Effluent Nitrogen in an Activated Sludge WWTP 3

[DrLewinstein]

What concentration of total nitrogen should we expect in the effluent of an extended air activated sludge plant? We will be nitrifying, but not denitrifying. Ammonia limit is 4 mg/L. We need to estimate total N for land application.

Thanks.

 

[DrLewinstein]

This is domestic wastewater in a package WWTP. (I couldn't figure out how to edit my post.) I'm assuming a 40 mg/L TKN influent.

 

[bimr]

Some nitrogen removal can be achieved by denitrification, which can remove 30 to 40 percent of the total nitrogen (TN) under optimum conditions. Average total nitrogen effluent concentrations in residential extended aeration units range from 17 to 40 mg/L.

http://www.epa.gov/nrmrl/pubs/625r00008/html/tfs1.htm

 

[jartgo]

I agree with bimr. It will ultimately depend on what concentrations you're putting in it and O&M schedules, but effluent TN will be relatively high without some specific nitrification/denitrification as part of the process (or a tert. filter). Without specific removal operations/process, 15% to 20% removal is all I'd count on.

Yours is a common problem, ammonia limit of 4 is relatively easy to achieve, but you haven't gotten rid of the nitrogen, it's only changed forms until the denit stage. And with land application, you're concerned with nitrogen, in all its forms.

 

[Watthour]

With some hesitation I would disagree with the statement that only 30-40% removal can be achieved with dedicated denitrification. I have MLE designs operating which take TKN from 55 mg/l to below 5 mg/l in the effluent - Without using flocculants and tertiary filtration.

As we all know, there are far too many variables affecting the process, and none of the data have been presented. The temperature of the mixed liquor, alkalinity, available carbon, and other factors have significant impact upon the effectiveness of denitrification.

As stated above, without a dentirification process the expectation for total nitrogen reduction should probably not exceed 25%. However, conversion may occur and if the effluent requirement is only for organic nitrogen limits a plant without denit may be viable.

 

[DrLewinstein]

Thanks to you all. Based on the understanding that we were not going to get below about 15 - 17 mg/L without denitrification, we decided to go ahead and add it in order to make our nitrogen balance work out for our land application area.

 

[bimr]

The key words in the post are "package WWTP". The design of a package plant will limit the performance.

http://www.epa.gov/waterscience/criteria/nutrient/files/bio-removal.pdf

 

[DrLewinstein]

Awesome paper! Thanks.

 

[ch81pc]

If your lanes are long enough, why not switch off the air to the first sections (30 min retention) to get the anoxic zone in as part of the exisitng lane? You may need to install some mechanical mixers (below the surface to prevent surface agitation and DO entrainment) to prevent settlement.
We operate an extended aeration ditch on this principal, with 1/3 of the length being mixed, but not aerated whihc gives very good results. If you FST's can handle it, you can up the MLSS in the system to get the same treatment in the remaining aearated sections.

 

[DrLewinstein]

If our plant were larger, this may be a good idea. However, instead of lanes, we will have small 10,000 gallon concrete tanks. We will have to have a partition to separate the aerobic from the anoxic. Thanks.