Integrated Catalytic Ozonation-persulfate Oxidation Process For High Concentration Acrylonitrile Wastewater Treatment

Acrylonitrile wastewater contains nitrile and nitrogen-containing heterocyclic compounds,which lead to high biological toxicity,organic content and poor biodegradability,thus present significant harms to the environment.Traditional biochemical treatment processes are difficult to treat acrylonitrile wastewater effectively.The main pollutents of wastewater in Fushun Petrochemical Acrylic Factory originate from acrylonitrile wastewater with high concentrations,the effluent of secondary biochemical wasterwater treatment still contained high concentration of organic nitrogen,resulting in the total nitrogen level still exceeding the wastewater discharge standard.In this study,an integrated catalytic ozonation-persulfate oxidation process was put foward to pretreat acrylonitrile wastewater.Sulfate radicals could be producted by thermal activation of persulfate utilizing the high temperature of acrylonitrile wastewater,mainwhile hydroxyl radicals could be produced by catalytic ozonation.The integrated advanced oxidation process could degrade refractory organic matters in wastewater to small molecular organics,carbon dioxide and water,leading to the improvement of its biodegradability,and removals of organic and total nitrogen.Therefore,the removal efficiency of the subsequent biochemical treatment systems could be promoted greatly.The following researches were investigated in this paper.(1)In lab-scale experiment,the effects of ozone concentration,persulfate dosage and pH on catalytic ozonation and persulfate oxidation were investigated to verify the feasibility of the integration of the two kinds of advanced oxidations.During the single-factor experiment of catalytic ozonation,the experimental results showed that the removal efficiency of pollutants was increased by 180%,with the increase of ozone concentration from 20 mg/L to 60 mg/L.Meanwhile,during persulfate oxidation experiment,with the increases of temperature and PS dosage in certain ranges,the removal efficiency of COD and organic nitrogen was increased.At reation time of 240 minutes,the removal efficiencies of COD and organic nitrogen were 47.3% and 33.6%,respectively,while the B/C ratio increased from the 0.09 to 0.35.Moreover,GC/MS analyses of the influent and effluent clearly demonstrated the decrease in nitriles and nitrogen-containing heterocyclic compounds.Thus,the integrated process had an obvious positive effect on reductions of COD,organic and total nitrogens and improvement of biodegradability.(2)Based on the lab-scale experiment results,a pilot-scale experiment was carried out.The Box-Behnken center combination design principle and Design-Expert 8.0 software were used for the design of this pilot-scale experiment.Moreover,the response surface analysis was applied to optimize the operational parameters.With the consideration of running cost limitation,the optimal operational condition was pH 8.9,ozone dosage 1 kg/m3,sodium persulfate dosage 0.8 kg/m3,the corresponding removal efficiencies of COD and TN were 40.7% and 26.1%,respectively,and the B/C ratio was increased from 0.08 to 0.32.(3)Based on the results of lab-scale and pilot-scale experiments,the engineering design and investment analysis of a pretreatment plant was implemented.With the treating waterwater capacity of 800 m3/d,the total investment of this pretreatment plant was 15.55 million RMB,and the total installed capacity was 301.47 kW.Regardless of the depreciation,the running cost was 9.55 RMB/m3(equivalent to 2.12 RMB/m3 of the total mixed wastewater treating capacity).