Filter media removal 1

[nilaypathak]

Hello,

At our Water Treatment plant, we do have three filters- due media (Sand + Anthracite), each has four cells ( 15' X 15'). All tanks are due for structural inspection for corrosion. Also, there are few welds failed at the bottom of the tanks. To fix the tank's weld, all media requires to pull out to replace the stress.

I am looking for input on how to pull all media from each cell and put it back. I got the price from one contractor, its $20K per cell, which in my opinion significantly high.

Thank you in advance for your time.

Regards,

Rakesh

 

[ashtree]

A vacuum truck is useful for the removal of the media and can do it quite quickly.
However it is not impossible to get into a filter and shovel out by using buckets and a hoist. But it is very hard work.
Whatever method you use to remove it you should allow to replace it because it will be very difficult to reuse the old media.

I have detailed below the steps for media replacement and getting back online that i use but you can modify accordingly.

1. Before adding any media, using a level and spray paint or marker, mark the depths of each layer on the filter walls. Each line represents the top of the layer.
2. Install gravel. Wear hearing protection if required but use respiratory protection at all times to protect against silica dust. Spread gravel and level correctly. When standing on gravel layers of different sizes use plywood to distribute your weight and don't walk directly on the gravel, after putting in the first layer.
3. Lay sand. Use plywood to stand on until a good depth ofr sand has been installed. Sand only needs to be roughly spread.
4. Slowly introduce water back into the filter using the lowest rate possible through the backwash system. This may require the throttling of the backwash pump. Fill until the water reaches the upper surface of the sand layer. Add sodium hypochlorite to the water at a rate to achieve a 1mg/l free chlorine residual. This will require 5-10mg/l dose.
5. Gently airscourthe filter to mix the hypo through the filter. Air scour at lowest rate possible (may have to throttle a valve) possible for about 5 mins. Let stand overnight if possible.
6. Backwash the filter using a low rate at first and gradually increase the flow rate. When the backwash is complete let the filter drain down. Enter the filter and scrape off any accumulated fines which can be 15-25 mm deep.
7. Repeat step 6 a couple of times until no more fines appear.
8. Add filter coal. Use respiratory protection and wear disposable overalls. Spread the coal media roughly as it will stabilise with washing.
9. Using the backwash system slowly refill the filter to the level that it drains to before commencing a backwash. Soak for a couple of hours if possible.
10. Backwash the filter at a slow rate initially to remove media fines. At the end of the backwash enter the filter and scrape off the fines from the surface (15-25mm).
11. Repeat 10 above until clean.
12. Recommission the filter.
13. Where possible filter to waste until the outlet turbidity becomes acceptable.(Close to 0.1ntu)
14. Return filter to service.





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

 

[nilaypathak]

Hi ashtree,

Thank you for the detailed reply. Are you referring vacuum truck as a hydro-vac truck?

I was talking to filter manufactured, they said filter media can be put it back in the filter. They generally pump into dewatering bags and put it back in the filter. I can not figure out how they can do this.

Thx,

Regards,

R

 

[ashtree]

Yes i do mean a hydrovac truck.
You can recover the media using a dewatering bag but it will still be difficult and you will probably loose 10-25% of it anyway. Likewise the media will probably get the different grades mixed up which will cause poor filter performance in the future.

Using a dewatering bag would allow you to pump out the media in water/media slurry, or perhaps even to backwash it out at a high rate if the system has enough capacity to carry over the media. The water/media slurry goes into the dewatering bag. The water oozes out over a few hours or a day leaving the media in the bag. You would then cut the bag open and scoop out the media.
Link to dewatering bags:

https://www.geofabrics.co/products/geotube

Yes it is possible but difficult.
My recommendation would be to replace the medai rather than try to reuse it.


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

 

[bimr]

Filter media doesn't last forever. Filter media breaks down over time, finer particles migrate to top during backwash. Some operators skim off the filter fines on the top of the media bed annually.

After five to ten years, the sand gradually loses its sharp edges and its ability to filter. When the media no longer effectively filters the water, you should change it

If the installation is over 10 years old, you should replace all of the media.

Media Replacement