Abstract

Methylene blue is widely utilized as biological stains, in printing and as commercial textile dye. The increasing presence of textile dye in wastewater for instance represents environmental hazards. Therefore, there is a significant interest in developing cost effective and environmentally friendly methods for methylene blue removal from industrial wastewater. Taking this into consideration, in the present study, twenty three locally isolated <em>Rhodococcus</em> strains were examined as biological tools for decolourization of methylene blue. Among the tested microorganisms, five locally isolated <em>Rhodococcus</em> strains demonstrated promising ability to decolourize methylene blue as evidenced by the change in the colour of the dye from dark blue to pale blue on nutrient agar plates. One particular strain namely <em>Rhodococcus</em> strain UCC 0003 formed clear zone around the colonies of the bacteria with the biggest diameter of 2.0 ± 0.1 cm after 2 days of cultivation time. This strain demonstrated good growth and completely decolourized 0.1 g/L methylene blue after 5 days of incubation period. Secondary characterization was carried out by comparing the ability of resting cells and immobilized cells of <em>Rhodococcus</em> strain UCC 0003 for efficient methylene blue removal. The results showed that the highest percentage of methylene blue decolourization was achieved by using polyurethane foam cubes as the immobilization matrix resulting in 83^a ± 1 % compared to that of 63^b ± 3 % when resting cells was employed as the biocatalyst. These findings clearly indicated that the immobilized cells of <em>Rhodococcus</em> strain UCC 0003 has a huge potential as biological tool to remediate actual wastewater containing methylene blue.