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"
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
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.
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
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.
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.
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"
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"
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 m[sup]3[/sup]/hr
Contaminants, h[sup]2[/sup]s, iron, manganese(unknown)
1) Raw water from a deep well
2) Buffer Tanks
3) Raw Water Tanks (300 c[sup]3[/sup]m
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.
