| In recent years, steel and coking industries produce a larger and larger amount of wastewater with the acceleration of the industrialization. Accordingly, the amount of wastewater that sewage plants discharge after processing also increases. However, the standard of zero discharging in steel and coking industries that "the 12th Five-Year Plan" suggests cannot be reached by sewage plants nowadays, which requires coking wastewater should have advanced treatment process to meet the requirement of recycling and accomplish the goal of zero discharging in the closed cycle of coking plants.Taking coking wastewater being treated by A2/O process of a coking plant in Linfen, Shanxi as study object, this thesis adopts Fenton method and persulfate oxidation method to advanced process coking wastewater respectively. The effect of the initial pH, the initial concentration of dosage, reaction temperature and reaction time were studied, and the change of UV254 and BOD5 in the processed water were investigated under the optimal conditions. The conclusions are as follows:(1) The experiment results indicated that the optimal reaction condition of Fenton method in deep processing coking wastewater is as follows:PH=3, initial H2O2 dosage is 15mmol/L, FeSO4·7H2O dosage is 3mmol/L, reaction temperature is 40℃, revolving speed is W=300r/min and reaction time T=120min. In the processed water, the removal rate of COD amounts to 54.29%, and chroma removal rate 87.88%, the solution is transparent with a tint of yellow. The removal rate of ammonia nitrogen is 57.91%. The processed water under the advanced treatment of coking wastewater by Fenton oxidation reaches the requirement of Emission Standard of Pollutants for Coking Chemical Industry (GB16171-2012).(2) The experiment results showed that the optimal reaction condition of persulfate oxidation on advanced treatment of coking wastewater are as follows:PH=8, the initial K2S2O8 dosage concentration is 2mmol/L, Fe2+ concentration is 2.5mmol/L (the ratio of mol is S2O82-:Fe2+=0.8:1), the reaction temperature is 40℃ and the reaction time is 120min. Under such circumstances, the removal rate of COD is 54.97%, the effluent concentration of COD is 96.67mg/L, The removal rate of ammonia nitrogen is 73.51%, and the chroma is reduced from 168 times to 28 times of transparency with a tint of yellow, the removal rate of it is 83.33%.Each index in the processed water reaches the requirement of Emission Standard of Pollutants for Coking Chemical Industry (GB16171-2012).(3) Under comparative study on advanced treatment of coking wastewater by two advanced oxidation, this thesis draws the following conclusions:a. when adopting Fenton oxidation method to deeply process coking wastewater, the removal rate of COD and chroma is slightly higher than using persulfate oxidation method, while for the removal of ammonia, Fenton method has a slight deficiency, and the degradation rate is not as high as persulfate oxidation method; b. after the advanced treatment of coking wastewater by the persulfate oxidation technology and Fenton oxidation technology, the biodegradability (BOD5/COD ratio) has increased notably from 0.033 to 0.366 and 0.688 respectively; c. Though the analysis of reaction conditions and pharmaceutical cost in the advanced treatment of coking wastewater, two advanced oxidation expenses are:Fenton oxidation ￥4.89/t, and persulfate oxidation of ￥3.91/t respectively. This thesis prefers persulfate oxidation activated by Fe2+ as the advanced treatment method and takes Fenton reagent oxidation method as an alternative. |
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