The Langmuir and Freundlich isotherms at 25 C for raw, DAB and sulfuric acid pre-treated DAB are shown in Fig. 2. Both models provided good fit to data (Table 3). The adsorption isotherms revealed that the Langmuir adsorption capacity of raw algal biomass and DAB was 6.0 mg g1 and 7.73 mg g1 , respectively, for the basic dye in an aqueous medium. Tsai et al. (2011) reported the adsorption capacity of methylene blue to be around 5.0 mg g1 for dead biomass of Chlorella sp. The sulfuric acid pretreated DAB showed enhanced adsorption capacity with Langmuir monolayer adsorption capacity of 7.80 mg g1 for the basic dye from an aqueous medium. This marginal enhancement in dye uptake may be
due to the marginal enhancement in surface corrugation and porosity as exhibited by SEM imaging. Also, the 1/n values of
RAB, DAB and sulfuric acid pre-treated DAB in the present study were less than 1, clearly indicating the algal biomass as a favorable adsorbent. These results clearly indicate that DAB could be used as an adsorbent for removal of basic dyes like methylene blue from aqueous solutions. The adsorption capacity of DAB is therefore comparable to or superior to various agricultural waste, microalgal waste and aquaculture waste based potential adsorbents (Table 2).