Abstract
Biosorption has emerged as a cost-effective and efficient alternative technology for removal of heavy metals which produce adverse health effects on humans and living organisms. In the present study the biosorption and desorption of cadmium, lead and zinc by Chlamydomonas variabilis, Anabaena constricta and Nitzschia linearis were evaluated. Algal species were isolated and cultivated on a large scale to get an intensive biomass sufficient for metal binding experiments. The experimental adsorption data were fitted to the Langmuir and Freundlich adsorption model. Characterization of the metal-loaded biosorbent by FTIR spectrum, TEM and EDX analysis confirmed that the metal ions can bind to anionic groups due to electrostatic attraction and sorption capacity is strongly influenced from the type and number of functional groups of the biosorbent. The maximum efficiencies of Cd, Pb and Zn removal using C. variabilis were 97.9%, 96.1% and 96.1% for oven dried biomass and 96.3%, 94.2% and 94.1% for activated biomass. For dried and activated biomass prepared of A. constricta the maximum percentage of removal of heavy metals were 95.1%, 93.7%, and 93.1% and 94.3%, 96.1% and 94.1%. The maximum removals by N. linearis were 95.5%, 96.6%, 94.8% for oven dried biomass and 93%, 94.5% and 93.8% for activated one respectively. There are no clear variations in biosorption of cadmium, lead and zinc by sun dried, oven dried and activated biomass of C. variabilis, A. constricta and N. linearis. It is better to use sun dried algae as low cost biosorbent for metals removal.

Key words: Biosorption, Cadmium, Lead, Zinc, Chlamydomonas variabilis, Anabaena constricta and Nitzschia linearis