BIOSORPTION BY CYANOBACTERIA - A SUSTAINABLE ALTERNATIVE FOR BIO-REMEDIATION
The world today heavily depends on Rare Earth Elements, also known as REE. They can be found in everything from LEDs and magnets to wind turbines and energy-efficient bulbs. However the REEs, true to their name are sparse in the earth’s crust. The urgent need and the unavailability of REEs further solidified the need to recycle them.
Certain biomass can passively concentrate and attach contaminants onto its cellular structure through the physiochemical process known as biosorption. In the recently conducted study, 12 species of cyanobacteria were analyzed for their ability to absorb 4 REEs - lanthanum, cerium, neodymium and terbium. Most of the species used were never fully examined for biotechnological potential. The study showed that a new uncharted species of Nostoc has the highest capacity for biosorption of ions of these four REEs from aqueous solutions, with efficiencies between 84.2 and 91.5 mg per g biomass. Using FT-IR spectroscopy the functional groups present in the biomass were identified. The biomass from cyanobacteria had a high concentration of negatively charged sugar molecules like hydroxyl (-OH) and carbonyl (-COOH)groups which act as chelating agents.
FT-IR spectrum of biomass samples :
Black- before incubation with cerium nitrate.
Blue- after incubation with cerium nitrate.
The study also found that increasing the pH steadily decreased the biosorption process and the process was comparatively more effective in the absence of other positive ions like Zn+2, Pb+2 etc. The cyanobacteria can absorb REEs up to 10% of its dry weight. The process is fast and can even be possible at lower concentrations of REEs (The cerium present in the solution was absorbed in the first five minutes). Thus biosorption offers an environmentally friendly and economical method for recovering and recycling REEs from diluted industrial wastewater.
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