Bioadsorption of Cr (VI) in aqueous solutions by pseudomonas koreensis immobilized in alginate beads

Water pollution by Cr is challenging due to its high toxicity. Most of chromium is released by industrial processes. Different methods have been developed to remove heavy metals from water, but they are expensive and not efficient for low concentrations. Microorganisms have received attention since they are able to grow in stress conditions. Bacteria living in water bodies near to mining are resistant to heavy metals; then, they have potential for bioadsorption applications. The purpose of this work was to isolate a microorganism tolerant to Cr from water bodies near to a mining zone. The isolated, Pseudomonas koreensis, was immobilized in alginate beads and its efficiency to remove Cr from water was evaluated. For isolation, serial dilution of samples was conducted; microorganisms were cultured in EMB, MacConkey and Mannitol salt agar and incubated at 30–35 °C for 24 h. The dominant colonies were replanted in nutrient agar supplemented with chromium and they were incubated at 30–35 °C until growth evidence. Species identification was done according to Bergey’s Manual and by 16 S rDNA sequencing. Alginate beads were prepared by slow continuous deposition method. Isolated bacteria were set in batch reactors together with alginate beads and nutrient medium to promote microorganism immobilization. The biofilm presence was confirmed through SEM. A random experimental design was used to determine the best amount of adsorbent in lab scale batch reactors. The concentration was taken as variable considering 15, 25 and 40 g. Temperature, pH, stirring and concentration of Cr (VI) were fixed at 30°C, 6.6, 150 rpm and 10 ppm, respectively. Samples from 0 to 56 h were taken. A variance analysis was performed. Chromium removal of 97% at 32 h was reached. Significative difference was observed related to adsorbent concentration and time. The best results correspond to 40 g of adsorbent.