Study On Cavitation Coupled With Heterogeneous Fenton Process And Acidification Decolorization Of Azo Dyes And Enhance Sludge Dewaterability

The treatment and disposal of textile effluents and excess sludge have become a serious problem,many studies are now focused on advanced oxidation processes(AOPs).Researches confirmed that the combination of HC and other treatment is very energy efficient and cost effective as compared to individual technique to treat the wastewater and sludge.The application of the combination of hydrodynamic cavitation(HC)and the heterogeneous Fenton process(HF,ZVI/H2O2)for the decolorization of azo dye Orange G(OG)has been demonstrated.The effects of operation conditions such as the inlet fluid pressure,initial concentration of OG,H2O2 and zero valent iron(ZVI),the fixed position of ZVI,and medium pH on decolorization efficiency were studied.The results revealed that the acidic conditions are preferred for OG decolorizaiton.The decolorization rate increased with increasing H2O2 and ZVI concentration and decreased with increasing OG initial concentration.Besides,the decolorization rate was strongly dependent on the fixed position of ZVI.The analysis results of degradation products using liquid chromatography-ESI-TOF mass spectrometry revealed that the degradation mechanism of OG proceeds mainly via reductive cleavage of the azo linkage due to the attack of hydroxyl radical.The present work has conclusively established that the combination of HC and HF can be more energy efficient and gives higher decolorization rate of OG as compared with HC and HF alone.A successful decolorization of Orange G was achieved by means of coupling zero valent iron(ZVI),H2O2 and ultrasound(US)under acidic pH conditions.The synergistic effect and characterization of potential roles of the factors including ZVI,tert-Butanol as radical scavenger,dissolved ferrous ions and H2O2 generated from sonication were evaluated in this sono-advanced Fenton process(SAFP)system.A clear synergy was evident in terms of decolorization rate and the TOC removal as the input of US enhanced the activity of the ZVI/H2O2 system.The results suggested that the ZVI was potential replacement for the Fe2+ ion.This remarkable activity was attributed to the capacity of Fe2+ formed and reduction of sonic-dissolved Fe2+ concentration by the formation of{Fe · Fe2+}.The modification of the condition of H2O2 addition such as the dosage and input method showed significant variations in terms of decolorization rate.This result indicated that the optimal external addition of H2O2 and input method is a limited factor of decolorization rate due to its comparatively insufficient generated by ultrasound.The hybrid treatment of ultrasound and acidification on sludge dewaterability as well as its mechanism has been investigated.Results indicated that the combined ultrasound and acidification treatment was effective for improving sludge dewaterability and moisture content decreased from 77.6%to 70.6%.Ultrasound and acidification played important roles in enhancing sludge dewatering process.Ultrasound was beneficial for sludge disintegration,but the flocs and cells in sludge break down cause surface area extended and more surface water is bound as well as capillary suction time(CST)increased.The addition of acid could reduce the negative zeta potential,increae flocs size and sludge dewaterability improving finally.Meanwhile,fluorescence analysis revealed that the fractions of polymers especially protein-like substances were the key organics related to sludge dewaterability,but not the humic acid-like and fulvic acid-like substances and the protein-like substances were effectively removed from sludge bulk after acidification treatment.Additionally,sludge dewatering performance could further improve by adding hydrogen peroxide and the moisture content decreased to 67.46%.The combination of hydrodynamic cavitation and acid treatment for improving sludge dewaterability has been investigated.The effect of combined ultrasound and acidification on sludge dewatering performance and the role of ultrasound and pH in improving sludge dewaterability were evaluated.A clear synergy was evident in terms of cake moisture and total solid contente.The results suggested that hydrodynamic cavitation was beneficial for sludge disintegration and intra-cellular organic matter such as EPS and bound water released to the medium.With acidification treatment,the protonation of negatively charged functional groups reduced the binding energy of hydrogen bonds and electrostatic interactions,which cause destabilization and flocculation of sludge particles,result in dewaterability improving finally.In HC-acid system,hydrodynamic cavitation causes floc fragile and tends to disintegrate in acid condition.