Nutrients removal by high-rate activated sludge and its effects on the mainstream wastewater treatment

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2024-01, Vol.479, p.147871, Article 147871
• Main Authors: Canals, Joan, Cabrera-Codony, Alba, Carbó, Oriol, Baldi, Mercè, Gutiérrez, Belén, Ordoñez, Antonio, Martín, María J., Poch, Manel, Monclús, Hèctor
• Format: Article
• Language: English
• Subjects: activated sludge; adsorption; anaerobic ammonium oxidation; chemical oxygen demand; denitrification; energy efficiency; energy expenditure; High-rate activated sludge; nitrogen; Nutrients ratio; Nutrients removal; Organic matter demand; oxidation; phosphorus; total Kjeldahl nitrogen; total phosphorus; wastewater; wastewater treatment
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2023.147871

[Display omitted] •HRAS achieves 23% TKN and 56% TP removal, exceeding primary clarifiers.•Nutrient removal in HRAS is independent of COD oxidation.•Higher OrgN and OrgP concentrations enhance efficient removal.•Discussion on subsequent N removal technologies based on HRAS effluent’s COD/TKN. Conventional wastewater treatment technologies often involve energy-intensive processes, creating a need for more sustainable and efficient solutions. The high-rate activated sludge (HRAS) process, characterized by short sludge and hydraulic retention times, demonstrates proficient chemical oxygen demand (COD) removal with minimal oxidation and energy expenditure, positioning it as a promising approach for achieving energy-efficient wastewater treatment. This study addresses the nutrient removal efficiency of a demonstration-scale pilot plant (35 m3·d-1) operating for 497 days. It investigates the correlation between nutrient removal efficiencies, COD fractions, and suspended solids removal in real wastewater, without primary clarification. The process consistently achieves average removal efficiencies: 23% for total Kjeldahl Nitrogen (TKN), 7.3% for N-NH4+, 56% for total phosphorus (TP), and 11% for P-PO43-. The superior TP removal is attributed to the high particulate influent fractions (81%), underscoring the pivotal role of settling efficiency. The HRAS process effectively controls TP peak values, although its influence on TKN peaks is somewhat limited. This underscores HRAS's proficiency in mitigating phosphorus spikes in influent wastewater. In contrast, the lower TKN removal is associated with diminished particulate inlet fractions (46%). Nutrient removal mechanisms in HRAS mirror those of COD, primarily revolving around adsorption and entrapment processes, as opposed to conventional biological pathways. It also highlights the independence of oxidized COD, nitrogen, and phosphorus removal. Furthermore, a comprehensive analysis of the COD/TKN within HRAS effluent unveils the presence of a short-cut nitrification/denitrification process, supplemented by Anammox in the sidestream, as the most suitable pathway for downstream nitrogen removal. This revelation signifies a substantial advancement and positions HRAS as a potential initial stage of a partial nitritation/Anammox (PN/A) process within mainstream wastewater treatment.