SDI is high more than 5

[LuckyBoy77]

Somebody can help me, please. Yesterday, I checked SDI after cartridge filter and the value is 5.44, sorry my English is bad. My pre-treatment use Lamela Clarifier, DMI and Carbon active.

 

[ashtree]

Okay, so i would assume you are getting considerable particulate fouling of your RO plant. Is this a new plant or has it been operating a long time?

Here are some basic things you should check for a start particularly if this is an old plant that has worked well in the past.
1) Has the quality of the raw water changed recently?
2) Are all your systems such as chemical dosing, sludge withdrawals, scraper systems, back washing of filters etc working as normal, has something changed, is it being operated differently, have some settings been changed or have you changed coagulants, or pH adjustment chemicals recently.
3)Are you maintaining a suitable chlorine residual 0.1-0.3 mg/l in your DMI filter. This will ensure that iron and manganese removal is maintained.
4) Check to make sure you are not getting fine particles coming from your carbon bed, assuming that this is granular carbon and not powdered.

The cartridge filter is there primarily as a last resort protection for the RO so normally you would not expect it to be significantly loaded. Therefore it is likely that the problem is up stream. But it is also likely that your cartridge filters need to be replaced. Looking at the color of the cartridge that is being replaced may tell you a lot about what is happening in the system. For example if they are a rusty red color it will likely be particulate iron causing you the problem. Manganese could be dark brown to black, bio-fouling could be red to black. Carry over of carbon particles will be black but the filter will be powdery and speckled when dried out.

Hopefully in looking at these things you will see what the problems may be and you will be able to solve it.

But if you have looked at the items above and this has not solved your problem then here are a couple of questions that you are going to have to answer to help us help you.
1) Have you ever done SDI tests before and what is the normal result.
2) Is the water from surface source such as a river or dam? What is the raw water quality in terms of iron , manganese, turbidity, conductivity, pH, etc. Has this changed recently.
3) What are all the treatment processes in the plant and what sort of chemicals are you using for coagulation, pH adjustment, oxidation etc. A sketch or a process flow diagram would be good if you have one.
4) You say the SDI is 5.4. What are some of the other parameters such as turbidity before the cartridge filters? Has this changed.
5) What is your raw water , and permeate flow. Have these changed?


Regards
Ashtree
"Any water can be made potable if you filter it through enough money"

 

[bimr]

Have your equipment supplier evaluate the pretreatment system.