Study Of Pilot Test On Pretreatment Of Chemical Fiber Wastewater And Treatment For Meeting Discharge Standard Of Mixed Wastewater

The wastewater which was researched in this article came from petroleum chemical fiber enterprise, which located in aromatic hydrocarbon base of LiaoYang petroleum chemical industry park, and domestic sewage from Hong Wei district. The main kinds of industrial wastewater were polyester wastewater, cutting fluid and cooling liquid wastewater. Petroleum chemical industrial wastewater was difficult to biochemical treatment, it had complex organic pollutant composition, water quality fluctuation, therefore, it required pretreatment, and then mixed with sewage before biochemical treatment. The main research content was as follows:Firstly, pilot-scale test of industrial astewater pretreatment was carried through using hydrolytic acidification and contact oxidation pretreatment, hydrolytic acidification with special inoculum and contact oxidation pretreatment and catalytic ozonation pretreatment, respectively. Comparing the COD, NH4+-N, TN removal rate and the change of the B/C of three pretreatments, the optimal pretreatment process was put forward. The experimental results indicated that COD removal efficiencies were 44.6% and 63.8%, NH4+-N removal efficiencies were 44% and 54.8%, and TN removal efficiencies were 44.6% and 63.8%, using hydrolytic acidification and contact oxidation pretreatment technology, hydrolytic acidification with special inoculum and contact oxidation pretreatment, respectively. For catalytic ozonation pretreatment process, COD and NH4+-N removal efficiencies were 63% and 16.4%, respectively, meanwhile the B/C ratio was obviously increased. In brief, the higher COD, NH4+-N and TN removals were acquired through hydrolytic acidification with special inoculums and contact oxidation pretreatment; while catalytic ozonation pretreatment process afforded similar COD removal and improved the B/C; but with lowest NH4+-N removal.Secondly, pilot-scale test was carried out for up-to-standard discharge of the whole treating system, combined hydrolytic acidification and contact oxidation for industrial wastewater with A/A/O-MBR for mixed wastewater (wastewater after pretreatment and sewage). The result indicated that, when the mixing ratio of industrial wastewater and sewage was 1:1-1:4, the average C/N ratio of the mixed wastewater after pretreatment was 3:1, leading to poor total nitrogen removals in A/A/O-MBR system with insufficient denitrification carbon. When the mixing ratio of industrial wastewater and sewage decreased to 1:8 and 1:10, total nitrogen removals in A/A/O-MBR system was improved with the average C/N ratio of 5.3:1. With high COD concentration (>500 mg/L) of industrial wastewater, when the mixed ratio of pretreatment wastewater and sewage was 2:1 (design objective for practical engineering), the optimization parameters of the whole treating system were as follows:aeration rates of contact oxidation tank, aerobic tank, and membrane tank were 0.5 m3/h,9 m3/h,5 m3/h, respectively; the reflux ratio of mid-sedimentation tank, anoxic tank, aerobic tank and membrane tank were 100%,50%,50% and 300%, respectively. Under this condition, the average COD and TN removal efficiencies were 74.9% and 40.5%, and average COD, NH4+-N and TN levels of membrane effluent were 49.0 mg/L,0.54 mg/L and 9.0 mg/L, respectively, which all met the first grade A standard. However, TP concentration of mixing wastewater was in the range of 20 to 33 mg/L, it was very difficult to meet the first grade A standards only through biological phosphorus removal treatment, so the subsequent chemical phosphorus removal should be applied subsquently.Finally, he NH4+-N and TN removal capacities of A/A/O-MBR biochemical systems for mixing wastewater was sufficient after catalytic ozonation pretreatment (by calculation). Considered the factors of both running cost and project feasibility, catalytic onation was recommended as the optimal industrial wastewater pretreatment process. Therefore, it was suggested that the whole treatment process up to standard was catalytic ozonation pretreatment for industrial wastewater and A/A/O-MBR for mixing wastewater.