Fed-Batch Decolourization of Mixture of Brilliant Green and Evans Blue by Bacteria Species Applied as Pure and Mixed Cultures: Influence of Growth Conditions

Abstract

Synthetic dyes, generally resistant, toxic and carcinogenic presents a substantial risk to the environment and health of human. The present study was aimed to decolourize a dye mixture (Evans blue and brilliant green) by selected bacterial strains cultivated at different growth conditions (e.g. unmodified, correction of pH value and supplementation with nutrients). The bacterial strains used as pure and mixed cultures include facultative anaerobes Aeromonas hydrophila (Abs37), Citrobacter sp. (Cbs50) and obligatory aerobe Pseudomonas putida (Pzr3). The efficiency of removal of all successive doses of dye mixture (4–5 doses, total load 170–200 mg/l) was tested in static conditions in fed-batch bioreactors. The modification of bacteria growth conditions influenced on decolourization efficiency: most advantageous was pH value correction combined with nutrient supplementation then pH correction alone and nutrient supplementation (final removal results 95.6–100%, 92.9–100% and 89.1–97.2%, respectively). The mixed bacterial cultures removed the total load of dyes with higher efficiency than pure strains (final removal 95.2–100% and 84.0–98.2%, respectively). The best results were obtained for the mixture of facultative anaerobe Citrobacter sp. and obligatory aerobe Pseudomonas putida which removed the highest load of dye mixture (200 mg/l introduced at five doses) in the shortest time (288 h), while the others pure and mixed cultures needed 425–529 h for removal four doses of dye mixture (total load 170 mg/l). The zoo- and phytotoxicity decreased after these processes (from V class of toxicity (extremely toxic) even to II class (low toxicity)). The main mechanisms of decolourization was biotransformation/biodegradation, supported by sorption.