Hydrothermal liquefaction (HTL) of microalgae for biofuel production is suffering from low bio-oil yield and high heteroatomic compositions owing to their low efficiency and selectivity to hydrolysis of cellular compounds. Hereby we report Keggin-type (MoÀ VÀ P) heteropolyacids (HPAs)-catalyzed HTL of microalgae for efficient low-nitrogen biocrude production. The increases of reaction temperature, reaction time, and vanadium substitution degrees of HPAs are favorable to biocrude yield initially, whereas a significant decrease of biocrude yield is observed owing to the enhanced oxidation of carbohydrates above the optimum reaction conditions. The maximum biocrude yield of HPAs-catalyzed HTL of microalgae is 29.95 % at reaction temperature of 300°C, reaction time of 2 h, and 5 wt% of HPA-4, which is about 19.66 % higher than that of control with 71.17 % less N-containing compounds, including 1,3-propanediamine, 1-pentanamine, and 2, 2'heptamethylene-di-2-imidazoline than that of control. This work reveals that HPAs with Brønsted acidity and reversible redox properties are capable of both enhancing biocrude production via catalyzing the hydrolysis of cellular compounds and reducing their nitrogen content through avoiding the Maillard reactions between the intermediates of hydrolysis of carbohydrates and proteins. HPAs-catalyzed HTL is an efficient strategy to produce low N-containing biofuels, possibly paving the way of their direct use in modern motors.

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A 40‐day feeding trial was conducted to investigate the effect of dietary microalgae Oedocladium sp. or Tribonema ultriculosum supplementation on growth performance, fillet fatty acid composition, skin pigmentation, and immune response of yellow catfish Pelteobagrus fulvidraco. Two hundred and seventy experimental fish (51.19 ± 1.17 g) were distributed among nine net cages (2 × 2 × 2 m3) in a randomized design and were fed diets containing 0% (control), 4% Oedocladium meal (Oedocladium), and 5% T. utriculosum meal (Tribonema) to apparent satiation twice a day. After the feeding trial, a hypoxic stress test was conducted to evaluate the effect of dietary microalgal supplementation on fish immune response. Compared to the control, microalgal supplementation did not affect fish growth performance. Dietary supplementation of T. utriculosum significantly increased fillet contents of palmitoleic acid by 100.44% and eicosapentaenoic acid by 12.51%, while the supplementation of Oedocladium meal in diet significantly increased the fish skin ventral lutein content by 61.6%. In addition, dietary Oedocladium or T. utriculosum supplementation significantly increased the plasma total superoxide dismutase activity (before hypoxic stress) and complement component 3 contents (after hypoxic stress). The addition of T. utriculosum meal also significantly increased the plasma immunoglobulin M content regardless of hypoxic stress. These results demonstrated Oedocladium sp. and T. utriculosum can be used to enhance fillet nutritional quality, skin pigmentation, and fish immune response.

The present study was to investigate the effect of dietary Tribonema ultriculosum supplementation on growth performance, fillet nutritional quality and immunity of rainbow trout Oncorhynchus mykiss (165.26 ± 0.57 g, mean ± SD). Three diets containing 0 (control), 50 g/kg and 100 g/kg T. ultriculosum (TU) were introduced to triplicate groups of the experimental fish for 90 days. Then, a lipopolysaccharide (LPS) stress experiment was conducted to evaluate the effect of microalgal addition on fish immune response. Compared to the control, microalgal addition significantly increased fish feed intake and growth. Dietary T. ultriculosum supplementation significantly increased the contents of palmitoleic acid, eicosapentaenoic acid (EPA) and docosahexaenoic acid in fillet. The addition of T. ultriculosum significantly increased the activity levels of spleen glutathione peroxidase (before LPS stress) and superoxide dismutase (after LPS stress), and simultaneously decreased the spleen malondialdehyde content compared to the control. In terms of the immune response, fish fed diets containing T. ultriculosum had a higher level of lysozyme activity (before LPS stress), immunoglobulin M content (before and after LPS stress) and hepcidin expression (after LPS stress) compared to the control. These results suggest that T. ultriculosum can be used to increase fish growth, fillet nutritional quality and immunity.