Removal of Azo dyes from aqueous solutions by biomass of brown algae Cystoseira indica

The effluent of textile industries is high dyefully and this is one of most problems for environmental health engineers. Two Azo dyes biosorption، direct black 19 and direct red 23، on Cystoseira indica، an invasive macroalga in Iran، has been investigated using visible absorption spectroscopy. Pre-treatment and chemical cross-linking with CaCl2، have been conducted in order to improve the stability as well as the biosorption capacity of the algal biomass. All measurements were conducted by UV-Visible Spectrophotometer. The effects of operating parameters such as contact time، pH، initial dye concentration and amount of biosorbent on the dye removal efficiency were investigated. The biosorption has been described in terms of isotherm and kinetic models; from the maximum adsorption capacity values، an estimation of the algal specific surface area was made. It has been found that biosorption kinetics can be described according to the pseudo second order model and biosorption equilibrated for 120 min (89. 3% of direct red 23 and 69. 02% of direct black 19 removed). Maximum biosorption found at pH 5 (2. 4mg/g). It also observed increasing initial dye concentration and decreasing biomass dosage would reduce dye removal. Isotherm studies also revealed the dye biosorption on algal biomass followed from Freundlich model. Biosorption of selected Azo dyes onto algal biomass، Cystoseira indica was fast and more dye is eliminated in the first hour. So، by determining the optimum conditions of contact time، pH، initial dye concentration and biosorbent dosage، Cystoseira indica can be used as an inexpensive sorbent for removal of Azo dyes from aqueous solutions.