DE Disposal 1

[RedBauer]

I'm looking for information on designing a lagoon or settling basin for DE backwash from a water plant. We have limited space at the water plant, however there is a vacant lot that we can utilize to construct a lagoon or settling basin.

Currently, I plan on designing a holding tank at the water plant and pumping the backwash to the lagoon for settling/treatment. I've found one source that says the lagoon should be approx. 4 times the backwash volume. This would equate to 100,000 gallons of storage, which is reasonable for our situation. The backwash frequency is approx. 1 month in the winter and every 10 days in the summer.

Does anyone have any different information or seen a similar situation? When it's time to clean the lagoon, what can we do with the DE? My initial thought is to place it in the sludge drying beds at the WWTP and send it to the landfill.

Thanks.

 

[bimr]

What are you planning to do with the backwash water? Let the backwash water run off or infiltrate?

 

[RedBauer]

Ideally, we'd like it to discharge to a nearby ditch.

 

[bimr]

The first step is to determine the permitting requirements. The regulation of these water treatment residuals is state specific and some states have more restrictive policies.

Here is an example of the State of Virginia's regulations for water treatment residuals:

http://www.deq.state.va.us/waterguidance/pdf/95002.pdf

The solids will concentrate in water treatment residual lagoons over time. One would expect that DE will concentrate in the manner of softening sludge to approximately 20% to 30% over time.

When it is time to dispose of the solids, you may consider the use of a mobile dewatering system. You should then be able to take the dewatered solids to a landfill.

 

[RedBauer]

I'm looking for additional information to size a pump station to transport the backwash volume to the lagoon system. I've designed several residential pump stations for leach fields, however this is a different animal. The average backwash flow rate is 270gpm and has a peak flow rate of 1000gpm. I'm planning on a duplex pump system. The pump station size is unknown and the flow rate of the pump is unknown. I'd rather not make up my own way of doing this.

Any suggestions on how to design the pump station?

 

[bimr]

The backwash tank is typically sized to hold the backwash volume generated in one backwash cycle.

Your filter run cycle is probably at least 24 hours.

Therefore, you can size your backwash pumps to empty the backwash storage tank within that filter run cycle. A practical approach would be to drain the backwash storage tank in approxmately 12 hours.

 

[RedBauer]

The total backwash volume is 30,000-60,000 gallons depending on the time of year and water quality. Backwash frequency is 10-30 days. Ideally, I agree with your approach, however we have very limited space and I'm not sure if the client would want to pay for a tank of that size.

A previous engineer working on the project suggested a 4,000 gallon pump station. Could the solution to this problem be an iterative approach. I check the maximum size tank that would fit for my situation, then size the pumps based on flow and storage available?

 

[bimr]

If you are interested in sizing a pump suction tank in order to pump the backwash offsite, then you need a tank sized for approximately 5 minutes retention.

 

[RedBauer]

Thanks, I think that will work. What's the difference between a pump suction tank and a pump/lift station?

 

[bimr]

They serve the same function. The pump suction tank is generally an above grade with a pump outside the tank.

 

[RedBauer]

New Question: This project stalled for a bit and now we're back on it.

I need to design a velocity dissipater for the inlet portion of my lagoon. I'll be discharging roughly 500 gpm through a 6" DIP or PVC pipe. I have a couple of options. One is place riprap at the outlet. However, the riprap will eventually clog and it will need to be replaced. The second option is to discharge into a concrete tank with baffles. Ideally, the DE will settle in the tank and the effluent will either percolate in the lagoon or eventually discharge to a ditch. Removable baffles will be installed to allow workers to shovel the accumulated DE.

The first option is a relatively easy design. However, I'm stuck on the second option. I can't seem to locate references to design a tank with baffles. Any help on placement, size, etc. would greatly be appreciated. Thank you.

 

[bimr]

If you intend to periodically remove solids, you might devide the lagoon into 2 or more cells similiar to a gravity dewater system.

What people normally do is that the flow is introduced into one end of the lagoon and the drainage is taken off the other end.

The EPA has a document Dewater Municipal Wastewater Sludges 625187014 that may be of some help to you.

 

[bimr]

Here is the document:

 

[dicksewerrat]

Check the content of the "sludge" . It may be a good fertilizer for sod farms, especially if the sod farm soil is acidic.
For your dissipator, turn the outlet pipe up. Put a cuple Rein. concrete MH sections ver the pipe. Drill some 2-3 inch holes in the MH walls. What doesn't flow out the holes will overtop the MH.

Richard A. Cornelius, P.E.

http://WWW.amlinereast.com