O/H/H/O Process for Total Nitrogen Removal: An Upgrade of the A/A/O Process for Coking Wastewater Treatment

For industrial wastewater with high chemical oxygen demand (COD) and nitrogen, traditional wastewater treatment processes fail to achieve stable removal of typical pollutants under the conditions of variable raw water quality and low energy consumption. In this study, a novel pre- and post-physicochemical synergistic oxic–hydrolytic and denitrification–hydrolytic and denitrification–oxic (P2PC-O/H/H/O) process with in situ sludge separation in respective bioreactors was developed, in which signature pollutants and TN were completely removed through an optimized allocation of energy and carbon source. The 180-day full-scale operation showed that optimal removal of COD and TN (with removal rates of 97.5 and 94.5%, respectively) can be obtained at influent loading rates of 1.5–1.7 kg COD (m3 days)−1 and 0.11–0.13 kg TN (m3 days)−1. In this process, O1 reactor ensured organic matter removal and pre-nitrification. Double H (H1 and H2) reactors allowed deep removal of TN through combined and coupled denitrification pathways. O2 reactor consolidated the overall treatment performance through decarbonization and nitrification. By P2PC, the refractory and easily biodegradable total organic carbon (TOC) was separated, achieving a qualitative and fractional utilization of electron donors. Analysis of the microbial community in the whole process indicated that Nitrosomonas (0.7–2.4%) and Nitrospira (0.3–1.7%) played a major role in nitrification. Ottowia (15.4–19.6%) and Limnobacter (1.8–7.4%) dominated in eliminating organic matter. The P2PC-O/H/H/O process with a four-sludge regime enabled a spatial allocation of functional microorganisms. The operation cost of the full-scale process was approximately 1.335 USD m–3. In short, this P2PC-O/H/H/O process, with high efficiency and stability in signature pollutant removal, will be a promising wastewater treatment technology to revolutionize the existing anaerobic–anoxic–oxic (A/A/O) process, adding a new dimension to industrial wastewater management.