| Coking wastewater usually contains high concentration of ammonia (600-800 mg-L-1), in the field of coking wastewater nitrification research and application, biological combined processes developed from the A/O process are more appealing. However, coking wastewater is complicated, containing a large number of toxic substances such as phenol, cyanide, various aromatic organic compounds, heterocyclic and polycyclic aromatic hydrocarbons, which has negative effect on biological nitrogen removal process, so it is still difficult to reach the discharge standards by current popular biological combined processes. For the issue that nitrification in biological treatment of coking wastewater is usually hard to achieve effectively, a novel A/O1/H/O2 fluidized bed combined process was designed and developed by our research group. In this study, the operation process and treatment effect were systematically analysed; the optimal conditions, influencing factors and biological inhibition mechanism to nitrification were studied. The new A/O1/H/O2 technology employed in coking wastewater treatment can achieve stable and efficient nitrification as well as effective degradation of organic compounds at the same time.In order to study the treatment effect of A/O1/H/O2 biological fluidized bed combined process, the monitoring datas adopted from commission period to the stable operation and operation process of different units were analyzed. The results showed that the second aerobic fluidized bed is the main process where nitrification occurred and ammonia nitrogen removal rate reached 99.3%, nitrification process can be highly efficient and stable thanks to the completion of the process before the second aerobic segment; ring-opening reaction and degration of most of the refractory heterocyclic compounds happened in anaerobic and anoxic processes, reducing toxicity while improving biodegradability of wastewater; the first aerobic fluidized bed removes most of the pollutants which can affect the nitrification process, such as COD, phenol, SCN-and CN-, the remove rate were 76.8%,99.7%,96.9% and 79.6% respectly, and create suitable conditions for nitrification in the second aerobic stage. The ammonia effluent concentration of biological system is continuously lower than 3 mg·L-1, which was much lower than the integrated wastewater discharge standards.To find out the optimal conditions for nitrification and mechanism of nitrification inhibition, the impact of environmental conditions and pollutant inhibitory factors of coking wastewater on the nitrification process were studied by experiment. The optimal parameters for nitrification were obtained as follows:ammonia concentration≈150 mg·L-1, temperature≈30℃, pH value≈8.5, DO= 3-4 mg·L-1, C/N= 4; the results can provide the guidance for the operating conditions of the project. According to nitrification inhibition in the project operation, typical pollutants such as ammonia, phenol, SCN- and nitrogen containing heterocyclic compounds were proved to be nitrification inhibitors. Results showed that it has slight substrate inhibition when ammonia concentration greater than 150 mg·L-1; phenol in low concentration (30 mg·L-1) can inhibit nitrification; ammonia oxidation inhibition rate can reach 78.1% when SCN- concentration is 380 mg·L-1, and the nitrite accumulate; half inhibitory concentration of four kinds of typical nitrogen heterocyclic compounds like quinoline, pyridine, indole and pyrrole on nitrification process were 112.46 mg·L-1,59.51 mg·L-1,9.89 mg·L-1 and 13.46 mg·L-1 respectly. The results indicated that nitrification process can be effectively react only in low COD concentration and low-toxic pollutants existing conditions.Nitrification is a key step in biological nitrogen removal process, it is vulnerable to the impact of changes in environmental conditions, particularly prone to be inhibited by toxic pollutants in coking wastewater, which is the important reasons that it is difficult for other biological processes to remove ammonia efficiently and stablely.Therefore, to improve the efficiency and maintain lasting stability of nitrification in coking wastewater treatment, the biological degradation characteristic of pollutants in coking wastewater should be investigated. A reasonable combined process which formed by a highly efficient carbon remove unit and a nitrogen remove unit should be employed, it will prevent nitrification inhibition impact of other toxic pollutants, on the basis of optimal operating conditions, stable and efficient nitrification process can be ensured.
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