Enhancement of azo dye decolarization by Dunaliella tertiolecta with conventional carbon sources

Abstract

In this study, the decolorization of Dye Bath (DB), and the three hydrolyzed dyes, namely Reactive Black 5 (RB-5), Reactive Orange 69 (RO-69) and Reactive Yellow 37 (RY-37) by marine microalgae Dunaliella tertiolecta, in a batch culture was investigated and the ability to utilize the azo dyes in the presence of co-substrates namely glucose and glycerol as an additional carbon and energy sources was discussed. Decolorization of dyes was determined by monitoring the decrease in the intensity of absorption at the maximum wavelength (lmax) of each of the dye solution. The color change and pH values of the culture media were monitored during the growth period of algae exposed to dyes in the presence and absence of glucose and glycerol. The individual and combined effects of DB, RB-5, RO-69 and RY-37 in the presence and absence of glucose and glycerol on the growth of Dunaliella tertiolecta were also examined. Algal growth was followed through optical density (OD750) measurements of the culture medium. Furthermore, algal growth was examined with different concentrations of glucose and glycerol. D. tertiolecta was found to be quite effective in the decolorization of all dyes. At low dilutions (30% and 60% (v/v)) of all DB, RB-5, RO-69 and all dilutions of RY-37 can be removed without co-substrate by the algae. However, addition of both concentrations of glucose and glycerol has some beneficial effects such as increasing the decolorization efficiency or decreasing decolorization period of all dyestuffs except RY-37. At concentrations beyond the IC25 values of dyes, decolorization achievement is decreasing due to the different structure and complexity of dyes. Considering the average 8-d IC25 and SC20 values expressed as % dilution (v/v), the order of toxicity was found as DB>RB- 5>RO-69>RY-37. Glucose and glycerol increased the stimulatory effect of all the tested chemicals on the growth of algae at a low concentration range, whereas the inhibitory effect at a high concentration range decreased. Glucose and glycerol did not affect the initial pH values and pH-changing trend of the medium containing dyestuffs, significantly.