Best method to measure flowrate at sewer connection.

[KirbyWan]

We have been estimating the outflow of our process room by measuring the water input, however the Department of Environmental Quality has indicated that we should be measuring the outflow. We need to measure the flow to determine the monthly average water use (per day) and the daily maximum water usage to comply with our permit. Our waste treatment process is performed on a batch process roughly once a week with additional flow that does not need to be treated from overflowing rinse tanks with all waste water being delivered through a final pH adjustment tank before releasing it to the sanitary sewer. The problem is we only use about 3000 gallons per day and the drain line is 3" PVC pipe, so we don't have a pipe that is 'full' to use an ultrasonic or magnetic flow meter. Someone suggested an ultrasonic flow meter that designed to be used with a weir to measure the flow rate.

How are outflow measurements commonly measured? I figure most places that have environmental permits have a similar problem to measure their outflow.

Thanks for your help.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[cvg]

Someone suggested an ultrasonic flow meter that designed to be used with a weir to measure the flow rate.

"Someone" would be correct, suggest a v-notch

References
1. U.S. Dept. of the Interior, Bureau of Reclamation, 2001 revised, 1997 third edition, Water Measurement Manual, available for online use or download at:

http://www.usbr.gov/pmts/hydraulics_lab/pubs/wmm/index.htm

 

[KirbyWan]

Thank you. I will contact a couple of companies to get quotes. I was thrown off by my assumption that this was for a much larger volume measurement than we have.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[KirbyWan]

So I checked out this website:

http://www.aquatechnologygroup.com/...-v-notch-weir-for-wastewater-treatment-plant/

And they have a calculation for determining flow rate. At the minimum head allowed, .2 feet, I calculate the flow rate using their formula they provide (223 GPM * .2 ft ^2.5 = 4 GPM) for the narrowest V-notch weir and come up with a flow rate of 4 GPM, which is about twice what our average flow rate is. I left them my info to size a system, but I was wondering if there was a system designed for much lower and intermittent flow rates?

Thanks for your input.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[bimr]

This is a difficult application. You can use a magmeter.

There are two options.

The first is to install the magmeter in a pipe dip so that the magmeter is always full.

The second method is to use the Flo-Dar:

http://www.hachflow.com/pdf/Flo-Station.pdf

You will need a sampling manhole with 6-Inch connections.

 

[agua84]

Low flows can be tough to measure on a continuous basis, but what about a batch basis? For a short term flow study, could you temporarily block the discharge pipe, divert the water immediately upstream to a sump, place a pump in the sump equipped with some sort of totalizing flow meter on the discharge piping, and direct the discharge piping to downstream of the temporary pipe block? Set it up, run the process to make sure it works, then check the totalizing flow meter periodically. Or else some sort of tipping or dumping vessel with a means to count the number of times it is filled. It depends on access to the discharge, though, and how nasty the waste water is. If the need is long term, bimr has the two best options.

 

[KirbyWan]

I was chewing over a sump set up like you suggest. That seems like the most straight forward way to meter our outflow. I would still like to get input on how people in a similar situation measure their outflow, or is this just uncommon and some other solution is used to estimate the outflow for small discharge situations.

-Kirby

Kirby Wilkerson

Remember, first define the problem, then solve it.

 

[bimr]

It is uncommon. Most times the sewer agency will accept the water meter readings and not require the flow to be measured. Suggest you review the situation again with the sewer agency and see if they will accept the water meter readings.