Mapping of Phosphorus at Rya Wastewater Treatment Plant - A Case Study of the Phosphorus Treatment at Rya Wastewater Treatment Plant

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Examensarbete för masterexamen
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2022
Författare
Byström, Frida
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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.
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Ämne/nyckelord
Enhanced biological phosphorus removal (EBPR), chemical precipitation, polyphosphate accumulating organisms (PAOs), drinking water sludge, orthophosphate, Iron(II) sulfate (FeSO4), activated sludge
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