Study Of Fouling Behavior Of Dissolved Organic Matter Solution Containing Fe³⁺ On PVDF Ultrafiltration Membranes Using Atomic Force Microscopy

Ultrafiltration technology has been widely used in the wastewater reuse and reclamation, and also getting more and more attention. Sewage mainly contains polysaccharides, proteins, nucleic acids, humic acids, organic acids and other cellular components. On the basis of theoretical researches in membrane fouing in the laboratory study, the sodium alginate（SA） have been used as surrogates for polysaccharides, which has a linear structure of 1,4--?-D- mannuronic acid and α-Lguluronic acid, bovine serum albumin（BSA） instead of proteins, which contains 607 amino acid, humic acids have been used as surrogates for nucleic acids,which has an aromatic ring and an aliphatic ring, also has a carboxyl group, a hydroxyl group, a carbonyl group, quinone group, methoxy and other major functional groups in the ring.Many researches found that iron content is much more than other metal element content in the industrial waste water,and also Fe³⁺ is as the coagulant used in the treatment of industrial wastewater. Therefore, this study was aim to investigate the effect of Fe³⁺ iron content and the solution pH on the membrane fouing in the UF process.Some results showed that with the increase of pH, the dominant role of membrane fouling from ionic complexation of HA to ferric hydroxide and then to repulsion of HA, and in contrast, those pollutants could mostly wash off by Citric acid. The adhesion forces of membrane-foulant and foulant-foulant in the different solution condition were investigated by atomic force microscopy（AFM） in conjunction with self-made PVDF colloidal probe and foulant-coated colloidal probe, respectively. In order to provide a theoretical basis for the application of water in the regeneration process. The conclusions achieved were as followed:（1） Results show that when Fe coexist with bovine serum albumin, then membrane fouling showd a tendency to increase and then to mitigate, with the increase of solution pH, which may be caused by the electrostatic interaction between BSA and Fe³⁺, and to form the colloidal substances. The main conclusions achieved were as followed:（1）The results show that the addition of Fe³⁺ into the BSA solution would cause more severe fouling at pH 3. And, at the same BSA concentration, the membrane exhibited a most sharply flux decline with 20 mg/l FeCl3, and aggravated the interaction between the metal ions and BSA. And then, along with the further increasing concentration of FeCl3, this effect decreases.（2） At the same conditions of pH and FeCl3, when BSA concentration of 20 mg/l, and gradually aggravated the flux decline, membrane fouling, and the electrostatic interaction between the metal ions and BSA.（3） However, membrane fouling behavior became more severely with pH increasing, the flux decline of the membrane was highest at pH 7.Because the BSA was adsorbed by the positively charged iron precipitate layer, which can easily interacted with Fe³⁺ and ferric compounds. Therefore, BSA/iron can more easily deposited onto the surface of the membrane. It was found that the interaction between metal colloid and BSA was spontaneous and the electrostatic interactions played key role, and aggravate membrane fouling at the pH was 7.（2） After adding Fe³⁺ in the alginate solution, with the increase of pH of the solution, SA adsorption of metal iron is the main cause of membrane fouling. The specific conclusions achieved are as followed:（1）Under the same conditions of pH and SA, along with the increasing concentration of FeCl3 solution, pollution pollutants on the surface of the film gradually increased. When FeCl3 concentration is 30 mg/l, and gradually aggravated the flux decay, membrane fouling, and the electrostatic interaction between the metal ions and SA.（2）Under the same conditions of pH and Fe Cl3, When SA concentration is 30 mg/l, and gradually aggravated the flux decay, membrane fouling, and the electrostatic interaction between the metal ions and SA.（3）While at the same concentration FeCl3 and SA, but the different pH conditions, when the pH of the mixed solution was 7, the surface of membrane was polluted seriously. Causing serious pollution not only because chemistry between each other, and with the pH value increases, the physical deposition of hydroxides which also aggravate fouling have a more serious impact. However, membrane fouling behavior became more severely with pH increasing, the flux decline of the membrane was highest at pH 7.Because the Fe³⁺ was adsorbed by the SA.（3） Adding Fe³⁺ into the SA/BSA solution would cause more severe fouling at p H 3, the specific conclusions achieved are as followed:（1）At the same pH and SA/BSA concentrations, membrane fouling behavior became more severely with concentration of FeCl3 increasing, and the membrane exhibited a most sharply flux decline with 30 mg/l FeCl3.（2）Under the same conditions of pH and concentration FeCl3, the membrane exhibited a most sharply flux decline with 15 mg/l SA/BSA, Because the BSA was adsorbed by the positively charged iron precipitate layer,which can easily interacted with Fe³⁺ and ferric compounds.（3）While at the same concentration of SA/BSA and FeCl3,but different pH conditions, membrane fouling behavior became more severely with pH increasing, the flux decline of the membrane was highest at pH 9. Causing serious pollution not only because BSA and SA form soluble complexes, and with the increase of pH, wherein the physical deposition of hydroxides also aggravate fouling produced a more serious impact.