Biodegradation of Highly Concentrated Phenol and Ammonia in the Presence of Oxyanions in Sequential A2/O MBBR System.

In this study, a sequential fed-batch anaerobic–anoxic–aerobic (A²/O) moving bed biofilm reactor (MBBR) (A²/O MBBR) system will be employed for the simultaneous treatment of highly concentrated phenol, ammonia (NH₄), and oxyanions [e.g., nitrate (NO₃) and sulfate (SO₄^2-)] from wastewater. The A²/O system efficiently removed phenol (99%) and NH₄–nitrogen [NH₄–N (95%)] with a 99% reduction in the chemical oxygen demand (COD) of the effluent for 3,000 and 200 mg/L of the maximum initial feed concentration, respectively with a 10-day hydraulic retention time (HRT). However, high removal of SO₄^2- was achieved under anaerobic conditions (96%) for 100 mg/L of the initial feed concentration. The increasing feed phenol concentration (1,500–3,000 mg/L) inhibited NO₃ reduction by releasing significant levels of NO₃ in the anoxic reactor effluent and increased the SO₄^2- accumulation in the anoxic and oxic reactors. Heterotrophic denitrification was reduced in the anoxic reactor by 15%–17% and increased the phenol concentration from 2,000 to 3,000 mg/L due to the highly toxic effect on the denitrifying microbes. NH₄ removal by the anaerobic (R1) and anoxic (R2) reactors reduced from 87% to 65% and 66% to 46%, respectively, and increased the phenol concentration from 1,500 to 3,000 mg/L but the oxic reactor showed stable performance. Scanning electron micrographs (SEM) of the carrier media showed the better adherence of well-grown round and rod-shaped mixed microbes in different environments. Bacillus licheniformis was identified as the dominant species in the anoxic and oxic reactors by the VITEK 2 COMPACT system. Similarly, Kocuria kristinae was the predominant microbe identified in the anaerobic reactor. The outcome of this study revealed that an A²/O MBBR system that had an established indigenous mixed microbial culture could be a feasible technique to treat highly concentrated phenol combined with NH₄ and oxyanions that are present in wastewater. [ABSTRACT FROM AUTHOR]