Phosphorus Recovery
Phosphorus Recovery and Energy Optimisation
AirPrex® is an innovative phosphorus recovery and sludge optimisation process that improves wastewater treatment efficiency. Hydroflux Epco partners with CNP CYCLES GmbH, a leading specialist in nutrient recovery and energy optimisation, to deliver this advanced solution.
Installed between anaerobic digestion and sludge dewatering, AirPrex prevents struvite formation by inducing controlled phosphorus precipitation. By adding magnesium and adjusting the pH, the system removes up to 90% of phosphate, reducing sludge disposal costs and decreasing polymer consumption by 15%. This results in improved dewaterability, lower maintenance requirements, and the recovery of valuable phosphorus for reuse.
The Issue – Uncontrolled Struvite Formation
Uncontrolled struvite formation is a common issue in wastewater treatment plants that use biological phosphorus removal, leading to operational challenges such as equipment damage, increased maintenance, and reduced biosolids dewaterability. The key contributing factors and impacts include:
- Anaerobic release of ortho-phosphate during the digestion process in plants using biological phosphorus removal
- Formation of magnesium ammonium phosphate (MAP), commonly known as struvite
- Elevated phosphorus levels in recycle streams
- Crystal deposits in pipework and pumping systems associated with filtrate returns, resulting in increased wear and maintenance
- Struvite accumulation in mechanical dewatering systems, leading to higher maintenance costs
- Reduced biosolids dewaterability due to phosphate presence
It is possible to precipitate the struvite under a controlled reaction using a magnesium-based chemical and to produce struvite as a byproduct that can be sold as an enriched fertiliser. Furthermore, there is a reduction in phosphorous within recycle loads by 80-95% and an increase of 2 – 4% dry solids in dewatered biosolids. The removal of phosphate from the biosolids results in a drier cake with less polymer demand.
How to remove Struvite
Various processes are available to remove struvite using different methodologies. These methods typically rely on controlled precipitation, whether in the digested sludge stream or filtrate streams. Its removal is achieved through a chemical precipitation reaction, where pH is carefully controlled and a magnesium source is added to facilitate separation.
AirPrex Patented P-Removal Process
AirPrex is an advanced process for sludge optimisation and phosphorus recovery. It is implemented after anaerobic digestion and before mechanical sludge dewatering, ensuring the efficient removal of phosphate from the digested sludge stream rather than the filtrate.
The AirPrex® system consists of one or more reactors equipped with aeration sparges. A magnesium-based compound, such as magnesium chloride, is added to the reactor to facilitate controlled struvite precipitation. The airflow to the sparges is regulated based on pH levels, ensuring optimal conditions for struvite formation. With a carefully managed residence time, the process allows struvite crystals to grow before being separated, enhancing phosphorus recovery and minimising operational issues caused by uncontrolled struvite buildup.
The crystals are then removed from the process using a solids classifier. There are two configurations for AirPrex: one allows the struvite to form as microcrystals, allowing them to stay in the sludge cake, and the other forms larger crystals to enable recovery.
Macro and Micro Versions of AirPrex
AirPrex is available in Macro and Micro versions, designed to cater to different wastewater treatment plant capacities and operational needs.
The Macro version is tailored for large wastewater treatment plants handling high phosphorus loads and significant sludge volumes. It incorporates larger reactors and advanced automation for efficient phosphorus removal and struvite recovery. By integrating seamlessly into large-scale operations, the Macro version provides substantial cost savings in sludge disposal and maintenance while supporting sustainable resource recovery. The extracted struvite can be repurposed for agricultural or industrial use, turning a waste byproduct into a valuable commodity.
The Micro version is ideal for small to medium-sized treatment plants with lower sludge volumes. It features a compact reactor system that optimises the dosing of magnesium chloride or magnesium hydroxide to induce controlled phosphorus precipitation. This setup effectively prevents struvite formation in critical areas while enhancing sludge dewaterability, reducing polymer consumption, and minimising maintenance requirements without the need for large-scale infrastructure upgrades.
Data from International Installations
Installation List
| Year | Site | Size (EP) |
|---|---|---|
| 2009 | Neuwerk, Germany | 630,000 |
| 2011 | Berlin, Germany | 1,000,000 |
| 2013 | Amsterdam, Netherlands | 1000,000 |
| 2019 | Medina County, USA | 100,000 |
| 2020 | Denver Metro WRP, USA | 4,000,000 |
| 2023 | Erlangen, Germany | 270,000 |
Phosphate Removal Data
| Site | Soluble P04-P in | Soluble P04-P out |
|---|---|---|
| Medina, USA | 100 | 20 |
| Ft Collins, USA | 440 | 39 |
| Denver, USA | 326 | 26 |
| Elgin, USA | 370 | 30 |
| Savage, USA | 400 | 30 |
| Berlin, GER | 330 | 12 |
Struvite Production
| Site | Sludge Vol | Struvite |
|---|---|---|
| Neuwerk, Germany | 1500 kL/day | 0.45 t/d |
| Berlin, Germany | 2000 kL/day | 1.9 t/d |
| AMS, Netherlands | 2500 kL/day | 1.5 t/d |
Summary
Several processes have been developed to recover struvite from wastewater treatment systems, with AirPrex being a preferred and proven solution. With over 20 successful installations dating back to 2009, AirPrex has demonstrated its effectiveness in managing phosphorus removal. Over the past decade, design enhancements have further optimised the process, integrating hydrolysis with controlled phosphate removal to achieve even higher struvite recovery rates.
By recovering phosphorus, AirPrex not only supports circular economy principles but also reduces maintenance costs associated with uncontrolled struvite formation. With increasing uncertainty around biosolids disposal costs, this technology presents a valuable opportunity for water utilities and local councils across Australia and New Zealand, helping to improve operational efficiency and sustainability.
From Concept to Completion
Hydroflux Epco’s engineers work closely with clients, contractors, and consultants to develop tailored solutions. Comprehensive design documentation is prepared, including process flow diagrams, equipment layouts, performance specifications, and integration plans for existing facilities and utility requirements. Careful consideration is also given to the handling, storage, and logistics of the by-products to ensure operational efficiency and compliance.
Our team of experts understands the complexities of struvite recovery and will always provide tailored advice on selecting, designing, and optimising the correct system in each case.
Get in touch with Hydroflux Epco today to learn how we can help streamline your wastewater treatment operations with reliable, high-performance phosphate recovery solutions.