Thursday, June 18, 2009
Author: Michael Gerdjikian
Every week I come into the lab, I do something completely new. My first week I simply ran water samples in the TOC, UV, and Spectrofluorometer. The following week I learned some of the procedures in doing a membrane autopsy. This includes cutting sections of known dimensions from fouled membranes, placing them in several prepared solutions, and sonicating them for a short while. The purpose of this is to characterize the constituents that are removed from the membrane during sonication and dissolved in the solutions. I’ve been using three different types of solutions; plain filtered water (called MilliQ), a basic solution of sodium hydroxide (pH~12), and the same basic solution with the tiny addition of sodium hypochlorite. In general, we expect there to be more removal as we move from the first to last solution. There were six membranes that I needed to characterize so there were a total or eighteen samples that I needed to test. Plus, we decided that I test how well the process works. In order to do this, I would prepare two more solutions and cut two more pieces of membrane for those. I sonicated them just as I did previously with the other samples. Then the next day, I prepared fresh solutions to put those test membranes in and sonicated them again. If the procedure worked properly, nothing should be removed from the membrane during this second sonication. That was all that I got done that Friday because that was also the day that IHE held the Special Symposium on Water/Wastewater Science and Technology for Sustainable Development in which I attended the entire event from 9:30-15:00. The following Monday, I started diluting the supernatant and preparing them for analysis. I was then able to run all of the samples, after filtering, in the spectrofluorometer and UV spectrophotometer while leaving enough of the sample to be sent for LC-OCD testing. After reviewing the results, I came to the conclusion that the process did not work the way we had hoped. The UV spectrophotometer was showing an absorbance from the test samples which shouldn’t have happened. The spectrofluorometer also showed intensity levels greater than the blank sample. This means that everything that could be removed from the membrane was not removed after just one sonication. There were also discrepancies in the trends of the F-EEMs that made me believe that the basic solution may have been contaminated. I decided to try to run some tests to see if I could find where the contamination may have been coming from. I began by simply running samples of MilliQ water under certain circumstances, such as straight from the machine or after being filtered through a syringe. All of the results should show zero intensities but that wasn’t the case. Neither I or Sergio understands why but the original blank shows zero intensity but any sample I run after that shows some level of intensity. After spending many hours testing the water under various conditions, I’m at a loss of what to do. I cannot continue to test the membrane supernatant until I figure out this problem.
On a new note, Sergio started showing me how to test the Modified Fouling Index (MFI-UF) of the different membranes at constant flux. It seems like the tricky part of this is going to be learning how to use the spreadsheets that he uses to gather all of the data. All I know is that I’m looking forward to getting off of the spectrofluorometer for a while to work on this.