Wastewater clarifier - weir material

[Dennis59]

Wondering if any of you have specified HDPE or PVC sheet material for a v-notch weir in a wastewater clarifier. I have almost always seen steel or aluminum or fiberglass in the field, but I would think that HDPE or PVC would be cheaper and more resistant chemically. I know there are issues with thermal expansion, but are there other reasons why HDPE or PVC would not make a good v-notch weir?
Thank you!

 

[bimr]

The common HDPE and PVC materials are not UV resistant. However, additives can be used to make these materials UV resistant.

In addition, PVC is a brittle material when cold and subject to breakage. That brittleness with temperature would rule out PVC,

The issue which you have already identified is thermal expansion. It is already difficult to construct the v-notch weir in a clarifier to be perfectly level. One would have to attach two materials (steel and plastic) with different thermal expansion to each other. I would expect that it would be difficult to maintain the shape of these materials over time.

 

[ashtree]

One of the plants that I am involved with has had PVC weirs for 40 plus years. I am not aware of the exact material its black and is still in quite good shape. These weirs replaced a painted steel weir many years ago and the PVC was bolted onto where the steel was previously bolted and has never given a problem. Whilst it gets cold here we do not have long periods of sub zero and no snow, so expansion may not be such an issue for this site.

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

 

[JedClampett]

I'd stay away from HDPE due to its large coefficient of expansion. We're in Arizona, so UV is a real concern.
[ul]
[li]Most of the time, the water going over the weir protects it from UV. Plus, we do ask for all the UV inhibitors.[/li]
[li]We've never had brittleness issues, but once again, most of my experience is in Arizona. But very cold temperatures are mitigated by the process water temperature. Of course, during winter shutdowns, it is exposed to cold.[/li]
[li]Most of our weirs are PVC. I don't think it's a huge cost saving, but it easier to work in the field.[/li]
[/ul]