Micro algal systems for biosequestration of heavy metals in aqueous solution

Ubiquity of heavy metals in the biosphere results in the introduction of huge amounts of toxic metals into the food chain and removal of these toxic and persistent contaminants is highly imperative. Chromium is an important environmental hazard and even the presence of relatively low concentration of chromium in effluent can significantly reduce the efficacy of biological sewage treatment. Microalgal biomass has been successfully used as biosorbing agent for heavy metals because microalgae use light as an energy source, facilitating the maintenance of metabolism in the absence of organic carbon sources and electron acceptor required by bacteria or fungi (Elizaberth and Priyadarshini, 2004). Blue green algae (BGA) are gaining increasing attention due to it being a rich source of vitamins and proteins. The biomass is capable of absorbing and adsorbing metal ions from aqueous solution even when the cells have been killed. This study deals with the accumulation of heavy metals Cr (VI) from the environment by the blue green algal systems such as Anabaena variabilis, Aulosira sp., Nostoc muscorum, Oscillatoria sp. and Westiellopsis sp. All the cultures exhibited growth even at higher levels of chromium and the biomass production decreased with the increase in the metal concentration. Metal binding by BGA has been profoundly influenced by the concentration of the metal. The removal of chromium varied with time and metal concentrations and the optimum time for maximum metal removal (75-80%) was found to be 14 days at an initial metal concentration of 10 mg L^-1. The maximum metal removal of Cr was noticed at 5 ppm with Anabaena variabilis followed by Oscillatoria sp. The results of the present study provided convincing evidence that metal sorption in effluents using BGA is a superior technology compared to conventional methods like precipitation, evaporation and ion exchange in terms of time and expense.