Optimizing Enhanced Biological Phosphorus Removal at WRRFs: Impact of Low DO Operation and Full-Scale Strategies

After construction upgrades and implementation of ammonia-based aeration control (ABAC), Hampton Roads Sanitation District's Virginia Initiative Plant (VIP) observed a 69 percent decrease in average dissolved oxygen (DO) concentrations, alongside a 53 percent reduction in average effluent total phosphorus (TP) concentrations from 2019 to 2023. This improvement in effluent quality coincided with the elimination of metal salt addition in 2023. Batch tests conducted from 2020 to 2024 indicated higher phosphorus release and aerobic uptake rates at lower DOs, even at higher temperatures, while 16S rRNA amplicon sequencing analysis suggested a community shift toward polyphosphate-accumulating organisms (PAOs). Statistical analysis revealed that low DO operation (DO concentrations below 1 mg O2/L) did not negatively impact effluent TP concentrations and were positively correlated with increased PAO abundance. High rates of denitrification fueled by internally stored carbon in the post-anoxic zone were found to co-occur with elevated PAO activity, and subsequent batch tests indicated post-anoxic phosphorus uptake rates ranging from 3 to 40 percent of the aerobic phosphorus uptake rates. Removing the aerobic phase in batch tests increased both anoxic phosphorus uptake and denitrification utilizing internally stored carbon. This emergence of post anoxic phosphorus uptake capacity is potentially attributable to the reduction in DO concentrations. The reduction in average aerobic SRT from 8.5 ± 0.4 days in 2021 to 5.7 ± 0.1 days in 2023 was significantly correlated with improved effluent phosphorus quality. An aerobic phosphorus uptake online analyzer at full-scale was demonstrated as an effective tool to indirectly monitor the health of the PAO population and provide continuous data for real time process optimization. Understanding the conditions that improve EBPR at full-scale is important to achieve more stringent phosphorus limits that are anticipated in the future. Implementing the above strategies can reduce aeration energy consumption, metal salt and external carbon requirements, and environmental footprints at WRRFs.

Name thesis:degree_name

Master of Science

Level thesis:degree_level

masters

Discipline thesis:degree_discipline

Environmental Engineering

Department dc:contributor.department

Environmental Science and Engineering

Grantor dc:publisher

Virginia Tech

Year dc:date.issued

2024

Author dc:creator

• Doyle, Riley Kate

Chairs dc:contributor.committeechair

• Pruden, Amy
• Bott, Charles B.

Committee member dc:contributor.committeemember

• Knocke, William R.

• EBPR
• PAO
• low DO
• internal carbon

Statement dc:rights

• In Copyright

Licence dc:rights.uri

• http://rightsstatements.org/vocab/InC/1.0/

Language dc:language.iso

en

Dc Identifier Other

vt_gsexam:41359

OAI identifier oai:identifier

oai:vtechworks.lib.vt.edu:10919/121084