Comprehensive potential evaluation of the bio-oil production and nutrient recycling from seven algae through hydrothermal liquefaction

Hydrothermal liquefaction (HTL) of seven algae was conducted at both 280 and 350 degrees C with a reaction time of 30 min and a mass ratio of 1/4 of algae to water to evaluate the utilization potential of bio-oil production and nutrient recycling in the aqueous by-product and solid residue particles. Chlorella and Nannochloropsis sp. exhibited the highest bio-oil yields at 280 degrees C (36.5% from Nannochloropsis sp.) and 350 degrees C (38.1% from Chlorella). Additionally, temperature had little effect on the energy recovery from Chlorella, Nannochloropsis sp., Spirulina, Cyanophyta and Euglena. The carbohydrates and lipids in the algae were primarily related to monoaromatic and single-ring heterocyclic compound generation in bio-oil. In addition, carbohydrates and proteins significantly affected oxygenated compound production. The sizable total carbon, ammonia nitrogen, total nitrogen and phosphate contents in the aqueous byproducts showed great potential as nutrient sources for algal cultivation and the production of value-added chemicals through recycling. Higher temperatures increased the percentage of ammonia nitrogen in the total nitrogen and reduced the phosphate concentration in the aqueous by-product. According to potential evaluation factors, Chlorella, Nannochloropsis sp., Spirulina, Cyanophyta and Euglena totally showed higher potential in terms of bio-oil production and aqueous nutrient recycling than Dunaliella salina and Enteromorpha prolifera, in which Nannochloropsis sp. exhibited the greatest utilization potential at investigated conditions.