Study On Advanced Treatment Of First Grade A Effluent With O₃+OA Combined Process

In order to reduce the pollution of the effluent from the sewage treatment plant to the receiving water and to alleviate the environmental pollution of the surface water,In recent years,some regions have set stricter emission standards for wastewater treatment(nearly Class IV).This project refers to the new requirements of the pollutant discharge limit of urban sewage treatment plant in Taihu basin.The O3+OA combination process is used to treat the first grade A effluent of the wastewater treatment plant and the ozone oxidation and aerobic,anoxic biofilm process devices are set up.The effects of the operating parameters of each unit on the removal of organic matter and nitrogen were studied separately and the optimal operating conditions of each unit were determined to achieve the best treatment effect of the combined process.The gas chromatography-mass spectrometer(GC-MS)was used to study the degradation mechanism of organic compounds in the O3+OA combination process.The main conclusions are as follows:(1)Ozone oxidation can reduce the organic concentration of the first grade A effluent and improve its biodegradability.In the ozone-contact oxidation unit,the removal rate of COD increased with the increase of ozone contact time.The removal rate increased rapidly in the first 25 minutes and reached 20.91%at 25min.The removal rate of COD increased with the increase of ozone flux and the COD removal rate did not change much when the ozone flux exceeded 3L/min.The removal rate of COD gradually increases with the increase of pH of raw water.Under alkaline conditions,the removal effect is better and the pH value of water decreases with the progress of ozone reaction.Adding activated carbon and hydrogen peroxide can improve the removal rate of COD,but the amount of increase is not obvious.Ozone oxidation has a weak oxidation effect on ammonia nitrogen which can transform a small amount of ammonia nitrogen and organic nitrogen into nitrate nitrogen.After ozone oxidation treatment,the B/C value of the first grade A effluent is increased from 0.1 to 0.2 and the biodegradability was improved.(2)Aerobic and anoxic biofilm process can effectively reduce the concentration of organic matter and nitrogen in water.In the stage of aerobic biofilm process,the concentration of COD and ammonia nitrogen in the effluent decreases with the increase of hydraulic retention time.When the hydraulic retention time is above 4h,the COD concentration of the effluent can be reduced to below 30mg/L and the ammonia nitrogen concentration is below lmg/L,the removal rates can reach 28%and 60%respectively.The removal rates can reach 28%and 60%respectively.In the stage of aerobic biofilm method,ammonia nitrogen can be converted into nitrate nitrogen.In the stage of anoxic biofilm process,the total nitrogen in effluent decreased gradually with the increase of methanol dosage and increased with the decrease of residence time.When the dosage of methanol is 30mg/L and the residence time is more than 3h,the total nitrogen concentration of the effluent can be less than 4mg/L,the added carbon source is fully utilized by denitrification,and the COD concentration of the effluent remains below 30mg/L.(3)Under the operating conditions that ozone contact time is 25 mins,ozone flux is 9 mg/min,pH is 8.5,hydraulic retention time of aerobic phase is 4h,adding 30 mg/L methanol As carbon source for denitrification and hydraulic retention time anoxic phase is 3h,the O3+OA combination process has good effect on treatment of the organic matter and nitrogen in the first-grade A effluent of the wastewater treatment plant.The effluent COD is lower than 30mg/L,ammonia nitrogen is lower than 1mg/L,TN is lower than 4mg/L,COD and ammonia nitrogen are both up to the surface water standard of Class IV,the removal rate of TN can reach 77%.The ozone oxidation stage mainly removes some organic matter,which improves the biodegradability of water.The aerobic biofilm process further reduces the concentration of organic matter.The denitrification effect of the combined process is realized by nitrification and denitrification.The ammonia nitrogen is mainly converted into nitrate nitrogen by nitrification in the aerobic biofilm stage,and the nitrate nitrogen is converted into nitrogen by denitrification in the anoxic biofilm stage.(4)After treatment by the O3+OA combination process,the types of volatile organic substances in the first grade A effluent are reduced:the number is reduced by 14 kinds compared with the original water and the peak area is reduced which means that the concentration of volatile organic substances is decreased.Before treatment,there are 68 kinds of main volatile organic substances in water,the main components are esters,alcohols,glycosides,alkanes,ethers.After treatment,there are 54 kinds,the main components are esters,glycosides,ketones,alkalis,alcohols,aldehydes,ethers.Some of esters are converted into bases and alcohols,and alkanes are removed.In the ozone reaction stage,volatile organic compounds with large molecular weight in wastewater can be converted into smaller molecules of alkanes,alcohols,esters,acids,etc.In the biofilm treatment stage biodegradable substances are further degraded by microorganisms,and at the same time,some microbial metabolites such as vitamins and esters are produced.The nitrile and pharmaceutical chemicals in the water were not completely removed,and the removal rate of 3-methylbenzophthalic acid(carcinogen)and organic nitrogen was low.