Spill Basin - Possible problems with design

[keremd8]

Hello,

This is my first thread, nice to meet you all.

I am a freshly graduated environmental engineer and I started working as a process engineer in the wastewater treatment area and I need some recommendations or ideas for a project that I am working on.

In the project we are working with wastewater from a dairy production. There are two parallel mixing and equalization tanks and two parallel spill basins. They are all going to be build underground. The spill basins will be filled with the floating sludge from the MAB through an overflow pipe (not in the 3D design yet) or in case of an emergency/spill, the wastewater directly will go to the spill basins.

There will not be an aeration in the spill basin and it is highly possible there is going to be a biogenic sulfuric acid corrosion on the concerete tank. That is why the senior engineers decided to go with a HDPE cover in all the tank. Then they tasked me to find out possible problems and what I offer to solve them. I already made some progress with some points but there are couple of things that I couldn't figure out yet and I need your help.

1. Firstly, in case of a spill, the basin will be filled with the pipes from a high point and the water will have a certain impact on one point continuosly which is covered with HDPE. Would that be a problem in the long term?
2. I would like to place a ladder in front of the plates that you see in the image. However the water has a high concentration of Chlorine (900-1500mg/l) and I am thinking a steel ladder that stays in the water would be problematic. I thought about having a stackable one that could be installed to the ceiling but because of the PE cover, I am not sure because i can't weld the PE to the steel and ensure there won't be any H2 leakage to the concrete between PE and the ladder.
3. We would like to have an automated element in tank in order to clean it and give the water a mix or even aerate time to time. Instead of an agitator, such a solution is being taught. But again it must be somehow installed to the ground or the wall that is covered with HDPE lining/coating.

You may see the plan in the images. The 3D design is made roughly. The PE cover is not shown in the images yet, but you can imagine that everything will be covered. If I missed something about the content, please let me know and I will try to give more information.

Edit: I wrote we need an agitator but we don't have that intention anymore. Therefore, Point 3 is edited.

 

[bimr]

How are you planning to install the HDPE? Have you considered anchor-lok lining?

https://www.atlasmin.com/_files/ugd/5306bd_405be529b6604a17bccd2f36e39a025a.pdf

I don't see a ladder on your illustrations. Why do you need a ladder?

If you don't have some type of mixing, the solids will settle out. Have you considered jet mixing with a pump?

It would help out if you provided a simple flow sketch.

 

[pierreick]

Hi,
In some countries (China) it's mandatory to install covers on the unit with connection points to scrubber or other treatment to clean the gas prior to release to atmosphere.
The bottom of the basins should be slopped in case of sludge formation with possibility for drain.
Pierre

 

[keremd8]

How are you planning to install the HDPE? Have you considered anchor-lok lining?

https://www.atlasmin.com/_files/ugd/5306bd_405be529b6604a17bccd2f36e39a025a.pdf

I don't see a ladder on your illustrations. Why do you need a ladder?

If you don't have some type of mixing, the solids will settle out. Have you considered jet mixing with a pump?

It would help out if you provided a simple flow sketch.

Thank you for the reply.

HDPE will be installed like in your example. The ladder is not in the image because as i mentioned, it is only a rough draw. We need the ladder for the assembly because there is no entry to the tank except from the gate, that is closed with a plate. I was also thinking we could install a permenant ladder because if someone has to go down in the tank, that would be the only option and then the question is how would be installed over the HDPE?

At this point, it is possible that we can say they must bring their own mobile ladder everytime, but the space is limited because it is an underground structure.

About the solids, they can settle down because in the end it will be directed to flotation tank or back to the mixing and equalization tank. I forgot to mention it, thanks. However, we would like to have a mixing as well. For example, it can be with a diving aeration unit that also spins around.

You may see the connections between the tanks in the image attached. However, this is not the finished product yet, it is opened to criticism and it is what I need.

Hi,
In some countries (China) it's mandatory to install covers on the unit with connection points to scrubber or other treatment to clean the gas prior to release to atmosphere.
The bottom of the basins should be slopped in case of sludge formation with possibility for drain.
Pierre

Thanks for your reply.

There will be an exhaust air collection pipeline along the walls of the mixing and equalization tanks. It will work with a negative pressure created by an aeration equipment. Through the windows and openings from spill basin, the air will be directed there as well because of the negative pressure, but it is highly possible that we cannot ensure total H2 gas removal. That is why we would like to cover all the concerete in spill basin.

About the slope in the basin, you are right and it is planned. There will be a slope ending at the collector pipes, which you see in the image. Sorry, the drawing is made quickly and roughly, it is not the finished product.
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I would like to clarify some points here. My concern is mostly about the assembly, because I do not want any damage on the HDPE lining. After the tanks are built with the lining, we need to come up with a plan how they will assemble a mixer equipment or the pipes (collector and the overflow from MT) through the walls and so on. Even if they do it in another way, i must be able to offer some ideas. So, it is good that you are pointing out what could go wrong even if it is a very little detail.

I found out that there are HDPE plates that could be welded to HDPE linings but it is advisible that you use these as little as possible not to damage the lining. The bolts can be screwed on these HDPE plates. Maybe someone already has an experience with these materials and inform us.

 

[bimr]

I wouldn't include a ladder. It appears that your tank will be a confined space and that would require that a harness and tripod will be necessary to enter the tank.

 

[keremd8]

I wouldn't include a ladder. It appears that your tank will be a confined space and that would require that a harness and tripod will be necessary to enter the tank.

Thank you!
That could be a good idea. I need to figure out how to seal the manhole with the PE lining, but it is still useful.
I am still open to critics.

I also found an HDPE pipe that sits inside the wall. Since it is made from HDPE, it can also be welded to the lining. I think it could be a big help within such a tank.

 

[bimr]

Contact ISCO and they can make a wall spool for you. You can weld the HDPE wall spool to the tank HDPE.

https://isco-pipe.com/applications/

 

[keremd8]

Contact ISCO and they can make a wall spool for you. You can weld the HDPE wall spool to the tank HDPE.

https://isco-pipe.com/applications/

Thank you for the suggestion. Probably I should have mentioned before but I am working in Germany

 

[pierreick]

Hi,
Why not using coating?

Elastomeric Spray-on Polyurea Coating for Waterproofing and Anti-corrosion (P-120) - YUXI

YUXI’s P-120 spray-applied polyurea coating is a two-component, fast-setting, highly elastic coating composed of isocyanate prepolymer, polyether amines, and amine chain extenders. It produces a highly durable anticorrosive, waterproofing membrane with strong adhesion to many types of surfaces...

yuxi-anode.com

For your consideration.
Probably cheaper option!
Pierre

 

[keremd8]

Hi,
Why not using coating?

Elastomeric Spray-on Polyurea Coating for Waterproofing and Anti-corrosion (P-120) - YUXI

YUXI’s P-120 spray-applied polyurea coating is a two-component, fast-setting, highly elastic coating composed of isocyanate prepolymer, polyether amines, and amine chain extenders. It produces a highly durable anticorrosive, waterproofing membrane with strong adhesion to many types of surfaces...

yuxi-anode.com

For your consideration.
Probably cheaper option!
Pierre

Thank you for your time!

We have checked the literature about different solutions and then the senior engineers decided not to go with it. At this point we cannot change this anymore, it is already decided.

I am quoting the related part from Durability of Covered Reinforced Concrete Containers in Sewer Works Construction (2006) by Lasse Petersen and Ludger Lohaus. This is a translation from the paper:

"Due to the use of unsuitable coating systems or unfavorable conditions, such as reverse-side moisture penetration of the concrete, osmotic blistering can occur. This reverse-side moisture penetration is always to be expected when the tanks are embedded in the ground.
Even with proper planning and execution, coatings inherently have a limited lifespan. The joint areas, in particular, are weak points in the coating. Coatings will likely need to be repaired or even completely renewed during the operational period. Regular inspections are therefore essential."