The Selection Of Oxidation Techniques On Pre-treatment And Advanced Treatment Of Coking Wastewater

Coking wastewater as the high toxic,refractory and highly concentrated industrial organic wastewater,showed up the properties of complicated components,inbalanced nutrition,nonbiodegradation,difficult for anaerobic degradation,high cost in advanced treatment.Biological treatment regarded as the core unit in the whole treatment process faced a lot of limitations like toxicity inhibition,long hydraulic rentetion time(HRT),high energy consumption and non-compliance achieving the emission standard.The combination between the stability of pre-treatment on biological process and the efficiency of advanced treatment on tailed wastewater,influencing the efficiency and economy,is the optimized direction which must be considered in coking wastewater treatment process.This research took steel plant wastewater in Shaoguan,Guangdong province for experimental object.Sodium hypochlorite,ozone and pulsed corona discharge designed by our team were chosen for the pre-treatment technology in order to increase the biodedradability,relieve toxicity restrain,aimed at improving the treatability.The verification experiments were carried out by sequential biological process with the most efficient and economic technology.On the basis of high-cost of current advanced treatment,ozonation and pulsed corona discharge were investigated,mainly concentrated on the removal of TOC,color and UV254 to achieve the target of emission or recycling.The results showed that pulsed corona discharge had the advantages over other oxidation methods both on pre-treatment and advanced treatment.The dominating influencing factors were pulse repetition frequency and delivered energy.Lower frequency,more delivered energy,the higher oxidation efficiency,indicating the resident ozone continue playing the role of oxidants.As to pre-treament,biodegradability can be dramatically increased.After second stage oxidation combined PCD with lime,COD can decrease from 3503 mg/L to 2108 mg/L with almost no existence of reduced substances.Then the biological treatment were conducted to verify the improvement of treatability,it showed the biological effluent can achieve the emission standards after pre-oxidation.As respect to the advanced treatment of biological treated coking wastewater from the plant,the results suggested that PCD and PCD combined with lime can obviously decrease TOC,color and UV254.During this treatment,initial p H and additional hydrogen peroxide had no influence on the oxidation.Second stage oxidation can decrease TOC,color and UV254 to 3.73 mg/L,25 HU and 0.675 cm-1,respectively.In addition,the analysis of three-dimensional fluroscence spectrum and GC-MS still indicated the decreasing components of major organic compounds except relatively slower degradation of PAHs,which demonstrated the residual TOC.During the experiment of adding lime,it mainly due to the formation of insoluble calcium salt like CaCO3 or CaC2O4 to accelerate the process of oxidation,as well as the reutilization of lime after calcination.The research confirmed the high efficiency and economical efficiency of pulsed corona discharge on treating real coking wastewater.In conclusion,the improvement of treatability for coking wastewater is due to the debasement on toxic compounds like phenol,sulfide,cyanide and thiocyanide,releasing of ammonia and increase on biodegradability,which can alleviate the treatment load for biological processes and reduce hydraulic retention time,achieving the emission standards.As for the advanced treatment on existing projects,pulsed corona discharge can reach the purpose for emission with low energy consumption.Combing PCD with lime can play the role of decreasing cost and increasing efficiency,which can lay the foundation of large-scale application for pulsed corona discharge.