| Summary: | There is a current need to develop low-cost strategies to degrade and eliminate industrially
used colorants discharged into the environment. Colorants discharged into natural water
streams pose various threats, including: toxicity, degradation of aesthetics and inhibiting
sunlight penetration into aquatic ecosystems. Dyes and colorants usually have complex aromatic
molecular structures, which make them very stable and difficult to degrade and eliminate
by conventional water treatment systems. The results in this work demonstrated that
heavy metal-resistant Rhodotorula mucilaginosa strain UANL-001L isolated from the northeast
region of Mexico produce an exopolysaccharide (EPS), during growth, which has colorant
adsorption potential. The EPS produced was purified by precipitation and dialysis and
was then physically and chemically characterized by Scanning Electron Microscopy, Fourier
Transform Infrared Spectroscopy, and chemical elemental analysis. Here, the ability of the
purified EPS produced to adsorb methylene blue (MB), which served as a model colorant, is
studied. MB adsorption by the EPS is found to follow Langmuir Adsorption Isotherm kinetics
at 25°C. Further, by calculating the Langmuir constant the adsorption capabilities of the EPS
produced by the Rhodotorula mucilaginosa strain UANL-001L is compared to that of other
adsorbents, both, microbially produced and from agroindustrial waste. The total adsorption
capacity of the EPS, from the Rhodotorula mucilaginosa strain UANL-001L, was found to be
two-fold greater than the best bioadsorbents reported in the literature. Finally, apart from
determining which heavy metals stimulated EPS production in the strain, the optimal conditions
of pH, heavy metal concentration, and rate of agitation of the growing culture for EPS production, was determined. The EPS reported here has the potential of aiding in the efficient
removal of colorants both in water treatment plants and in situ in natural water streams.
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