Nutrient recycle from defatted microalgae (Aurantiochytrium) with hydrothermal treatment for microalgae cultivation

[Display omitted] •Nutrient recycle from defatted microalgae for microalgae cultivation is evaluated.•N and P can be recovered from defatted microalgae by hydrothermal treatment.•Nutrient efficiency depends on reaction conditions of the hydrothermal treatment.•Hydrothermal treatment at high temperature conditions produce anti-growth agents. Defatted heterotrophic microalgae (Aurantiochytrium limacinum SR21) was treated with high temperature water (175–350°C, 10–90min) to obtain nitrogen and phosphorous nutrients as a water soluble fraction (WS). Yields of nitrogen and phosphorous recovered in WS varied from 38 to 100% and from 57 to 99%, respectively. Maximum yields of nitrogen containing compounds in WS were proteins (43%), amino acids (12%) and ammonia (60%) at treatment temperatures of 175, 250 and 350°C, respectively. Maximum yield of phosphorous in WS was 99% at a treatment temperature of 250°C. Cultivation experiments of microalgae (A. limacinum SR21) using WS obtained at 200 and 250°C showed positive growth. Water soluble fractions from hydrothermal treatment of defatted microalgae are effective nitrogen and phosphorous nutrient sources for microalgae cultivation.