Performance Of Ozonation-two Stage BAF Treating Polyvinyl Chloride(PVC)Centrifugal Mother Liquid Wastewater And Pilot Design

Aiming to solve the high energy consumption problem in the existing processing unit of polyvinyl chloride(PVC)centrifugal mother liquid wastewater treatment plant in Shenghua Chemical Industry Park in Hebei Province,experimental research was proposed to adjust and optimize the existing process parameters.In this work,the core process ozonation-two stage biological aerated filter(BAF)for PVC centrifugal mother liquid wastewater treatment was selected as the main research object to investigate the effects of primary BAF as well as the parameters including hydraulic retention time(HRT)and aeration on the removal efficiency of PVC centrifugal mother liquor wastewater;the effects of ozonation process on the removal efficiency of PVC centrifugal mother liquid wastewater and three typical organic pollutants(polyvinyl alcohol,iso-octyl alcohol and ?-methylstyrene);the removal effects of ozonation influential factors(contact reaction time of ozone,ozone dosage and initial pH)on the three target pollutants;the effects of different catalysts including activated carbon,Ni/Al2O3,Fe/Al2O3,Cu/Al2O3 and Mn/Al2O3 on the oxidation of PVC centrifugal mother liquid wastewater as well as the best catalyst and dosage by analyzing the respective ozonation products of the three pollutants.Finally,the removal efficiency of coupled catalytic ozonation and secondary BAF were evaluated and a pilot-scale process were designed.The results showed that the best HRT and dissolved oxygen(DO)of the primary BAF treating PVC centrifugal mother liquid wastewater were about 1.9 h and 4 mg/L respectively,the removal rate of COD and ammonia nitrogen were 66.42%and 26.93%respectively;an initial pH>7.0 was benefit forthe ozonation treatment of PVC centrifugal mother liquid wastewater,the optimal contact reaction time and ozone dosage were 60 min and 32 mg/L respectively under which conditions the removal rates of COD and TOC reached 75%and 18%respectively.The optimum reaction time and ozone dosages for polyvinyl alcohol,iso-octyl alcohol and a-methylstyrene in PVC centrifugal mother liquid wastewater were:25 min and 136 mg/L;60 min and 312 mg/L as well as 60 min and 32 mg/L,respectively.Under the above optimum reaction conditions,the removal rates of the three target pollutants were 98%,85%and 99%,respectively.Through GC-MS analysis,it was found that after ozonation,polyvinyl alcohol chains were broken and further reacted to form oxalic acid 1-ethyl ester,while iso-octyl alcohol and a-methylstyrene formed isooctanoic acid and acetophenone respectively.Activated carbon showed the best catalytic effect in the process of catalytic ozonation of PVC centrifugal mother liquid wastewater with different catalysts.When the active carbon dosage was 15 g/L,the reaction time was 30 min and the ozone concentration was 32 mg/L,the COD removal rate was 55%,which was higher than the total rate of that treated by activated carbon adsorption(19%)and ozonation alone(23%),besides,the BODs/COD ratio was found to be increased by 0.4 indicating an significantly improvement of wastewater biodegradability.The catalytic ozonation and secondary BAF coupling process had good wastewater treatment effects,the removal rates of COD and ammonia nitrogen in the secondary BAF were 73%and 20%respectively.Finally,basing on the experimental results,design a 50 t/d pilot-scale testing device,including design calculations and equipment selection.