| Semi-coking wastewater is a typical refractory organic wastewater with high pollutant concentration and complex composition.Discharge of this wastewater into the water body without treatment will cause serious harm to the environment.At present,most of the semi-coking production enterprises use traditional biochemical treatment methods to treat the wastewater.Due to the low biodegradability of the wastewater,the treatment cost is high and the effluent is difficult to meet discharge standards.Therefore,new treatment processes for such wastewater is highly demanded.It is difficult to meet the discharge standards when semi-coking wastewater is treated by physical,chemical or biological method alone.Therefore,this thesis explores a new coupled wastewater treatment technology,using a combination of high gravity-enhanced ozone oxidation and biological process to treat semi-coking wastewater.Ozone oxidation pretreatment technology is used to improve the biodegradability of the wastewater and create good conditions for subsequent biological treatment.Through carrying out a series of experimental studies,the processes and operating conditions suitable for the treatment of the semi-coking wastewater were obtained,which provided theoretical basis and guidance for the design and application of actual projects.The main research results are as follows:(1)Ozone treatment in rotating packed bed(RPB)of the effluent of the first biochemical system in a semi-coking production company in Yulin City,Shanxi Province was conducted.The effects of ozone concentration,RPB rotating speed,gas-liquid ratio,wastewater pH,water temperature and RPB stages on ozone utilization and wastewater treatment were investigated.The experimental results show that for semi-coking wastewater with COD of 340 mg/L,BOD5/COD(B/C)of 0.18,pH of 7.77,and temperature of 24.7?,the COD removal of the effluent was 19.7%,and B/C increased to 0.34 under the conditions of gas volume of 90 L/h,ozone concentration of 50 mg/L,gas-liquid ratio of 5:1,RPB rotating speed of 1500 r/min and two stages of RPB treatment.(2)Under suitable operating conditions,the biodegradability of the effluent improved significantly after ozone oxidation treatment.After biochemical treatment,the COD of the effluent was maintained at about 240 mg/L,and the COD removal efficiency of the combined process was above 30%.Under the same biochemical treatment conditions,the effluent without ozone oxidation treatment was maintained at about 300 mg/L,and the COD removal efficiency was only about 10%.It shows that the high gravity ozone oxidation treatment can greatly promote the biodegradability of the semi-coking wastewater,and can reduce the COD of biochemical effluent.(3)A pilot test of the combined process of high gravity-enhanced ozone oxidation and biological system for the treatment of effluent from the primary biochemical system of the semi-coking wastewater was carried out.Under suitable ozone oxidation conditions,the water samples were treated by two stages of RPB and the effluent was subsequently treated by the biochemical system.The COD of the biochemical effluent reduced from 350 mg/L in the original biochemical system to 240 mg/L,and the COD removal efficiency increased from 15%to about 40%.By analyzing the operating cost,it is found that the operating cost of the new process was about 1.23 yuan/ton of water.(4)The high gravity-enhanced ozone oxidation process was optimized by using ozone gas in series in two-stage RPB treatment,so as to achieve the effect of improving ozone utilization and saving costs.Under suitable operating conditions with ozone concentration of 60 mg/L,the ozone utilization in the two-stage RPB treatment was 67.0%,the COD removal was 15.2%,and B/C increased from 0.06 to 0.15;When the ozone concentration was 78 mg/L,the ozone utilization in the two-stage RPB treatment was 59.6%,the COD removal was 22.5%,and the B/C increased from 0.06 to 0.20.The results show that the use of ozone in series can improve the ozone utilization efficiency significantly,enhance the biodegradability of the wastewater and save the production cost. |
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