Vol.:(0123456789) 1 3 Biomass Conversion and Biorefinery https://doi.org/10.1007/s13399-022-03157-x ORIGINAL ARTICLE Infuence of culture age and environmental conditions on the decolorization and biodegradation of Reactive Orange 13 by Bacillus sp. SBT8 Ayşe Avcı 1  · Ayşe Yıldırım 1  · İnci Cerit 1  · Semra Yılmazer Keskin 2  · Mohammed Hamk 1,3  · Can Serkan Keskin 2  · Omca Demirkol 1 Received: 26 March 2022 / Revised: 23 July 2022 / Accepted: 25 July 2022 © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2022 Abstract The release of azo dyes from industrial efuents is a serious environmental concern because of their colors and unfavorable impact on water quality. One method for combating their release is biological degradation. In this study, the potential of a newly isolated Bacillus sp. SBT8 strain for the decolorization and degradation of Reactive Orange 13 (RO13) was investi- gated. Conditions favorable for decolorization including temperature (25–42 °C), pH (5.0–10.0), culture age (0–24 h), and dye concentration (25–200 mg/L) were determined. Adding RO13 during the mid-exponential phase (8 h following inocula- tion) accelerated the rate of decolorization. Efcient decolorization was observed in broad pH (6.0–10.0) and temperature (25–35 °C) ranges with the optima at pH 7.0 and 33 °C, respectively. A complete decolorization was observed at pH 7.0, 35 °C, and 25 mg/L dye concentration in 48 h. Increased dye concentrations (over 100 mg/L) had inhibitory efects on the degradation of dye as measured after 48 h: 25, 50, and 100 mg/L dye concentrations were decolorized by 100, 83.58 ± 3.07, and 42.68 ± 3.02%, respectively. Decolorization and biodegradation were confrmed by UV–VIS spectroscopy, FTIR, and LC–MS. The analysis with FTIR afrmed the cleavage of the azo bond and the formation of novel products. The metabolites were determined by LC–MS analyses and a possible biodegradation pathway was proposed. Phytotoxicity was tested on Lens culinaris and the non-toxic nature of the metabolites was revealed. This study provides insights into the potentiality of Bacillus sp. SBT8 isolate on the decolorization and biodegradation of azo dyes. Keywords Bacillus · Reactive Orange 13 · Azo dye · Biodegradation, Decolorization 1 Introduction Azo dyes are synthetic dyes with very complex structures containing substituted aromatic rings linked with at least one azo group (-N = N-) [1, 2]. They are extensively utilized by the textile, leather, cosmetics, paper, and food industries and account for 50–60% of global dye production [3, 4]. The textile industry is the biggest consumer of azo dyes and unfortunately, 10–15% of the dye is released with the efuents [5, 6]. The dyes released without treatment lead to serious environmental and health problems because they are toxic, change the water pH, increase biological and chemi- cal oxygen demand, and cause intense coloration, which can impede photosynthesis [7–9]. Hence, the treatment is essential for the protection of human and plant health and the environment [10]. Various physicochemical techniques are applied for the treatment including membrane fltration, coagulation, adsorption, and reverse osmosis [11, 12]. How- ever, current methods are expensive, largely inefective, and involve complex unit operations [6, 13]. Biological methods are alternatives to physicochemical processes as they are more adaptable, cost-efective, and environmentally friendly [14, 15]. Microorganisms are able to metabolize the dyes owing to intracellular or extracellular enzymes such as peroxidases, azoreductases, laccases, and * Ayşe Avcı aysea@sakarya.edu.tr 1 Department of Food Engineering, Faculty of Engineering, Sakarya University, 54050 Sakarya, Turkey 2 Department of Chemistry, Faculty of Arts and Sciences, Sakarya University, 54050 Sakarya, Turkey 3 Food Science and Quality Control Department, Halabja Technical College of Applied Sciences, Sulaimani Polytechnic University, Zamaqi, Halabja, Iraq Content courtesy of Springer Nature, terms of use apply. Rights reserved.