Abstract
The potential disrupting effects of Azo dye on wastewater nutrients removal deserved more analysis. In this study, 15 days exposure experiments were conducted with alizarin yellow R (AYR) as a model dye to determine whether the dye caused adverse effects on biological removal of both the dye and nutrients in acclimated anaerobic–aerobic–anoxic sequencing batch reactors. The results showed that the AYR removal efficiency was, respectively, 85.7% and 66.8% at AYR concentrations of 50 and 200 mg l−1, while higher AYR inlet (400 mg l−1) might inactivate sludge. Lower removal of AYR at 200 mg l−1 of AYR was due to the insufficient support of electron donors in the anaerobic process. However, the decolorized by-products p-phenylenediamine and 5-aminosalicylic were completely decomposed in the following aerobic stage at both 50 and 200 mg l−1 of AYR concentrations. Compared with the absence of AYR, the presence of 200 mg l−1 of AYR decreased the total nitrogen removal efficiency from 82.4 to 41.1%, and chemical oxygen demand (COD) removal efficiency initially decreased to 68.1% and then returned to around 83.4% in the long-term exposure time. It was also found that the inhibition of AYR, nitrogen and COD removal induced by a higher concentration of AYR was due to the increased intracellular reactive oxygen species production, which caused the rise of oxidation–reduction potential value and decreased ammonia monooxygenase and nitrite oxidoreductase activities.
Highlights
Azo dyes are primary contaminants in dyeing process effluent (DE) [1,2]
When alizarin yellow R (AYR) concentration was up to 400 mg l21 (SBR3), the effluent concentration of AYR increased to 447.4 + 2.4 mg l21 and there was no net AYR removal, it was found that the sludge was inactivated
The decolorization efficiency of the sequencing batch reactors (SBRs) was negatively related to the inlet concentration of AYR and more than 200 mg l21 of inlet AYR was too much for the SBR reactor to handle
Summary
Azo dyes are primary contaminants in dyeing process effluent (DE) [1,2]. Owing to their harmful health effects and& 2018 The Authors. Azo dyes are primary contaminants in dyeing process effluent (DE) [1,2]. Owing to their harmful health effects and. Azo dyes are recalcitrant under aerobic conditions, but could be transformed into their corresponding aromatic amines under anaerobic conditions [3,4,5]. Haug et al [4] suggested that an aerobic process should follow the anaerobic reduction to further degrade the poisonous aromatic amine by-products into simple compounds. The anaerobic–aerobic sequential treatment process is a feasible approach towards achieving complete degradation of azo dyes [6]
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