Investigation Of Polycyclic Aromatic Hydrocarbons (PAHs) In Textile Dyeing Wasterwater By Ultrasound-fenton Treatment

Textile dyeingwastewater,which has the characteristics of large color,high organic content,complex composition,large p H variation,large water quality change,and difficulty in biodegradation,ranks the third in the total industrial wastewater discharge in China.It's recognized as one of the most difficult to treat industrial wastewater in the environmental protection industry.Dye,containing a large amount of persistent organic pollutantss?POPs?,including polycyclic aromatic hydrocarbons?PAHs?,will increase the difficulty of the treatment of wastewater.In order to reduce the amount of organic matter in wastewater,the treatment of textile dying wastewater containing PAHs by using US-Fenton was reported in this paper.In this study,simulated wastewater containing PAHs?Nap,Ace,Phe,Flu,Pyr?was treated with US-Fenton to explore the effects of different reaction factors on the degradation of typical PAHs,such as ultrasonic power,initial p H value,H₂O₂ dosage,reaction temperature,the molar ratio of Fe²⁺and H₂O₂,to investigate the reaction kinetics of US-Fenton on PAHs.In addition,the study chose Phe with a high content of PAHs as representative,detecting the intermediate products by GC-MS to infer the reaction mechanism and degradation pathway under US-Fenton.It provides a theoretical basis for the degradation of POPs such as PAHs in textile dyeing wastewater by advanced oxidation process.Experimental results indicated that:Under the single-factor experimental conditions,the reaction temperature,the concentration of Fe²⁺and H₂O₂,the power of ultrasound and the initial p H have significant effects on the degradation of PAHs by US-Fenton.The five PAHs could be oxidized and degraded within 60 minutes,and the degradation was in accordance with the pseudo first-order dynamic equation.With the increase of temperature,Fe²⁺and H₂O₂dosage,the degradation rate and reaction rate constant of the five PAHs also increased.For experiments in which the initial p H value affected the US-Fenton system,under conditions of US=300W,H₂O₂=36 mmol/L,T=30?,H₂O₂:Fe²⁺=10:1,Nap and Ace hadthe highest degradation rate and reaction rate constant at the initial p H value of4.0,with 93.0%(0.042min^-1)and 89.3%(0.033min^-1),respectively;the degradation rate and reaction rate constant reached the maximum value of Phe,Flu,and Pyr are under the reaction conditions of pH 3.0,with 90.2%(0.035min^-1)?82.2%(0.025min^-1)and85.5%(0.025min^-1),respectively.For ultrasonic power,under conditions of H₂O₂=36mmol/L,T=30?,H₂O₂:Fe²⁺=10:1,p H=3.0,the degradation rate and reaction rate of Nap at the ultrasonic power of 500 W were the maximum,with 93.2%(0.050min^-1);the degradation rates of the four PAHs,Ace,Phe,Flu,and Pyr increased first and then decreased with the increasing ultrasonic power,and reached the highest with the ultrasonic powerof 300W,with 86.1%(0.033min^-1)?90.2%(0.035min^-1)?82.2%(0.025min^-1)and 85.5%(0.025min^-1),respectively.During US-Fenton process,the degradation products of phenanthrene were detected as 9H-Fluoren-9-one,?1,1'-Biphenyl?-2,2'-dicarboxaldehyde,4-Hydroxy-9-fluorenone,9,10-Phenanthrenedione.Under the reaction mechanism of PAHs and Fenton,the degradation pathway of Phe was obtained.The degradation pathway was mainly divided into two parts:one was the main attack on the 9,10 sites,which formed phenolic substances,and then it reacted with the trivalent iron ions producing quininesin the system or C-C single bond within 9,10 siteswas directly attacked by the hydroxyl radical,which obtained9,10-Phenanthrenedione and?1,1??-diphenyl-2,2?-dicarbaldehyde;the second major attack sitein additionto 9,10 sites,4 sites were also attacked,followed by quinine reaction and oxidation of the broken chain to achieve 4-hydroxy-9-fluorenone.The four intermediates continue to be oxidized to form simple structures such as carboxyls,phenols,and aldehydes,which are then mineralized.The degradation of Phe provides a theoretical basis for US-Fenton degradation of 16 kinds of PAHs in wastewater.