The chemist from RUDN University together with colleagues discovered that the green algae C. Sorokiniana can purify wastewater from toxic lead. At the same time, the algae change their metabolism and accumulate more lipids — this improves their properties as raw materials for biofuels. The results are published in Environmental Technology & Innovation.
Lead is one of the most common heavy metals that pollute the environment. The level of lead pollution is constantly growing because of its use in the production of batteries, paints, and fuel. Basically, lead enters the environment through the wastewater of production facilities. From there, it affects the entire ecosystem. One of the ways to purify water from lead is bioremediation. Toxic metal is absorbed by microorganisms that become resistant to it, for example, through increased accumulation of lipids. RUDN University chemist together with colleagues investigated the possibility of using microalgae Chlorella Sorokiniana for bioremediation. Chemists have also shown that the protective mechanisms of algae not only reduce the level of pollution, but also increase the potential of using microorganisms as biofuels.
“To manage and survive under metal-induced stress, many microalgae have evolved different mechanisms that include lipid accumulation as a defense mechanism against toxic heavy metals. Chlorella sp. to be more tolerant of lead compared to other species of microalgae. This may be due to their smaller size and larger cell wall surface area. We studied the short and long-term effects of Pb on microalgae and the optimization of the Pb concentration that promotes maximum lipid accumulation and lead tolerance in Chlorella sorokiniana”, said Vinod Kumar, RUDN University professor.
Chemists put C. Sorokiniana in fresh water with different concentrations of lead chloride and lead oxide (50 to 600 mg per liter). C. Sorokiniana was also cultivated in fresh water containing algae growth media used as a control sample. To evaluate the short-term effect of lead contamination, chemists tested the samples after 96 hours. The long-term effect was evaluated 14 days after the start of the experiment. Scientists harvested microalgae using a centrifuge and then dried biomass was treated with chloroform/methanol to extract lipids. Lipids were converted into biodiesel with methanolic H2SO4 and analyzed by gaschromatography-mass spectroscopy.
After 96 hours, 50% of the algae did not survive in a solution with 565 mg/l of lead chloride and 191 mg/l of lead oxide. Chemists called these values the maximum level of lead contamination that C. Sorokiniana can withstand. At the same time, in a lead-contaminated environment, algae accumulate almost twice as many lipids — 97 mg per liter per day compared to 58 mg in a clean environment. Lead also changes the composition of lipids — in a polluted environment, microalgae accumulate more saturated fatty acids (SAFA) and monounsaturated fatty acids (MUFA). This improves the properties of C. Sorokiniana as a raw material for biofuels.
“The results of this study conclude that C. sorokiniana has a strong tolerance to Pb and therefore may serve as a potential candidate for the bioremediation of wastewater. This finding also revealed elevated lipid levels in microalgae cells, indicating their role as a biofuel feedstock for biodiesel development. The lipid profile indicated altered lipid profiles under Pb stress and elevated levels of SAFA and MUFA. Thus, it can serve the dual purpose of bioremediation and bioenergy”, said Vinod Kumar, RUDN University professor.