Development of a mixed culture-based combined process for simultaneous removal of higher concentrations of phenol and NH4-N from wastewater

• Simultaneous removal of higher concentrations of phenol (99 %) and NH 4 -N (94 %). • Effective treatment of pre-treated coke oven wastewater with 96 % phenol removal. • Developed combined heterotrophic and autotrophic processes involving anammox. • Suitable for treating wastewaters with COD to NH 4 -N ratios ranging from 1.6 to 3.3. This study develops a mixed culture-based combined process in a dual-stage packed media bioreactor integrating nitrifiers and denitrifiers for the simultaneous removal of phenol and NH 4 -N. The bioreactors operated sequentially in down-flow and up-flow modes, respectively, enabling oxic-anoxic and anaerobic-oxic conditions. During 441 days of continuous operation, using synthetic wastewater and with varied COD to NH 4 -N ratios from 1 to 3.33, the process demonstrated remarkable removal efficiencies: up to 99 % for phenol, 94 % for NH 4 -N, and 88 % for total nitrogen (TN). The corresponding rate of elimination (g/L. d) was: phenol 0.446, NH 4 -N 0.423, and TN 0.396, respectively. This was achieved at a 2-day hydraulic retention time, with initial influent concentrations of 900 mg/L for both phenol and NH 4 -N. The application of the developed process for the treatment of pre-treated coke oven wastewater for 64 days demonstrated sustained removal efficiencies to the extent: of phenol (96 %), NH 4 -N (75 %), and TN (67 %). The corresponding rate of elimination (g/L. d) was: phenol 0.312, NH 4 -N 0.518, and TN 0.462, respectively. Batch studies and microbial molecular techniques of biomass drawn from the reactors confirmed the presence of a mixed culture capable of nitrogen removal involving heterotrophic nitrifiers and aerobic denitrifiers, autotrophic nitrifiers and heterotrophic denitrifiers and anammox species. The developed process scheme shows promise for treating phenol-containing industrial effluents effectively with COD to NH 4 -N ratios ranging from 1.6 to 3.3, leveraging the synergetic actions of both autotrophic and heterotrophic microbes. The study supports majorly UN Sustainable Development Goal 6 by advancing water quality and sustainable water use practices through innovative wastewater treatment technologies.