Research On Coking Wastewater/Landfill Leachate Treatment Technology Based On Hydrodynamic Cavitation

Both coking wastewater and landfill leachate are typical organic wastewater of high concentration and difficult to degrade,with complex composition and numerous harmful pollutants,which can cause serious environmental pollution if not treated effectively in time.This thesis takes the biochemically treated coking wastewater from a coking plant and the landfill leachate produced by a domestic waste landfill as the research objects.The main research content was the removal effect of basic water quality indicators such as chemical oxygen demand（COD）and UV absorbance at a wavelength of 254 nm（UV254）.The advanced treatment study of coking wastewater and landfill leachate was carried out using a combined process based on hydrodynamic cavitation（HC）.The technical route of coagulation-HC/Fenton advanced treatment of coking wastewater and the technical route of HC/K₂FeO₄-secondary coagulation-ammonium magnesium phosphate precipitation method（MAP）to treat landfill leachate were proposed.The main research conclusions include the following aspects:（1）Experimental exploration of coagulation-HC/Fenton advanced treatment of coking wastewater.Taking COD as the main test index,the coking wastewater biochemical effluent was pretreated by coagulation method,and then was oxidized by Fenton alone,HC alone and HC/Fenton alone.The results show that:（1）The best coagulant was ferric chloride.When the dosage was 800 mg/L,the removal effect of COD was the best,and the removal rate is 71.49%;（2）For Fenton oxidation alone,the molar ratio of H₂O₂:Fe²⁺was 4:1,the amount of H₂O₂ was50 m M/L,and reaction time was 80 min,the COD removal rate was 62.41%;（3）For HC/Fenton oxidation,H₂O₂ dosage 50 M/L,and the COD removal rate was 95%in 40 min.The research found the reaction rate of the HC/Fenton process was 3 times that of the single Fenton process.（4）Coagulation-HC/Fenton was used for advanced treatment of coking wastewater.The COD removal rate of 98.51%,and the residual COD of tail water was 3.4 mg/L.The treatment effect was good.The treatment process did not require to adjust p H,and the effluent could be discharged directly.（2）HC/K₂FeO₄ oxidation-secondary coagulation-MAP treatment of landfill leachate raw water experimental study,the main test indicators were landfill leachate COD,UV254,BOD₅,TOC,NH₃-N and wastewater biodegradability.The results shown that:（1）The optimum reaction conditions for HC/K₂FeO₄ were p H 4,K₂FeO₄ dosage of 1.5 g/L,and HC reaction for70 min.The removal rates of COD,UV254,TOC and BOD₅ were 51.9%,69.96%,38.53%and18.84%,respectively.After HC/K₂FeO₄ treatment,the BOD₅/COD value was 0.61,compared with the raw water,the improvement rate reached 69.4%,and the HC effluent reached the standard of complete biodegradability;（2）The best coagulant in the secondary coagulation was PFS.The coagulation conditions were p H=7,the dosage of PFS was 1.2 g/L,rapid stirring for2 min,slow stirring for 30 min,and precipitation time 30 min.The removal rates of COD,TOC,UV254 and BOD₅ were 50.08%,42.93%,44.46%and 44.64%,respectively.The residual amounts of COD and BOD₅ were 915.4 mg/L and 620 mg/L,respectively,the BOD₅/COD after treatment was 0.677,and the biodegradability of the effluent was improved by 86.11%compared with the raw water;（3）The best process for MAP was:add magnesium salt and orthophosphate at the same time and stir to dissolve,then adjusted p H.The reaction conditions were p H=9,n(Mg²⁺):n（NH₄⁺）:n(PO₄^3-)=1.1:1:1.1,reaction time was 20 min,and the removal rate of NH₃-N was 98.41%.The residual amount of NH₃-N was 48.74 mg/L,which meets the wastewater discharge standard（<50 mg/L）;（4）Using the mixed process of HC/K₂FeO₄-secondary coagulation-MAP to treat landfill leachate,the total removal rates of COD,UV254,TOC,BOD₅ and NH₃-N were:77.19%,83.9%,65.92%,61.59%and 98.63%,respectively.