Pilot-scale development of a semi-continuous system for biohythane production using hydrothermally pretreated mixed Napier grass and microalgae

Abstract

This study demonstrated scaling up of two-stage anaerobic digestion (TSAD) for biohythane production from mixed Napier grass and microalgae hydrothermal hydrolysate in a semi-continuous digester in a lab-scale to pilot-scale system. The lab-scale experiments gave the maximum hydrogen production rate (HPR) (129.1 mL-H2/L·d) and methane production rate (MPR) (340.2 mL-CH4/L·d) at the hydraulic retention time (HRT) of 2.6 and 25 days, respectively. The optimal HRTs were applied to a pilot-scale system and attained a biohythane production rate of 473.5 L-biogas/m3·d, containing 54.2 % CH4, 35.3 % CO2, and 2.9 % H2. Microbial community analysis revealed Methanobrevibacter sp. dominance (9.9 %) in Pilot-D1 (hydrogen-producing digester). This dominance led to undesirable methanogenic activity and reduced hydrogen yields. However, robust methanogenic populations in Pilot-D2 (methane-producing digester) enabled satisfactory methane production. Considering its renewable nature, biohythane production at full scale presents a promising alternative to fossil fuels and contributes to cleaner energy solutions.