Research On Membrane Fouling And Fouling Control During Ultrafiltration Of BAF Process Effluent

Membrane technology has many advantages in the fields of urban water supply and sewage treatment, in order to increase service life of membrane module and lower the cost, researching on the process of membrane fouling and control methods is of great significance. Based on the project of Pinggu reclaimed wastewater treatment plant（Beijing Origin Water Technology Co., Ltd.）, this thesis investigated the membrane fouling mechanism and membrane fouling control during ultrafiltration of BAF process effluent.The rejections of DOC, UV₂₅₄ and COD_Crin BAF process effluent after ultrafiltration werenegligible, only about 5%. Howerver, the removal effects on turbidity and particulate matterswere remarkable. The turbidity value of treated water was less than 0.2NTU and the removal efficiency of particulate mattersreached up to 95%. During ultrafiltration, the flux decline and transmembrane pressure（TMP） rise were observed. Scanning electron microscope（SEM） was used to analyze the membranes fouled by BAF process effluent. The images showed that BAF process effluent contaminants deposited on the surface of UF membrane and formed a thick cake layer.Dissolved organic matter（Ef OM）was isolated into four kinds components as follows: hydrophobic acids（HOA）, hydrophobic bases（HOB）, transphilic neutrals and acids（TPI）, and hydrophilics（HPI）. Among different fractions of EfOM, the order of the fouling potential was consistentlyHPI>HOB>HOA>TPI. Results also showed that compared with other fractions, HPI and HOB presented much more irreversible fouling. The UF membrane flux decline became more serious with increasing transmembrane pressure, when transmembrane pressure exceeded 70 kPa. Compared with neutral conditions, the extent and rate of flux decline was greatest at pH 4.5 and slightest at pH 10.5, which indicated the inorganic matters were not the major pollutants. In the presence of Ca2 +, the proportion of irreversible fouling was lower than which in the absence of Ca2 +. Moreover, the Molecular Weight Cut Off（MWCO） of UF membrane played an important role in ultrafiltration. The membrane fouling seemed more severe when the MWCO of UF membrane was low（ 10kDa） than high（100 kDa）.In order to control the membrane fouling, three feasible pretreatment methods were selected: oxidation, adsorption and coagulation pretreatment. KMnO4 was used as oxidant in this study, the results showed that it was ineffective on membrane flux decline and the proportion of irreversible fouling.However, pre-adsorption of powdered activated carbon（PAC） could remove DOC and UV254 efficiently, and the removal rates of organic pollutants, such as fulvic acids, humic substances and soluble microbial products, were achieved 40%-60%.Using Aluminium chlorohydrate（PACl） as coagulant could effectively improve the ultrafiltration performance and reduce the proportion of irreversible fouling. Among these three chemicals, the order of membrane fouling control potential was consistently PACl>PAC>KMnO₄.