Fully automatic online SDI instrument

Fully automatic online SDI instrumentHow is it calculated?
Simple SDI can automatically calculate the SDI value of a water sample based on the attenuation of permeate flow rate when it passes through a new 0.45 μ m filtration membrane in the SDI instrument within 15 minutes. In order to ensure the measurement accuracy of water sample permeation flow rate, the Simple SDI instrument maintains a constant inlet pressure of 30psi.
Measure the flow rate during the collection of 500mL water samples at the beginning of the experiment and for the next 5, 10, and 15 minutes. The SDI value (percentage attenuation per minute) indicates the degree of membrane blockage that may be caused by the particle and axillary material content in the influent. The American Society for Testing and Materials (ASTM) D4189-95 specifies that a time interval of 15 minutes is required for accurate and standardized SDI value testing. The SDI values of 5 minutes and 10 minutes are only estimates of the SDI value of 15 minutes (SDI15).
In addition to calculating the SDI value for 15 minutes, the attenuation of water sample permeation flow rate can also be determined by converting the SDI value into another indicator parameter: fouling factor (PF value), which provides a reference for determining the degree of fouling of the RO membrane. The PF value percentage is relatively high, and the RO membrane may be blocked by particles at a faster rate. The PF value is between 1% and *, which means that the membrane component will be clogged.

determinationFully automatic online SDI instrumentThe steps are as follows:
1. Connect the SDI analyzer to the sampling point (no filter membrane is installed inside the analyzer at this time).
2. Open the valve on the measuring instrument and rinse it for a few minutes.
3. Close the valve on the measuring instrument, and then use blunt tipped tweezers to place the 0.45 µ m filter membrane into the filter membrane fixture.
4. Confirm that the O-ring is intact, accurately place the O-ring on the filter membrane, then cover the upper half of the filter membrane fixture and fix it with bolts.
5. Slightly open the valve and slowly loosen 1-2 butterfly bolts while the water flows to remove air from the filter membrane.
On the basis of ensuring that all the air has been exhausted and the water flow is continuous, tighten the butterfly bolt again.
7. Open the valve and adjust the pressure regulator until the pressure remains at 30psi.
8. Use a suitable container to collect water samples, and start recording with a timer as soon as the water sample enters the container. The time required to collect 100ml of water sample is T0 (seconds).
After 15 minutes of water sample flow, collect the water sample again in the container and record the time taken to collect the water sample, denoted as T15 (seconds).
10. Close the sampling inlet ball valve, loosen the butterfly bolt of the microporous membrane filtration container, and remove the filter membrane for storage (as a sample for physical and chemical testing). Wipe dry the microporous filter and the microporous membrane support plate.

So what is a manually measured SDI instrument?
The manual SDI pollution index measuring instrument consists of an inlet pipe, a pressure regulating valve, a pressure gauge, and a membrane replacement filter. When measuring the SDI value, only a stopwatch and a 500ml measuring cylinder are needed for testing. The manual SDI pollution index tester can be installed on site and stored in the toolbox after on-site measurement and testing, or it can be directly fixed at the sample water pipeline with a fixture. After testing, the outlet ball valve can be closed. The manual SDI pollution index tester is small in size and light in weight, but the entire testing process requires personnel to operate it without leaving their hands, which is quite tedious. Sometimes we also refer to this SDI instrument as an online SDI measuring instrument or a portable SDI measuring instrument.

SDI measurement summary:
SDI measurement is based on the determination of blocking coefficient (PI,%). The measurement involves continuously adding a certain pressure (30PSI, equivalent to 2.1kg/cm2) of the tested water to a 0.45 µ m microporous filter membrane with a diameter of 47mm. The time T0 (seconds) required to filter 500ml of water and the time Tt (seconds) required to filter 500ml of water again after 15 minutes are recorded. The blockage coefficient PI (%) is calculated according to the following formula
PI=（1-T0/Tt）X100
SDI15=PI/15
In the formula, 15 is 15 minutes. When the pollutants in the water are high, the filtration volume can be taken as 100ml, 200ml, 300ml, etc., and the interval time can be changed to 10 minutes, 5 minutes, etc