landfill leachate pumping 2

[sledneck34]

I have a pumping station in one of my sewer districts which pumps leachate from a capped landfill. The problem is that after a few months, the pumps and piping in the wet well become clogged with what appears to be iron or clay. The 4" force main is reduced to the size of a quarter after just 6 months. This leads to premature pump failure. Anyone with a similar experience and possible solutions. Thank you.

 

[Unotec]

Looks to me that the capping is quite poor. You might want to try a settling system and/or a decanter. Should it be iron you will need to precipitate it and possibly flocculate it.
Depending on the conditions of the fluid, a filter at the suction might prove useful too.
Might want to mention tto the stake holders that the capping needs to be worked on.

 

[rconner]

While I am not an expert in this field I would think a good start might be to get a leachate/water analysis (and maybe even massage the data derived therefrom, with calaculation of scale forming tendency indices etc.) -- I don't know where to go from there, but I would think treatment menioned by others may depend some on what you find.

 

[CivEnvEng98]

sledneck, I have dealt with a landfill LS before. This one handled leachate as well as domestic...roughly 50/50 flow from each source. Of course that station had serious corrosion issues, and a similar buildup of "unknown" materials, besides the obvious grease, that would line the walls, rails, floats, and anything else in contact with the water. But the station worked...albeit one that was high maintenance. The fact that a good amount of flow to the station was domestic did help dilute the leachate (ha....dilution with sewage was a good thing).

Do you have any ability to dilute the leachate in the station? domestic force mains nearby? a groundwater or stormwater source? Anything?

How much leachate per day is going to this station?

Also, are you sure you are getting 2 feet per second velocities in the FM?

I would also suggest keeping in mind that a pigging station or a pressure cleanout might help. This would allow the Utility to either 1) flush the line periodically or 2) send a "pig" through to clear any obstructions.

 

[sledneck34]

Thanks for the info CEE98. Velocities are right at the 2 fps. I do have a pigging vault outside the station, but still have no way to clean the lines from the pumps to the pig vault. Dilution is a good idea, but this station is in a very remote area. Did you ever try a coagulant or a polymer to maybe change the charge of the sediment to keep it off the pipes?

 

[CivEnvEng98]

I wonder if landfill leachate is consistent enough to respond well to chemical addition.

You really need to have the waste stream characterized to see what's in it. Maybe chemical addition would work, but I personally hate to think of adding more maintenance headaches to the situation.

The only other solution I can think of is to tap into the FM just in front of the pigging vault and run some temporary piping back into the station. I suspect that since the friction losses would be greatly reduced you could send some pretty good flows through the station & valve vault piping and get a good scouring velocity. Just make sure your pump motors are not power limited before doing so and that you properly restrain the temporary piping.