AirPrex® – Addressing the Issue of Struvite Formation in BNR Plants

January 25, 2024

Struvite leads to several maintenance issues within a sewage treatment plant, typically in the mechanical sludge dewatering systems and the associated downstream infrastructure such as return pipework and pumping. Cleaning and removal of struvite is costly and can cause significant long term damage to pump internals and sludge dewatering systems.

AirPrex® is a chemical reaction process that is fitted downsteam of an anaerobic digestor and prior to sludge dewatering. The process removes struvite from sludge and even allows for the recovery of the struvite as a fertiliser.


  • Struvite is removed from the process, reducing maintenance costs
  • Dewaterability of sludge increases by 2 – 4%DS as the phosphates are removed, leading to reduced OPEX
  • Polymer consumption is reduced by approximately 10 – 15%, further reducing OPEX
  • Struvite can be recovered as a fertilizer
  • 80% reduction in return phosphate loads to the bioreactors


  • AirPrex® Macro – recovers and harvests the struvite from sludge to enable use as beneficial fertilizer
  • AirPrex® Micro – keeps the struvite crystals within the sludge phase (ie within the sludge cake) to enable beneficial reuse of the sludge cake

There are over 30 operating references in Europe, Asia and USA. The very first AirPrex® systems have been operation for well over 15 years and have used in treatment plants with capacities ranging from 20MLD to 500MLD.

To learn more about AirPrex® please CLICK HERE or contact Hydroflux on 1300 417 697.

About the Hydroflux Group

The Hydroflux Group aims to deliver the highest level of engineering and scientific know-how to the emerging issues of sustainability, climate adaptation and environmental protection with a specific focus on water and wastewater.

As part of its vision and mission, Hydroflux has always taken its climate responsibility seriously. In 2022, Hydroflux became Australia’s first water treatment and technology company to achieve Climate Active carbon neutral certification for its organisation and products. It knows that partnering with customers and clients is the most significant impact it can have in its journey. The Group employs over 100 staff and operates throughout Australia, New Zealand and the Pacific Islands, with office locations in Sydney, Melbourne, Brisbane, Perth, Auckland, Suva and Portsmouth.

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