Yang, Fenghua, Yang

Fenghua Yang, licensed professional enginer (PE) in the state of IL, and board certified environmental engineer (BCEE) by The American Academy of...

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About Yang, Fenghua

Fenghua Yang, licensed professional enginer (PE) in the state of IL, and board certified environmental engineer (BCEE) by The American Academy of Environmental Engineers and Scientists (AAEES). Fenghua is currently working as senior environmental research scientist in the Metropolitan Water Reclamation District of Greater Chicago. Prior to this, she worked as senior project manager for the Milwaukee Metropolitan Sewerage District. Additionally, she has one year of experience working in the Iowa Department of Natural Resources, permit section, and 10 years experience in the consulting business as a process engineer, project manager and lead engineer. Fenghua's current work focuses on the evaluation of new and innovative technologies to improve wastewater treatment and resource recovery.

Yang, Fenghua

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Description: Side-by-Side Full-Scale Demonstration of Enhanced Biological Phosphorus Removal...

Side-by-Side Full-Scale Demonstration of Enhanced Biological Phosphorus Removal Operated With Low Dissolved Oxygen and Routine Dissolved Oxygen Conditions

Abstract

INTRODUCTION
Aeration accounted for 30% to 60% of the total energy consumption at biological nutrient removal (BNR) facilities (Appelbaum, 2002). Traditionally, for BNR, it was believed that sufficient aeration should be provided to maintain a dissolved oxygen (DO) level of 2.0 mg/L or greater in the aerobic zone for efficient phosphorus (P) uptake and nitrification (USEPA, 2010). Recent full and pilot-scale studies have shown that P and ammonia nitrogen (NH3-N) removal will not be compromised with low DO concentrations. A study with full-scale wastewater reclamation plants (WRPs) operated at a DO regime of 0.2â€“0.7 mg/L showed that simultaneous nitrification and denitrification was promoted, and P removal improved (Jimenez et al., 2018). At the Trinity River Authority of Texas Central Regional WRP, low DO (0.2â€“0.5 mg/L) improved nitrogen (N) and P removal and reduced aeration energy consumption (Downing et al., 2017). A continuous flow pilot-scale treatment train operated at the Nine Springs WRP over a 16-month period deployed a stepwise decrease in aeration from a DO concentration of 2.0 mg/L to an average of 0.33 mg/L. They observed stable operation with nearly 90% P removal, nearly 70% of nitrite and nitrate N (NOx-N) removal, and an estimated 25% reduction in energy use for aeration (Keene et al., 2017).
The Kirie WRP is a conventional single-stage nitrification WRP with a design average flow of 52 million gallons per day (MGD). The activated sludge system consists of six three-pass aeration tanks. Tanks 5&6 were operated as a separate sludge system from Tanks 1-4. Waste sludge from tanks 5&6 was pumped to the tanks 1-4 returned activated sludge (RAS) channel. The Kirie WRP has been operated at a DO setpoint of 2.0 mg/L toward the end of Pass 3 at all the six aeration tanks since it started EBPR in 2015 using conventional anaerobic/oxic configuration. A seasonal change in EBPR performance was observed with elevated effluent ortho-phosphorus (ortho-P) levels in every late summer/fall. It was suspected that this phenomenon may be due to glycogen accumulating organisms (GAOs), which tend to thrive in wastewater with high temperature, carbon, and DO. Kinetic batch experiments by Carvalheira et al (2014) suggested that polyphosphate accumulating organisms (PAO) have a higher affinity for oxygen than GAO, and therefore, low-DO operation may favor PAO activity over GAO.
OBJECTIVE AND METHODOLOGY
In this study, we aimed to operate two test aeration tanks 5&6 with low DO points for over a year to cover seasonal variation and compare the performance and air savings of test tanks with control aeration tanks 1-4 operated at a DO setpoint of 2.0 mg/L. The effect of low DO operation at test aeration tanks 5&6 was evaluated by gradually reducing the DO setpoint from 2.0 mg/L to 1.5 mg/L, then to 1.25 mg/L, and finally 1.0 mg/L while maintaining the control aeration tanks 1-4 at a DO setpoint of 2.0 mg/L. Low-DO operation was carried out from February 2018 to May 2019. Figure 1 shows the actual DO concentrations in the aeration tanks 4 (pass 3) and 5 (passes 1, 2, and 3) over the comparison period. The actual DO in the plug flow aeration tanks ranged from 0.15 mg/L at the front of the tank to the setpoint at the end of the tank. The performance of control and test tanks were compared in terms of air savings, ortho-P removal, NH3-N removal, NOx removal, in-situ and ex-situ nitrification rates, and microbial analysis for GAOs population.
RESULTS
Air Savings Figure 2 shows the total air supplied to tanks 4, 5, and 6. The air supplied to tanks 5&6 reduced significantly when compared to tank 4. Table 1 summarizes the average air savings over comparison period. Average air savings of 8-26% were achieved in the test tanks 5&6 when compared to the control tank 4.
Low DO Operation Impact on EBPR, Nitrification, and NOx-N RemovalFigures 3, 4, and 5 provide performance comparisons between test tanks 5&6 and control tanks 1-4 in terms of ortho-P, NH3-N, and NOx-N removal, respectively. Tanks 5&6 outperformed tanks 1-4 in terms of ortho-P removal throughout the testing period except from 9/24/18 to 9/30/18 when the activated sludge from tanks 1-4 and 5&6 was mixed during the RAS channel cleaning. Tanks 1-4 maintained low effluent ortho-P (0.2-0.4 mg/L), but tanks 5&6 showed high effluent ortho-P (1.2 - 3.0 mg/L) for about one week before it decreased to around 0.2 mg/L. It appears that the selected PAOs in low DO environment were able to adapt to the high DO environment in Tank 4 immediately. However, the selected PAOs in the high DO environment needed an adaptation time of approximately one week when suddenly being changed to a low DO environment. Tanks 5&6 outperformed tanks 1-4 for NOx-N removal throughout the testing period except from 9/17/18 to 9/30/18. The reason is unclear but the reduced performance of NOx-N removal in the test tanks 5&6 also happened over the period when the sludge from the control and test tanks got mixed. Reduced NH3-N removal was observed in test tanks 5&6 immediately after reducing the DO setpoints, but the removal improved after a few months of operation. This agrees with the observations of Keene et al. (2017) that efficient low-DO nitrification requires adaptation of the microbial communities in the activated sludge.
Nitrification Rate Comparison Both In-situ and ex-situ specific nitrification rates (NR) were measured once every other week during the period with low DO operation. The Statistical tests showed that there were no significant differences in the mean in-situ specific nitrification rates and mean ex-situ maximum specific nitrification rate between the control and test tanks. Detailed analyses will be provided in the manuscript.
Microbial Analysis Results Figures 6 and 7 summarize the GAO population versus effluent ortho-P levels from the test tanks 5&6 in 2017 (DO setpoint of 2.0 mg/L) and 2018 (DO setpoints of 1.0 to 1.25 mg/L), respectively. The GAO population decreased from the range of 10,000 to 70,000 GAOs/mgVSS in 2017 to 1,000 to 12,000 GAOs/mgVSS in 2018.
CONCLUSION
This study showed that gradually lowering the DO setpoints from 2.0 mg/L to 1.0 mg/L improved EBPR performance and denitrification. The effluent NH3-N concentrations were elevated at times after lowering DO setpoints but recovered after a few months of operation. Tanks operated with Low DO observed reduced GAO population. Nitrification rate assays suggested that both mean in-situ and ex-situ nitrification rate were comparable between the control and test tanks. Operating aeration tanks with low DO setpoints reduced the air consumption by 8-26%.

We operated two aeration tanks with low DO points for over a year and compare the performance /air savings with control tanks (DO setpoint of 2.0 mg/L). GAO population reduced significantly. Improved EBPR performance and denitrification were improved. The effluent ammonia-N concentrations were elevated after lowering DO setpoints but recovered after a few months of operation. Mean ex-situ nitrification rate were not impacted. Average air savings of 17-22% were observed.

SpeakerYang, Fenghua

Presentation time

15:40:00

16:00:00

Session time

15:30:00

17:00:00

TopicIntermediate Level, Energy Production, Conservation, and Management, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Yang, Fenghua

Author(s)Fenghua Yang1; Thaís Pluth2; Richard Campbell, Jr.3; Katarzyna Lai4

Author affiliation(s)Metropolitan Water Reclamation District of Greater Chicago, IL1; Metropolitan Water Reclamation District of Greater Chicago, IL2; Metropolitan Water Reclamation District of Greater Chicago, IL3; Metropolitan Water Reclamation District of Greater Chicago, IL4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158699

Volume / Issue

Content sourceWEFTEC

Word count19

Base text size -

Yang, Fenghua

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