In this post, I would like to focus the effect of photocatalysis, in this case represented by Titanium dioxide and UV irradiation for organic particle distribution, which is natural organic matter, represented by Dissolved Organic Carbon, humical acid. I would like to know which organic particle size in responsible for fouling of TiO2-UV membrane.
Let’s review first for neat membrane without TiO2-UV. Here’s screenshot of particle distribution of my experiment based on DOC and UV254.
Below 1 kD was 27.6%, none for 1-15 kD, 44% for 15-50 kD, and 28% above 50 kD, this is for DOC based particle size distribution. As you can see, for UV254, particle size below 1 kD was lower than that of DOC based, 8.3% respectively. None for 1-15 kD, suggested that particle size ranging from 1-15 kD were -3%. 63% for 15-50 kD and the last is 31% above 50 kD, the result above 50 kD is similar with DOC based. Note that raw water was having 8.795 ppm and UV254 absorbance was 0.7692.
After TiO2-UV irradiation for 1 hour, DOC became 3.1955 ppm (63% removal) and UV254 absorbance 0.1524 (80% removal). There was difference for DOC after TiO2-UV, due to different treatment. After the batch for 1 hour, I split the sample, one is without screening by 0.45 micro membrane to filter TiO2-UV, and another with screening. DOC after 0.45 micro membrane screening was 3.1955 as presented above, while DOC without screening (turbid water) was 6.15. There was some confusion why this happens. My guess was, this showed that TiO2 particles have ability to absorb the humic acid particle, thus after screening, only 3.1955 ppm remaining on the water. Does it true? Does TiO2 really have power to absorp humic particles? Perhaps next experiment will make things clearer.
Anyway, now let us see the organic particle distribution with membrane exposed by TiO2-UV irradiation. First picture based on 3.1955 as initial DOC, while the second use 6.15 ppm DOC as initial DOC, the UV254 used was the same, because to obtain UV254, the samples must be filtered first.
The result are for UV254 based 48% below 1 kD, -43% 1-15 kD (I know the result is invalid), 58% 15-50 kD, and 36% above 50 kD. DOC based 3.1955 ppm, 82% below 1 kD, -25% 1-15 kD, 22% 15-50 kD, and 21% above 50 kD. For DOC based 6.15 ppm, 42% below 1 kD, -13% for 1-15 kD, 11% for 15-50 kD, and 59% above 50 kD. Now, I want to talk the ideal factor first.
First, since I used UV254, means that I filtered the samples, thus it must be uniform for DOC based, meaning that I must put into account the result taken by filtering the samples with 0.45 micro membrane, in this case 3.1955 ppm. Second, the fraction amount should result in 100%, and without any fraction below 0% (negative value), which means the result is not good. What I am going to do is to repeat the experiment.
Despite of the bad result, I would like to try to interpret the result, which particle size contribute fouling to TiO2-UV membrane only by seeing the graph based on UV254 and DOC 3.1955 based, let’s see if these results confirming each other.
The results from figure above were similar. Note that the difference between raw water above 15 kD and TiO2-UV water means the lost, or the removal obtained by TiO2-UV irradiation. TiO2 was suspended 2.96 gr for 3 L of humic acids solution. Although I still have so many quetions marks on my head right now, but based on DOC figure above, seems that after TiO2-UV batch, more particle size below 1 kD was formed. This means less rejection of TiO2-UV membrane for both 1 kD membrane and 15 kD membrane. However, by looking at figures above, particle size that responsible for TiO2-UV membrane fouling were between 15 kD above. Despite that during the photocatalysis process particle size above that were also removed, but still probably the remaining particles contribute a lot to the fouling.
Pictures above tell me that during the photocatalysis, there is a rejection of DOC, thus will remain a few groups of 15-50 kD and above 50 kD. This few groups should be pretty well screened by 15 kD TiO2-UV membrane. But the fact tells the opposite. The DOC removal during photocatalysis was 76%. This means only 17% of 15-50 kD plus above 50 kD that needed to be removed by 15 kD TiO2-UV membrane to give total result 76%+17% equals to 93%. But after experimentation, 15 kD TiO2-UV membrane instead gave very bad result compare to neat membrane without TiO2-UV, to only around 60% of DOC rejection. This also can means, that 60% probably due to photocatalysis while membrane did fail to screen 15-50 kD and above 50 kD organic particles. The question is why? Another assumption that maybe its because TiO2 gave higher affinity on membrane surface thus more water can pass through. Another is may be because the TiO2 portion amount immbolized on membrane surface does not a lot enough to photocatalyze all the organic particles.
However, I cannot say much about this yet. Need further confirmation.