Studies on bioremediation of Zn and acid waters using Botryococcus braunii
The effects of Zn(II) on Botryococcus braunii in terms of growth and the photosynthesis-respiration metabolism as well as the ability of this microalgae to remove zinc present in wastewaters is described. The photosynthetic and respiration rates (CO2 and O2) are affected by increasing metal concentration in solution, and therefore B. braunii growth rate decreases to a half, nevertheless the maximum value of biomass reached (770 ± 40 ppm) is the same and the biomass remains viable throughout the range of concentrations studied (0-80 ppm). B. braunii exposed the ability to reverse the acidic conditions of the medium, showing a pH increase from 5.2 ± 0.2 till values above 8.0 ± 0.4, favoring the precipitation of different zinc (hydr)oxide and other slightly soluble salts. Zn(II) specific removal increases along with initial metal concentration and with pH. The net adsorption capacity was determined, and the Freundlich, Langmuir and Hill models were applied, results demonstrate that the experimental data obtained for zinc is best described by the Hill model. The stoichiometric relationship between H+ release and zinc uptake in slightly acidic conditions is 1:1, and the adsorption kinetics follows a pseudo-second order model. The amount of metal removed from solution increase significantly when metabolic processes are involved, with respect to adsorption (non-metabolic process). The continuous removal of the metal was achieved along 200 days, reaching a maximum value of zinc removal of 3.4 gr/ gr. The remediation of heavy metals such as zinc, nickel and copper, as well as nitrates present in a leachate obtained from bioleaching of sediments of a contaminated stream (Reconquista River) was successfully performed. B. braunii surface was characterized using scanning electron microscopy (SEM) and energy disperse X-ray spectroscopy (EDS). All the data that support the above findings are presented in the "dataset" file attached, where in each sheet the corresponding crude data is presented and the figures embebed in the corresponding paper are attached for a better interpretation of the data presented.