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coagulant

coagulant

(OP)
We dose coagulant before sand filter Is it necessary to determine the dosage every day? and why? Please

Thank you

RE: coagulant

Did you try a JAR TEST first?.

RE: coagulant

(OP)
I am asking Is it necessary to determine the dosage every day through a JAR TEST

RE: coagulant

It depends. If your raw water quality changes enough everyday to cause a process upset then maybe you do need to.

If your raw water is relatively constant and your process is performing well and nothing is changing then maybe you don't. You would simply use the dose settings you used the day before. But you probably should still grab a sample of the water from the flash mixer and put it on the jar tester just to double check that everything is okay. Doing it this ways saves the time of measuring out chemicals etc and helps to test under actual plant conditions and dosing.

Even if conditions are stable and things are going well you should still do jar tests regularly to test whether the current dose rates pH etc is still optimum. The only way you can do this is to set up a number of jars and trial different rates and compare them with the current dose rates.

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

RE: coagulant

(OP)
SDI is high,We always change cartridge filter and we also do many CIP

RE: coagulant

I assume that you have an RO after the coagulation process if you are talking about SDI and cartridge filters. But what is the question.

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

RE: coagulant

Agree with ashtree, if your raw water quality changes to cause a process upset then it is mandatory. If this is a surface water, the water quality may be constantly changing. You may be interested in doing a coagulant study to determine the optimum coagulant.

If the SDI is always high, then the pretreatment scheme is inadequate.

A preferable filter scheme is to use a 2 stage filter. The first stage is a higher flow rate filter. The second stage filter is a slower flow rate polishing filter.

It may be impossible to achieve a low SDI with just a single stage filter.

RE: coagulant

(OP)
Thank you, Can you please give me more information about 2 stage filter system

RE: coagulant

The 2 stage filter system that bimr is referring to would incorporate a filtration system in the first stage that would remove larger particles and hopefully the largest amount of the solids by mass. The second stage would have a greater degree of filtration in terms of particle size but would be much less able to handle solids. You would have to conduct a particle size analysis to know exactly what technology would be required and the sizing of each filtration unit. But for example stage 1 might be a multimedia filter that would remove 95% of particles down to a size of 10 micron.
The stage 2 unit might be a cartridge filter that will remove 99% of particles down to a size of 1 micron.
The multimedia filter should be removing a very large percentage of the total suspended solids remaining in the feed water after clarification, because this can be easily back washed at a regular interval when blocked. The cartridge filter unit should be removing very little in terms of percentage of the total suspended solids and is there primarily as a safeguard against breakthrough and a final polishing step.The cartridge filter would have to be replaced though as these cannot normally be back washed.

You might want to consider an ultra-filtration process in lieu of a 2 stage filtration process.

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

RE: coagulant

(OP)
our exist pretreatment consist of multimedia filters then cartridge filter 20 micron then 5 micron

RE: coagulant

Okay.
The example i used before was simply an example and it does not necessarily mean that its correct for your circumstance. You might use a two stage process utilising 2 multimedia filters with the first stage relatively coarse media working on a high filtration rate capturing the larger particles and a second stage with very fine media but a quite slow filtration rate to capture finer particles as I think bimr is suggesting. A cartridge filter would only be used as a second stage if the amount of particles left in the water was quite low and you had a large amount of filtration area.

Cartridge filters on RO plants are typically only there to protect the membranes against catastrophes and as a last resort. Typically onl a few small amount of solids or particle removal is achieved.


If the process you have is going to be successful the coagulation/sedimentation/ clarification process should be removing most of the solids and particles. The multimedia filters should then remove most or the remaining particles down to maybe 10 micron(but perhaps lower) and turbidity should be quite low probably about 0.1 ntu. The cartridge filters should now have very little to do if everything upstream is working okay and you should get at least a couple of weeks before a change is required.

But this does not appear to be happening. But you have said that you are constantly changing cartridges and that SDI is always high.So either the process is unsuitable for the conditions or something is not working correctly, or both. SDI is a measure of the particles trapped on a 0.45 micron filter paper and the smallest micron filtration you have is nominally 5 micron.(Not that these filters should be seeing much loading if everything is designed correctly) That does not necessarily mean that it won't work but with surface water it can be very difficult to maintain a very high level of very fine particle removal with the process train you have.

So a couple of questions:

1) Has this process ever worked okay?
2) Has there ever been some form of particle size analysis done to make sure that the treatment process is appropriate for RO pre-treatment given the water source?
3) Is this a seasonal problem related run off or river flows?
4) Is there any bio-fouling issues with the cartridges and RO?
5) Has the hydraulic and solid loading on the filtration units ever been checked?
6) Do you routinely measure turbidity at various stages in the plant?
7) Which cartridge requires changing the most frequently 5 micron or 20 micron?




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

RE: coagulant

The 2 stage filter that I am suggesting consists of high rate media filter (6 gpm/ft2) followed by a slow rate media filter (3 gpm/ft2).

Inline coagulation should also be used.

Cartridge filter should be considered a backup filter, not a working filter.

I have seen this setup reduce the SDI to acceptable levels when processing surface waters.

RE: coagulant

(OP)
Please see my answer about ashtree question

1) Has this process ever worked okay? yes
2) Has there ever been some form of particle size analysis done to make sure that the treatment process is appropriate for RO pre-treatment given the water source? this process deigned by specialist water treatment company
3) Is this a seasonal problem related run off or river flows? our water source is deep well
4) Is there any bio-fouling issues with the cartridges and RO? please see attached 5 micron cartridge filter photo
5) Has the hydraulic and solid loading on the filtration units ever been checked? No
6) Do you routinely measure turbidity at various stages in the plant? No,But we measure SDI
7) Which cartridge requires changing the most frequently 5 micron or 20 micron? 20 micron

RE: coagulant

Thanks for the information.

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?

The next question is how long has this plant been in operation? You said that the plant has previously worked okay. How long ago was that and for how long did it work okay?

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?
Have you changed coagulant or dosage, or injection point?
Has filter operation changed? Is there a longer or shorter period between back washing? Has the backwash rate changed? Have you changed the media? Have you inspected the filter media to make sure it has not been lost, its not mud balled and its clean?
Have you had a change in operator in this time?


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?
When they dry out is the residue on them powdery and easily removed or does it stay stuck on the filter?
What do the 20 micron cartridges look like?


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

RE: coagulant

Assumed that you had a surface water application as inline filtration is more appropriate for surface water. Please post a water analysis.

This looks to be more of a problem with iron. Without an elevated pH and/or chlorine injection, it may be difficult to precipitate the iron in the short time that the water is passing through a filter.

The typical problem with wells is dissolved iron which will turn to insoluble iron with the addition of air. It is generally easier to remove the iron in the dissolved state than try to precipitate the iron.

Do you also have a problem with hydrogen sulfide as you posted about it some time ago. Hydrogen sulfide is difficult to remove and it takes an extended time to precipitate hydrogen sulfide.

A water softener may be used to remove the dissolved iron. Sources of air must be eliminated for this process.

RE: coagulant

Thanks for putting up the analysis.

It would seem that the iron is quite low although it does not say whether it is total iron or soluble iron. Based on the fact that the levels are roughly the same before and after the sand filters we would have to assume it is in the soluble form. This should be low enough to be giving very little problem and i would expect to see the cartridge filters more orange than brown if iron was the main culprit.
Although the conductivity is about the same many parameters are significantly different between the two analysis generally getting worse in 2013. Unfortunately not all the same parameters have been tested.
If the turbidity truly was 50NTU in 2009 i would question the process train selected. At that turbidity it would be normal to choose a clarifier rather than rely on contact filtration. I note the 2013 analysis shows turbidity at 10 ntu. This will require the media filters to be performing well to achieve a low SDI. A filter inspection may tell you a lot.

How good are your records on things like dose rates from the past?
I would suggest you work through some of the questions i posed in my earlier posts. This might show a clearer trend if you have adequate data.


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

RE: coagulant

The first observation is that the well was not properly installed, or sampled correctly, or the analysis is incorrect. It is very unusual to have turbidity and COD in a deep well. The presence of these parameters indicates the well may be contaminated with surface water.

In a deep well the iron should be dissolved and the water sample should be perfectly clear when drawn. On standing in contact with the atmosphere, the water should slowly cloud and finally deposit a yellowish to reddish brown precipitate of ferric hydroxide.

The recommended treatment would also depend somewhat on the capacity of the system which you have not stated. I am assuming the water system is small.

I recommended two stage media filtration as posted above. In addition, I would also recommend a water softener after the filtration as the filtration will not remove the hydrogen sulfide in the short retention time provided by a filter. The use of a water softener tends to significantly improve the operation of the RO system (in terms of less frequency of cleaning).

If the turbidity is due to the iron, then go with just the water softener.

You should have a laboratory determine what is causing the COD and quantify the hydrogen sulfide.

As mentioned above, some details are missing from the water anaylsis. Before you spend money to improve the system, have a laboratory do a bench test of the proposed improvements.

RE: coagulant

(OP)
Please what parameter we should do analysis?
please give me more information about water softener to be use as pretreatment for RO

our system capacity is 120 m3/hr

This week SDI becomes higher than before it's becomes more 5
last days we had heavy rain

RE: coagulant

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.

RE: coagulant

(OP)
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

RE: coagulant

Unfortunately i can't get the backwash photos to open.

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

RE: coagulant

The problem i have is that they are in an .RAR format and i cannot open them.

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

RE: coagulant

(OP)
this attachment the sand filter after backwash

RE: coagulant

Thanks. I can open these files.

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"

RE: coagulant

(OP)

Please see my answer about ashtree question


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

RE: coagulant

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"

RE: coagulant

(OP)
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

RE: coagulant

So are you saying that you currently have aeration before your media filters?

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

RE: coagulant

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"

RE: coagulant

(OP)
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

RE: coagulant

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).

RE: coagulant

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"

RE: coagulant

would you also convert the file from the .rar format to pdf?

RE: coagulant

Unfortunately your attached file is in a CAD format.
Unfortunately not all of us have CAD software readily available.

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

RE: coagulant

Thanks.
You mention an air injector. Can you tell me which diagram that is on and what is its tag ID.
The P and IDs look like you spray water into every tank for aeration , is this correct.?

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

RE: coagulant

(OP)
we inject compressed air (19 l/min) before each the three sand filter units( please see attached drawing you will see the raw water coming from tank T10.10 and T10.20 injected by compressed air then we have static mixer then coagulant dosing)

we collect deep well water in buffer tank which far of our water treatment plant location and raw water tanks around 1500meter

RE: coagulant

I assume you mean you have dosing then static mixing.

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

RE: coagulant

(OP)
in fact coagulant dosing after static mixer (this is the design from the water treatment company)the static mixer after compressed air injection

RE: coagulant

Air dosing and coagulant addition in the same pipe is very unusual. The air is normally injected much further upstream to allow more oxidation time.

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. That is why you have post-oxidation occuring downstream in the cartridge filters.

With just the use of the existing equipment, the only remedy is to try chlorine oxidation. This may work if the problem is iron, but may not work if the problem is hydrogen sulfide. Chlorination may be expensive depending upon the amount of material that has to be oxidized. Any remaining chlorine after oxidation will have to be removed with sulfite to avoid problems with the RO equipment.

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).

What does the water treatment company have to say in this matter? It seems that they supplied you with a defective treatment scheme.

RE: coagulant

(OP)
thank you bimr, if we assume the problem coming from hydrogen sulfide please what is the best treatment for that? Because as previous post from ashtree it seems not iron problem from cartridge filters color

RE: coagulant

Previous posts indicated what to do if hydrogen sulfide is present.

However, it is best not to jump directly into solutions without a complete understanding of what the problem is. You really need to determine if it is hydrogen sulfide, iron, or a combination of both.

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).

What does the water treatment company have to say in this matter? It seems that they supplied you with a defective treatment scheme.

RE: coagulant

(OP)
we changed our exist sand filters to two stage but nothing change SDI still high around 6

RE: coagulant

When you first posted November 2016), the assumption was that this was a surface water application because of the high SDI. The 2 stage filter was proposed for surface water filtration.

On January 14, you disclosed that this was a well application. Wells should not have suspended solids. The 2 stage filter is not appropriate for well applications.

At this point, it should be obvious that the reaction times for iron, manganese, and hydrogen sulfide are very long. Air oxidation of hydrogen sulfide will take several hours while the water transit time through the filters is only in minutes. That means the air oxidation reaction will be completed after the water has passed through the filters so you may actual experience have higher suspended solids in the effluent of the filter than in the inlet to the filters.

However, it is best not to jump directly into solutions without a complete understanding of what the problem is. You really need to determine if it is hydrogen sulfide, iron, or a combination of both.

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).

What does the water treatment company have to say in this matter? It seems that they supplied you with a defective treatment scheme.

RE: coagulant

(OP)
Please find below water analysis of deep well:
Turbidity: 0.53 FNU
TDS: 3840 mg/L
pH: 6.57
Iron 0.05
Conductivity 7180 us/cm
Sulfide Content 3490 ug/L


And The Sulfide Content after pretreatment 7 ug/L

RE: coagulant

At 6.5 pH you could remove 60-70% of the sulfide as H2S with an stripper such as a packed tower. If you lowered the pH to around 5 100% of the sulfide will be in the gaseous form and most could be removed with a packed tower.

The other option would be to get rid of all the "aeration" and air injection steps in the existing plant to try to keep the water anaerobic. This would stop/reduce the conversion of the sulfides to elemental sulfur and as a gas the hydrogen sulfide will pass straight through the filters and membranes and it might reduce the fouling of your cartridge filters.But you must eliminate all sources of aeration to be successful, and don't use chlorine or any other oxidants either.

Depending upon what the ultimate use of the water is you may then have to strip off or oxidize the sulfides that will be in the permeate, otherwise you may get objectionable tastes and odours.




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

RE: coagulant

In saying that though sulfur fouling is normally creamy to yellow and most would end up on the RO membranes. Your cartridges are brownish which says to me that whilst sulfur oxidation may be occurring there is probably also something else that is causing a fouling problem as well. Did you get any other tests done. If so can you post the results?

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

RE: coagulant

It has been difficult to understand the situation when the details have been received piecemeal. I reread the posting above and summarized it below.

What is known:

Deep Well Supply
Capacity of 120 m3/hr
Contaminants, h2s, iron, manganese(unknown)

1) Raw water from a deep well
2) Buffer Tanks
3) Raw Water Tanks (300 c3m
4) Coagulant dosing and air injection inline
5) Buffer tank
6) Sand filters (6 filters with 1600mm Dia x 2500mm HT)
7) 20 micron cartridge
8) 5 micron cartridge
9) RO

Problem:
High SDI after filters


Observations:

It looks like the sand filters are fouled from the picture. You need to replace the filter media and repair or replace strainers/underdrain. Check the filter bed depth, you should have approximately 24-Inches. Check the backwash flow rate as the media may have been washed out. One would suspect that the strainers/underdrain are partially clogged which will cause channeling through the filter.

Recommendations:

1. Water treatment equipment should be lined or made of corrosion resistant materials. You can see corrosion products on the top of the filter bed.

2. Don't understand the air injection at the filters. The water contaminants should be oxidized by the transit time through the buffer tank and raw water tanks.

3. An aeration should have been installed on the top of the buffer tank to release the hydrogen sulfide and aerate the water.

4. The filters should be multimedia instead of sand filters. The filters should have a rinse cycle to improve the effluent. The filters should have an air scour to assist the backwashing step.

5. Have the coagulant supplier make a recommendation on the coagulant dosage. The dosage should be more or less constant.

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