Enhanced Removal Of Polycyclic Aromatic Hydrocarbons From Textile Dyeing Sludge By Combing Ultrasound And Fe~0/EDTA System

As a pillar industry of national economy,textile industry has developed rapidly in recent years.In the textile industry,considerable dyes and additives are added in the production process.These additives lead to the formation of refractory intermediates during multiple wastewater treatment.The refractory intermediates include polycyclic aromatichydrocarbons?PAHs?.Due to their hydrophobic nature,PAHs remain on precipitated.Meanwhile,PAHs are highly toxic,persistent and refractory,which may pose a potential threat to the ecological system in the process of sludge disposal.In this study,based on the source of reduction strategy,an ultrasound?US?technology enhanced a zero valent iron/EDTA/Air?ZEA?system was employed to remove PAHs in textile dyeing sludge.The specific objectives of the present study were:?1?to compare removal efficiencies for 16 PAHs in textile dyeing sludge by ZEA,US/Air,and US/ZEA treatments,respectively;?2?to investigate the effects of different parameters,including ZVI and EDTA dosages,ultrasonic density and pH on removal efficiencies of PAHs;?3?to evaluate the mechanisms of US enhanced the production of reactive oxygen species?ROS?,and to explore the role of ROS in PAHs removal in the US/ZEA system.Compared with US/Air and ZEA treatments,US/ZEA treatment could be more effective for the removal of PAHs from textile dyeing sludge.The?₁₆ PAHs removal efficiencies of the three systems were US/ZEA?70.1%??29?ZEA?42.0%??29?US/Air?32.9%?at 60 min.The removal efficiency of low molecular weight PAHs was higher than that of high molecular weight PAHs in three systems.The removal of PAHs in the three systems could be well fitted by pseudo-first-order kinetic equation.EDTA concentration,ZVI dose and ultrasonic density had a great influence on PAHs removal.The results showed that EDTA of 2.0 mM,ZVI of15g/L and ultrasonic density of 1.08 w/cm³ were optimal for removing?₁₆ PAHs from textile dyeing sludge.However,unlike traditional Fenton process,the US/ZEA system could be used for PAHs removal with a wide pH range?3-6.25?.Therefore,natural conditions?initial pH=6.25?was selected for PAHs removal to avoid sludge acidification in this study.The synergy indices of all PAHs being treated by the US/ZEA system were>1.0,indicating that US had a synergistic effect on removal of 16 PAHs.Because US could:?1?promote ZVI corrosion into Fe²⁺by continuous cleaning and refreshing the ZVI surface;?2?reduce the difficulty of O₂ activation reaction,and thus promote the production of H₂O₂;?3?enhance disruption of sludge particles to release PAHs from the cavity of sludge,and facilitate the reaction between PAHs and ROS.In the US/ZEA system,PAHs could be degraded by three ROS?·OH,O₂.^-/HO₂.and Fe?IV??and be absorbed by ZVI.Under natural conditions,for the removal of?16 PAHs,the contributions of·OH,O₂.^-/HO₂.,Fe?IV?and adsorption were 13.9%,25.4%,16.0%and 14.8%,respectively.However,·OH had a strong effect on 16 PAHs removal under acidic conditions?initial pH=3.0?,and the contribution value reached 45.5%for?₁₆ PAHs removal.In addition,the iron coagulant remaining in textile dyeing sludge was an important source of Fe²⁺and Fe³⁺,promoting the spontaneous generation of ROS in the US/ZEA system.This study provides important insights into the application of a US/ZEA system to remove PAHs from textile dyeing sludge.