Optimizing Enhanced Biological Phosphorus Removal at WRRFs: Impact of Low DO Operation and Full-Scale Strategies
| Autor: | Doyle, Riley Kate |
|---|---|
| Jazyk: | angličtina |
| Rok vydání: | 2024 |
| Předmět: | |
| Druh dokumentu: | Diplomová práce |
| Popis: | 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. Master of Science Excess amounts of phosphorus discharged into aquatic ecosystems can lead to eutrophication, a process where algal blooms deplete the oxygen needed for other aquatic life, resulting in large scale mortalities. Water Resource Recovery Facilities (WRRFs) employ chemical, biological and/or physical means to remove phosphorus from discharged water to prevent eutrophication. Enhanced biological phosphorus removal (EBPR) is a process that takes advantage of microorganisms known as polyphosphate-accumulating organisms (PAOs) to remove phosphorus from the water. PAOs can store high amounts of phosphorus in their biomass when they are subjected to alternating anaerobic and aerobic conditions. The phosphorus is then removed with the PAOs by settling and wasting the biomass. The conventional operational approach at WRRFs is to maintain an aerobic phase with dissolved oxygen (DO) concentrations above 2 mg O2/L to maximize phosphorus uptake. However, Hampton Roads Sanitation District's Virginia Initiative Plant (VIP) observed a 69 percent decrease in average DO concentrations, alongside a 53 percent improvement in effluent phosphorus quality from 2019 to 2023. Batch tests conducted from 2020 to 2024 indicated higher phosphorus release and aerobic uptake rates at lower DO concentrations, while microbial analysis revealed a community shift toward PAOs. Recent batch tests conducted in 2023 indicated phosphorus uptake rates in the anoxic phase that ranged from 3 to 40 percent of the phosphorus uptake rates in the aerobic phase. This emergence of anoxic phosphorus uptake capacity is potentially attributable to the reduction in DO concentrations. These results highly suggest that low DO operation (DO concentrations below 1 mg O2/L) does not negatively impact EBPR performance. In fact, low DO concentrations were positively correlated with increased PAO abundance. Low DO operation can reduce aeration energy consumption, operational costs, and environmental footprints of WRRFs. Furthermore, VIP implemented other operational strategies to optimize EBPR and monitor PAO activity, including an aerobic phosphorus uptake online analyzer. This analyzer was demonstrated as an effective tool to indirectly monitor the health of the PAO population and provide continuous data for real time process optimization. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
| Externí odkaz: |
|