Protein potential of Desmodesmus asymmetricus grown in greenhouse as an alternative food source for aquaculture.

During ten months, batch culture of Desmodesmus asymmetricus microalgae was carried out under greenhouse conditions. The inoculation ratio was 1:1 (inoculum:treated water). The cultures were maintained for 5 days with natural light and constant aeration mixed with carbon dioxide. The biomass was concentrated by centrifugation and dried by lyophilization; subsequently, total proteins and amino acid concentration were quantified. A relationship between biomass production and seasonal variation was observed, the lowest dry biomass production was recorded in June (38.8 ± 1.0 mg L-1 day-1) and July (43.3 ± 0.1 mg L-1 day-1); while the highest values ​​were greater than 70 mg L-1 day-1 in March. There was a high positive correlation between wet and dry biomass (r = 0.97, p < 0.001) with a mean conversion of 26%. The mean percentage of protein was 26.1 ± 2.6%, the highest percentage was registered in March (31.03 ± 1.48%) as well as the concentration of amino acids. Regarding amino acids, arginine obtained the highest concentration (4.08 ± 0.43 g 100 g-1), followed by aspartic acid (3.36 ± 0.23 g 100 g-1), while the lowest values were for methionine (0.55 ± 0.21 g 100 g-1), histidine (0.77 ± 0.07 g 100 g-1) and tyrosine (1.01 ± 0.17 g 100 g-1). Finally, according to the essential amino acid index (in fish ≥ 0.90, in crustaceans > 0.80), the biomass of D. asymmetricus has potential as a food supplement for the production of feed in aquaculture.

Evaluación del potencial de Desmodesmus asymmetricus y Chlorella vulgaris para la remoción de nitratos y fosfatos de aguas residuales / Potential assessment of Desmodesmus asymmetricus and Chlorella vulgaris for removal of nitrates and phosphates in wastewater

Resumen En este estudio evaluamos las microalgas Chlorella vulgaris y Demodesmus asymmetricus, con el fin de determinar la proporción de microalgas que remueven la mayor concentración de nitrógeno y fósforo en aguas residuales de una planta de tratamiento. Se realizó un diseño de mezclas de las microalgas con el agua residual durante 9 días, con fotoperiodo 12:12 h, en un invernadero. Las mayores eficiencias de remoción de nitrógeno (principalmente NO3 -N y NO2 -N) y fósforo (PO4 ) se observaron en los tratamientos con mayor proporción de D. asymmetricus, entre ellos sobresalió el tratamiento T3 (25% C. vulgaris / 75% D. asymmetricus) donde se removió el 100% de nitrógeno y 77.1% de fósforo. De igual manera con el oxígeno disuelto (OD), el T3 obtuvo el mejor resultado alcanzando una media de 25.50 ± 0.28 mg/L. Finalmente, de acuerdo con el análisis del diseño de mezclas, se determinó que la mezcla óptima de microalgas que logra la mayor producción de OD y la mayor remoción, fue la proporción de 6% de C. vulgaris y 94% de D. asymmetricus en un tiempo de cultivo de 9 días. En conclusión, las microalgas demuestran su capacidad de biorremediación de aguas residuales domésticas.

Abstract In this work, we evaluated the proportion Chlorella vulgaris and Demodesmus asymmetricus microalgae, that removes the highest concentration of nitrogen and phosphorus in wastewater from a treatment plant. A mixture design was employed in this study, for 9 days, with 12:12 h photoperiod, in a greenhouse. The highest nitrogen removal efficiencies (mainly NO3 -N and NO2 -N) and phosphorus (PO4 ) were observed in treatments with the highest proportion of D. asymmetricus, including T3 (25% C. vulgaris / 75 % D. asymmetricus), where 100.0% nitrogen and 77.1% phosphorus were removed. Likewise, T3 obtained the best result of dissolved oxygen (DO), achieving average of 25.50 ± 0.28 mg/L. Finally, according to the analysis of the mixture design, the optimal microalgae mixture was determinated that achieves the highest DO production, and the highest removal was the proportion of 6% of C. vulgaris and 94% of D. asymmetricus in 9 days cultivation time. In conclusion, microalgae have shown their capacity for bioremediation of domestic wastewater, which is an alternative to consider.