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Abstract

The present study involves usage of more efficient and eco-friendly zirconium-doped, fluoride-resistant fungal biosorbents for removal of excess fluoride from groundwater. It was observed that >94% fluoride removal was possible at optimal conditions for the four fungal species studied. The adsorption isotherm studies indicated that zirconium-doped Aspergillus ficuum SIT-CH-2, Aspergillus terreus SIT-CH-3, and Aspergillus flavipes SIT-CH-4 were best described by Freundlich isotherm and zirconium-doped Penicillium camemberti SIT-CH-1 fitted well with Langmuir adsorption isotherm equation. The pseudo-second-order kinetics model showed the best fit for all of the four zirconium-doped fungal species for the fluoride biosorption.

In the present work, an economical, more selective and a bio-compatible fluoride removal technique has been developed by using zirconium impregnated Chlorella protothecoides and Nannochloropsis oculata, which represents a combination of biological and physiochemical methods. The optimization of the effect of various factors such as pH, initial fluoride concentration, biosorbent dose and contact time was carried using a central composite design of response surface methodology. A maximum removal of fluoride ions of 92.2% was observed using zirconium-doped C. protothecoides. The adsorption isotherms and kinetics of the adsorption process were studied. The Langmuir isotherm model well expressed fluoride biosorption onto zirconiumdoped N. oculata and the Freundlich isotherm model fitted well the data of zirconium-doped C. protothecoides. The correlation coefficients indicate that the fluoride biosorption onto zirconiumdoped N. oculata, and C. protothecoides biosorbents correlated well with the pseudo-second-order kinetic model. The existence of co-anions decreased fluoride removal from aqueous solution. The biosorbent was regenerated using NaOH, distilled water and HCl and used for four cycles.

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