The Study In Treating Coking Wastewater By Ferrate(?)-Fenton Combined Process

The development of our social,economy,scientific and technological not only improved our living standard,but also caused serious water contamination problems.Coking wastewater is a kind of recalcitrant organic wastewater.And with high biotoxicity,teratogenicity,carcinogenicity and mutagenicity,polycyclic aromatic hydrocarbons?PAHs?are a typical class of refractory organics in coking wastewater.Due to its biotoxicity and chemical stability,PAHs can not be degraded easily in the nature,and some of them will enter the food chain to pose a threat to human health.Except the organic contaminates,there are also amount of small coal particles,which have a poor settling property and thus will cause problems for the purification of coking wastewater.In this study,phenanthrene?PHE?,which is a typical organic of PAHs,was selected to be the target pollutant.And a series of beaker experiments were conducted to investigate the performance of potassium fe rrate-Fenton combined process and provide theoretical basis for the further practical application.First use the single factor experiment to investigate the reaction between ferrate???and PHE.The results shows that ferrate???has a high efficiency in the process of PHE degradation.And in neutral environment,ferrate???showed the best oxidizability.The rising temperature had the effect to promote the reaction,but this effect was not obvious.Moreover,there was a positive correlation between the increase of ferrate???concentration and PHE degradation,and a inverse correlation between the increase of PHE concentration and PHE degradation.The study of reaction kinetics finds that the process of the reaction conforms to a pseudo first order.Based on the results of single factor experiment,an orthogonal experiment was designed to investigate the degradation of PHE by the method of ferrate???-Fenton combined process.The results shows that the optimum condition of the reaction was: pH=5,the reaction time of ferrate???and Fenton was 40 s and 15 min,respectively,and in consideration of the cost,the optimum proportion of added reagents was 3:1:6?PHE:K₂FeO₄:H₂O₂,n/n?.The influence of added Fenton's reagent?FeSO₄?dosage was also be researched.The research finds that FeSO₄ was not necessary for ferrate???-Fenton combined process.The change of TOC in the process of the reaction shows that only a small part of PHE was completely mineralized in this experiment.Ferrate???-Fenton combined process was found significantly outperformed ferrate???technology and Fenton process.In this research,the electric potential on the surface of coal particles was measured to investigate the influence of ferrate???-Fenton combined process on the flocculation of coal particles.The result shows that the surface of coal particles has a negative charge,and the electric potential approached to zero when p H decreased.With the increase of added ferrate???dosage,the absolute value of electric potential decreased firstly and increased subsequently.The research also shows that the proper addition of cation has the effect to improve the settling performance of coal particles.Moreover,the addition of H₂O₂ also can improve the flocculation of particles.Ferrate???and H₂O₂ complement each other and make the flocculation more efficient.In the end,the purification effect of coking wastewater by ferrate???-Fenton combined process was evaluated.The result shows that the optimum condition for ferrate???-Fenton combined process was: p H=5,the molar ratio of added chemical was 1:6?K₂FeO₄:H₂O₂,n/n?,reaction time of K₂FeO₄ and H₂O₂ are 40 s and 15 min respectively.Under this optimum condition,the removal rate of COD,NH₃-N and SS were 69.27,75.95 and 89.81%,respectively.Ferrate???-Fenton combined process also has the effect that decolorizing the coking wastewater.