Study On Removal Of Iron And Manganese In Groundwater By Preoxidation And Ultrafiltration Combined Process

As an important source of drinking water in China,groundwater with high concentration of iron and manganese was widely distributed due to geological reasons.With the improvement of drinking water quality standards,traditional iron and manganese removal technology of groundwater could not achieve the water quality requirement.The ultrafiltration technology,based on the advantages such as no need to add drugs,stable water output and effective retention,has become an emerging technology in the area of removing iron and manganese in groundwater in recent years.Due to the fact that single ultrafiltration process could not achieve the retention of ferrous and manganese ions,the combined process of preoxidation and ultrafiltration was generally applied to groundwater.However,the effect of simultaneous oxidation of Fe2+ and Mn2+ in water could not be achieved during the operation of preoxidization-ultrafiltration combined process,and serious membrane fouling was caused by generation of oxides,which hindering the stable operation of combined process.In this thesis,the aeration oxidation,chlorine dioxide agents oxidation(ClO2)and contact oxidation(manganese sand filter)were selected to compare the ferrous and manganese ions removal efficiency and turbidity changes focusing on the simultaneous oxidation of ferrous and manganese ions and membrane fouling resistance.Based on the of different peroxidation,the selected aeration-manganese sand filter-ultrafiltration combined processes was further study in condition of continuous running.Through the effect of Fe2+ and Mn2+ removal,the turbidity interception and the redox potential change of combined process,the effect of manganese sand active coated film on increasing redox potential was found.the synergistic effects on removal of Fe2+ and Mn2+ and membrane fouling resistance were reveale by characterizing manganese sand active coated film and membrane foulants.The main research contents and conclusions were as follows:(1)the aeration oxidation,chlorine dioxide agents oxidation(ClO2)and contact oxidation(manganese sand filter)were selected to comparing the removal effect of Fe2+ and Mn2+ and turbidity changes in water.It was found that the aeration and chlorine dioxide had a better oxidation effect on Fe2+,and manganese sand filter had a better oxidation effect on Mn2+.Specifically,as the aeration rate was 1 L min-1 and more,the Fe2+ removal ratio was over 95%,but the Mn2+ removal ratio was less than 10%;The removal ratio of Fe2+ and Mn2+ could reach 94.3%and 27.05%in ClO2 oxidation experiment,respectively;The removal effect of manganese sand filter was tend to be stable within 90 min,the removal ratio of Fe2+ reached 81.3%,and 62.5%for Mn2+.In terms of turbidity,the aeration oxidation was shown significant fluctuations.As the aeration rate was 3 L min-1,the turbidity was reach 13-14 NTU;The overall fluctuation of turbidity of chlorine oxidation was within the range of 0.20±0.05 NTU;The turbidity of manganese sand filter oxidation was high at the initial stage,with a decreasing to 1 NTU over 60 minutes.(2)In order to achieve simultaneous oxidation and simultaneous removal of Fe2+ and Mn2+,the technologies with different oxidation effects of Fe2+ and Mn2+were combined.Researches on aeration-manganese sand filter-ultrafiltration combined process and ClO2-manganese sand filter-ultrafiltration combined process were indicated that,the aeration-manganese sand filter-ultrafiltration has better simultaneous removal effect of iron and manganese,but the Mn2+ removal effect of ClO2-manganese sand filter-ultrafiltration was limited.In the aeration-manganese sand filter-ultrafiltration combined process,Fe2+ was not detected in the effluent after membrane module,and the Mn2+ concentration was less than 0.1 mg L-1;In the ClO2-manganese sand filter-ultrafiltration combined process,the removal ratio of Fe2+in the effluent after membrane module can reach 99%,but removal ratio of Mn2+ was between 25%and 45%,which unable to meet quality standardand.(3)The integration test of Aeration-Manganes sand filter-Ultrafiltration(AMU)combined process was carried out to study the effect of membrane fouling resistance during continuous operation.It showed that Fe2+ removal mainly occurs in the aeration section,and Mn2+ removal in manganese sand filter,and the manganese sand filter can significantly increase the redox potential in water.To explore the oxidation principle of manganese sand filter,the physical morphology and chemical composition of manganese sand were further investigated.The image of SEM showed the existence of needle crystals and active coated film on manganese sand.The upper layer of manganese sand mainly formates iron active coated film,which contains almost no manganese atoms.The lower layer of manganese sand mainly formates manganese active coated film,which had a higher manganese atoms composition and little iron atoms.The morphological features and composition of membrane foulants were characterized,which shown that the compositon of it was same to manganese sand coated film.Because of the long-term hydraulic retention,preoxidation process could compeletely oxide Fe2+ and Mn2+ into crystals and form manganese sand active coated film.The membrane foulants eventually caused little blockage,which means effectively reduction of the membrane fouling.(4)The integrated process of AMU was applied to Tiehe Water Treatment Plant,Xinjian County,Nanchang City,Jiangxi Province.During the commissioning process,the water samples including raw water,effluent after aeration,manganese sand filter and membrane module were collected,and the water quality including Fe2+concentration,Mn2+ concentration,oxidation-reduction potential,pH value and turbidity were measured.The results showed that the water quality was stable over 40 days,and Fe2+ and Mn2+ were effectively removed with the continuously increasing of redox potential in the water.In this study,the simultaneous removal of Fetu and Mn2+ and membrane fouling resistance were achieved by applying the selected AMU combined process,and finally it was successful to apply the combined process to practical engineering.Overall,this study provides theoretical basis and engineering experience on the promotion of AMU combined process.