Comparison of four fermentation systems for conversion of pretreated lignocellulose to microbial biomass and subsequent production of biocrude

Biocrude, derived from biomass, is a promising alternative to fossil fuels. Pyrolysis and hydrothermal liquefaction methods are commonly employed to produce biocrude; however, a convenient approach involves microbial conversion and alkali pretreatment. In this study, the performances of various fermentation systems for the direct conversion of pretreated lignocellulose into microbial biomass were evaluated. The energy consumption, time for fermentation, microbial biomass production, and the remaining lignocellulosic conversion residue at the end of cultivation were determined for each system. The solid-state fermentation (SSF) system was carried out in a channeled bioreactor using the fungus Phanerochaete chrysosporium, which consumed the least amount of energy (0.02 kW), however, required 28 days of fermentation, whereas the continuous stirred-tank reactor (CSTR) system used 4.44 kW, however, required only 6 days. The rotary disc reactor system was the least efficient because it consumed 4.8 kW and required 32 days, the highest energy and time demands, respectively, and produced 7.1, 3.8, and 2.5 g/L less biomass than those of the SSF, CSTR, and airlift reactor, respectively. Conversely, energy consumed for hydrothermal liquefaction was 0.74 kW to reach 300 °C and 25 MPa, whereas wet pyrolysis required 1.26 kW to reach 500 °C. During fermentation, the solid fraction of lignocellulose was converted into microbial biomass, which was then mixed with black liquor via chemical pretreatment. This mixture was evaporated, ultimately completely converting the lignocellulose into biocrude.