Turbidimeter Maintenance
Cleaning
Turbidmeters should be checked before running any test in the flocculator. The turbidimeters tend to become clogged and usually give highly inaccurate readings after running for over 6 hours. Due to the low flow rate through the turbidimeters flocs tend to collect in the turbidimeter vials and settle out. This means that they need to be checked before a test is run and sometimes data collected after this length of time should be assessed carefully.
Turbidimeter vials should be emptied and washed out with distilled water. There is a bottle near the tube settler pump for this purpose and distilled water can be obtained from the lab in the treatment plant. Swish for about 10 seconds and empty (note: if acid is used the water needs to be dumped down the lab sink). If there is still buildup or the glass is dirty wrap two Kim wipes around a brush until it is covered and use that to scrub the inside of the vial.
Remember to tightly seal the vials and to wipe with a Kim wipe before replacing in order to avoid fingerprints or other marks, which would cause inaccurate readings.
If the turbidimeter reads dessicant, the dessicant needs to be changed. When looking down on the turbidimeter from the top there are four silver screws, one on each corner. When these are removed the entire top of the turbidimeter including vial and display can be lifted. It is inside this compartment that the desiccants are located. The desiccants are important because they keep the compartment with the turbidimeter vials dry. A humid chamber can cause condensation on vials that will give false readings.
When this occurs bring the desiccant back to Hollister room 150 and leave it in the heating oven overnight at 100ºF. This will regenerate the desiccant and it will become active again.
How to Calibrate Turbidimeters
Turbidimeters need to be recalibrated every two months. The calibration kit is located in the AguaClara Lab in Hollister Hall. Perform the following steps to successfully calibrate turbidimeters.
1. Get the turbidity standards kit from the AguaClara lab in the basement of Hollister Hall.
2. Wipe down the standards vials with kimwipes if they have any dust on the outsides of them (the turbidimeters measure turbidity by shining a beam through the vial, so dust or dirt or scratches messes that up).
3. Turn on the power strip, and plug in the turbidimeters as necessary.
4. Turn on the first turbidimeter (pick one).
5. Remove the top of the turbidimeter (unhook the horizontal pins holding the top of the turbidimeter in place and slide the top of the turbidimeter up and out).
6. Hit the 'mode' button to start calibration.
7. When the screen displays '1000' next to 'config', slide the 1000 NTU standard vial into the top of the turbidimeter and hit the 'enter' button ( a leftward pointing arrow). Wait as the screen counts down to zero.
8. When the countdown is done, the screen will flash '10' next to 'config'. Put the 1000 NTU vial back in the standards kit and slide the 10 NTU standard vial into the turbidimeter. Hit 'enter' again and wait for the screen to count down to zero.
9. Repeat for the 0.2 NTU sample as above. Now the turbidimeter is calibrated.
10. Turn off the turbidimeter. Repeat steps 4-9 for the remaining turbidimeters.
Sampling line
A common problem that occurs is that the lines from the sampling point to the turbidimeters fill with sediment and the pump is unable to get water through them. If this happens, you should remove the clogged line, including all connections, and clean them. As this is a common problem, you may want to clean the lines before starting an experiment to increase your chances of a successful experiment. Back washing them may also help solve this problem. Some times clogs form the inlet valve for the raw water sampling line. Toggling the valve to increase and decrease pressure in the line should solve this problem.