Treatment Of Coking Wastewater By Ozone Combined With Fenton Process

Coking wastewater is a typical toxic and refractory wastewater with high concentrations of COD,ammonia nitrogen,phenol and cyanide,which poses a serious threat to the ecological environment.Due to the complexity of the composition of coking wastewater and the cost,the existing treatment process cannot effectively reduce the COD and cyanide concentration of the coking wastewater to make it meet the discharge standards.In order to reduce cyanide and COD in coking wastewater economically and effectively,ozone and Fenton process were used to treat coking wastewaterCOD and cyanide in coking wastewater were treated by ozone combined with two-stage Fenton process,and the influence of factors such as p H,ozone concentration,Fe²⁺concentration,H₂O₂ dosage and temperature at different stages was investigated.The optimized process conditions were:the reaction temperature 30?,p H 3,ozone 1000 mg/L,2000 mg/L Fe SO₄·7H₂O and 640 mg/L H₂O₂ in the first-stage Fenton process,500 mg/L Fe SO₄·7H₂O and 480 mg/L H₂O₂ in the second-stage Fenton reaction process.After p H was adjusted to 7.5,PAC and PAM were added for precipitation and flocculation.The final COD removal rate of the effluent was 71%,the total cyanide concentration of the effluent was 1.11 mg/L,and the easily liberatable cyanide concentration was 0.37 mg/L.Aiming at the problem of cyanide concentration exceeding the standard,Cu SO₄·5H₂O was used to replace Fe SO₄·7H₂O for Fenton reaction,and the concentrations of total cyanide and easily liberatable cyanide of the final effluent were reduced to 0.09 and 0.07 mg/L,respectively.Aiming at the problem of COD concentration exceeding the standard,the final effluent was irradiated with gamma irradiation.When the radiation absorbed dose was 25 k Gy,COD was reduced to 40 mg/L.Atomic absorption spectrophotometer and atomic fluorescence spectrometry were used to detect the concentration of heavy metal ions in coking wastewater.After treatment,the concentrations of Cu,As,Hg,Se and Pb in coking wastewater were lower than 0.05mg/L,and Mn and Fe concentrations also decreased.The change of organic matter in coking wastewater during the reaction process was studied by the analysis of UV spectrum and gas chromatography/mass spectrometry(GC/MS).It was found that after ozone treatment,quinoline,indole,pyridine,phenol and other substances in coking wastewater were greatly reduced.After Fenton reaction,the polycyclic aromatic hydrocarbons in coking wastewater were reduced,and finally,some refractory substances such as alkanes,aldehydes and small molecular acids remained in the effluent.