Competition Relationship Between Polycyclic Aromatic Hydrocarbons (PAHs) And Organic Matter In Textile Dyeing Sludge By Ultrasound-fenton Treatment

Textile dyeing sludge,which is the largest amount of industrial sewage sludge,used to be categorized as a Strict Control Waste by the local environmental protection agency of Guangdong Province in China.As a sink of dyes and organic by-products,over 750 organic compounds were detected in textile dyeing sludge.Among these,attention to polycyclic aromatic hydrocarbons(PAHs)should be prioritized for their highly teratogenic,carcinogenic and mutagenic properties.Due to the complexity of components in textile dyeing sludge and the biorecalcitrance of PAHs,conventional treatments make a limited contribution to the removal of PAHs.As an emerging technology,the ultrasound(US)-Fenton process could improve the degradation efficiency of PAHs by their cavitation effect and mechanical shearing action.However,many studies mainly focused on the removal efficiency of organic pollutants.Only a few have studied the interaction between target organic contaminants and other organic matter in a solid matrix during advanced oxidation process(AOPs).Therefore,it is very necessary to characterize the SOM in textile dyeing sludge and clarify the relation between PAHs degradation and SOM fractions.In this work,the impact of organic matter on the degradation of polycyclic aromatic hydrocarbons(PAHs)in textile dyeing sludge by ultrasound-Fenton process has been studied.Elemental analysis,thermogravimetry analysis,and solid-state 13 C NMR spectra were applied to characterize different SOM before and after US-Fenton treatment.While,the degradation efficiencies of PAHs were determined at various oxidation intensities(Fenton's reagent of 20,70,and 140 mmol/L,ultrasonic densities of 0.36,0.90,and 1.80 W/cm3,and reaction time of 15,25,and 40 min).The relative importance of structural properties,content and composition of sludge organic matter(SOM)fractions for PAHs degradation were further discussed.The main finding of these studies could be summarized as follows.The SOM contents of four textile-dyeing sludge samples were 32.02,43.14,44.49 and50.64%,respectively.These values are much higher than those previously reported in soils and sediments.The higher SOM content can be attributed to the heavy use of synthetic-dyes,surfactants,and detergents in textile industry.The organic pollutants,which are generallydifficult to remove by wastewater treatment,are more likely to accumulate in sludge.The carbon functionalities are dominant by the aromatic and aliphatic carbon,which the total proportion accounted for 93.44,90.86,92.98 and 94.67% composition of the carbon functionalities,respectively.Higher polarity was observed in the case of original SOM relative to the value after US-Fenton treatment.The recalcitrant organic matter decreased significantly after treatment.In contrast,the labile fractions increased slightly.The results proved that the US-Fenton treatment could partly mineralize SOM and that increasing the oxidant doses could only result in the decomposition of recalcitrant organic matter into the labile one.16.32-31.13% of SOM had degraded after ultrasound-Fenton treatment,confirming the competitive relation between SOM and PAHs for degradation.Even though degradation was competitive,significant degradation efficiency was still obtained for PAHs by US-Fenton process.The maximum degradation efficiencies of ?16PAHs were 80.80,75.91,75.52 and84.40%.The correlation analysis comfirmed that the PAHs adsorbed onto SOM with a lower content,higher polarity,and a larger proportion of labile organic fractions were more prone to degradation.Furthermore,equimolar amounts of aromatic moieties consumed more oxidant for degradation compared to aliphatic compounds,while the latter fractions were preferentially oxidized because of their easy degradability.Moreover,as the SOM was oxidized into fractions with more lability,it further improved the biodegradability of textile dyeing sludge.Therefore,US-Fenton treatment could not only effectively degrade PAHs,but also modify SOM.This study provided important insights into the role of SOM fractions in the removal of HOCs by AOPs.