Sono-advanced Fenton-like Degradation Of Aromatic Amines In Textile Dyeing Sludge:Mechanisms And Toxicity Evaluation

Due to the complexity of dyeing and finishing processes,large amount of dyes and auxiliaries added therein are converted into hazardous organics in the sewage treatment processes,and these organics are finally transferred into textile dyeing sludge,which strongly restrain the disposal of textile dyeing sludge.As a class of typical persistent organic pollutants,Aromatic amines?AAs?are continuously detected in textile dyeing sludge.Considering the outstanding capacity of pollutant reduction from the source,advanced oxidation process?AOP?which was integrated by ultrasound?US?with a Fenton-like?zero-valent iron/EDTA/air,ZEA?system,was proposed for the removal of the refractory and carcinogenic aromatic amines?AAs?in textile dyeing sludge.Also,the detoxification effects of the integrated AOP on textile dyeing sludge were evaluated to assess the appropriateness of industrial sludge's agricultural use.The scope of the present study comprised of the following:?1?investigation of several significant experimental parameters on AA degradation in different systems;?2?comparison among different systems on the degradation of AAs and the revelation of the stimulative role of ultrasound therein;?3?exploration of the role of sludge iron functions in the EDTA/air system;?4?identification of the dominant ROS in the US/ZEA system;?5?verification of the effects of different treatments on the physico-chemical properties of textile dyeing sludge and the toxicity towards plants and aquatic organisms as well as the relationship between one another to study the detoxification mechanism of US/ZEA.Studies have shown that US density,dosages of EDTA and ZVI,and initial pH have significant effects on the removal of AAs from sludge.The optimum reaction parameters were:US density of 1.08 W/cm³,ZVI dosage of 15 g/L,EDTA dosage of1.0 mM and initial pH=8.60.Under the same initial conditions,the removal efficiencies of AAs were in an order of US/ZEA?83.88%?>ZEA?72.27%?>US?51.03%?within60 min and US/ZEA?92.40%?>ZEA?72.88%?>US?51.79%?within 90 min.Analyses of energy dispersive X-ray fluorescence spectrometer?XRF?and X-ray photoelectron spectroscopy?XPS?demonstrated that there is a large amount of iron oxide in the sludge,which would also form a heterogeneous catalytic reaction system with EDTA/Air to impose degradation effect on AAs.In the US/ZEA system,the contribution rates of Fe?IV?,O2.^-and·OH to AAs were 33.84%,25.36%and 19.44%,respectively.The synergistic effects of US on the ZEA system were as follows:?1?US can continuously activate the ZVI surface to maintain its reactivity;?2?the cavitation effect can produce·OH,promoting the degradation of AAs;?3?ultrasonic disintegration effect can release AAs in the cavity into the liquid phase to react with the ROS,and besides,?4?iron oxides in the sludge were also released to participate in the aquatic iron cycle,thereby accelerating the formation of ROS.Among the three treatments,US caused the least change in the physicochemical properties of the sludge,but the biodegradability of the sludge was also reduced to the weakest.The ZEA system can effectively detoxify the sludge,but the excessive amount of EDTA would also have a negative impact on the fertility of the sludge.However,the integration of US and ZEA could avoid this situation,as US promoted the degradation of EDTA and POPs,thus causing the least inhibition or even a noticeable stimulation of plant growth when the sludge dosage was 7.5 t_dw/ha.Aquatic organism toxicity tests further confirmed that US/ZEA treatment realized the most significant toxicity reduction,leading to the lowest fatality rates.This study could be instructive in providing guidance for industrial sludge management considering its detoxification and resource utilization.