Nitric Acid for Effluent Neutralization 2

[mdnpe]

Does anyone have any experience using concentrated nitric acid for pH adjustment of effluent? We routinely use nitric acid for pressure filter acid cleaning and have a good storage tank and control system available. I am looking at a possible method of injecting 5-30 gpm of 65% nitric acid into an 8" underground fiberglass sewer pipe for pH control. 100-150 gpm of water must be added to control the heat of reaction to maintain temperature at or below 125 F at higher acid rates. However, I am considering potential for localized flash boiling and pipe damage from inadequate mixing. I am considering using a 2" Kynar injection pipe for the acid inserted in the direction of water flow that would have multiple perforations to promote good mixing similar to a Resistoflex mixing tee.

 

[kenvlach]

Lots of experience with nitric acid neutralization, both dilute and concentrated.
Do not inject concentrated nitric into an underground pipe. Too much downside potential when something (pH sensor, pumps, valves, water flow) goes wrong. Risk of excesss nitric siphoning, too. Also, in most places (e.g., US) your local POTW or EPA regulator will not give approval for such a treatment system. They need access for sampling, plus you need recording of your effluent pH. Also, I think you would get pH oscillations beyond your limits (mine are pH 6-10).

Use an aboveground mixing tank for neutralization.
Hope this helps,
Ken

 

[mdnpe]

Thanks for your advice. I was looking for a way to prevent fume generation in the local area from the acid addition. Do you have a feel for maximum nitric acid concentration to avoid fuming when diluted with water?

 

[Quentin]

Mdnpe,

how did you get on with this pH adjustment system? I am looking at doing something very similar except with sulphuric acid

Quentin

 

[bimr]

Quentin

Your question should be over on the Waste disposal & treatment Forum.

An inline pH correction system will probably never work. You need mixing and reaction times. See this thread:
pH system - Design criteria
Thread161-110441

 

[mdnpe]

Quentin, the system I described in my original post was installed last Spring except I used a teflon pipe to introduce nitric acid underneath the water in acid sewer sump instead of a mixing tee. We have an acid sewer system and alkaline sewer system and a fairly long run of pipe after they combine before discharge into treatment system. There is plenty of reaction time so this was not a concern for me. I agree with Bimr you may need an entirely different setup for fine tune control. In our case, the system has worked fine and is used only a few times a year to prevent pH > 12.5 entering earthen treatment basin during upset conditions.