Abstract
Simultaneous ammonium–nitrogen (NH₄⁺–N) removal and orthophosphate–phosphorus (PO₄–P) biomineralization was studied in two granular sludge sequencing batch reactors treating urban sidestream centrate through the one-stage partial nitritation–anaerobic ammonium oxidation (anammox) process. By adding an external source of calcium, concomitant conversion rates of up to 0.32 g NH₄⁺–N/(L·days) and 12 mg PO₄–P/(L·days) were measured while reaching water-phase removal efficiencies of ca. 80% of the NH₄⁺–N and 70% of the PO₄–P loaded. The mineral cores formed inside the granules were mostly composed of hydroxyapatite (HAP), which is a recoverable phosphate salt. Yet, the high mineralization of the sludge and its excessive purge from the bioreactor limited the microbial activity in the long term. In this sense, the densest granules, accumulated at the bottom of the bioreactor, were the most susceptible to being harvested because they were the richest in HAP, but at the same time, they contained the highest percentages of anammox bacteria.
Highlights
Phosphorus (P) is an essential element for all living organisms
Different methods can be applied in wastewater treatment plants (WWTPs) to achieve P recovery.[5]
The main parameters characterizing the performance of both PNA sequencing batch reactors (SBRs) during the four operational phases described above (440 days in total) are shown in Table 1 and Figure 1A−C
Summary
Phosphorus (P) is an essential element for all living organisms. This nutrient is absolutely necessary for sustaining agri-food production, and its demand rises alongside the growth of the global population.[1] Currently, mined phosphate rock (i.e., apatite-type ores) is the primary source of P, but this is a finite resource, which is unevenly distributed around the world.[2] The European Union (EU) depends on the import of P, and it has identified phosphate rock and P as 2 of the 27 critical raw materials having high importance to the EU economy and having a high risk associated with their supply.[3]. The crystallization and precipitation of low-soluble salts are commonly used, based on the combination of the dissolved orthophosphate (PO4) with a metal ion, e.g., calcium (Ca), magnesium (Mg), or iron (Fe)
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