pH, iron, manganese, and hydrogen sulfide concentrations should be determined in the field since these parameters are not stable.
Water samples must be tested on-site, or immediately stabilized for laboratory analysis. Sample bottles with stabilizing chemicals should be obtained from the laboratory that does the analysis. Careful sampling according to laboratory recommendations is critical to ensure accurate and reliable results. In general, the requirements will involve delivery of a refrigerated sample within 48 hours of collection. Sulfide concentrations are reported by laboratories in units of milligrams per liter (mg/l) or parts per million (ppm).
Regarding: "This week SDI becomes higher than before it's becomes more 5 last days we had heavy rain"
You said this water was from a deep well. Deep water wells should not be affected by rain.
Please see my answer about ashtree question
To be clear about your process based on what you have said so far these are the steps:
1) Raw water from a deep well.
2) Coagulant dosing and i assume some sort of mixing.
3) Sand filters
4) 20 micron cartridge
5) 5 micron cartridge
6) RO.
Is this correct? yes
The next question is how long has this plant been in operation? with new sand filters since 2013You said that the plant has previously worked okay. How long ago was that and for how long did it work okay?i need time to review our records
If the plant had previously worked okay for a long time and now it doesn't implies that something has changed.
How easy that will be to determine will depend on how good your records and testing has been over the whole period of operation.
If you have no records and no test data then it will be difficult, if you have a lot of data then it may be easy. Here are a few things to consider:
Has the raw water quality changed? i already sent water analysis 2009 and 2013
Have you changed coagulant or dosage, or injection point?No
Has filter operation changed?No Is there a longer or shorter period between back washing?We do backwash every 40hr Has the backwash rate changed?No Have you changed the media?No Have you inspected the filter media to make sure it has not been lost, its not mud balled and its clean?please see attached photo sand filter was in operation for 34hr
Have you had a change in operator in this time?yes
With regards to the photos of the cartridge filters, are the two on top that are very brown more recently replaced than those below that have significant white patches on them? these filters we changed them in the same time from two RO's
When they dry out is the residue on them powdery and easily removed or does it stay stuck on the filter?i will check next time
What do the 20 micron cartridges look like?i will send photo next time
Did you by any chance collect any of the larger chunks that can be seen on top of the filter surface? It would be particularly interesting to know what they are.
The amount of dirt on top of these filters after 34 hours is significant and bimr's posts here are relevant. Deep well water is normally clean. I regularly see RO plants with a similar process train as yours on deep well water go for a week or more between backwashes and even then the backwash water is almost clean. How much media filter area do you have and what is the flow rate?
Under the current conditions it will be very difficult to guarantee a low SDI and it does not surprise me that the 20 micron filter regularly fouls.
How deep is your deep well and do you know how it is constructed?
Do you have access to a turbidity meter?
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
Did you by any chance collect any of the larger chunks that can be seen on top of the filter surface? It would be particularly interesting to know what they are. Please let me know what shall i do to know what they are
The amount of dirt on top of these filters after 34 hours is significant and bimr's posts here are relevant. Deep well water is normally clean. I regularly see RO plants with a similar process train as yours on deep well water go for a week or more between backwashes and even then the backwash water is almost clean May be not the same pretreatment process may be they use Chlorination. How much media filter area do you have and what is the flow rate? we have 6 filters with 1600mm Dia x 2500mm HT.and about the flow rate each 3 sand filter feed with pump 45m3/hr in Parallel
Under the current conditions it will be very difficult to guarantee a low SDI and it does not surprise me that the 20 micron filter regularly fouls.
How deep is your deep well 650 meter and do you know how it is constructed? i will try to get its file if you think this important to you
Do you have access to a turbidity meter? our turbidity meter is damaged long time and i am waiting new one i think i can provide it this week
The large chunks on the surface may give a clue as to what is causing the fouling. If you can collect several of those large chunks it would good to see if they are hard or soft or what are they exactly.
I am involved in the operation of two RO plants on deep wells and one has almost an identical process train to your plant. The feedwater to both of these plants is very clean, typically much less than 1ntu. It would be good to have a turbidity reading both before and after filtration.
The filtration rate is about 7m/hr which is reasonably conservative and should be okay.
It would be good to know the details of the well construction as this may indicate the source of the turbidity.
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
may be the Online oxidation of H2S by injection of air before sand filters not enough and we have to add a chlorine oxidation. what do you think? please
As far as possible you should avoid adding chlorine ahead of the RO as this will then add a de-chlorination step.
RO membranes typically fail very quickly in the presence of free chlorine.
If H2S is a problem it might be easier to use a packed tower degasser to strip off the H2S but it does depend on the raw water chemistry. What we have seen so far the water test results are not sufficient to be able to advise on this with any certainty. A lower pH would make the air stripping of H2S more efficient.
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
So are you saying that you currently have aeration before your media filters? yes
pH 7.28 @ 38degree.C for our raw water before injection of air
If H2S is a problem it might be easier to use a packed tower degasser to strip off the H2S but it does depend on the raw water chemistry. What we have seen so far the water test results are not sufficient to be able to advise on this with any certainty.please let me know all parameter required to be analysis so i can send sample to laboratory
Stripping of sulfides is dependent on pH. In treating aulfur waterws, the most important fact is that carbon dioxide comes out of solution much more easily. As the carbon dioxide comes out, the pH rises, in the wrong direction of air stripping. At pH value 5, about 98% of sulfide is present as hydrogen sulfide. On the other hand, at a pH of 9, only one half on one percent is present as hydrogen sulfide.
Regarding: may be the Online oxidation of H2S by injection of air before sand filters not enough and we have to add a chlorine oxidation. what do you think? please
Oxidation by hydrogen sulfide by air is a very slow process and may take hours to complete. That means hydrogen sulfide will not be completely oxidized within the filter retention time.
pH, iron, manganese, and hydrogen sulfide concentrations should be determined in the field since these parameters are not stable.
Water samples must be tested on-site, or immediately stabilized for laboratory analysis. Sample bottles with stabilizing chemicals should be obtained from the laboratory that does the analysis. Careful sampling according to laboratory recommendations is critical to ensure accurate and reliable results. In general, the requirements will involve delivery of a refrigerated sample within 48 hours of collection. Sulfide concentrations are reported by laboratories in units of milligrams per liter (mg/l) or parts per million (ppm).
Its good that you can now give some turbidity readings. It is obvious that something is happening between the well and the buffer tank and as bimr previously suggested it might be the oxidation of iron. But given that we don't know what process steps are occurring in what sequence and after every discussion there seems to be another step we did not know about before it could be anything.
For example is the buffer tank before or after the air injection process.
Although we have asked this question before can you either list the process steps or draw a process flow diagram for the plant.This should include chemical injection points.
Regards
Ashtree
"Any water can be made potable if you filter it through enough money"
