A Study On Performance And Mechanism Of An Ozone And Biological Aerated Filter(BAF) Process Treating Biologically Treated Petrochemical Wastewater

Advanced treatment technologies are required to ensure biologically treated petrochemical wastewater meeting China’s current emission standard（GB 31571-2015）.In this paper,the treatment effects of the biological aerated filter（BAF）and related ozonation methods,as well as their combination processes treating biologically treated petrochemical wastewater were studied.Optimal parameters and mechanisms of ozone and biological aerated filter（BAF）processes treating biologically treated petrochemical wastewater were also investigated.Main results were shown:（1）COD of the biologically treated petrochemical wastewater usually can not meet the standard.Hazardous and refractory organics in the wastewater include benzenes,alkanes,heterocycles,alcohols,esters,ketones,acids and amines,etc.Benzenes,alkanes and heterocycles showed a relatively significant content of 100⁶00μg/L.The contents of the six hydrophobicity/hydrophilicity fractions showed the order of hydrophilic neutral（HiN）>hydrophobic acid（HoA）>hydrophobic base（HoB）>hydrophilic base（HiB）>hydrophobic neutral（HoN）>hydrophilic acid（HiA）,and HiN made up 42.2%of the total fractions.Moreover,the contents of the fluorescent organic compounds showed the order of aromatic amino acid-like organics>soluble microbial by-product>fulvic acid-like organics>humic acid-like organics.（2）COD of the BAF effluent is in the range of 37.3¹21.8 mg/L（can not meet the emission standard）,with the average removal efficiency of 28.5%.The contents of 2-（chloromethyl）-1,3-dioxolane,benzonitrile,indene,naphthalene in the BAF effluent were 20.0,0.135,0.016 and 0.413μg/L,respectively.This showed that many refractory organics still existed in the BAF effluent.Organics with apparent molecular weight<1860 Da and the HiA organics both accumulated in the BAF effluent.Moreover,fluorescent organic compounds were seldom removed by BAF.（3）Compared with the performance of the wastewater treated by single ozone and ozone/hydrogen peroxide technology,the COD of the effluent treated by ozone/catalyst ozonation technology can be steadily below COD discharge limit（60 mg/L）with its average COD concentration of 53 mg/L.The optimal ozone contact time is 60 min and the ozone dosage is 35 mg/L_water for ozone/catalyst technology.However,only 0.83 unit of COD in wastewater could be removed by per unit of ozone.Organics with apparent molecular weight<500 Da,fluorescent organic compounds,as well as the HiN and HiA organics can be effectively removed by BAF.（4）Compared with coupled catalyzed ozone/BAF,the integrated catalyzed ozone/BAF technology(optimal ozone dosage 5 mg/L_water)effluent can meet the emission standard.Meanwhile,the 5.30 unit of COD in the wastewater can be removed by per unit of ozone.Therefore,integrated catalyzed ozone/BAF technology can be recommended to treat biologically treated petrochemical wastewater.（5）On the conditions of the integrated catalyzed ozone/BAF technology,organics with apparent molecular weight<500 Da can be effectively removed at 75¹25 cm height of fiter media.Both the catalyzed ozone and BAF units can promote the generation of biodegradable organics,beneficial for synergistic reaction of ozonation and bio-oxidation on refractory organics.（6）Alkanes,alcohols,nitriles,and heterocycles and the organics with apparent molecular weight<250 Da could probably be assimilated by Gemmatimonadaceae and Saprospiraceae.The organics with apparent molecular weight 250⁵00 Da relate closely with Acidobacteria.Gemmatimonadaceae,Saprospiraceae,and Acidobacteria could promote the biodegradability,and could resist certain range of residual ozone（0.05⁰.11 mg/L）in wastewater.