Enhanced Degradation And Optimization Of Organics In Tail Water Of Petrochemical Wastewater By O₃-BAC

With China's industrial wastewater emission targets increased every year,most petrochemical wastewater treatment plants are faced with huge pressure of upgrading.In order to satisfy the increasingly stringent requirements of water quality emission standards,it is urgent to develop appropriate advanced treatment technologies.Tail water of a petrochemical wastewater plant in North China contained many organic materials with unsaturated bonds.The organics with relative molecular weight < 1k Da in water accounted for 69% of the total amount of organics in wastewater.The B/C value of wastewater was less than 0.1,which indicated that the biodegradability of the tail water was poor.In this research,O3-BAC combined process was used for advanced treatment of tail water of petrochemical wastewater plant.Based on the analysis of water quality,the operation parameters of ozonation unit and biological activated carbon unit were optimized.The effects of separate operation,combined operation and catalytic ozonation on organic matter removal,relative molecular weight distribution and organic structure were also investigated or compared.In addition,the shock resistance capacity of combined process was investigated.On the basis of the research mentioned above,the following results are obtained.The adsorption process of activated carbon to tail water conformed to the pseudo first order kinetic model.After inoculation,BAC system mainly removed the small molecular organics whose molecular weight were < 1k Da.The test results showed that,the best removal efficiency of COD and UV254 could be obtained when the empty-bed residence time was 1.5 h.The removal efficiency were 30% and 36%,respectively.The biodegradation process of BAC mainly occurred in the upper layer of the packing layer(front from the water inlet 50 cm).Ozonation unit was mainly used to convert refractory macromolecular organics into small molecules,which could improve the biodegradability of wastewater.Under the condition of ozone(O3)dosage of 20 mg/L and single stage contact time of 40 min,the B/C of the effluent increased to 0.28,and the removal efficiency of COD and UV254 reached the best.The removal efficiency were 20% and 31%,respectively.After ozonation,the proportion of small molecules with molecular weight of < 1k Da increased from 69% to 87%.In particular,catalytic ozonation could promote the transformation of organic structure in wastewater,enhanced the utilization of ozone,and further improved the biodegradability of wastewater.The promotion effect was more obvious when the ozone dosage was insufficient.When the empty bed residence time of BAC was 1.5 h,ozone dosage was 20 mg/L and single stage contact time was 40 min,the removal efficiency of COD and UV254 by the combined process were 40% and 55%,respectively.The concentration of COD in effluent could be stabilized below 30 mg/L.Besides,the combined process had the capability of shock load resistance.The water quality shock could be solved by increasing the ozone dosage to 30 mg/L.