| Urban sewage is an important potential water resources.As the change of life style of urban residents, the polysaccharide content in the urban sewage increase and caused the complex variability of membrane fouling behavior in the process of urban wastewater treatment technology. This study selected sodium alginate(SA) as a typical representative polysaccharide foulant, and the different p H, cation ions and organic matter(humic acid and bovine serum albumin were choose as humus and protein substances, respectively) as the research environment, at the same time, the different hydrophilic/hydrophobic poly(vinylidene fluoride)(PVDF) membrane and different membrane materials including cellulose acetate(CA)/poly(ether sulfone)(PES)/poly(vinylidene fluoride)(PVDF) were chosed as the experimental membrane.The XDLVO theory was used to analyse the fouling behavior of SA under different solution conditions. The fouling filtration experiment and the mathematical model of membrane fouling were used to analyse fouling mechanism of SA under different environment. This experiment also investgated the effect of hydrophilic/hydrophobic property of ultrafiltration membrane and membrane materials on the SA fouling behavior, which provided theoretical research basis for improving the quality of the polysaccharide wastewater treatment and reducing the operation cost and so on. The results showed that:1. Zeta potential of SA decreased from-9.72 m V to-21.4 m V when p H increased from 4 to 11. Zeta potential of SA increased from-15.43 m V to-7.61 m V and-7.86 m V when the presence of Ca2+ and Na+, respectively, which meaned the stability of SA decreased. The particle size of SA increased obviously at the presence of Ca2+,(increased from 138.4nm to 138.4 nm), which showed that the SA was reunion.2. XDLVO theory analysis showed that: hydrophobic free energy decided the value of the interface adhesion free energy, the change of environmental solution affected the the polarity tension component of the SA and membrane, resulting in the change of hydrophobic free energy between SA and membrane. The improve of hydrophilization of ultrafiltration membrane interface, increase of solution p H, the introduction of coexisting metal ions could effectively increase the polarity of the surface tension of the membrane interface and SA, increase the adhesion between membrane and foulant free energy, and reduce membrane pollution tendency of SA. In the same solution condiction, adhesion free energy of hydrophilic PVDF/PVA ultrafiltration membrane was higher than that of hydrophobic PVDF membrane. The adhesion free energy of SA+HA on CA membrane was the highest in the three kinds of ultrafiltration membrane.The influence of mixing ratio of SA+BSA on the adhesion free energy was not obvious.3. The the data of membrane fouling filtration experiment showed that with the increase of p H, the membrane fouling of single SA, SA+HA and SA+BSA mixed system were reduced. The presence of Na+, SA flux attenuation curve was not obvious, the irreversible fouling index and blocking resistance decreased. Ca2+ caused the significant increase of SA flux attenuation rate and filter cake resistance. The presence of HA and BSA made the increase of SA irreversible adsorption and blocking resistance. The fouling behavior of SA on hydrophilic PVDF/PVA membrane was less than that of hydrophobic PVDF membrane no matter which solution conditions. The fouling behavior of SA+HA on CA membrane was less than that of PES and PVDF ultrafiltration membrane. The theoretical analysis results were proved by flux attenuation and mathematical model of membrane fouling and provided basic research basis for the modified ultrafiltration membrane and pretreatment.4. The theoretic prediction of membrane fouling and actual filter experiment had a good correlation, however, there was no correlation when the presence of Ca2+, which maybe result in the polarity of Ca2+. |
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