Achieving nitritation in an aerobic fluidized reactor for coking wastewater treatment: Operation stability, mechanisms and model analysis

Abstract The presence of toxic compounds in coking wastewater is challenging for water treatment, but it also offers opportunities for the selection of specific bacterial populations based on different sensitivities. The potential selective inhibitory effect of toxic compounds in coking wastewater was employed here to inhibit nitrite oxidizing bacteria (NOB), allowing stable nitritation in a long-term experiment using a biological fluidized bed reactor. The main challenge was to identify the appropriate toxic compound loading range that would effectively inhibit NOB but allow ammonium oxidizing bacteria (AOB) to work, by variation of organic loading rate (OLR) and dissolved oxygen (DO). An OLR of 0.80–1.35 kg·m−3d−1 permitted nitritation with a nitrite accumulation rate (NAR) above 80.5%. DO regulation was used to control the extent of nitritation which resulted in different NH4+-N/NO2−-N ratios. The bacterial populations present under the various operation conditions were characterized by high-throughput sequencing, demonstrating presence of Nitrosomonas species as the main AOB, while Nitrospira species (typical NOB) were successfully suppressed. Batch activity experiments with the sludge demonstrated stronger inhibition from SCN− on NOB (IC50 = 40.01 mg·L−1) than on AOB (IC50 = 308.12 mg·L−1). A mathematical model was developed based on the differential inhibition by SCN− and phenol on NOB and AOB, which predicted the optimal conditions for stable nitritation, in line with the experimental data. These findings may help to promote the design and optimization of operation condition for nitritation of coking wastewater, and has potential for nitrogen removal via nitrite (e.g. Anammox) in the treatment of industrial wastewater containing toxic compounds.