen and biomethane; pre-treatments, batch, and continuous mode studies Khalid Z. Elwakeel a, *, 1 , Ahmed M. Elgarahy b, 2 , Huda M. Alghamdi a, 3 , Mohamed El-Qelish c, 4 a University of Jeddah, College of Science, Department of Chemistry, Jeddah, Saudi Arabia b Environmental Chemistry Division, Environmental Science Department, Faculty of Science, Port Said University, Port Said, Egypt c Water Pollution Research Department, National Research Centre, El Buhouth St., Dokki, 12622 Cairo, Egypt A R T I C L E INFO Editor: Stefanos Giannakis Keywords: Climate Change Catering waste Dark Fermentation Biohydrogen Scaling up Circular economy ABSTRACT Dark fermentation has emerged as a sustainable bio-based economy for bio-fuels production in accord with “carbon neutrality”. Herein, catering waste was collected, pre-treated with a series of multilevel (acidic, alkaline, Triton X100, ultrasonication, and microwave radiation) pathways, and employed as substrates to inspect their characteristics on two-stage mesophilic biohydrogen/biomethane production process through batch assays under initial pH of 6.5, and 7.5, respectively. The fndings revealed that the optimized pre-treated catering waste (CW) with Triton X-100 recorded the highest biohydrogen, and biomethane production yield of 5.9 mL/g VS added (BHP of 368.5 mL), and 17.7 ± 26.8 mL/g VS (BMP 1108.5 mL), at 37 ◦ C, respectively. Overall, the kinetic data was strongly matched with the Gompertz equation (R 2 = 0.92–0.99). Afterward, the pre-treated Triton X-100-CW was introduced into a second series of continuous experiments (continuously stirred tank reactors) for sequential production of biohydrogen/ biomethane. An average yield of biohydrogen and biomethane production of 22.24 ± 2.29 mL/g VS, and 98.7 ± 10.4 mL/g VS was accomplished at hydraulic retention time (HRT), and organic loading rate (OLR) of 1.0 day, 91.5 gCOD/L.day and 10.0 days, 7.2 gCOD/L.day, respectively. Economically, the confgured system displays a total energy yield of 1.634 KWh/KgVS, and the inspected 1600 kg CW produces about 2614.41 KW/day. As such, the present work broadens a salience pattern for scalable upcycling of CW organic constituent stream into biohydrogen/biomethane for potential applications in the energy sector. 1. Introduction Nowadays, the rising demand for energy resources associated with the uncontrollable overpopulation, and depletion of non-renewable energy resources has become a fast-growing transboundary issue, jeopardizing the survival of our sphere [1]. Moreover, the apparent global grappling with the climate change phenomena has become an incredible challenge to adapt to its calamitous environmental conse- quences (cause-effect integration). Compared with the monitored rate of the planet’s average temperature increase (e.g., 1 ◦ C) before the indus- trial revolution, the continued warming is certainly expected to rise to 1.5 ◦ C and 3 ◦ C, and between 4 ◦ C and 8 ◦ C, by the middle of this century, and 2100, respectively, in case of non-curbing of greenhouse gas emissions [2]. Only 7.4% of climate funding, according to the most current Global Landscape of Climate Finance Report, is designated for adaptation, demonstrating the signifcant mismatch between the supply and the need for fnancing for adaptation [3]. Furthermore, the entan- gling of climate change effects with other major global matters such as the COVID-19 pandemic is starkly promoting the discourse of develop- ment (rethinking) a more sustainable and cutting-edge tactical indus- trial strategies (post-Corona era) to pave the transition way of clean energy for sustainable growth. Ensuring an entire food supply is a key component of upholding the living creature’s rights. However, numerous statistical and assessment models tremendously revealed that climate change affects food security (e.g., productivity, yield, quality, and prices) [4]. In particular, the food * Corresponding author. E-mail address: kelwkeel@uj.edu.sa (K.Z. Elwakeel). 1 https://orcid.org/0000–0002-8853–284X 2 https://orcid.org/ 0000–0003-4959–2652 3 Scopus ID: 57211775940 4 https://orcid.org/ 0000–0001-6157–6626 Contents lists available at ScienceDirect Journal of Environmental Chemical Engineering journal homepage: www.elsevier.com/locate/jece https://doi.org/10.1016/j.jece.2023.110955 Received 2 August 2023; Received in revised form 23 August 2023; Accepted 3 September 2023