Biological Carriers To Strengthen Nitrogen And Carbon Removal In A/O-MBR Process For Oil Refining Wastewater Treatment

In recent years,as laws and regulations are more and more stricter,new requirements have been proposed on environmental protection and pollution control in oil-refining companies,and the discharge standards for wastewater from the petroleum and petrochemical industry have become stricter.At present,the“Petroleum Refining Industry Pollutant Discharge Standard”（GB31570-2015）has been implemented and the Shaanxi Petrochemical Industry has issued a stricter local standard“Shaanxi Province Yellow River Basin Comprehensive Discharge Standard”（DB/61 224-2018）,The effluent of the sewage should meet the standard of COD≤50 mg/L,NH₄⁺-N≤1 mg/L,TN≤15 mg/L are required.The implementation of new standards,the increase of pollutant discharge indicators and the upgrade of discharge standard have posed serious challenges to the effluent discharge of Shaanxi Refining and Chemical companies,especially for TN removal.This study addressed the problems of poor impact resistance and excessive TN of the A/O-MBR process of a wastewater treatment plant in a petrochemical company in Shaanxi Province.First,the operation status of the sewage treatment plant was comprehensively evaluated,and the process improvement strategy is proposed.On this basis,the A/O-MBR pilot test system was built to optimize the process operating conditions by adjusting the parameters such as carriers addition ratio,reflux ratio,and HRT,so effluent was stable and meet the standard.Ind.ASM-Petrochem model was proposed by using Simulink software to express the model in simulation language,establish a simulator,and simulate the actual pollutants removal process under the optimal working conditions in combination with the model parameter values.The main conclusions are as follows:（1）The compliance rate of COD and NH₄⁺-N of the refinery sewage plant is high,but occasional over-standard phenomenon will occur.The TN effluent has been unable to meet the standard above 15 mg/L.It is necessary to improve the system’s impact resistance and strengthen TN removal.（2）A/O-MBR pilot system was established,and 20%（polyurethane and MBBR filler 1.4:1）bio-carrier filler was added to the aerobic tank O₁pool of the pilot plant,which can effectively improve the system’s resistance to water quality impact load,When the influent COD≥400 mg/L and NH₄⁺-N≥30 mg/L,the two pollutants in the effluent can still meet the standard;but TN≥15mg/L,the denitrification rate of the process through the beaker experiment The main reason for the determination and further analysis of the TN over-standard is that the system denitrification volume is insufficient.（3）In view of the problem of insufficient denitrification volume,the anoxic tank was expanded and transformed,and the original aerobic tank O₁was transformed into an anoxic tank A₂.At HRT=24 h,the total reflux ratio was 300%（200% Liquid backflow and 100%activated sludge backflow）Return to the A₁tank of the anoxic tank,and the feed ratio of the O₁tank is 20%.The effluent COD≤50 mg/L,NH₄⁺-N≤1 mg/L,TN≤15mg/L,stable and lower than DB/61 224-2018.（4）The Ind.ASM-Petrochem model can effectively simulate the pollutant removal characteristics under optimal working conditions.However,due to the neglect of the toxic substances in the process,more actual data is needed to adopt in the model.