| At present,there have several problems for the sewage treatment in China,such as high cost of process operation energy consumption and high sewage treatment,and low removal efficiency of denitrification and phosphorus.Therefore,it is necessary to apply new technologies and methods to reduce the cost and achieve the urban sewage treatment.Compared with traditional technologies,the forward osmosis(FO)with low energy consumption,and low pollution and recyclable of membrane.Therefore,the FO can be used in treatment of municipal sewage.This study will be associated with biological methods,and the TFC-ES membrane from Hydration Technology Innovations(HTI)as FO membrane materials,the sea water from Tuandao Cape in Qingdao Island as draw solution,and the sewage after pretreatment of biological methods as raw liquid.This batch experiments studied the water flux,the pollutant entrapment rate and osmosis membrane pollution of FO,and carried out experiments on the treatment of sewage by biological methods associated with FO separation process,which can provide theoretical and technical support for recycling and reusing of municipal sewage.First of all,in order to reduce the pollution degree of membrane by sewage,we pretreated the sewage by SBR reactor.We adjusted the parameters of pretreatment reaction system to achieve optimum treatment effect;Secondly,the effects of membrane orientation and cross flow velocities on the permeation membrane separation system were studied.The effects of membrane orientations results showed that,the initial water flux in PRO model is higher than in FO model,but the decrease of the water flux in the PRO mode is larger than that in the FO model;and water flux is relatively stable in FO mode,and the COD,ammonia nitrogen,TN,TP interception effect of sewage were better than in PRO mode.The effects of cross flow velocities results showed that the higher the cross flow velocity,the higher the water flux,which indicated that increasing the cross flow velocity can reduce the concentration polarization and membrane contamination;the larger cross flow velocity,the higher COD,ammonia nitrogen,TN and TP permeation capacity,and lower interception rate of the membrane,which indicated that high cross flow velocity can reduce the interception effect of contamination from sewage on membrane.Finally,contaminated membranes after cleaned were studied by water flux test,constant osmotic pressure,FTIR and SEM.The results showed that,(1)after the same cleaning type,the cleaning efficiency of FO and PRO model was 99.19% and 93.45%,respectively,and water flux almost restored to as new membrane.This indicated that the contaminated membranes in this two operating modeswere reversible and the contaminants are only loosely distributed on the surface of the membrane without being compacted,and the contaminants deposited on the membrane surface can be cleaned by simple physical method,and the water flux has a good recovery;(2)under same constant osmotic pressure,the concentration polarization changed during system operation,resulting the vicinity of the film formed a boundary layer different from the main body of raw material liquid or the draw solution.With the increasing of time,the accumulation of pollutants on membrane continued,which resulted the formation of a cake layer on the surface of membrane.The osmotic pressure of the solution increased on the side of the cake layer,resulting from the pressure decreased between two sides,which led to water flux decreased;(3)the infrared spectrum of cake layer indicated that the pollutants contained sugar and proteins.The results of SEM of membrane before and after adsorbed pollutants under two models showed that the FO membrane with less polluted and can be restored to the initial state after simple physical cleaning. |
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