In Vivo and In Vitro Decolorization of Disperse Azo Dyes Using <i>Aspergillus</i> <i>niger</i>

Abstract

Dyes can be considered the main contaminants of textile effluents, which have a heterocyclic complicated structure. Disperse dyes are one of the most commonly used classes of dyes with an insoluble nature and low molecular weight. In this study, the elimination of disperse dyes from aqueous medium was investigated by Aspergillus niger fungi using in vivo and in vitro methods. According to the in vitro decolorization results, the fungi showed high biosorption capacity for three different disperse dyes. At an initial dye concentration of 330 mg/l, the adsorption capacity of A. niger measured 225.3 mg/g for Disperse Yellow 23, 127.4 mg/g for Disperse Blue 183, and 176.3 mg/g for Disperse Red 1. Complete dye removal was achieved at lower initial concentrations after a 6-h operation. The results showed that the biosorption process favored acidic conditions, and the adsorption capacity and rate were higher at pH 4.5. Moreover, the kinetics of the adsorption process for all dyes followed the pseudo–second-order kinetic model. An in vivo decolorization test was also performed, in which A. niger was inoculated in a dye-containing medium to investigate the possible biodegradation of the dye by fungi during its growth. The biodegradation process was studied by Fourier transform infrared spectroscopy (FTIR) and high-performance liquid chromatography (HPLC) methods. The results obtained showed a maximum biodegradation of 49.77% for Disperse Red 1, whereas the decolorization for other dyes was mainly based on biosorption. The industrial wastewater treatment plans in most dyeing houses consist of preliminary coagulation and flocculation tanks followed by biological wastewater treatment by activated sludge. According to the results of this study, A. niger could be applicable in both wastewater treatment steps in industrial plans. A. niger, as a nonharmful microorganism, could be used as a good adsorbent in the coagulation tanks, replacing the chemical coagulants. The adsorbed dye in A. niger’s body mass could easily be separated because of its bulky structure. Because dye removal in this method is nearly complete, the effluent could be used in the same dyeing process without much refining process. Using A. niger in biological aerobic procedures could also be practicable according to the results. A. niger could grow in the aerobic condition of biological tanks and simultaneously degrade and adsorb dye molecules. On the other side, A. niger is commercially used for the production of citric acid, and some enzymes and the body mass produced by these industries could be considered for dye removal processes. The use of A. niger as a biosorbent or degradant for dyes still could be studied in several aspects. The study of the degradation mechanism of different dyes by precise tests like liquid chromatography (LC)-mass is an ongoing study by the current team. Also, using A. niger for real wastewater from dyeing houses and optimizing the dye removal parameters for industrial application is a future research perspective in this case.