Biological Nitrogen and Phosphorus Removal From Wastewater Under Low Dissolved Oxygen (LDO) Conditions

Author

Bashar Al-Daomi, Portland State UniversityFollow

Sponsor

Portland State University. Department of Civil & Environmental Engineering

First Advisor

Bill Fish

Term of Graduation

Fall 2023

Date of Publication

12-6-2023

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.) in Civil & Environmental Engineering

Department

Civil and Environmental Engineering

Language

English

Subjects

Biological Nitrogen and Phosphorus Removal from Wastewater, continuous aeration system, intermittent aeration system, Low Dissolved Oxygen (LDO) conditions

DOI

10.15760/etd.3696

Physical Description

1 online resource (xviii, 177 pages)

Abstract

Studying simultaneous nitrogen and phosphorus removal under low dissolved oxygen and limited external organic carbon conditions is of great importance due to its potential to improve wastewater treatment, and it requires further investigation. This study examines the complexities of the integration of different technologies for nutrient removal, investigating parameters like sludge residence time (SRT), carbon-to-nitrogen (C/N) ratio, Anaerobic/Oxic (A/O), and Anaerobic/Oxic/Anoxic (A/O/A) systems, continuous and intermittent aeration regimes, and air OFF/air ON periods ratios for efficient nitrogen and phosphorus removal.

Two continuous aeration systems were implemented: The first aimed to carry out a simultaneous nitrification and denitrification (SNdN) process for nitrogen and phosphorus removal under low dissolved oxygen (DO) and C/N ratio conditions. This system operated with 4.5-5-day total sludge age in a single-stage anaerobic/oxic (A/O)-SBR, performing stepwise DO reduction at varying DO setpoints (4.0-5.0, 2.0-2.2, 1.2-1.4, 0.45-0.55, and 0.3-0.4 mgO₂/L). The second system combined low DO-enhanced biological phosphorus removal (EBPR) with post-anoxic denitrification in a single-stage setup at a total sludge age of 9-14 days. DO setpoints were 0.8-1.0 mgO₂/L for anaerobic/oxic (A/O) phases and 0.5-0.6 mgO₂/L for anaerobic/aerobic/anoxic (A/O/A) phases.

The third system aimed to investigate the feasibility of applying an intermittent aeration strategy for the simultaneous removal of nitrogen and phosphorus under low dissolved oxygen (DO) conditions of 0.35-0.5 mgO₂/L. The system employed varying reduction ratios for air-off to air-on periods, precisely 1.67, 1.25, 1.57, and 2.0. Additionally, C/N ratios were maintained around 6.4, 7.4, and 5.8, aiming to explore the impact of the C/N ratio on nitrogen and phosphorus removal.

The obtained results from continuous aeration studies demonstrated robust and consistent removal efficiencies of NH₄+ and TIN under low DO conditions (0.3-0.4 mgO₂/L) under short SRT reaching 97.1±0.4% and 71.5±2.3%, respectively, with effluent concentrations as low as 1.39±0.19 mg/L for NH₄+ and 13.5±1.0 mgN/L for TIN. Similarly, COD and TP removal efficiencies were achieved at low DO levels, measuring 90.1±1.2% and 78.7±3.1%, respectively. Notably, the results showcased the ability to achieve a remarkable SNdN efficiency of 73.64% for wastewater with a C/N ratio of 4.64. Distinguishing from other studies on the SNdN process, this research highlighted its unique capability to reduce the demand for organic carbon for nitrogen removal. Remarkably, under longer SRT and a higher C/N ratio of 6.8, high removal efficiencies were achieved for COD, NH₄+, TIN, and TP, measuring 93±0.3%, 94.4±0.5%, 67.9±2.1%, and 95.7±0.6%, respectively. The resulting effluent concentrations were low: 22.7±1.0 mg/L, 2.7±0.2 mg/L, 15.3±0.8 mg/L, and 0.5±0.1 mg/L for COD, NH₄+, TIN, TP, respectively. The results highlighted that integrating low DO-A/O/A could be an economical approach for effective TIN and TP removal under low DO and C/N conditions. Concurrently, the simultaneous nitrification and denitrification (SNdN) process proceeded during the aeration stage at 38.3%.

The intermittent aeration study's findings demonstrated notable removal efficiencies: COD, NH₄+, TIN, and TP were removed with efficiencies of 89.75±0.24%, 95.79±1.27%, 78.01±1.94%, and 93.34±0.49%, respectively. This translated to low effluent concentrations of 37.45±0.71 mg/L, 2.39±0.78 mg/L, 12.48±1.41 mgN/L, and 0.83±0.07 mg P/L for COD, NH₄+, TIN, TP, respectively. The results indicated that ratios of non-aerated to aerated periods set at 1.57 and 1.67 were more effective in achieving stable nitrogen and phosphorus removal within 6 and 7 hours of the treatment cycle. These conditions resulted in SNdN efficiencies and nitrogen accumulation rates (NAR%) of 85.1%, 80.2%, 31.1%, and 42.3%, respectively. Prolonging the non-aerated periods bolstered denitrification capacity and phosphate uptake while adjusting both aerated and non-aerated durations impacted nitrification and denitrification processes.

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Persistent Identifier

https://archives.pdx.edu/ds/psu/41133

Recommended Citation

Al-Daomi, Bashar, "Biological Nitrogen and Phosphorus Removal From Wastewater Under Low Dissolved Oxygen (LDO) Conditions" (2023). Dissertations and Theses. Paper 6564.
https://doi.org/10.15760/etd.3696