Down flow vs up flow for calcite

[Mass_ tech89]

hey guys.

Curious to what system is preferable in treating acidic water using calcite.

My supply house really pushes the non backwashing units for water treatment. I have installed both but I always thought backwashing units were superior. However recently I was speaking to a rep who said that down flow units performs just as well along with having water saving benefits easier install etc... I haven't been doing water treatment long enough to have a strong opinion so what are you guys thoughts.

 

[Mikey]

I'm not sure what's to backwash. It looks like the main byproducts of the acid-carbonate reaction would be CO2 and water. (Treading on thin ice here, chemistry-wise.)

 

[Sponsor]

 

[Bannerman]

With granular media, down flow tends to keep the media more tightly packed which will increase water contact with the media as opposed to flowing around the spaces between the granules. Up flow will tend to loosen the media, especially at higher flow rates.

Even with down flow, water will take the path of least resistance and will eventually carve paths through the media (channelling), particularly at lower flow rates. Channels will permit a less restricted path from the tank inlet to the outlet which the water flowing will have reduced contact with the media.

Backwashing will periodically re-classify (redistribute) the media to eliminate the potential of channelling. In addition, backwashing will also flush away any sediment and debris which enters the media tank in the raw water.

 

[Mass_ tech89]

Thank you guys for your input. so you both agree that they, for most applications are similar in there effectiveness

 

[Bannerman]

Channelling is more common in up flow. As up flow often doesn't use a backwashing control valve, channelling is more difficult to correct. For this reason, down flow would be more effective.

http://support.cleanwaterstore.com/blog/adding-filter-media-to-upflow-neutralizers/

 

[_John_]

I prefer downflow because it also adds sediment filtration to your system as well.

 

[Akpsdvan]

Is there any amount of iron in the water?

 

[ditttohead]

Upflow is really only considered acceptable if the flow is rate is known and minimally variable. For applications where the flow rate changes, downflow is preferred. Downflow also offers considerable physical filtration. When we spec upflow, we use far less media in the tank due to the potential of higher flow rates causing the media to clog the top screen.