Bio-oil production from oleaginous microorganisms using hydrothermal liquefaction: A biorefinery approach

The urge for alternative forms of energy to meet the demands of the ever-growing population is a primary concern throughout the world. With the improvement in technologies, biomass seems to be a potential feedstock for conversion to bio-oil by either pyrolysis or hydrothermal liquefaction (HTL). The latter is advantageous as wet biomass can be used directly without any pretreatment, and HTL also produces useful byproducts along with bio-oil. The use of oleaginous microorganisms such as algae, bacteria, and yeasts as biomass feedstocks for the HTL process is more beneficial compared to other conventionally used feedstocks such as lignocellulosic biomass, owing to their high oil content and fast growth rate even on cheaply available substrates. This paper provides an insight into the advantages and detailed information on different oleaginous microorganisms, their composition, and the use of wastewater as their substrate for cultivation. It also emphasizes HTL as an appropriate thermochemical conversion process for biomass processing and production of bio-oil as well as the different process parameters affecting the HTL technology. An integrated HTL based sustainable biorefinery approach for resource recovery in the form of energy is also discussed in detail, along with the future research perspectives in this field.