Treatment of Synthetic Coking Wastewater Using a Sequential Oxic–Anoxic Upflow Packed Bed Bioreactor System

Abstract

In this study, a two-stage sequential oxic–anoxic packed bed bioreactor (PBR) was designed with polyurethane foam cubes as microbial immobilizing materials for the removal of phenol, cresol, and NH3-N from synthetic coking wastewater. The hydrodynamic conditions of the PBR were enhanced by applying a ceramic gas diffuser, implementing a cross-flow design, and encasing a perforated disc covered with a nylon wire mesh. The hydrodynamic conditions of the oxic unit were assessed and found to be superior to simple PBR, with an increase in mixing time tm95 > 70%, oxygen mass transfer coefficient kLa > 53%, and gas hold-up > 36%. Maximum phenolic degradation was achieved at optimum loading rates of 950 and 675 mg L−1 day−1 for phenol and cresol, respectively, with Rhodococcus pyridinivorans strain PDB9T and Pseudomonas citronellolis NS1 in the oxic unit of PBR. An NH3-N-oxidizing bacterial consortium was isolated from coke oven wastewater, which could remove 96% NH3 (nitrification) at an initial concentration of 200 mg L−1 in the oxic unit of the integrated PBR system. Similarly, a mixed microbial consortium isolated from Paradeep fertilizer wastewater could remove NO3 by more than 95% at an initial concentration of 150 mg L−1 in the anoxic unit of the integrated PBR system. Overall, in the sequential oxic and anoxic bioreactor system, more than 93% phenol, 88% cresol, and 99% NH3-N removal was achieved from synthetic wastewater containing 1,000 mg L−1 phenol, 500 mg L−1 creosol, and 200 mg L−1 NH3-N using the isolated P. citronellolis NS1, R. pyridinivorans strain PDB9T N1, and microbial consortium at a hydraulic retention time of 18 h.