Meet your Lagoon's Ammonia Limits, no matter how cold winter gets.

Learn More about How to Meet Ammonia Limits

Your challenge:


Reduce TAN to <1mg/L: You need to achieve effluent Total Ammonia-Nitrogen levels down to <1 mg/L, even in the cold of winter, something your existing lagoons just can’t do.

Save space, time, and money: You’d like to do it on a compact footprint, and as usual, the simpler to operate and more inexpensive the solution, the better.

Our technology:

Achieve <1 mg/L ammonia
in water that is <1°C

Nexom is the exclusive source for the SAGR, a simple, powerful tool for fully nitrifying lagoon effluent in any climate. The SAGR consists of a clean stone bed that is fully aerated. In a typical configuration, water flows through the substrate horizontally, and a layer of insulating wood chips, mulch or shredded tires at the surface prevents ice formation in the bed, allowing the system to treat wastewater that is near freezing (<0.5°C).

Why do you need a SAGR? Lagoons are incredibly powerful ecosystems that cost-effectively, naturally remove a host of wastewater’s most harmful components with a minimum of operations or maintenance requirements. But lagoons often struggle to remove ammonia in winter for four reasons:

  1. If a facultative (un-aerated) lagoon freezes over, access to atmospheric oxygen is cut off, which is needed by nitrifying bacteria.
  2. Nitrifying bacteria require a surface to grow on, something that is not plentiful in a lagoon.
  3. The heterotrophic bacteria that consume cBOD5 tend to dominate nitrifying bacteria, meaning cBOD5 needs to drop below 25mg/L before nitrification can begin in earnest. Cold temperatures slow the metabolism of the heterotrophs. More of the lagoon retention time is required for BOD removal, reducing the available HRT for nitrification.
  4. Both the reproduction rate and the metabolism of the nitrifiers themselves slow as the water temperature drops. The low reproduction rate means that new biomass does not form quickly enough to make up for the reduced consumption of ammonia that occurs due to the lower metabolism.



Key advantages:

Reduces Total Ammonia to <1 mg/L year-round, even in <0.5°C water

Polishes cBOD to <5 mg/L, TSS to <10mg/L, and provides effluent disinfection

Low O&M requirements similar to a conventional aerated lagoon

Reduces emerging substances of concern

  • Nitrification in any climate
  • Post-lagoon polishing
  • Airport de-icing fluid treatment
  • Decentralized wastewater treatment
  • Water reuse applications

How it works

Creating the ideal environment for nitrification

As the lagoon effluent flows horizontally through the bed, the high-DO environment encourages nitrifying bacterial growth on the plentiful surface area provided by the clean stone. Influent distribution and effluent collection chambers prevent short-circuiting in the bed, and the bed itself is sized to enable full cBOD polishing as well as full nitrification, even in the cold. And to compensate for the slow nitrifier metabolism and reproduction in cold water, the SAGR’s patented Step-Feed process prebuilds and stores nitrifying bacteria while the water is warm so that they are already in place when winter comes. At the same time, the stone in the bed buffers the water temperature to prevent the cold influent from shocking the existing bacteria.

Using the patented Step-Feed process, the SAGR overcomes each of the four factors that would otherwise prevent nitrification:

  1. Oxygen: The stone bed is fully aerated, meaning there is plenty of dissolved oxygen for the nitrifying bacteria even in the dead of winter.
  2. Surface area: The clean stone is sized to optimize hydraulic conductivity as well provide ample surface area for the nitrifying bacteria to grow on.
  3. Competition from cBOD: SAGR beds are sized to provide cBOD polishing in addition to nitrification.
  4. Cold water temperatures: Because nitrifying bacteria grows much more slowly in cold water, the SAGR process prebuilds and stores nitrifying bacteria while the water is warm so that it is already in place once metabolism and reproduction slow in cold water, setting it apart from other attached growth nitrifying technologies.


Cutaway view of a SAGR:

A. HDPE liner prevents infiltration while sacrificial walls help the SAGR maintain its shape during construction.
B. Influent distribution chamber ensures influent is spread across the width of the bed.
C. Clean stone provides surface area for bacteria while preventing temperature shock. Mulch-covered for insulation.
D. Linear aeration covers the base for fully-aerobic conditions.
E. Effluent collection chamber is gravity fed to minimize O&M.

Relevant Case Studies

Shellbrook, SK

Shellbrook’s objective was to treat its wastewater to the standards set by the CCME (Canadian Council of Ministers of the Environment), which Saskatchewan Environment was in the process of adopting.

read more
Pilot Butte, SK

Back in 2014, Pilot Butte’s population had just climbed past 2,500, and with several developments in progress, the Saskatchewan municipality needed to upgrade their two-cell facultative lagoon system to allow for more treatment capacity.

read more
Park View, Iowa

Sanitary district upgrades lagoons for full cold weather ammonia nitrification within existing footprint.

read more

What it delivers

Full nitrification in near-freezing water while maintaining O&M simplicity

Ammonia reduction (nitrification) can be consistently and reliably achieved at water temperatures below 0.5°C in climates where primary and secondary lagoons are ice-covered for much or all of winter. Providing treatment with very low water temperatures eliminates the need for heating the water, insulating, increasing depth or decreasing the retention time of lagoon cells to retain heat.

Want to know what a SAGR could do for your lagoon-based system?

Submit your RFP today and our on-staff professional engineers can help you size and design a SAGR™ cold-climate nitrification system to meet your wastewater treatment requirements.


Is a cover required on the upstream lagoons?

No. A cover is not required on the upstream lagoons as the SAGR is designed to treat effluent at very low temperatures, eliminating the need to retain process heat.

Is there data from systems operating at full design loads and flows?

Yes. Nexom has collected thousands of data points from dozens of sites, including sites operating at 100-200% of full design flows. Facilities across North America have shown consistent nitrification year round with water temperatures as low as 0.2°C.

Are there systems operating in climates as cold or colder than the proposed application site?

Yes. Installations across Canada and the USA include some of the coldest populated areas in North America. Data from these sites demonstrate that the SAGR provides consistent nitrification in hostile climates.

Does the system require any wasting of solids (WAS)?

No. Nitrifying biomass generate very few solids. Most of the solids generated by the heterotrophic bacteria removing the BOD are contained upstream in the lagoon system. The SAGR is designed so that any solids that are generated in the bed aerobically digest within the pore space of the media. The SAGR retention time is designed such that any inert solids that do accumulate in the bed do not need to be removed throughout the design life of the system.

What are the maintenance requirements?

The only moving parts in the system are the blowers supplying oxygen to the SAGR process. Typically, an operator will perform a system inspection using a check-list and maintain the blowers by changing lubricating oil, drive belts and inlet filters as required. Annually, the operator will initiate the patented step feed process by manipulating the influent control valves.

Is the system compatible with future upgrades?

Yes. The SAGR nitrification module is fully compatible with other Nexom lagoon-based process. Phosphorus can be removed with the infini-D Zero-Downtime Phosphorus Removal process (which includes chemical addition prior to cloth disk filtration) and a wide range of Total Nitrogen limits can be met through the use of pre-anoxic zones within the lagoon system or combined with BioPorts dentirifying MBBRs.