INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

Backwash NTU

Backwash NTU

(OP)
Hey guys,

I'm working on the design of an equalization basin for recycling backwashed water (this includes filter to waste as well) to the headworks of a traditional water treatment plant. Public health requires the recycled water to be no more than 2 ntu when sent back to the headworks.

I need to determine the detention time of the eq tank in order to avoid under sizing it...

What kind of correlations between turbidity and settling rates can I assume?

Thanks in advance




RE: Backwash NTU

The typical clarifier has a guarantee of 10 mg/L effluent, probably should do 3-5 mg/L if operated correctly.

If you have a 10 MGD plant, the total solids is 10 mgd * 10 mg/L * 8.34 = 834 lbs/ day.

The typical filter wastes 5% of the throughput. For the 10 mgd plant, that would be 0.5 mgd per day.

That would give you a backwash solution turbidity of 200 mg/L.

The backwash storage tank is usually sized for 1-2 backwash volumes.

RE: Backwash NTU

(OP)
Thanks for the feedback. I'm also wondering if the settling rate for backwash particles is known would this be enough to justify a detention time.

For example, if my average backwash turbidity was 20 ntu with a settling velocity estimated to be 0.25 ft/hour could i then say that four hours after a backwash the top foot of the equalization tank would be below 2 ntu?

Is there a rule of thumb for this?

RE: Backwash NTU

Have never seen anything like that. Since, the standard clarifier has less than an hour of retention, you would expect that most solids should drop out in approximately 1 hour.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close