Three Microalgae Strains Growth and Lipids Production Based on Human Urine Solutions Supplemented with Four Metals

The recent use of dry baths allows the separation of urine from wastewaters with no dilution and without mixing with human faecal material nor detergents, etc. Human urine can be used as culture medium for microalgae because of its high nitrogen and phosphorus concentrations. Nevertheless, a culture medium to grow microalgae requires some other compounds with less concentration including some metals. We assessed the effect of adding Fe, Co, Mo and Zn at specific concentrations, defined by a Box–Behnken experiment design, as well as the effect of metal concentrations on biomass growth and lipid accumulation. The levels of each variable were selected considering the concentration of metals in the Bold Basal Medium (BBM), twice this value and half of that concentration. Human urine supplemented with two metals (Fe and Zn or Fe and Co) was a feasible alternative to the BBM medium. Higher biomass concentrations, lipid production and, hence, lipid quota were obtained with the selected alternative medium. Similar conditions were obtained for the three strains evaluated in this study. In Chlorella vulgaris, an increase of biomass yield (23%) was obtained with the medium designed in this study but lipid production never exceeded the one obtained with the reference medium. Biomass yields (66 and 59%) and lipids production (97 and 23%) were simultaneously increased in Scenedesmus sp. and Chlorococcum humicola. In C. vulgaris, Fe and Co positively affected growth. Scenedesmus, was affected negatively by Co, Mo, and Zn. C. humicola was affected positively by Zn and negatively by Fe. It was demonstrated that it is feasible to replace complex media like BBM by a formulation consisting of a urine dilution supplemented with only two metals.