Nutrient recovery and biomass production by cultivating Chlorella vulgaris 1067 from four types of post-hydrothermal liquefaction wastewater

Cultivating microalgae in post-hydrothermal liquefaction wastewater (PHWW) can realize nutrient recovery, wastewater purification, and biomass production. This study investigated Chlorella vulgaris 1067 growth and nitrogen (N), phosphorous (P), and carbon (C) recovery from PHWW using 2 x 2 factorial experiments: two typical microalgae feedstocks (a low-lipid high-protein microalga, Nannochloropsis sp., and a high-lipid low-protein microalga, Chlorella sp.) for hydrothermal liquefaction (HTL) and two typical biocrude-aqueous separation methods (vacuum filtration and ethyl ether extraction). Results indicated that the feedstock and biocrude-aqueous separation method influence biomass production and nutrient recovery. PHWW from the high-lipid low-protein feedstock was advantageous to biomass production and nutrient recovery. C. vulgaris 1067 showed the best growth in 28.6 % PHWW obtained by vacuum filtration from Chlorella sp. Biomass production reached 1.44 g L-1 and N, P, and C recovery reached 209.25, 17.35, and 2588.00 mg L-1, respectively. For the PHWW obtained from Nannochloropsis sp. and ethyl ether extraction, C. vulgaris 1067 showed better growth in 6.7 % PHWW. The biomass reached 0.67 g L-1 and N, P, and C recovery reached 147.19, 11.60, and 1150.00 mg L-1, respectively. Regulating the pH value daily promoted the tolerance of microalgae to PHWW. Higher total organic carbon concentration, C/N ratio, volatile acid concentration, and lower nitrogen organic compound concentration in PHWW led to higher biomass and nutrient recovery. The ethyl ether extraction method for PHWW from low-lipid high-protein feedstock is one suggestion way to operate an environment-enhancing energy system efficiently.