RESUMEN
The biodegradation performance of azo dyes can be enhanced under low salinity conditions, but the internal biodegradation mechanism is still unclear. Aerobic granular sludge (AGS), a salt-tolerant biological wastewater treatment technology, was used in this study to explore the enhancement mechanism of acid orange 7 (AO7) degradation at low salinity level (1.0 %). Results indicated that the AGS structure and reactor performance were almost unaffected by different AO7 concentrations (5-10 mg/L). Compared with salt-free conditions, the AO7 removal efficiency was elevated by 9.9 %-19.0 % at 1.0 % salinity level, owing to the enrichment of AO7 decolorizing bacteria (e.g. Acinetobacter) and functional enzymes (e.g. FMN-dependent azoreductase). The up-regulated genes involving in the key metabolic functions (e.g. carbon metabolism and oxidative phosphorylation) promoted the electron and energy production, thereby facilitating the AO7 decolorization and degradation. These results aid understanding of the enhancement mechanism of AO7 biodegradation under low salinity conditions from macroscopic and microscopic perspectives.
Asunto(s)
Salinidad , Aguas del Alcantarillado , Aguas del Alcantarillado/microbiología , Aguas Residuales , Bacterias/genética , Bacterias/metabolismo , Compuestos Azo/química , Colorantes/químicaRESUMEN
Nano zero-valent iron (NZVI) has been widely used to improve refractory wastewater treatment. However, the rapid dissolution of NZVI causes a waste of resources and an unstable bioaugmentation. Herein, to verify the essential role of slow release of NZVI on biological systems, a core-shell structured Fe@C composite was developed to demonstrate the long-term feasibility of Fe@C for enhancing azo dye biodegradation in comparison to a mixture of NZVI and carbon powder (Fe+C). The 150 days of long-term reactor operation showed that, although both Fe@C and Fe+C enhanced azo dye degradation, the former achieved a better performance than the latter. The strengthening effect of Fe@C was also more durable and stable than Fe+C. It may be due to the fact that the carbon layer of Fe@C could interact with extracellular polymeric substances (EPS) through physical adsorption and chemical bonding to form a stable buffer to regulate NZVI dissolution. The buffer layer could not only regulate the attack of H+ on NZVI to reduce its dissolution rate but also complex released Fe2+ and neutralize OH- to alleviate the passivation layer formed on the NZVI surface. Moreover, microbial community analysis indicated that both Fe@C and Fe+C increased the abundance of fermentative bacteria (e.g., Bacteroidetes_vadinHA17, Propionicicella) and methanogens (e.g., Methanobacterium), but only Fe@C promoted the growth of azo dye degraders (e.g., Clostridium, Geobacter). Metatranscriptomic analysis further revealed that only Fe@C could substantially stimulate the expression of azoreductase and redox mediator (e.g., riboflavin, ubiquinone) biosynthesis involved in the extracellular degradation of azo dye. This work provides novel insights into the bioaugmentation of Fe@C for refractory wastewater treatment.
Asunto(s)
Aguas Residuales , Contaminantes Químicos del Agua , Matriz Extracelular de Sustancias Poliméricas/química , Carbono , Anaerobiosis , Electrones , Hierro/química , Compuestos Azo , Contaminantes Químicos del Agua/análisisRESUMEN
The biodegradation of dyes remains one of the biggest challenges of textile wastewater. Azo dyes are one of the most commonly employed dye classes, and biological treatment processes tend to generate recalcitrant aromatic amines, which are more toxic than the parent dye molecule. This study aimed to isolate bacterial strains with the capacity to degrade both the azo dye and the resulting aromatic amines towards the development of a simple and reliable treatment approach for dye-laden wastewaters. A mixed bacterial enrichment was first developed in an anaerobic-aerobic lab-scale sequencing batch reactor (SBR) fed with a synthetic textile wastewater containing the model textile azo dye Acid Red 14 (AR14). Eighteen bacterial strains were isolated from the SBR, including members of the Acinetobacter, Pseudomonas and Oerskovia genera, Oerskovia paurometabola presenting the highest decolorization capacity (91% after 24 h in static anaerobic culture). Growth assays supported that this is a facultative bacterium, and decolorization batch tests with 20-100 mg AR14 L-1 in a synthetic textile wastewater supplemented with yeast extract indicated that O. paurometabola has a high color removal capacity for a significant range of AR14 concentrations. In addition, a model typically used to describe biodegradation of xenobiotic compounds was adjusted to the results, to predict AR14 biodegradation time profiles at different initial concentrations. HPLC analysis confirmed that decolorization occurred through azo bond reduction under anaerobic conditions, the azo dye being completely reduced after 24 h of anaerobic incubation for the range of concentrations tested. Interestingly, partial (up to 63%) removal of one of the resulting aromatic amines (4-amino-naphthalene-1-sulfonic acid) was observed when subsequently subjected to aerobic conditions. Overall, this work showed the azo dye biodegradation potential of specific bacterial strains isolated from mixed culture bioreactors, reporting for the first time the decolorization capacity of an Oerskovia sp. with further biodegradation of a recalcitrant sulfonated aromatic amine metabolite.