Study On The Characteristic Of DOM In A WWTP Secondary Effluent Via Multi-pretreatments And Control The Ultrafiltration Membrane Fouling

DOM?Dissolved organic matter?has been regarded as a major organic foulant resulting in UF membrane fouling in wastewater reclamation.This study investigated the characteristic of DOM in a WWTP secondary effluent in Wuhu,China.Analysis of its mechanism for membrane fouling.The effects of multi-pretreatments,including coagulation,adsorption and pre-oxidation,via adding Al₂?SO₄?₃/diatomite composite,FeCl₃,GAC and O₃ to control DOM fouling of UF membrane.Discusse the change of DOM in the secondary effluent after multi-pretreatments,thereby affecting the ultrafiltration membrane fouling.We analyzed the mechanism of contamination with ultrafiltration membrane and DOM.Main research contents and results are as follows:?1?The molecular weight of DOM in a WWTP secondary effluent was main <4000 Dalton,accounting for 50.6%.The hydrophobic acids accounting for 42.8%,the transitional hydrophilic acids accounting for 19.1% and the hydrophilic organic matters accounting for 38.1%.Which were separated by the combined XAD-4 and XAD-8 resin.These fractionations resulted in the decrease of the flux of 4000-Dalton PES membrane by 32.8%,29.9% and 18.6% and the increase of the membrane resistance by 106.6%,92.2% and 58.6%,respectively.Combining MW?molecular weight?distribution,3DEEM?3D excitation-emission matrix?fluorescence and FI-IR?Fourier transform infrared spectroscopy?analysis,the transitional hydrophilic acids were identified of protein-like substances,with the MW in the range of 4000-30000 Dalton.Hydrophilic organic matters were lipid-like substances with its MW less than 6000 Dalton.The hydrophobic acids were humic acid-like substances with MW less than 4000 Dalton,which easily caused UF membrane fouling.?2?When ultrafiltration system is running.At the pH 3^-11,the membrane flux increase with pH.Divalent ions such as Ca2+ and Mg2+ compared to monovalent Na+ and K+ cause membrane flux decrease serious,and the higher of the concentration,the decreaser of the flux.After ultrafiltration membrane has been polluted,we should clean them.Chemical cleaning,such as NaClO,HCl,NaOH compared with ultrasonic cleaning and physical backwash has more recovery of flux.?3?The membrane fluxes increased 18.1%,8.1%,5.3% and 0.1% and membrane resistances decreased 58.9%,28.9%,178% and 2.2%,when the optimal adding dosages of Al₂?SO₄?₃/diatomite composite,FeCl₃,GAC and O₃ were 400 mg L^-1,80 mg L^-1,80 mg L^-1 and 6mg L^-1,respectively.The DOM of 10000-30000 Dalton MW,mainly protein-like substances,in the secondary effluent was dramatically reduced by adding Al₂?SO₄?₃/diatomite composite,FeCl₃ and GAC,while adding Al₂?SO₄?₃/diatomite composite was available for removing humic acid-like substance simultaneously.The O₃ addition not removed,but only oxidized protein-like and humic acid-like substances of DOM into the fraction of <4000 Dalton MW.The DOM fraction of <6000Dalton in WWTP secondary effluents easily arouse The UF blocking,which was humic-like substances.?4?Four kinds of ultrafiltration pretreatment,Al₂?SO₄?₃/diatomite composite,FeCl₃,GAC and O₃,make the TOC removal rate was 60.81%,51.24%,43.51%,39.74%,UV254 removal rate accounting for 45.37%,37.21%,31.07 %,49.02%,the COD removal rate accounting for 56.89%,48.24%,40.93%,37.15%,ammonia nitrogen removal rate accounting for 51.72%,39.47%,52.97%,43.21%,All of them the removal rate of turbidity was 100%.Al₂?SO₄?₃/diatomite compared to other pretreatments was best.