Development of an integrated anaerobic/aerobic bioreactor for biodegradation of recalcitrant azo dye and bioenergy recovery: HRT effects and functional resilience

The efficacy of combined continuous anaerobic-aerobic systems to treat 2-Naphthol Red dye-containing industrial wastewater was investigated. A laboratory-scale of upflow anaerobic sludge bed (UASB) followed by an aerobic process was conducted at a hydraulic residence time (HRT) of 24, 12, 6, and 3 h. The integrated systems showed high performance on the COD removal and decolorization under an HRT of 6 h. The maximum chemical oxygen demand (COD) degradation reached 85.6% and 92.4% in the UASB and the aerobic reactor at organic loading rates (OLR) of 12.97 g COD L−1 d−1, respectively with 98.4% colour removal. At 3 h HRT, the performance of the UASB reactor was deteriorated sharply, however it showed high resistance and rapidly full functions were recovered after stress removal. The maximum methane yield reached 13.3 mmol CH4 g COD−1 d−1 at HRT 6 h and the proposed systems and operating conditions could be extended to full-scale applications. [Display omitted] •The combined systems achieved 98.4 and 98.9% colour and COD removal, respectively.•The maximum bioenergy recovery reached 139.6 MJ m−3 wastewater•The UASB performance appeared to be more resilient to the inapt decrease in the HRT•The combined systems are expected having a better economic performance under HRT 6 h