Treatment Of Coal Chemical Wastewater With Ozone-based Advanced Oxidation Processes Enhanced By High Gravity Technology

A large amount of organic wastewater will be produced in coal mining and processing.The coal chemical wastewater,with its complicated compositions,usually contains high chemical oxygen demand（COD）,chroma and total dissolved solids.In recent years,ozone-based advanced oxidation processes（OAOP）have been gradually applied to the treatment of coal chemical wastewater due to its clean characteristics and high degree of organic mineralization.However,because of the low mass transfer efficiency between ozone and wastewater,the conventional gas-liquid contactors often result in low ozone absorption efficiency and poor treatment effect of wastewater.Thanks to the high mass transfer efficiency,short residence time and small volume,high gravity technology exhibits application prospect in the field of organic wastewater treatment.Therefore,this study investigated the treatment of two kinds of typical real coal chemical wastewater by the high gravity technology combined with OAOP.Different OAOP were used in the treatment of these two kinds of wastewater in a high-gravity device-rotating packed bed（RPB）,and appropriate process parameters were determined.In addition,a mass transfer model was established based on artificial neural network（ANN）to predict the volumetric mass transfer coefficient(6 in the above processes with RPB,and the predicted(6 was compared with the experimental(6 to determine the modeling parameters for guiding the scale-up of RPB.The research results are shown as follows:（1）The effects of different process parameters on COD removal percentage and(6 of coal gasification wastewater in the O₃@RPB and O₃/Fenton@RPB processes were investigated.In the O₃/Fenton@RPB process,when the rotating speed was 800 rpm;initial p H was 4.0;O₃concentration was 20 mg·L^-1;H₂O₂ concentration was 2.5 mmol·L^-1;gas-liquid ratio was 6:1;Fe²⁺concentration was 0.5 mmol·L^-1,the COD removal percentage and B/C value reached 35%and 0.45,respectively,both higher than those in the O₃@RPB process（COD removal percentage15%,B/C 0.22）.The gas chromatography-mass spectrometry analysis of the wastewater shows that after the O₃/Fenton@RPB process treatment,the content of phenolic organic compounds in the wastewater and the toxicity to microorganisms were significantly reduced,so the biodegradability of wastewater was efficiently improved.The sequencing batch reactor was used to further degrade COD of the O₃/Fenton@RPB process effluent.It was found that the O₃/Fenton@RPB-SBR tandem process can effectively reduce the COD and chroma of the wastewater.Thus,the COD concentration of the SBR effluent reduced to 20-60mg·L^-1,and the chroma reduced from 256 times to 64 times,reaching the wastewater reuse or discharge standard.（2）The effects of different process parameters on COD removal percentage and(6 of high salinity mine water in the O₃@RPB and O₃/H₂O₂@RPB processes were investigated.In the O₃/H₂O₂@RPB process,when the rotating speed was 1200 rpm;O₃ concentration was 60 mg·L^-1;gas-liquid ratio was 6:1;H₂O₂ concentration was 5.58 mmol·L^-1,the COD removal percentage reached about 35%,higher than that in the O₃@RPB process（COD removal percentage was 20%）.The decolorization rate of the wastewater treated by the two processes reached 75%,and the chroma decreased from 128 times to 32 times,which is beneficial to improving the whiteness and purity of salt in the subsequent evaporation crystallization process.（3）An ANN mass transfer model was established to analyze and predict the volumetric mass transfer coefficient(6 in the O₃/Fenton@RPB and O₃/H₂O₂@RPB processes.The results showed that the relative deviations between the predicted and experimental values were less than±20%and±10%,respectively,suggesting that the ANN mass transfer model has a good prediction performance.