Study On Treatment Of Simulated Secondary Effluent From Urban Wastewater Treatment Plants By RPB-O₃ Process

China is one of the severely water-deficient countries.Water resources crisis affects people's life and national development.Reuse of secondary effluent from urban wastewater treatment plants(UWTPs)is one of the most effective ways to alleviate the crisis of water resources.The secondary effluent from UWTPs contains a variety of inorganic ions and a large amount of bacteria,which are usually carriers and disseminators of diseases,threatening human health and environmental safety.Therefore,it is crucial to choose an effective and harmless disinfection process to inactivate bacteria in the reuse of secondary effluent.Ozone disinfection is a safe and efficient technology,and its effect is better than disinfection processes containing chlorine.Ozone absorption efficiency is one of the key factors affecting the disinfection effect in the ozone process.Rotating packed bed(RPB)is a high-gravity device which can intensify ozone-liquid mass transfer and increase the absorption percentage of ozone.In this study,RPB was employed as a device for ozone absorption to intensify the effect of ozone disinfection process on the simulated secondary effluent.The effects of various process factors and inorganic salts on the treatment of simulated secondary effluent by the RPB-O3 process were investigated in terms of degradation percentage of fulvic acid(DFA),removal percentage of UV254(R254)and logarithmic inactivation of Escherichia coli(LE),and the following conclusions were reached:(1)The effect of various factors on the treatment of simulated secondary effluent by the RPB-O3 process was investigated.It was found that DFA,R254 and LE decreased with the increase of temperature,initial concentration of FA and liquid flow rate.DFA,R254 and LE increased with the increase of ozone concentration and rotation speed of RPB.With the increase of pH,R254 rose but LE declined.The suitable operating conditions to treat simulated secondary effluent by the RPB-O3 process were determined as RPB rotation speed of 1000 rpm,ozone concentration of 8.3 mg/L and liquid flow rate of 30 L/h,and LE reached 5.0 under these conditions.(2)It was found that NaHC03,Na2S04,CaCl2,NH4C1,MgCl2 and KCl had negative effect on the treatment of simulated secondary effluent by the RPB-O3 process.R254 and LE decreased with the increase of NaHCO3 concentration.R254 and LE decreased,while DFA declined slightly with an increasing Na2SO4 concentration.LE decreased,while DFA and R254 exhibited the tendancy of decline when CaC12,NH4Cl,MgC12 and KC1 concentrations increased.(3)The effect of various factors on the treatment of simulated secondary effluent containing NaHCO3,Na2SO4 and CaC12 respectively by the RPB-O3 process was investigated.The suitable operating conditions to treat simulated secondary effluent containing 100 mg/L NaHCO3 by the RPB-O3 process were determined as RPB rotation speed of of 800 rpm,ozone concentration of 14.7 mg/L and liquid flow rate of 20 L/h.The suitable operating conditions to treat simulated secondary effluent containing 200 mg/L Na2SO4 were determinded as RPB rotation speed of 800 rpm,ozone concentration of 7.7 mg/L and liquid flow rate of 30 L/h.The suitable operating conditions to treat simulated secondary effluent containing 100 mg/L CaCl2 were determinded as RPB rotation speed of 600 rpm,ozone concentration of 8.0 mg/L and liquid flow rate of 30 L/h.