Influence of pretreatment on AMWD (apparent molecular weight distribution) of dissolved organics in the secondary effluent and membrane structure parameter model analysis for ultrafiltration

This study analyzed the characteristics of the apparent molecular weight distribution (AMWD) of the secondary effluent organic matter and investigated the effect of various applicable pretreatment technologies for ultrafiltration (UF), including coagulation, powdered activity carbon (PAC) adsorption and O₃-PAC process, on the AMWD of effluent and the flux decline. The influence of molecular size distribution on the mean pore size and pore density of membrane was then evaluated with the model of membrane structure parameter. The results showed: (1) after different pretreatments, the AMWD of raw water changed, coagulation could effectively remove high molecular weight organics, PAC adsorption was effective in removing low molecular weight organics, due to ozonization and PAC adsorption and O₃-PAC pretreatment could remove both high molecular weight and low molecular weight organics; (2) the AMWD had great influence on membrane permeation, after different pretreatments, the AMWD of raw water changed and the variation of membrane permeation was also different; (3) the influence factors a₁and a₂ of the mean pore size and the membrane pore density of different pretreatment water samples were used as indexes which calculated through experiment and the model of membrane structure parameter. The influence of AMWD in water samples on the membrane mean pore size and pore density were then evaluated, which showed that low molecular weight organics could easily cause interior adsorption, and high molecular weight organics could easily cause membrane surface blocking.