| dc.description.abstract | The objectives of this study are aimed to investigate the degree and kind of membrane fouling formed from the ultrafiltration (UF) of the tertiary treatment water in an industrial park, and to evaluate the feasibility of removing membrane fouling by ozone. The material of membrane used in the experiments was polyvinylidene fluoride (PVDF), as it could resist the corrosion of ozone. In order to assess the degree and kind of membrane fouling, the first step was to investigate the water quality characteristic of the tertiary treatment water and then set up the basic characteristics of the membrane, such as the initial permeate flux, the membrane resistance, and the pore size of UF membrane. In order to offer the reference for the real factory operation, a bench-scale membrane system was performed in the experiments to evaluate the fouling removed by three kinds of different ozonation, such as influent preozonation, ozone in-line dosing and ozone backwashing.
Experimental results showed that the removal efficiency of iron, manganese and SDI was 62%, 30% and 88%, respectively, after the 5µm prefiltration and UF without ozone. From the FTIR analysis of membrane fouling, results showed that the organic functional groups were aromatic rings and a few linear chain compounds of chromophore and auxochrome in dyestuff. So the tertiary treatment water may induce the colloidal fouling and organic fouling in the UF system. Experimental results also showed that preozonation could improve the tertiary treatment water and UF permeate quality. When the time of preozonation was increased more, improvement of water quality and effect of UF were enhanced more. When the ozone gas mass flow rate was 13.99 mg/min and the time for preozonation was 4 minutes, the removal efficiency of iron in the tertiary treatment water and the UF permeate was 62% and 100%, and meanwhile, the average particle size of the former decreased from 682nm to 380nm and the latter decreased from 400nm to 280nm, and the permeate flux increased from 60% to 80% of the initial flux, respectively. However, when increasing the preozonation time more, the water quality and the effect of filter were worse.
It was observed that when injecting into influent by ozone after blocked of the membrane, the permeate flux only increased from 60% to 80% of the initial flux. But, it was observed that when injecting into influent by ozone continuously, the permeate flux could maintained to 90% of the initial flux. It is demonstrated that the effect of the former is better than the latter. It was also observed that the permeate flux still maintained to 90% of initial permeate flux about 120 minutes from the beginning by ozone backwashing. According the above investigation, ozone in-line dosing and ozone backwashing are more suitable for inhibiting the membrane fouling.
On the whole, the reason why the permeate flux could be increased within ozonation were the molecular degradation and the particle destabilization. Moreover, ozonation could produce the oxygenated functional groups and increase hydrophile of tertiary treatment water. Because PVDF material was a hydrophobic membrane, so it could reduce the hydrophobic matter absorbed on the membrane surface. Comparing the FTIR analysis of fouling without and with ozone, the removal mechanism of organic fouling with ozonation was the destruction of aromatic ring and the breaking of macromolecule organic matters. The removal mechanism of inorganic fouling was also the ozonation of organic matter. The ozonation might produce the oxygenated functional groups that might couple with cations to form complexes and increase the solubility of scaling matters. | en_US |