Study On Enhanced Coagulation Coupling Filtration To Remove Ndma

N-Nitrosodimethylamine(NDMA)is a kind of nitrosamine compound with extremely strong carcinogenic ability.In recent years,there have been reports in the world about the pollution of surface water by NDMA.At present,nitrosamine disinfection by-products have been detected in drinking water in Canada,the United States,the United Kingdom,Spain,Japan and China.NDMA is not only found in source water,but also in the inflow,outflow and pipe network water of the water supply system.The removal of NDMA in surface water by using PAC / PDMDAAC composite coagulant for enhanced coagulation and filtration process was studied in this paper.First,according to the literature,the enhanced coagulation coupling filterwas established under the experimental conditions.And then,on basis of verifying the running stability of the established coagulation coupling filter device,it was explored that the possibility of enhanced coagulation coupling filter to remove NDMA.Finally,several technological factors for enhanced coagulation coupling filtration to remove NDMA in surface water were preliminary explored.The main contents are as below:(1)Establishment of laboratory filtration equipment.Based on the literature and the actual production conditions of the water plants,a set of laboratory column filtration devices with a filter layer of 18 cm and filter material of a certain specification of sand(0.6～0.8 mm)or activated carbon(0.6-1 mm)were experimentally designed and built.By examining the turbidity of the settling water and the filtered water under the selected raw water conditions,the operation stability of the standard coagulation device used in the experiment,the established filter device and the enhanced coagulation coupling filter device were verified.The results showed that the established coagulation-coupling filtration device and operating conditions could be operated stably.Therefore,it laid the foundation for the follow-up research in this paper.(2)Exploration on the possibility of enhanced removal of NDMA by the enhanced coagulation coupling filtration process.In the experiment,four types of filtration methods,such as a column filter device with sand and activated carbon as the filler,filter paper,and membrane,were compared.With reference to the 2NTU standard of the residual turbidity in supernatant from some domestic water plants,the inorganic coagulant PAC was used for the coagulationfiltration treatment of campus Zixia Lake water by using inorganic-organic composite coagulant PAC / PDMDAAC.The results showed that the coagulation and sedimentation of the four filter materials mentioned above could all remove NDMA to a certain extent.However,the operation cycle of the filtration methods was: sand filtration ≈ activated carbon filtration >> filter paper and filter membrane;the NDMA removal rate and filtration efficiency of the filtration methods were exactly the opposite.Furthermore,when the columnar filtering device filters 3000 ～ 5000 m L of 2 NTU effluent,the filtering efficiency attenuation could be still stable within 20%.Therefore,it laid the foundation for the subsequent research on the enhanced removal of NDMA by enhanced coagulation coupling filtration.(3)Preliminary exploration of enhanced coagulation coupling filtration for NDMA removal process.Based on the enhanced coagulation coupling filter device and its operating process conditions established above,by using the PAC / PDMDAAC composite coagulants which had both the intrinsic viscosity of 0.34,1.53 and 2.71 d L / g for PDMDAAC,and the mass ratio of 10%,15 % and 20% for PDMDAAC to PAC in the composite coagulant,the change regulation of the NDMA content before and after the treatment of composite coagulant enhanced coagulation coupled with sand filtration and activated carbon filtration was investigated,under controlling the supernatant in about 2.0 NTU.Thus,the process of enhanced coagulation coupling filtration to remove NDMA was preliminary explored.The results showed that the enhanced coagulation coupled with filtration had a significant of enhanced removal effect on NDMA in water.The removal effect of the process was not only higher than that both using only PAC coagulation and using PAC coagulation coupled with filter,but also increased with the increase of PDMDAAC mass ratio to PAC.And especially,that the PDMDAAC sample of 1.53 d L / g and a mass ratio 20% were used in composite coagulant for enhanced coagulation coupled with charcoal filtration had the best NDMA removal rate of 39%.(4)Understanding the mechanism of enhanced coagulation coupling filtration process to remove NDMA.First,based on the basic principle of enhanced coagulation to remove suspended colloidal particles by using coagulants and composite coagulants,the turbidity removal rate and the change of NDMA removal rate were correlated,and it was found that the two had a positive correlation.Secondly,from the turbidity comparison of filtered water obtained by using supernatant with similar residual turbidity,it was found that the filtered water obtained by enhanced coagulation treatment with reduced amount of PAC in the composite coagulant,not only the turbidity,but also the removal rate of NDMA has advantages over that by using PAC only.Finally,by comparing the change of turbidity and NDMA removal rate of using the two filter materials,it was found that the turbidity removal rate of sand filtration was often better than that of activated carbon filtration,while NDMA removal rate was the opposite,when the supernatants with similar turbidity.Therefore,the mechanism of NDMA removal could be conjectured: The composite coagulant firstly enhanced both the coagulation to remove suspended particles in the water body and the removal of the NDMA adsorbed by the particles via sedimentation.Then,the filter effectiveness was also largely improved by changing the charge and polarity on the surface of the suspended particles,increasing their retention and adsorption of the particles carrying the NDMA on filter material surface to remove NDMA,once more.In particular,for the small molecule NDMA which was the part of them freely dissolved inthe water body,the capillary pores peculiar to the activated carbon particles played their unique adsorption function in removing them,partially.