The Advanced Oxidation Treatment Of Cyanide In The Coking Wastewater

Coking wastewater has many different kinds of pollutants, is complicated composition, containing a large number of refractory material, whose biodegradability is poor, at the same time, wastewater is toxic, high chromaticity, etc. In recent years, treatment technology, such as biochemical treatment, coagulation sedimentation, activated carbon adsorption and wet catalytic oxidation, etc. is widely used in the treatment of coking wastewater at home and abroad. COD, phenol and ammonia nitrogen in coking wastewater could be effective removal after treatment, however, the concentration of cyanide, which is as one of the main pollutant, remains high and can not meet the increasing requirement of water quality. Cyanide except a few stable double salts, is toxic, especially will become highly poisonous hydrocyanic acid in acid environment. Cyanide can combine with high iron cytochrome enzymes in human, to generate ferricytochrome oxidase and lose oxygen transfer function, resulting hypoxia and suffocation in the body. At presnt, there are many treatment methods of cyanide wastewater, including biological method, alkali chlorine, ozone, electrolysis, ion exchange, activated charcoal catalytic oxidation, acidic precipitation-neutralization method, etc. But the process of coking wastewater treatment engineering design involves little specialized processing unit for cyanide. In view of this, second level biochemical effluent in a coking plant was treated with three advanced oxidation treatment techniques, including chemical precipitation combining Fenton, ozone oxidation and ozone catalytic oxidation, respectively. On the basis of single factor experiment, response surface methodology was applied to optimize the total cyanide and easy release cyanide removal process conditions by adopted the reasonable design scheme, which was as follows:Firstly, chemical precipitation combining Fenton was used to remove cyanide in coking wastewater. The influence of the addition of FeSO4, H2O2and the initial pH of solution on the total cyanide and easy release cyanide removal rate was investigated, and based on this, response surface methodology was applied to optimize the total cyanide and easy release cyanide removal process conditions by adopted the reasonable design scheme. The results indicated that the addition of FeSO4and the initial pH of solution were significant model terms in this case. Regression analysis and verification results showed that optimization experiment applying response surface methodology was feasible. Under175μL/L H2O2,265mg/L FeSO4and the pH5.10concentration, nearly97.35%of the total cyanide and65.66%easy release cyanide could be removed, and at this moment the concentration of the total cyanide and easy release cyanide were0.272mg/L and0.231mg/L, which could achieve national discharge standard.Secondly, ozone oxidation was used to remove cyanide in coking wastewater. The influence of the addition of O3, reaction time and the initial pH of solution on the total cyanide and easy release cyanide removal rate was investigated, and based on this, response surface methodology was applied to optimize the total cyanide and easy release cyanide removal process conditions by adopted the reasonable design scheme. The results indicated that the addition of O3, reaction time and the initial pH of solution were significant model terms in this case. Regression analysis and verification results showed that optimization experiment applying response surface methodology was feasible. Under74mg/L O3and the pH3.0concentration, nearly72.48%of the total cyanide and65.86%easy release cyanide could be removed after42min reaction, and at this moment the concentration of the total cyanide and easy release cyanide was2.923mg/L and0.231mg/L, which could not achieve national discharge standard.Finally, ozone catalytic oxidation was used to remove cyanide in coking wastewater. The influence of the addition of O3, catalyst and the initial pH of solution on the total cyanide and easy release cyanide removal rate was investigated, and based on this, response surface methodology was applied to optimize the total cyanide and easy release cyanide removal process conditions by adopted the reasonable design scheme. The results indicated that the addition of O3, catalyst and the initial pH of solution were significant model terms in this case. Regression analysis and verification results showed that optimization experiment applying response surface methodology was feasible. Under84.35mg/L O3,120mg/L catalyst and the pH9.26concentration, nearly91.38%of the total cyanide and73.12%easy release cyanide could be removed, and at this moment the concentration of the total cyanide and easy release cyanide were0.884mg/L and0.183mg/L, which could achieve national discharge standard. In summary, chemical precipitation combining Fenton treatment of cyanide is the most effective treatment, ozone oxidation is the worst. The production rate of? OH was improved due to the use of catalyst; therefore, ozone catalytic oxidation had higher ozone utilization and stronger ability of oxidation than that in ozone oxidation process.