Biodegradation mechanism of direct blue 15 (DB15) and effect of NaCl on the removal efficiency in anoxic/oxic SBR system with synthetic textile wastewater containing DB15 (STWW + DB15)

摘要

The application of an anoxic/oxic sequencing batch reactor (SBR) system for treatment of synthetic textile wastewater containing Direct Blue 15 (STWW + DB15) was carried out to observe the DB15 biodegradation mechanism and its intermediates. The effect of various NaCl concentrations on the system removal efficiency was also investigated. The results showed that NaCl had a more repressive effect on the growth and activity of heterotrophic carbonaceous compound removal bacteria than on nitrogenous compound removal bacteria (both nitrifying and denitrifying bacteria). The highest biochemical oxygen demand (BOD5), chemical oxygen demand (COD), DB15, total nitrogen (TN) and total Kjeldahl nitrogen (TKN) removal efficiencies of 96.29% +/- 0.74%, 95.81% +/- 0.30%, 90.61% +/- 0.82%, 87.9% +/- 0.24% and 85.03% +/- 0.20%, respectively, were detected for STWW + DB15 at hydraulic retention time of 3 d and mixed liquor suspended solids of 2,000 mg/L. The lowest BOD5, COD, DB15, TN and TKN removal efficiencies of 30.01% +/- 3.48%, 33.26% +/- 0.92%, 26.93% +/- 1.42%, 51.49% +/- 0.31% and 49.77% +/- 0.87%, respectively, were detected for STWW + DB15 containing 14% NaCl (w/v). Moreover, NaCl had a stronger repressive effect on nitrifying bacteria than on denitrifying bacteria. Observation of the biodegradation mechanism of DB15 in the anoxic/oxic SBR system revealed that the azo bond of DB15 was first degraded to 1-amino-8-naphthol-3,6-disulfonic acid and 2-ethoxy-4-methylaniline at the anoxic period of the reaction step, and then 1-amino-8-naphthol-3,6-disulfonic acid was further degraded to 2-naphthol at the oxic period of the reaction step.