COMPARATIVE STUDY OF CHROMIUM BIOSORPTION USING BROWN, RED AND GREEN MACRO ALGAE
Release of chromium by tannery industry is one of the major environmental problems and its removal is getting considerable attention. Chromium removal efficiency of Padina tetrastromatica Hauck (Brown algae), Gracilaria edulis S.G Gmelin (Red algae) and Ulva reticulata Forsskal (Green algae) were compared. The best biosorbent was screened based on the percentage of uptake of chromium in three different forms such as powdered biomass, pretreated biomass (0.4N H2SO4) and carrier based seaweed biosorbents. Maximum of 50.85% of chromium removal was exhibited by Padina tetrastromatica, which is higher than the powdered biomass of other two seaweeds. Optimum process parameters were found as 8g/L of biomass concentration, pH-4 and 6 hours of exposure time for all the seaweeds under study. Protonation of powdered biomass of seaweeds enhanced the biosorption rates from 18 to 30%. Among the carrier based seaweed biosorbents, maximum of 89% of chromium removal was obtained in Padina tetrastromatica with rice bran as a carrier system. It was found as the best biosorbent for chromium removal from commercial tannery effluent. Desorption experiment was demonstrated for the reuse of biosorbents. Qmax was 50 mg/g for Padina tetrastromatica and Gracilaria edulis. Ulva reticulata showed 20 mg/g of Qmax in Langmuir isotherm. Freundlich constant 1/n (m) of Padina tetrastromatica and Gracilaria edulis was 0.731, 0.760 respctively and for Ulva reticulata, it was 0.996. Significant R2 values obtained denotes that biosorption of chromium by seaweeds can be best described by Langmuir and Freundlich isotherms. FTIR and SEM-EDAX analysis of seaweeds revealed the possibility of interaction between the chromium and polysaccharide functional groups on the seaweed surface