Removal of chromium(VI) from saline wastewaters by Dunaliella species

Abstract

Some industrial wastewaters contain higher quantities of salts besides chromium(VI) ions so the effect of these salts on the biosorption of chromium(VI) should be investigated. The biosorption of chromium (VI) from saline solutions on two strains of living Dunaliella algae were tested under laboratory conditions as a function of pH, initial metal ion and salt (NaCl) concentrations in a batch system. The biosorption capacity of both Dunaliella strains strongly depends on solution pH and maximum. Chromium(VI) sorption capacities of both sorbents were obtained at pH 2.0 in the absence and in the presence of increasing concentrations of salt. Chromium(VI)-salt biosorption studies were also performed at this pH value. Equilibrium uptakes of chromium(VI) increased with increasing chromium(VI) concentration up to 250–300 mg l −1 and decreased sharply by the presence of increasing concentrations of salt for both the sorbents. Dunaliella 1 and Dunaliella 2 biosorbed 58.3 and 45.5 mg g −1 of chromium(VI), respectively, in 72 h at 100 mg l −1 initial chromium(VI) concentration without salt medium. When salt concentration arised to 20% (w/v), these values dropped to 20.7 and 12.2 mg g −1 of chromium(VI) at the same conditions. Both the Freundlich and Langmuir adsorption models were suitable for describing the biosorption of chromium(VI) individually and in salt containing medium by both algal species. The pseudo second-order kinetic model was successfully applied to single chromium(VI) and chromium(VI)-salt mixtures biosorption data.