| Efficient removal of dissolved manganese in groundwater is an important approach to ensure the health and safety of drinking water.In this study,a Birnessite functional layer coupled with a gravity-driven ceramic membrane(GDCM)filtration reactor was developed to investigate the water purification efficacy and water production efficiency of GDCM manganese removal from groundwater.Firstly,the long-term water treatment efficiency with 300 kDa pre-deposited manganese oxide(300 kDa-MnOx)in 105 days was investigated based on the constructed Birnessite functional layer upon the ceramic membrane surface through pre-oxidation..The results showed that the pre-deposited manganese oxide facilitated the maturation of the Birnessite functional layer and enhanced manganese removal.Moreover,the manganese removal rate would be decreasing to 75%when reducing the membrane retention molecular weight in the gravity-driven ceramic membrane reaction from 300 kDa to 15 kDa.In addition,long-term operation of the constructed Birnessite functional layer coupled with constant pressure ceramic membrane reactor was beneficial to manganese removal due to the longer hydraulic residence time caused by the higher membrane contamination resistance.In order to improve the water production efficiency of the gravity-driven ceramic membrane coupled with Birnessite functional layer,the layer with enhanced porosity was constructed by depositing newly formed manganese oxides(MnOx)attached to powdered activated carbon(PAC)on the membrane.The results presented that manganese biological removal has been enhanced due to the enriched bacteria(10~3 MPN/mL)and iron bacteria(Mn OB)(10~3 MPN/mL)on the ceramic membranes coupled with PAC-MnOx.The main manganese bacteria were identified as Hyphomicrobium based on the microbial community analysis.Besides,a functional layer on the surface of the gravity-driven ceramic membrane was generating as the periodic dosing of PAC-MnOx in start-up stage leading to the promoted autocatalytic oxidation of manganese oxides.And after 15 days of operation,the stable membrane flux remained at 41 L/(m~2·h)and the effluent manganese ion concentration was lower than 0.089 mg/L.Moreover,based on the laser scattering particle analyzer(LASP),the average particle size within the biofilm of 70.9?m was greater than that in the GDCM,which was larger than that of primary paticles(48.5?m).The difference could be attributed to the attachment of newly formed manganese oxides on the PAC carrier,which increased the functional layer porosity and enhanced the water production efficiency.Based on the characterization analysis,the structural change of the functional layer constructed on the gravity-driven ceramic membrane reactor was confirmed.X-ray photoelectron spectroscopy(XPS)results showed that Mn(III),the dominant valence in MnOx,contributed to the excellent catalytic oxidation ability of Birnessite functional layer,which was also demonstrated by Raman analysis and X-ray diffraction(XRD).The conversion of MnOx to the newly formed Birnesssite was effectively promoted by the uniform flower-like birnessite(Birnessite)structure.And the MnOx nearby the GDCM was converted to the newly formed Birnessite with the filtration time continuing.Therefore,it is promising of the developed gravity-driven ultrafiltration system combined the advantage of PAC and Birnessite to serve as an effective filtration system,which is particularly suitable for decentralized water supply sanitation facilities in small areas. |
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