Towards phosphorus circularity: biofilm EBPR with subsequent struvite production at the Hias WWTP: insights from full-scale and laboratory testing

ABSTRACT With the objective of reducing its CO2 footprint and moving towards circularity by recovering influent phosphorus, Hias wastewater treatment plant (WWTP) has developed a novel biological removal process (the Hias Process) which combines enhanced biological phosphorus removal (EBPR) and moving bed biofilm reactor and is now operating at full scale. Additionally, a struvite reactor is installed to capture phosphorus from the resulting sludge. In this work, the performance of the WWTP and particularly the biological phosphorus removal process and struvite reactor is assessed with regards to circularity and recovery of phosphorus. The Hias Process demonstrates stability and effectiveness even in cold climates and during stormwater events. Introducing the Hias Process reduced the use of precipitation chemicals, leading to a lower carbon footprint. The combination of the Hias Process with subsequent struvite reactor contributes to increased phosphorus circularity. That is achieved through improved plant availability of phosphorus in biosolids and the production of struvite. Main factors affecting recovery of phosphorus are identified and include the use of precipitation metals, bypass of the EBPR, and temperature's impact on PO4 release from EBPR sludge. This study aligns with Sustainable Development Goals and emphasizes efficient phosphorus recovery through the Hias Process and struvite reactor.