Endogenous bioethanol production by solid-state prefermentation for enhanced crude bio-oil recovery through integrated hydrothermal liquefaction of seaweeds

The present study evaluated the action of endogenous bioethanol produced during solid-state fermentation of Ulva spp. on subsequent hydrothermal liquefaction (HTL). HTL of raw biomass (RB) was compared with HTL of the fermented biomass after bioethanol separation (F-Aqua) and HTL of the whole fermentation broth containing the bioethanol (F-Eth). Optimization of fermentation conditions increased the ethanol yield efficiency (Yeff) and specific ethanol yield (SEY) from 23.55% and 0.120 g g-1 sugar consumed to 43.97% and 0.224 g g-1 sugar consumed, respectively. TGA and FTIR analysis confirmed noticeable changes in the thermal profile and func-tional groups of the fermented residue with increased volatiles and lower ash content. Among different HTL treatments, F-Eth showed the highest bio-oil yield of 24.96% at 250 C, which was 37.7% and 39.0% higher than that of RB and F-Aqua, respectively. In addition, hydrocarbons and esters in the bio-oil represented the dominant compounds in F-Aqua and F-Eth, altogether 28.28% and 68.58%, respectively, compared to 17.96% in RB. Economic analysis for a proposed 100 ton year-1 plant confirmed that HTL of the whole fermentation broth containing endogenous bioethanol enhanced the gross energy output to 8.152 GJ ton-1, which represented 4.2 -time, 51.1%, and 23.3% higher than individual bioethanol production, individual bio-oil production, and sequential bioethanol/bio-oil recovery, with the highest net annual profit of 29553 US$ compared to 23391 US$ for the sequential production.

Automated summary

This study evaluated the impact of endogenous bioethanol produced during solid-state fermentation on hydrothermal liquefaction. Optimization of fermentation conditions increased ethanol yield efficiency and specific ethanol yield. Hydrothermal liquefaction of the whole fermentation broth containing endogenous bioethanol enhanced bio-oil yield and economic benefits.