From: R Quigley
Sent: Wed Dec 26 13:47:31 2018
To: Andy Peters
Cc: Gerald Fisher; Jake Ehredt
Subject: FW: Lagoon Question
Importance: Normal
From: tmolatore
Sent: Wednesday, December 26, 2018 12:35 PM
To: R Quigley
Subject: FW: Lagoon Question
Ryan,
Here is some additional information concerning the high effluent ammonia levels in Molalla.
He notes that influent ammonia is about 47 mg/L, based on a per capita flow of 50 gpcd, without any I/I. With I/I, it’s much lower, which is the case in Molalla.
I inquired with Triplepoint Environmental because I was thinking that the dredging operation may have been the catalyst to the high ammonia levels. Triplepoint Environmental are lagoon experts, they specialize in lagoon retrofits, and do a lot of work in the Midwest.
Anyways, you might want to also forward this information to Andy.
Thanks,
Tyler J. Molatore, PE
The Dyer Partnership Engineers & Planners, Inc.
759 W. Central Ave.
Sutherlin, Oregon 97479
(541) 459-4619
(541) 784-5095 (cell)
From: Tom Daugherty [mailto:tomd@tpenv.com]
Sent: Wednesday, December 26, 2018 11:26 AM
To: tmolatore
Subject: RE: Lagoon Question
Tyler,
Yes, we have seen ammonia spikes in similar scenarios as you describe. The good news is re-acclimation of the pond system generally restores to previous treatment levels – and better. What we learning over time is the re-acclimation can take up to a year dependent on multiple variables including pond configuration, weather, ADF, and HRT.
A couple things come to mind in the scenario you describe:
1) Something in the pond has caused an oxygen demand, taking it away from where it used to go.
2) Given a summer solids dredging (partial) - solids were stirred (more intermittent O2 demand from the aerobic layer), a solids cap was removed and benthal feedback likely occurred (and may still be occurring). If the BOD effluent value surged a month or two after dredging to a value of > 30 mg/L, nitrification could have been interrupted or slowed as the BOD eating bacteria (heterotrophs) outperform nitrifiers (autotrophs) until the BOD value is <30 mg/L. If this is a single facultative pond, the desired BOD value of < 30 would likely be somewhere mid to 2/3rds way through the pond – not at effluent. This allows for some residence time for nitrification in the last portion of the pond.
3) If nitrification was interrupted/slowed as a result of dredging, it may not have fully restored prior to colder weather and potential continued benthal feedback – akin to pulling back the reins on a horse.
4) The theoretical bottom for nitrification to occur is 39.2F (water temp) and the autotrophic nitrifiers move more slowly as the water nears that temp.
5) Many small systems do not monitor ammonia influent values but 47 mg/L is a typical value for municipal wastewater without I/I.
6) I assume the solids were dewatered and hauled away. If they were Geo-tubed and decanted back to the pond, the decant is typically high strength ammonia and would be a contributor.
A case in point is Eagle Sewer District in Eagle, ID. They relined ponds, installed new aeration and started up Dec 2017 – cold. The BOD started in the 60s, fell to 20’s by June and were in the teens last week, a year after startup. Ammonia has been same out as in over that time but starting to nitrify. A key point on ESD is the 2 MGD lagoon system actually discharges to the West Boise plant so design criteria was 60 mg/L BOD effluent and no criteria for ammonia. The takeaway is the 12 month-ish acclimation period from a radical revamp of the system mixed with cold weather startup.
Time is on the side of your client. The removal of solids will improve HRT which will improve treatment likely concurrent with spring warming. A more rapid solution would be to add some air.
Thx,
Tom
From: tmolatore [mailto:tmolatore@dyerpart.com]
Sent: Wednesday, December 26, 2018 10:07 AM
To: Tom Daugherty
Subject: Lagoon Question
Tom,
We are the City engineer for a City that has a facultative lagoon that has an ammonia limit of 16.7 mg/L (monthly average). They’ve never had issues with ammonia compliance, and typically achieve < 10 mg/L effluent ammonia. They did, however, this past summer, dredge some solids (not completely) from the lagoon. This winter they are having some elevated effluent ammonia levels. Have you noticed higher effluent ammonia levels after removing sludge from lagoons? With infiltration/inflow, the 16.7 mg/L limit shouldn’t be a problem. They have good pH values, and remove most of their BOD. Effluent BOD is typically < 15 mg/L. I was just curious if post-dredging of lagoon solids can influence effluent ammonia, by stirring up some solids, etc.
Thank you,
Tyler J. Molatore, PE
The Dyer Partnership Engineers & Planners, Inc.
759 W. Central Ave.
Sutherlin, Oregon 97479
(541) 459-4619
(541) 784-5095 (cell)