Application Of Steel Slag Activated Persulfate Oxidation Technology In Coking Wastewater Treatment

Coking wastewater is a kind of typical industrial wastewater with high concentration,which is difficult to degrade and has poor biodegradability.It can usually be solved by A/O,A²/O and other process technologies,but it has the disadvantages of long hydraulic retention time,high energy consumption and difficult effluent quality to meet the standard.The stability of the pretreatment process to the biological effluent is also an aspect that must be considered in the coking wastewater treatment process,which affects the energy consumption and economy.In addition,the effluent color and COD of A/O and A²/O processes can not meet the requirements of the discharge standard of pollutants for Coking Chemical Industry（GB16171-2012）.High effluent color and cod have always been the difficulties in coking wastewater treatment.Therefore,it is imperative to seek efficient and low-cost pretreatment methods and advanced treatment methods.Persulfate advanced oxidation technology is a new high-efficiency,green and low-carbon process technology,which has received widespread attention in recent years.Compared with other methods,persulfate oxidation technology has the advantages of being soluble in water,more stable and easy to transport.Steel slag refers to the slag formed in the process of iron making.It is the main solid waste of iron and steel enterprises.Its components are mostly oxides of calcium,iron,aluminum and other elements.Steel slag has the advantages of easy water separation,reuse and low cost.Using steel slag to activate persulfate is also a way of solid waste reuse.In this paper,the treatment of coking wastewater by steel slag activated persulfate（PS）oxidation coupled with SBR process and advanced treatment of coking wastewater by steel slag activated persulfate（PMS）oxidation were studied,and the feasibility of the two treatment methods was explored,and the treatment effects under different influencing factors were investigated,which provided theoretical basis for the application of the two treatment technologies in coking wastewater treatment.In the first part,the treatment of coking wastewater by steel slag activated PS oxidation coupled with SBR process was studied,and the feasibility of pretreatment of coking wastewater by steel slag activated PS was investigated.The effects of initial p H,PS concentration,dosage of steel slag and reaction time on the pretreatment of coking wastewater by steel slag/PS system were studied,and the effect of SBR process on the pretreatment of coking wastewater by steel slag activated PS was studied,as well as the comparative analysis of organic matters before and after coking wastewater pretreatment by SBR process.In the second part,the influencing factors of advanced treatment of coking wastewater by activating PMS with steel slag were studied,and the effects of advanced treatment of coking wastewater by steel slag/PMS,steel slag/PS and steel slag/H₂O₂were compared.The steel slag materials before and after the reaction were characterized,and the changes of organic matter and toxicity of coking wastewater before and after advanced treatment were analyzed.The following conclusions are obtained:（1）The study on pretreatment of coking wastewater by steel slag activated persulfate oxidation shows that:The steel slag/PS system has a certain effect on the pretreatment of coking wastewater.In the steel slag/PS system,the phenol,COD and B/C in the effluent of coking wastewater increased first and then decreased with the increase of p H.with the increase of PS concentration,the removal rates of phenol,COD and B/C also increased first and then decreased.With the increase of steel slag dosage,the removal rates of phenol,COD and B/C increased;When the phenol concentration of coking wastewater raw water is273.01mg/l and COD is 2204.29mg/l,the pretreatment effect of coking wastewater is the best under the experimental conditions of initial p H 5,steel slag concentration 5g/L,PS concentration 14mmol/L,temperature 30℃and reaction for 5h.At this time,the removal rates of phenol and COD are 34.14%and 16.93%respectively,and the biodegradability is improved from 0.19 of raw water to 0.44;The biodegradability of wastewater treated by steel slag/PS system is improved.The results of SBR process for the effluent of steel slag/PS system show that the biodegradability of coking wastewater has been greatly improved,the COD removal rate has increased from 53.52%to 57.78%,and the removal time has been shortened from 42h to 36h;The steel slag/PS system coupled SBR process can effectively treat the biochemical effluent of coking wastewater.The results show that COD decreases from 2204.29 mg/L of raw water to 454.18 mg/L of SBR effluent,and the average removal rate is 79.40%;The comparative analysis of organic matter before and after coking wastewater pretreatment and after SBR process shows that steel slag/PS system can remove most aromatic proteins,The steel slag/PS system can remove some aromatic-like protein substances and soluble microbial metabolites in the raw water of coking wastewater.The effluent treated with steel slag/PS system for 5h can improve its biodegradability.After SBR process,most aromatic-like protein substances and soluble microbial metabolites can be removed.（2）The research on the advanced treatment of coking wastewater by steel slag activated hydrogen persulfate shows that:The steel slag/PMS system has good treatment effect on the chroma and COD of biochemical effluent of coking wastewater.In the steel slag/PMS system,with the increase of steel slag dosage,the chroma and COD removal of biochemical effluent of coking wastewater first increase and then tend to be stable;With the increase of PMS concentration,the removal of chroma and COD increased first and then tended to be stable;Too high or too low initial p H value is not conducive to wastewater treatment;The optimum conditions for the treatment of biochemical effluent from coking wastewater by steel slag activated PMS system are:5g/L steel slag,7mmol/L PMS,no adjustment of initial p H,temperature of 30℃and reaction for 3h.Under these conditions,the removal rates of chroma and cod were 82.99%and 62.89%respectively;Steel slag can activate three common oxidants H₂O₂,PS and PMS.The oxidation capacity of steel slag/H₂O₂and steel slag/PS system is significantly lower than that of steel slag/PMS system;With the increase of steel slag use times,the removal rate of COD decreases gradually;After the steel slag is used for 5 times,the removal rate of COD is 38.73%,indicating that the reusability of steel slag is good.After the biochemical effluent of coking wastewater is treated by steel slag/PMS system,the toxicity of water sample effluent becomes smaller,which indicates that the highly toxic organic substances in the biochemical effluent of coking wastewater are degraded and further transformed into low toxic and non-toxic substances;The three-dimensional fluorescence spectrum of biochemical effluent from coking wastewater shows that the steel slag/PMS system can partially remove aromatic-like protein substances,soluble microbial metabolites and humic-like acids.