calcium Scale buildup in pipes 2

[pivot]

hi all,
I am designing a system to effectively control the scale build up in the pipes .At the time we put the waste water in a mixing baisn .The From there we are pumping the waste water to a bio reactor .Water comes to this basin from strom water drains not concrete ones but just open drains.We are getting scale build up in the pipes (calcium scale build up)and also we are getting higer sludge in the bio reactor .Besides that we are getting high fluorides as well.What might be the cause of the calcium scale built up in the pipes and how it can be treated.The PH of the water is between 9-11
Thanks a lot in advance

 

[drFCraft]

Probably precipiatated hydroxides of various sorts (calcium, + other cations present). If possible, intermittent cleaning with diluted acid + mechanical removal of scale could be a solution to the problem.

 

[bimr]

It should be immediately obvious that scale buildup is due to the high pH of the solution causing calcium and magnesium salts to precipitate out of solution.

The remedy is to add acid to lower the pH of the solution.

Waste treatment unit processes normally operate in the pH range of 8-9 pH units anyway.

 

[pivot]

PH lowering seems to be feasible option.
What about Silica and Quartz content .
The water is high in sillica and quartz .Can it be
a reason for additional scale build up besides high PH
Are there any special pumps that can handle this type of water
Thanks

 

[bimr]

What about Silica and Quartz content?

Silica and quartz will not cause any scaling. Silica and quartz are the components of sand and my settle out.

You should calculate the langelier index of the water. That would give you an idea of the pH necessary to prevent scaling.

http://www.env.gov.nl.ca/env/env/waterres/Surfacewater/Langelier/Langelier.asp