Mapping of Phosphorus at Rya Wastewater Treatment Plant - A Case Study of the Phosphorus Treatment at Rya Wastewater Treatment Plant
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Typ
Examensarbete för masterexamen
Program
Infrastructure and environmental engineering (MPIEE), MSc
Publicerad
2022
Författare
Byström, Frida
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
Phosphorus (P) is an essential building stone for humans and plants, but it can
cause eutrophication when discharged into water bodies. Wastewater is one of the
main inputs of phosphorus into freshwater sources, and treatment of phosphorus
through chemical and biological methods is essential to reduce the concentrations
reaching recipients. Rya wastewater treatment plant (WWTP) is located in Gothenburg,
Sweden, and employs simultaneous chemical precipitation for the reduction
of phosphorus with iron(II) sulfate (FeSO4). Sufficient P removal is achieved at
Rya WWTP even as the dosage of FeSO4 is low compared to recommended levels
of chemical dosing given in literature. A mass balance of the P at the WWTP was
constructed combined with laboratory tests measuring P-release/uptake and chemical
precipitation with drinking water sludge (DWS) to investigate possible processes
within the plant contributing to phosphorus removal besides the chemical precipitation
with FeSO4.
The primary reduction of P, around 85% of the total reduction, can be observed
after the addition of FeSO4 over the activated sludge (AS) basins and the secondary
settling tanks (SSTs) for both total P (Tot-P) and orthophosphate as P (PO4-P) at
Rya WWTP. The remaining reduction of 15% occurs in the denitrifying moving bed
biofilm reactor (DMBBR) for the PO4-P and through the disc filters (DF) for the
suspended phosphorus. The P-release and uptake batch test indicated that bio-P
bacteria with the ability to release and store P is present in the AS at the plant.
Combined with the observed presence of polyphosphate-accumulating organisms
(PAOs) at Rya WWTP through participation in the MiDAS project, the results
indicate bio-P treatment at the plant, but to what extent remains undecided. The
aluminium in the DWS showed that it could precipitate PO4-P, which means that a
reduction of ca. 15-18 tonnes/yearly of PO4-P occurs before the water reaches the
AS basins at Rya WWTP. The contribution from the DWS to PO4-P reduction, the
presence of PAOs in the AS basins and their ability to store and release P are two
possible explanations for the low effluent concentrations of P with the sparse dosage
of FeSO4.
Beskrivning
Ämne/nyckelord
Enhanced biological phosphorus removal (EBPR) , chemical precipitation , polyphosphate accumulating organisms (PAOs) , drinking water sludge , orthophosphate , Iron(II) sulfate (FeSO4) , activated sludge