A pilot scale hydrothermal liquefaction of sewage water grown Chlorella sorokiniana for bio-oil production—a sustainable integrated approach

The study provides an innovative sustainable integrated route for efficient production of bio-oil through hydrothermal liquefaction of Chlorella sorokiniana grown in sewage water in an open race pond of 20,000-L capacity. The average specific growth rate and doubling time for C. sorokiniana was 0.1 h -1 6.9 h with reduction of 66.66%, ammonia 33.3% nitrate, 50% sulfate, 61.1% COD, and 58.8% of BOD respectively. The C. sorokiniana was harvested using auto flocculation cum decantation method and found to have 64.24% carbon and 12.08% hydrogen. The microalgae subjected to hydrothermal liquefaction in pilot scale 50 L HTL reactor for bio-oil production. 60.43 % of bio crude oil was obtained under optimized conditions. GCMS study reveals that bio-crude oil mostly contains hydrocarbons like amides, ketones, alcohols, amines, aldehydes, oxygenated compounds, fatty acids, and fatty acid methyl esters. The presence of alkanes, alkenes, aldehyde, amines, amides, esters, carboxylic acid, alcohols, and halo-compounds was also confirmed by FTIR. The presence of high concentration of hydrocarbons in the obtained bio-oil is an indicative of a high-quality oil that can be used in neat and blended form with conventional diesel fuel after some modification. Graphical abstract