Efficient removal of dyes from seawater using as biosorbent the dead and living biomass of the microalga Phaeodactylum tricornutum: equilibrium and kinetics studies

Dyes are used in many applications with their consequent discharge into aquatic environments. Alternative methods of pollutant removal, such as biosorption, are currently necessary to achieve an efficient, low-cost, and environmentally friendly process. The biomasses, living and dead, from the microalga Phaeodactylum tricornutum were studied to determine their ability to remove three dyes, Methylene Blue, Crystal Violet and Safranin from seawater. The removal properties were determined as a function of contact time, initial dye concentrations, and pH, and characterized with the determination of the point of zero charge (pHPZC) and FTIR. The highest removal capacity was obtained with crystal violet (66.4 mg g−1), without significant differences between both biomasses and following a pseudo-fourth order kinetics, indicating a high affinity for said dye. Maximum removal capacity for methylene blue was 18.9 mg g−1 with significant differences between both biomasses until the concentration of 10 mg L−1, the dead biomass being more effective since this dye would present difficulties to enter the living cells. The kinetics was of pseudo-third order. Safranin obtained a removal capacity of 19.6 mg g−1 with also significant differences between both biomasses up to a concentration < 10 mg L−1, but with living biomass being more effective and a sigmoidal kinetics, indicating that this dye would more easily enter living cells. Photodegradation of these dyes and isotherms were also analyzed to properly characterize the process. The results demonstrated that the biomass of P. tricornutum eliminated efficiently these dyes from a solution with high ionic load (seawater).