News from Schwing Bioset

Pima County, AZ, Tres Rios WRF Biosolids System Upgrades – Part Four: NuReSys Nutrient Recovery System


Written by Josh DiValentino


Background: The district of Pima County, AZ, operates a total of eight wastewater treatment plants. The Tres Rios Water Reclamation Facility (WRF) is the centralized biosolids processing facility for all Pima County plants. Tres Rios WRF currently operates 24/7/365 at a 30 MGD capacity, with a projected flow of 50 MGD in 2030. The facility process is; BNR, Anaerobic Digestion, Dewatering, and Land Application of biosolids.

The Tres Rios facility has battled struvite build-up in pipelines and equipment following anaerobic digestion for many years. A combination of Ferric Chloride downstream of the digesters for struvite control as well as dilution water in the centrate return lines was used to slow struvite build-up. In 2009 the facility began to gather data for side stream treatment to precipitate struvite. Starting with the “big picture,” all possible options were considered, from harvesting struvite from centrate streams to sequestering struvite within the digestate. An on-site pilot study was also conducted to determine levels of performance that could be expected. Ultimately the goals of the project were to stop struvite scaling issues, eliminate the need for Ferric Chloride and dilution water addition, and reduce the phosphorus return loading to the plant. This led to the project moving forward to treat digestate and remove phosphorus by sequestering the produced struvite within the biosolids.


The First NuReSys System in North America for Struvite Management: The project is being delivered through a Construction Manager At Risk (CMAR) method via an evaluated bid process. Schwing Bioset, Inc. (SBI) was selected as the system provider in August 2018. The primary objective is to precipitate struvite within the digestate stream for removal with the biosolids. By converting a minimum of 85% of the available orthophosphate into crystalline form (or leaving no more than 50 ppm remaining in reactor effluent), the phosphorus recycle stream back into the plant is broken. Additionally, due to the flexibility and two stage operation of the NuReSys technology, power demands are roughly 1/3 of the performance guarantee values (based on another technology), resulting in significant annual savings.

The design of the system was finalized through the CMAR design contract with HDR Engineering. During the design process Pima County, HDR, and Schwing Bioset were able to integrate several important features into this design, the following model details the implemented concept (Figure 1 shown below):


NuReSys - Schwing Bioset RenderingSystem Specifications:

  • 300 gpm (400 GPM peak)
  • 2.7% Dry Solids
  • 280 mg/l PO4-P in
  • 85% conversion or less than 50 mg/l PO4-P out

As previously noted, the NuReSys system employs a unique two (2) step process to precipitate struvite in a controlled environment and optionally harvest, on either Digestate or Centrate streams. The first step is pH adjustment. In the CO2 Release Tank the system releases CO2 via coarse bubble aeration to raise the pH to optimum process conditions. The CO2 Release Tank will also consume most of the magnesium remaining in the digestate, producing Magnesium Ammonium Phosphate (otherwise referred to as MAP, or struvite) prior to chemical addition taking place in the Crystallizer. The second crystallization step doses a reagent, commonly MgCl2, as necessary to complete the struvite reactions.

The Pima County system is currently set up to treat digestate flow following the Anaerobic digesters. The precipitated struvite then becomes entrained in the Biosolids and exits the plant with the dewatered cake. The figure below (Figure 2 - NuReSys Digestate Configuration) illustrates this configuration.

NuReSys Digestate Graphic - Schwing Bioset

The NuReSys system at the Tres Rios facility has two unique design features that both the District and the CMAR found advantageous during the selection process:

1.) Dual CO2 Release Tanks were offered as shown in Figure 1 above. Normally a single tank is used for pH adjustment, however in this case, splitting the aeration step into two tanks allowed for optimal blower selection (hybrid type blowers), and improved turn-down efficiency. The result is a highly flexible system that consumes the least amount of electricity possible. Through the 60-day performance test power consumption was measured as roughly 1/3 the specified maximum allowed which will translate into significant long-term operational savings.

2.) Future conversion to Hybrid Configuration. The system is designed such that it can be converted to a Hybrid configuration by simply replumbing and redirecting flow from the Centrate lines (following centrifuge dewatering) to the Crystallization tank. This conversion would allow the system to recover up to 90% of the struvite produced (vs only up to 50% recovery possible with the current Digestate configuration), should struvite recovery be of interest in the future. The figure below (Figure 3 - NuReSys Hybrid Configuration) illustrates how the equipment can be reconfigured in the future to operate in Hybrid mode.

NuReSys Hybrid Graphic - Schwing Bioset


As of Spring 2021, the system is fully operational running in Digestate mode and completed final performance testing. More importantly, the system is exceeding the specified performance criteria for PO4-P removal and Tres Rios is realizing the following benefits:

  • Discontinued its Ferric Chloride addition after the digester as well as dilution water operations saving $400,000 annually.
  • Improved dewatering has lowered annual hauling costs by $600,000
  • An as yet unquantified savings as the centrifuges are no longer being opened and cleaned every two weeks as was required prior to implementation of the NuReSys technology.
  • With an average PO4-P concentration of 25 mg/l leaving the NuReSys system, the process has broken the phosphorus loop returning to the plant. PO4-P concentrations in the digesters have trended downwards from the 280 mg/l the plant was experiencing on start-up to less than 200 mg/l by the time the performance testing commenced.

    All combined, the system will save the County hundreds of thousands of dollars annually. While there are numerous NuReSys systems operating in Europe, Schwing Bioset Inc. and Pima County are proud of the first NuReSys installation that will serve as the flagship in North America (shown below is Figure 4 - Installed NuReSys System at Tres Rios WRF).


Tres Rios NuReSys System - Schwing Bioset


Click here to read more about our products and processes (or here to go directly to our Struvite Recovery page), then contact us to learn more about this project or find out how we can help your plant too. 


Check out Josh’s previous Pima County Project stories here:

Part One: Cake Pumping

Part Two: Live Bottom Bins

Part Three: Mobile Screw Press Dewatering


 Download Our Brochures    or Application Reports

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Tags: Struvite Recovery, Nutrient Recovery, Water Reclamation Facility, NuReSys, Nutrient Management

Recovering a Valuable Nutrient From the Wastewater Stream


Published in TPO Magazine, August 2019


Phosphate recovery technology offered by Schwing Bioset can be tailored to meet each facility’s specific operating challenges


Resource recovery is a major trend in wastewater treatment — to the task of cleaning water, facility teams are adding the capture of energy and nutrients.

One increasingly popular type of technology is the capture of phosphorus as struvite, which has market value as a fertilizer additive. One entry in that sector is Schwing Bioset, which offers a phosphate and nitrogen recovery technology under license from Belgium-based NuReSys.

The offering is unique in that it is not necessarily designed to extract revenue from nutrient capture, although that option is available. The process is designed to be tailored to each facility’s objectives in dealing with phosphate-related issues.

Besides nutrient recovery, the process has the benefits of preventing buildup of struvite scale in treatment equipment and improving dewaterability in biosolids. Wim Moerman, chief technology officer for NuReSys, and Chuck Wanstrom, director of new business development with Schwing Bioset, talked about the technology in an interview with Treatment Plant Operator.


Click here to read the full interview.


Nutrient Management Plant


To learn more about Schwing Bioset’s Nutrient Management solutions, visit our website here or contact your Region’s Representative.


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Tags: Wastewater Treatment, Struvite Recovery, Nutrient Recovery, Phosphorus Removal, Nutrient Harvesting

NuReSys Technology for Struvite Recovery to be Built in Braunschweig/Germany


WEFTEC is the perfect place to learn more about our Struvite and Phosphorus Recovery technology. Stop by the Schwing Bioset booth (Hall C, booth 1828) and talk with our Schwing Bioset and NuReSys representatives.

If we won't see you at WEFTEC, you can learn more in the press release below, by visiting our Struvite Recovery webpage, or by contacting one of our regional reps.


PRESS RELEASE  09/24/2016


NuReSys technology for struvite recovery to be built in Braunschweig/Germany.

NuReSys is proud to announce that the Municipality of Braunschweig, assisted by PFI Planungsgemeinschaft GbR regarding unbiased evaluation of the different offers, has awarded its future phosphorus recovery plant to the combination Bremer-Pro-Aqua and NuReSys. The requirements of the tender were quite challenging and therefore the solution offered had to be versatile and flexible. The flow can vary from 8 to 25m³/h and the PO4-P levels between 300 and 800 ppm. The combination offered a tailor made solution which not only takes into account the phosphate recovery but also any post and preceding processes. Dipl. Ing. Thomas Meyer from Bremer-Pro-Aqua says: "We had a first collaboration with NuReSys when back in 2006 we built a phosphorus recovery plant in Altentreptow. This was an industrial plant in the dairy sector. Also this time the collaboration with NuReSys was correct and we felt very much on the same wavelength.”

Visit us at Weftec 2016 New Orleans (26-28 Sept.)  -  Booth 1828 Hall C,  SCHWING BIOSET


Struvite Recovery               Struvite Recovery


NuReSys Nutrient Recovery Technology



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Tags: Struvite Recovery, Nutrient Recovery

Recover Phosphorus from Waste Stream for Beneficial Reuse


Posted by Kelly Kramer

At wastewater plants utilizing anaerobic digestion, Struvite commonly forms and creates issues with pipes clogging and equipment being damaged as a result of scaling.  Additionally, tanks can accumulate Struvite, which requires periodic removal and creates an additional expense to plant operations.

Schwing Bioset Struvite Recovery Bio-Stru Product

Schwing Bioset’s Nutrient recovery system recovers Ortho Phosphate and Ammonia Nitrogen from wastewater while offering great benefits to the treatment plant, not only by significantly reducing phosphorus in the waste stream, but also preventing unwanted scaling and accumulations, and creating a valuable end product.  The phosphorus forms a stable Struvite crystal that can be marketed and sold for beneficial reuse, thus keeping excess phosphorus out of the local waterways and helping close the phosphorus recycling loop. 

The article, "The Six Natural Resources Most Drained by Our 7 Billion People," posted on The Guardian, discusses phosphorus and provides a resourceful link to learn more about this essential nutrient and it's role in food production.

To learn more about how Schwing Bioset can help your plant with Nutrient Management, visit our website, call us at (715) 247-3433, or email us at


Nutrient Management Air Stripper Schwing Bioset 


Download Our Nutrient Recovery Brochure



Tags: Beneficial Reuse, Struvite Recovery, Nutrient Recovery, Phosphorus Removal

Phosphorus Removal and Nutrient Harvesting Continuing Education


Written by Eric Wanstrom, March 22, 2016

Schwing Bioset is pleased to announce the Schwing Bioset Phosphorus Removal and Nutrient Harvesting paper has received accreditation and official approval for continuing education credits in New York State.  

Schwing Bioset’s Nutrient recovery system recovers Ortho Phosphate and Ammonia Nitrogen from wastewater while offering great benefits to the treatment plant, not only by significantly reducing phosphorus in the waste stream, but also preventing unwanted scaling and accumulations, and creating a valuable end product.  The phosphorus forms a stable Struvite crystal that can be marketed and sold for beneficial reuse, thus keeping excess phosphorus out of the local waterways and helping close the phosphorus recycling loop.   

Engineers and operators can receive one (1) hour of CEU credits for attending a presentation on these topics.  Please contact us to schedule the presentation for your office or plant.

You can learn more about the NuReSys Nutrient Harvesting Process at the links below.


For questions or comments, please email this blogs author, Eric Wanstrom, call 715.247.3433, and/or visit our website.


Schwing Bioset Nutrient Harvesting


Tags: Wastewater Treatment, Continuing Education, Struvite Recovery, Phosphorus Removal, Nutrient Harvesting