An Oxic–Hydrolytic–Oxic Process at the Nexus of Sludge Spatial Segmentation, Microbial Functionality, and Pollutants Removal in the Treatment of Coking Wastewater

Toxic inhibition and wash-out of nitrifying bacteria in traditional single-activated sludge processes frequently cause instability of nitrification in industrial wastewater treatment and limit the total nitrogen (TN) removal efficiency. A novel oxic–hydrolytic–oxic (O/H/O) process based on a three-sludge regime was developed to treat coking wastewater with a high C/N ratio and biological toxicity. The results demonstrated that high COD removal (89.6%, 91.3%, 90.4%, and 87.1% in four different modes) was achieved with the complete elimination of phenol, sulfide, total cyanide, and thiocyanate. TN removal varied from 14.0% to 88.7% at an influent flow of 1.6–2.0 kg of COD m–3 day–1, depending on prenitrification, internal recycling, and the presence of a sufficient carbon source for denitrification. The first oxic (O1) and hydrolytic (H) reactors made predominant contributions to the removal of organic and toxic pollutants. The removal of these pollutants guaranteed a stable and favorable environment for nitrification in the second oxic (O2) reactor, in which high ammonium removal was observed because of the predominance of Nitrosomonas and Nitrospira. The O/H/O process has the potential to become a promising industrial wastewater treatment process because it promotes functions that are independent of microbial and process stability with respect to the removal of pollutants, especially nitrogen.