Continuous anaerobic digestion of zucchini stem after pretreatment

Abstract

Anaerobic digestion (AD) is a widely used technology for converting organic wastes into biomethane with the advantages of clean energy production and few environmental impacts. Zucchini stem (ZS), the main waste produced from zucchini cultivation, is a potential feedstock for AD due to its high moisture and organic contents. This study investigated the methane production performance and system stability of ZS in continuous AD mode with the increase of organic loading rate (OLR). Moreover, to improve the methane production efficiency, KOH, NaOH, and alkaline hydrogen peroxide (AHP) pretreatments were also performed. The results showed that raw ZS gave a daily methane yield (DMY) of 182.1 mL g VS − 1 d −1 and volumetric methane yield (VMY) of 0.546 L L −1 d −1 at an OLR of 3.0 g VS L −1 d −1 . At the same OLR, 2% KOH-pretreated ZS significantly enhanced the DMY to 236.0 mL g VS − 1 d −1 and the VMY to 0.708 L L −1 d −1 , with a biodegradability (B d ) of 56.3%, which was 29.7% higher than that of raw ZS. However, NaOH- and AHP-pretreated ZS could not achieve stable methane generation at an OLR of 2.0 g VS L −1 d −1 . This study forms a foundation for future industrial applications of ZS; the investigated approach not only utilizes this waste efficiently and reduces its environmental pollution but also produces renewable biomethane energy and may improve the energy structure in rural areas. • Continuous anaerobic digestion (AD) of pretreated zucchini stem (ZS) was explored. • 2% KOH pretreated ZS performed stably and efficiently continuous AD system. • The highest volumetric methane yield was 0.708 L L -1 d -1 after 2% KOH pretreatment.