Black Colored Water from Groundwater that Turns Clear After Time

[Joe H]

Hello, I currently work at a water treatment facility that treats groundwater. Recently the in-fluent water we've been receiving is almost pure black. My first thought was manganese, and am having it tested to see if Mn is present. Here's the part that confuses me: If I leave the water alone after an hour or two, the water becomes clear. Correct me if I'm wrong but manganese doesn't just aerate right?

Does anyone have any ideas what this could be? Whatever it is, it's making it to our multi media filters (after a sediment tank) and forcing us the backwash much more frequently. Has anyone experienced this before? Any Input would be very much appreciated! Thank you so much!

I really apologize if this has been talked about in another thread I could not find anything.

 

[bimr]

Black water is usually associated with hydrogen sulfide present in groundwater. Sulfur-reducing bacteria present in groundwater use sulfur as an energy source to chemically change sulfates to hydrogen sulfide.

Have you had the well inspected? Does the water smell like rotten eggs?

 

[Joe H]

Thank you for the response Bmir.

Yes one of the main things we treat in the plant is hydrogen sulfide (with H2O2 oxidation / filtration). The concentration of the in-fluent hydrogen sulfide hasn't changed (roughly 8 ppm) despite the color completely changing. We also test the in-fluent of settle-able solids with the use of an Imhoff cone, in which there were none detected. This is leading me to believe it's some kind of suspended solid (since its getting through the sediment tank anyhow). Is it possible it's some sort of volatile organic matter that aerates after some time? And doesn't have the required time/ability to aerate before it hits the MM filters?

I'm not sure how i'd be able to treat/fix this...

 

[itsmoked]

If yo have a sand filter could it be break-thru, that once the channel is created eventually washes clear? Is your backwash ever black?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[Joe H]

Thank you for the response!

We use multi media filters ( anrthacite / Fine - course garnet / Crushed rock). The backwash color used to be a standard milky white (after the Hydrogen sulfide was oxidized). But since the in fluent water has changed to black the backwash has taken more of a "muddy" brownish color. The backwash has never been black.

 

[LittleInch]

So is this continuous flow from a well or set of wells and comes through in batches or just when you start a well that had been stationary for a while?

Has anything changed in your supply system?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[Joe H]

This is a continuous flow treatment plant. As far as the where the source of the groundwater is coming from, that I cant say specifically. Our company is sub contracted for their water treatment purposes, so they choose when and what wells to drain, we just clean it. They did start draining out of new wells which is when this black water problem originated. Our contractor is building a subway and need to dewater the ground water "blocking" where the tunnel will be built, so they have no choice but to drain this water (and we have no choice but to clean it lol).I have notified them, and were trying to figure out just what the heck this is.

Thanks for reply!

Just to add some more info:
Our Continuous Flow Treatment Plant Setup:

http://files.engineering.com/getfil...62887b87ee8a&file=Treatment_Plant_Setup_2.png

(ignore the sulfides/turbidity, all of that is old)
The color of the water:

http://files.engineering.com/getfile.aspx?folder=b0f61d02-f323-4ceb-a518-24b1420ae33e&file=t_=_0.jpg

On that second picture I have one cap on to see if the "blackness" is actually aerating.

 

[bimr]

Yes one of the main things we treat in the plant is hydrogen sulfide (with H2O2 oxidation / filtration). The concentration of the in-fluent hydrogen sulfide hasn't changed (roughly 8 ppm) despite the color completely changing. We also test the in-fluent of settle-able solids with the use of an Imhoff cone, in which there were none detected. This is leading me to believe it's some kind of suspended solid (since its getting through the sediment tank anyhow). Is it possible it's some sort of volatile organic matter that aerates after some time? And doesn't have the required time/ability to aerate before it hits the MM filters?

This is certainly a result of hydrogen sulfide and the black material is ferrous sulfide. This material is extremely finely divided and it takes a very small quantity to blacken the water. After sitting for awhile, water like this may appear to be clear when viewed under direct light. However, I suspect that the water you are describing is not exactly clear, but instead contains a very finely divided colloid of sulfur. If you shine a light through it, you should be able to see the Tyndall light scattering effect.

The black water may clear up as the piping is flushed as this type of black water usually occurs in stagnant waters where bacteria has reduced some of the sulfate to sulfur.

Regarding your flow diagram, the peroxide oxidizes hydrogen sulfide, not reduces. In addition, you may want to renovate the filters as they should be producing a better effluent quality.

 

[bimr]

We use multi media filters ( anthracite / Fine - course garnet / Crushed rock). The backwash color used to be a standard milky white (after the Hydrogen sulfide was oxidized). But since the in fluent water has changed to black the backwash has taken more of a "muddy" brownish color. The backwash has never been black.

"The product of the oxidation is predominately elemental sulfur, which appears as a yellow colloid (if underdosed) or a white colloid (with complete oxidation."

Sulfide Oxidation with Hydrogen Peroxide (H2O2)

 

[ashtree]

When you say you leave the water alone for a while and it clears up do you mean that it is sitting in a tank of some kind and not flowing?
Is there any pH change related perhaps to the release of CO2 between the times when the water is black and when it clears up?


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

 

[Joe H]

Thank you all for the responses ill try to address each question:

Bmir: If it is ferrous sulfides, would it make sense that the filters would clog (catch more) faster? Is the iron also being oxidized? (turning into it's own colloid?). And sorry for the "Reduction" mistake, I made that flowchart when I first started at the plant haha. Interestingly enough I ran my own little experiment to see if aeration of the "blackness" was occurring. I put two samples in two jars. One without a lid, one with a lid. When I came in to work this morning I noticed the one without the lid is much clearer than the one wit the lid. Would this indicate aeration? The rotten egg smell is gone, has the sulfide aerated? Pic Attached:

ashtree: The samples I collected sit in jars (like the picture blow)

Before Time = 0:

http://files.engineering.com/downlo...02-f323-4ceb-a518-24b1420ae33e&file=t_=_0.jpg

After Time = 18:

http://files.engineering.com/getfil...d-d91b-4b1b-ac66-948d65e300b1&file=t_=_18.jpg

 

[bimr]

An increasing influent TSS will decrease the filter run time. Iron should also be completely oxidized by the peroxide.

To do a good job of filtering this colloidal material, a filter aid may be beneficial. Colloidal material is so fine that it may pass through a filter.

Yes aeration; oxygen from the air will oxidize the hydrogen sulfide slowly over time to ferrous sulfide, but it will take a much longer time than the peroxide and the time may vary with pH.

Over time, the hydrogen sulfide odor dissipates. That is an example of why it is difficult to get good samples of well water that contain hydrogen sulfide.

To repeat, it does not take much ferrous sulfide to blacken the water as shown by the small amount of material that has settled out in the jar. And the clearer sample in the jar contains colloidal sulfur.

By the way, is this a CCS project?

 

[Joe H]

Thanks a million Bmir. We do actually have black material floating around inside of our sediment tanks so this seems to exactly whats going on.

Not sure what a CCS project means... so probably not lol.

So to sum up and to just wrap my head around this (let me know if I get something wrong here):

*The black color comes from the ferrous sulfides (which is a precipitate?) which is also a TSS, and is making the hydrogen sulfide black (really black)? Is the blackness a combination of H2S and the Ferrous sulfide? Like once the H2S leaves is it just a black solid material floating around? I wonder what the chemistry is behind this...

*The fact that the blackness goes away over time is due to the H2S aerating to ferrous sulfides? or just that the H2S is aerating by the outside air and what remains is the sulfur (darker tint water), and since no H2S is left, the blackness goes away and the ferrous sulfides become visible?

*When we H2O2 oxidize the H2S in our sedi tanks, what is happening to the ferrous sulfides? Is it just turning into FeOH? or some sort of sulfate?

 

[bimr]

*The black color comes from the ferrous sulfides (which is a precipitate?) which is also a TSS, and is making the hydrogen sulfide black (really black)? Is the blackness a combination of H2S and the Ferrous sulfide? Like once the H2S leaves is it just a black solid material floating around? I wonder what the chemistry is behind this...

Sulfide exists in three forms in the hydrogen sulfide system, hydrogen sulfide (H2S), bisulfide ion (HS-), and sulfide ion (S2-). The sum of these three compounds is commonly referred to as total sulfide.

The peroxide oxidation process is problematic with an incomplete oxidation that can create colloidal sulfur and polysulfides; the design and control is difficult; and turbidity is produced.

The iron (Fe) that is present combines with the sulfur (S) to form ferrous sulfide (FeS), the black material.

]
*The fact that the blackness goes away over time is due to the H2S aerating to ferrous sulfides? or just that the H2S is aerating by the outside air and what remains is the sulfur (darker tint water), and since no H2S is left, the blackness goes away and the ferrous sulfides become visible?

Air is a powerful oxidizer of both iron and hydrogen sulfide. It quickly converts ferrous iron (as FeS) to precipitate ferric iron (Fe(OH3), and it converts hydrogen sulfide to elemental sulphur.

 

[bimr]

Not sure what a CCS project means... so probably not lol.

I was thinking CCS is the abbreviation for Clear Creek Systems, maybe not.

 

[Joe H]

Thank you so much Bmir!

Update: Our metals test came back from our influent/mid point samples. apparently we have a massive amount of Mg, Mn, and Fe (51000 ppb, 50 ppb, 1000 ppb respectively). Luckily our permit does not require us to treat those metals (were dealing with groundwater), but you are correct in the iron being the real problem. Our Lab Results:

After Oxidation/Sedimentation tanks:
Multi-Media Effluent:
The Fe is being eliminated by 90%
The Mn is being eliminated by 0%
The Mg is being eliminated by 0%

GAC Effluent:
The Fe is being eliminated by 0%
The Mn is being eliminated by 0%
The Mg is being eliminated by 6%

So the Iron is what's causing our multi media filters to clog so fast. Now the question is, what can be done about it? Were still required to oxidize the hydrogen sulfide in our water, but isn't some of our H2O2 oxidizing the iron as well? Do you have any suggestions on how to deal with this? Any tips will be greatly appreciated! Thanks again.

On a side note: Do you think that the extremely high concentration of Mg can have a negative effect on the system? We're actually implementing Ion Exchangers at the end of our system to deal with Cu, Pb, and Zn. Do you think the Mg will completely demolish/use-up the Resin?

 

[bimr]

Update: Our metals test came back from our influent/mid point samples. apparently we have a massive amount of Mg, Mn, and Fe (51000 ppb, 50 ppb, 1000 ppb respectively). Luckily our permit does not require us to treat those metals (were dealing with groundwater), but you are correct in the iron being the real problem. Our Lab Results:

These are naturally occurring elements and at the amounts that you have listed will not be regulated by NPDES permit.

So the Iron is what's causing our multi media filters to clog so fast. Now the question is, what can be done about it? Were still required to oxidize the hydrogen sulfide in our water, but isn't some of our H2O2 oxidizing the iron as well? Do you have any suggestions on how to deal with this? Any tips will be greatly appreciated! Thanks again.

While the amounts of these materials may be large to you, the amounts are actually on the low side. I have witnessed well water iron levels as high as 20-30 mg/L. Just keep backwashing as required by high filter pressure differential.

On a side note: Do you think that the extremely high concentration of Mg can have a negative effect on the system? We're actually implementing Ion Exchangers at the end of our system to deal with Cu, Pb, and Zn. Do you think the Mg will completely demolish/use-up the Resin?

Some of the Cu, Pb, and Zn will be removed by the filter. 51 mg/L is not that high of a magnesium level, but will exhaust a water softener, if that is the ion exchange system that you are using. You will have to periodically regenerate the water softener or whatever resin that you are using. Another element, calcium, will also consume the resin capacity.

Is this a Clear Creek Systems project? I ran into the same problem several years ago when the consulting engineer proposed a similar system to take out metals and did not understand that the other background hardness elements would use up the resin capacity. He then compounded the error by ordering a spare charge of resin for $100 K because he thought the resin would be exhausted. When we left the job site at the end of the (remediation) project, the (spare) resin was still siting there waiting for the owner to dispose of.

 

[Joe H]

Thanks again Bmir, you're my new hero.

No this isn't a CCS project but my predecessor was just as equally incompetent! I'm still fairly new to water treatment so I'm still learning new stuff everyday, but I still had a better grasp on what was going on here than he ever did... I inherited this plant on the verge of ruin, I'm trying to keep this sinking ship afloat!. Thanks again Bmir, I owe you a beer!