Recycling of catering waste for sequential production of biohydrogen and biomethane; pre-treatments, batch, and continuous mode studies

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 findings 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 (R2 = 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 configured 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.