TiO2-UV batch for UF fractionation

The result of my experiment employing TiO2-UV was not satisfying. In terms of flux, TiO2-UV membrane showed severe decline after 30, 60, and around 90 minutes. Not only that, the rejection of membrane coated by TiO2 under UV exposure was lower than naked membrane. This probably due to smaller molecule as a result of the breaking caused by photocatalysis process. After certain minutes, it is possible that TiO2-UV react with the HA, braking bonds within HA molecules, the molecules become smaller, thus it will penetrate the pore of TiO2-UV, so the DOC will be much higher than naked membrane. How about flux? my logic says if the rejection is lower, so the flux should be better as flux and rejection usually work on the opposite way. If the flux better, usually rejection worse, vice versa.

What had happened with my experiment was the flux of TiO2-UV membrane of 1, 15 and 50 kD, showed more decline than naked membrane, their steady flux even lower than naked membrane, not only that, the accumulated permeate produced by TiO2-UV membrane gave lower volumn as well compare to naked membrane. Wow!!! My hypothesis would be, after certain minutes of operation, bigger molecule of HA will attach on additional surface of TiO2 attached on the surface membrane. Sort of double deposition on the surface of the membrane. This will of course worsen the flux, thus automatically will lessen the permeate volumn. On the other hand, the smaller HA molecules as a result of bond breaking by photocatalysis process will easily pass through the membrane, especially there was a result that TiO2 would increase affinity of membrane surface. This will of course give smaller molecules of HA bigger chance to pass through.

At this step, I want to confirm about the rejection. Why the rejection of TiO2-UV is worse than naked membrane. Is it really because HA molecules broken by TiO2-UV? That is why I will do confirmation experiment. What I am going to do is, I make HA first, then I split up to 2, one for TiO2-UV batch, one for control. I will set up TiO2-UV batch, put HA the same concentration I applied for previous experiment, then I put TiO2 in suspension inside the solution, UV exposure, I will run for approximately 1 hour for the first try. Measure the DOC before and after the batch operation. The filtrate will be passed through 1 kD naked membrane.

In my dream, I assume after TiO2-UV batch, probably DOC 7 ppm (22% removal). Then after the membrane, probably around 1.5 ppm (78%). If the control after the membrane showed 1 ppm, means the particle >1 kD was 89%, then the conclusion will be for control particle < 1 kD is 11% while for TiO2-UV particle <1kD is 17%. So, TiO2-UV indeed decrease NOM particle to < 1 kD as much as 6%. The same analogue would apply for 5 and 15 kD, of course there will some adjustment by susbtrating the result with 1 kD result. What I would like to know is the procedure for TiO2-UV batch. I have read several papers, so I have to set up the batch first.

Setting up TiO2-UV Batch
Humic acid was obtained from Aldrich. The photocatalyst was titanium dioxide powder, P25 Degussa. The pyrex photoreactor used in batch experiments. TiO2 in aqueous solution was kept in suspension in the reaction vessel with a magnetic stirrer to ensure uniform distribution of photocatalysis. The reaction vessel was also jacketed with water for cooling purposes and to control the solution temperature (20oC). The UV lamp was placed at the inner periphery of the quartz glass tube. UV mercury lamp used was Philips 254 nm, TUV 8W/G8 T5.

A solution of 9 ppm humic acid concentration was used for all batch experiments, because it is a representative level of organic presence in water surface in Taiwan, and it also allows appropriate analysis. All humic acid for this experiment were screened by 0.45 microgram membrane filter (Whatman, cellulose acetate). 0.1 mg/8 ml equals to 12.5 mg/L, this amount was equal with the concentration coated on the surface of the membrane. 12.5 mg/L (0.125%) of TiO2 was used as photocatalyst and suspended by stirring in 1 L of humic acid solution. The solution was aerated by an air pump and the constant air flow rate. The pH is measured for humic acid solution, adjusted to 7 by adding sodium hydroxide or sulfuric acid. The illumination started after the addition of TiO2. Samples were collected after 1 hour, and screened with 0.2 micro membrane to filter TiO2, and then measured for Dissolved Organic Carbon (DOC) by TOC analyzer.

UF Fractionation
The experimental study will be performed in a lab scale. The apparatus consists of ceramic membrane produced by TAMI industries. Commercial humic acid (Aldrich) was employed for the experiments. The purpose is to know the apparent molecular weight distribution of humic acid. The ultrafiltration used for fractionation are 1 kD, 5 kD, 15 kD, 50 kD, optionally 100 kD.

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