Removal of chromium ions by agar immobilized cells of the cyanobacterium Anacystis nidulans in a continuous flow bioreactor

Abstract

Anacystis nidulans, an isolate from the polluted waters, was able to grow in Chu-10 medium with Cr up to 100 μM concentration. Free and agar immobilized cells of the organism having 1 mg of protein removed 35 and 43 nmol of Cr, respectively, from the medium in 6 h. At pH 7.0, the rate of Cr removal by free and immobilized cells increased by 54% and 56%, respectively, over uptake by cells in medium. At a fixed concentration of 30 μM Cr, in terms of unit biomass, a cell density equal to 200 μg of protein/ml was found to be optimum for maximum Cr removal. The efficiency of the continuous flow bioreactor (12.5 × 2 cm) loaded with agar immobilized cells at a fixed concentration of Cr (30 μM) and fixed biomass load (10 mg protein) was compared at different flow rates. The metal removal efficiency of the bioreactor depended on the flow rate. The reactor functioned with 86% efficiency of Cr removal for 6 h at a flow rate of 0.05 ml/min. With increased flow rate, the efficiency of the reactor decreased. The operative time of the reactor at a flow rate of 0.05 ml per min was 48 h, and it decreased to 5 h at a flow rate of 0.5 ml/min. The significance of these results in Cr removal from the industrial effluents is discussed.