Miller, Mark

Mark Miller is a senior process engineer with Brown and Caldwell based out of Charlotte, North Carolina. His technical expertise includes enhanced biological nitrogen and phosphorus removal, high-rate activated sludge processes, whole-plant modeling, process automation, and treatment optimization. Mark also specializes in field work to characterize waste streams, diagnose treatment issues, and support designs to improve treatment processes.

Titles from this speaker

A Journey of Upgrades and Innovations to Achieve Capacity Improvements at Metro Water Services' Central WRF

Abstract

Introduction The Central WRF has undergone significant upgrades to improve its treatment efficiency and capacity. With a rated capacity of 125 MGD and peak secondary flow of 350 MGD, the facility's treatment process includes preliminary treatment, PCs, aeration tanks (ATs), SCs, and UV disinfection. A key upgrade was the conversion of the aeration tanks from draft tube aerators to fine bubble diffused aeration and from two-pass, complete-mix reactors, to a plug-flow A/O process. This upgrade came with several unique challenges due to the sidewater depth of the tanks exceeding 30 ft. The draft tube aerators were inefficient at mixing resulting in pockets of low DO or anoxic conditions and thus reduced nitrification efficiency and promoted low DO filamentous bulking and foaming. The deep tanks were also followed by SCs with a sidewater depth of 16-ft. These conditions would result in nitrogen gas dissolving into the process water in the deep ATs that would evolve in the SCs causing poor settling and floating sludge blankets. The design criteria for diffused aeration at such depths were also not available from manufacturers or in the limited literature. The deepest diffuser submergence that manufactures could factory test their diffusers at was 23 ft. Therefore, assumptions of SOTE had to be made during design that accounted for potentially lower SOTE values than expected due to the air-side oxygen depletion during bubble transit. The assumed values were validated after startup and commissioning by performing off-gas testing. Methods Relevant tank improvements in each of the 8 ATs included anaerobic selector zones, baffle walls, a new aeration system, surface wasting stations, and degassing zones. The new aeration system included blowers, control valves and airflow meters, instrumentation, and fine bubble diffusers. The efficiency of fine-pore diffusers was calculated in clean water according to the ASCE (2006) standard and in wastewater via off-gas testing (ASCE, 2018). Plug-flow was achieved by installing RFP baffle walls in a serpentine manner and divided into 5 aeration zones as shown in Fig. 1. Since the PC effluent and RAS are added separately to the anaerobic zones, an influent chimney was used to direct the influent to the bottom of the anaerobic zone where it would come into close contact with the incoming RAS flow as shown in Fig. 2. To degas the mixed liquor before the SCs, a novel solution was implemented that included mid-depth coarse bubble aeration at the end of the aerobic zones as shown in Fig. 2. This system is critical at peak flows because the degassing that occurs in the aerated effluent channels between the ATs and SCs is significantly reduced at such short retention times. To help control and reduce nuisance foaming, surface wasting stations were installed in each AT as shown in Fig. 3. As the mixed liquor flows past the wasting station, a surface baffle directs any foam to the wasting station and is wasted from the system. Results and Conclusions The anaerobic selector zone has been instrumental in improving sludge settleability. Selector zones create an environment with a high F/M to out-select filamentous organisms, favoring floc-formers with high substrate uptake rates. The first two upgraded ATs were put in service in Jun 2022, resulting in an immediate drop in SVI as demonstrated in Fig. 4. The SVI continued to stabilize as additional pairs of upgraded ATs were put in service in Sep and Nov 2022. SVI averaged 235 +/- 92 mL/g for Oct 2021 — May 2022, and subsequently averaged 91 +/- 41 mL/g for June 2022 — Dec 2022. The SVI has also started to track with changes in F/M: when F/M is greater than 1, SVI averages 69 +/- 18 mL/g. This suggests that selector zone operation is critical for SVI stability. The new surface wasting stations also contributed to improved settleability by removing nuisance organisms accumulated in surface scum that cause foaming and bulking. Rapid reductions in the scum layer were observed after the first upgraded ATs were put in service. A comparison of the surface scum of the SCs before and after upgrades are provided in Fig. 5. As shown in Fig. 6, the average effluent ammonia concentration was approximately 2.5 mg /L (Jan 2021 — May 2022) and after the initiation of the upgrades fell to consistently below the detection limit of 0.4 mg/L (>95% of samples). As shown in the plot, the effluent ammonia has not peaked above 2 mg/L even though the plant operates at an aggressive SRT of 6-8 days year-round. Off gas testing of three ATs was carried out to assess the change in performance with different diffuser age (2, 6, and 10 months of operation). The off-gas testing results are compared to the design assumptions and clean water testing in Table 1. The assumed alpha and fouling factors used to correct the clean water performance for field conditions aligned well with the values measured in the AT with 2-month-old diffusers. The fouling factors decreased significantly for the 6- and 10-month-old diffusers. This information supported the recommendation that the diffusers should be inspected and cleaned at least annually to maintain adequate efficiency. In conclusion, the upgrades at the Central WRF, including the replacement of the draft tube aerators with a fine bubble aeration system, have significantly improved plant performance. The full paper and presentation will contain expanded discussions and all technical detail

Recent upgrades to the deep aeration tanks at the MWS Central WRF have improved sludge settleability, nitrification reliability, and reduced nuisance foam. Key improvements included anaerobic selector zones, baffle walls to reduce short-circuiting, a new aeration system, surface wasting stations, and degassing zones. To degas the mixed liquor before the clarifiers, an innovate solution was implemented that included mid-depth coarse bubble aeration at the end of the aerobic zones.

SpeakerMiller, Mark

Presentation time

16:30:00

17:00:00

Session time

15:30:00

17:00:00

SessionOptimizing Design for Increased Capacity

Session number228

Session locationRoom 349

TopicFacility Operations and Maintenance, Intermediate Level, Municipal Wastewater Treatment Design

Author(s)

Miller, Mark, Jimenez, Jose, Bauhs, Kayla, Yarosz, Douglas, Rosso, Diego

Author(s)M. Miller1, J.A. Jimenez2, K. Bauhs3, D. Yarosz3, D. Rosso4

Author affiliation(s)1Brown and Caldwell, NC, 2Brown and Caldwell, FL, 3Brown and Caldwell, TN, 4University of California, Irvine, CA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159630

Volume / Issue

Content sourceWEFTEC

Word count17

Advancing Low-Energy Biological Nutrient Removal through Low Dissolved Oxygen Operation: Is Biological Selection the Key?

Abstract

Introduction In the activated sludge process (ASP), dissolved oxygen (DO) is an important factor for aeration cost, nitrification efficiency, nutrient removal, and N2O emission. Even though, the term 'low DO' has been used in a somewhat subjective manner and can vary depending on the context and specific requirements, the overall objective of this study is to pave the way for full-scale implementation of low DO BNR through scientific investigation to systematically answer questions on the impact of DO concentrations on nitrification, denitrification, BPR, microbial ecology, and greenhouse gas emissions. This abstract presents results developed as part of the WRF No. 5083 titled 'Advancing Low-Energy Biological Nitrogen and Phosphorus Removal.' Methodology To quantify the impact and benefits of low DO operation in the capacity and performance of existing ASP, several participating facilities that were operating at low DO and high DO conditions were studied as part of this project. Long-term operational data from the facilities was assessed and compared with the baseline information collected during the literature review. Mixed liquor samples from the participating utilities were collected and assessed through lab-scale studies. Low dissolved oxygen control and batch test procedures were developed as part of the project and used to investigate the impact of low DO on biokinetic rates. This information provided a unique comparison and tabulation of important biokinetic parameters to better understand the implications of low DO BNR on plant capacity and performance. In addition, this provides guidelines for the selection of proper important biokinetic coefficients for process modeling. Results and Discussion Bench-scale, and full-scale experiments were conducted to investigate the impact of DO concentrations on nitrification, denitrification, BPR, microbial ecology, and N2O emissions with the goal to advance low DO BNR. The following biokinetic insights were collected as part of this study. Nitrification: Specific nitrification rates for ASP operating with long-term exposure to low DO conditions were approximately 60-80% of the nitrification rates at high DO as presented in Figure 1. This study concluded that long-term low DO operation results in a shift in the nitrifier community structure, with comammox, and in some case ammonia oxidizing archaea, being selected over ammonia oxidizing bacteria. Experimental results confirm that these communities selected under stable low DO operation have a higher oxygen affinity than AOB and Nitrobacter-related NOB. TIN Removal: The maximum TIN removal rates were found at DO concentrations ranging from 0.2 to 0.5 mg/L. At this DO range, the nitrification rate equals the denitrification rate, which would therefore lead to complete SND in non-carbon limiting conditions as depicted in Figure 2. At DO concentrations of less than 0.2 mg/L, the TINRR is inhibited by nitrification and at DO concentrations higher than 0.5 mg/L, TINRR is limited by denitrification. This observation may change from plant to plant since there are multiple parameters that could affect the results including floc size and porosity, mixing intensity, and microbial population. Biological Phosphorus Removal: Biological phosphorus removal is not impacted by low DO operation. Based on the experimental results from 12 full-scale plants, the low DO phosphorus uptake rates measured in this study were higher compared to the P uptake rates for high DO/ conventional systems. Phosphorus uptake rates slows down significantly when the DO is 0.1 mg/L suggesting that the KDO for PAO is lower around 0.1 mg/L. N2O Emissions: In this work, pilot and bench-scale testing demonstrated that long-term exposure of biomass to low DO does not result in an increase in total N2O emissions (Fig. 3a). Even though this study did not investigate the specific N2O production mechanisms and pathways associated with low DO BNR, the work suggests that the N2O emissions are lower than conventional high DO systems since the relative abundance of AOB and Nitrobacter-related NOB are relatively low (Fig. 3b) limiting the N2O produced via NH2OH oxidation pathway and nitrifier denitrification by AOB. In the low DO BNR systems, Nitrospira-related NOB and comammox were dominant nitrifiers suggesting they do not have the same reduction pathways of NO2 and NO to N2O and therefore produce less N2O comparable to AOB. Conclusion DO is an important parameter influencing aeration cost, nitrification efficiency, nitrogen and phosphorus removal efficiency, treatment plant capacity and N2O emission. As presented in this study, there are several WRRF that utilize low DO operation in the ASP achieving effluent water quality with respect to N and P and require less energy than conventional ASP. The DO setpoints in such plants vary depending on loading conditions, aeration controls, and operator's preferences. Therefore, selecting a single DO setpoint to represent low DO BNR is difficult. Based on the experimental results obtained during this study, low DO can be defined as the bulk liquid DO concentration or range in the aerobic zones where simultaneous N and P removal reactions occur, often ranging from 0.2 mg/L to 0.5 mg/L. Results from this study demonstrate that long-term exposure to biomass at these DO concentrations allow for biological selection of microorganisms with very high oxygen affinities.

In the ASP, DO is an important factor for cost, nitrification efficiency, and N2O emission. The objective of this study was to investigate the impact of DO concentrations on nitrification, denitrification, BPR, microbial ecology, and N2O emissions. Based on the experimental, low DO can be defined as the DO concentration or range in the aerobic zones where SND reactions occur, often ranging from 0.2 to 0.5 mg/L allowing for biological selection of microorganisms with very high oxygen affinities.

SpeakerJimenez, Jose

Presentation time

13:40:00

13:50:00

Session time

13:30:00

15:00:00

SessionMicrobial Ecology Selection Under Low DO Concentration

Session number409

Session locationRoom 253

TopicAdvanced Level, Energy Production, Conservation, and Management, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)

Jimenez, Jose, Miller, Mark, Bauhs, Kayla, Sturm, Belinda, Wittman, Megan, Dold, Peter, Fevig, Stephanie

Author(s)J.A. Jimenez1, M. Miller2, K. Bauhs3, B. Sturm4, M. Wittman4, P. Dold5, S.M. Fevig6

Author affiliation(s)1Brown and Caldwell, FL, 2Brown and Caldwell, NC, 3Brown and Caldwell, TN, 4University of Kansas, KS, 4, 5Envirosim Associates Ltd., ON, 6South Platte Renew, CO

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159576

Volume / Issue

Content sourceWEFTEC

Word count16

Evaluating Nitrogen Oxides Transformations at Low Dissolved Oxygen Concentrations

Abstract

This paper was presented at WEFTEC 2023 in Chicago, IL.

This study evaluates nitrogen oxides transformations at low-DO concentrations. Microbial community data coupled with biokinetics, and detailed process modeling facilitated an analysis of the fundamental mechanisms associated with SND and its interaction between biomass and intermediate nitrogen oxide species and readily biodegradable COD.

SpeakerJimenez, Jose

Presentation time

08:30:00

08:50:00

Session time

08:30:00

10:00:00

SessionLow Carbon BNR Fundamentals and Controls

Session locationRoom S502 - Level 5

TopicAdvanced Level, Facility Operations and Maintenance, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Jimenez, Jose

Author(s)J. Jimenez 1; J. Boltz 2 ; M. Miller 3; K. Bauhs 5; B. Sturm 6; B. Rittmann 7; J. Jimenez 1;

Author affiliation(s)Brown and Caldwell 1; Woodard and Curran 2 ; Brown and Caldwell 3; Brown and Caldwell 5; University of Kansas 6; Arizona State University 7; Brown and Caldwell 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159062

Volume / Issue

Content sourceWEFTEC

Word count10

Description: Introducing a Series of New ASTM Standards Relating to Specifications and...

Introducing a Series of New ASTM Standards Relating to Specifications and Performance Protocols for Stormwater Control Measures

Abstract

ASTM Committee E64 on Stormwater Control Measures (SCMs) has published a series of new standards relating to specifications and performance protocols for manufactured water quality treatment devices (MTDs) including hydrodynamic separators (HDSs), media filters, and trash & debris capture technologies. These consensus-based ASTM standards have been developed to objectively measure the performance of these technologies to provide improved assurance on the efficacy of tested and verified technologies. This presentation will discuss the ASTM standards process and how it produces consistent quality procedures and products for the benefit of all stakeholders. An overview of these standards will be provided to gain insight into their rationale and essential elements. This presentation will also explore the potential benefits of using these standards as part of an SCM regulatory program; and what implementation of these standards within an authority having jurisdiction (AHJ) could look like. The prospect of a national validation process for ASTM standards via the Stormwater Testing and Evaluation of Products and Practices (STEPP) initiative will also be discussed. The overall intent of the ASTM standards process is to provide a high level of confidence to AHJs that the MTDs will provide long term and consistent treatment to meet water quality goals. Two E64 Subcommittees have been established to develop standards for both laboratory and field testing as E64.01 and E64.02, respectively. To date, laboratory standards include general specifications, standards applicable to HDSs, standards for media filtration, and a standard for trash & debris capture. General specifications address standard terminology for SCMs, silica-based test sediment and weighting factors for TSS removal on an annual basis. HDS standards and working items apply to TSS performance testing methods and data analysis, hydraulic characteristics and head loss, as well as scour testing to support online installations. Filtration standards and working items consider hydraulic characteristics, test sediment, performance testing and scour testing. The trash & debris capture standard is unique to laboratory protocols since it applies to manmade and natural materials >5 mm (5,000 microns) in two directions and uses a 'cafeteria style' approach for six testing elements. A standard for microplastics testing is also in progress. The first field-testing working standard addresses the use of autosamplers for the collection of paired influent and effluent flow-weighted composite samples. The development of new laboratory and field specifications and protocols is an ongoing effort with updates to existing standards occurring as the stormwater industry continues to advance MTD technologies and testing methodologies.

This paper was presented at the WEF Collection Systems and Stormwater Conference, April 9-12, 2024.

SpeakerMiller, Mark

Presentation time

14:30:00

15:00:00

Session time

13:30:00

15:00:00

SessionCollaborative Initiatives

Session number05

Session locationConnecticut Convention Center, Hartford, Connecticut

TopicConstruction, Funding, Green Infrastructure, Laboratory Methods And Analysis, Program Management, Public Utility, Rates, Stormwater Control Measure, TMDLs, Water Quality, Watershed Management

Author(s)

Miller, Mark

Author(s)M. Miller1

Author affiliation(s)AquaShield, Inc. 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Apr 2024

DOI10.2175/193864718825159336

Volume / Issue

Content sourceCollection Systems and Stormwater Conference

Word count18

More Than Just Energy Savings: Understanding the Benefits of Low DO Operation

Abstract

Introduction
Although advanced aeration controllers based on either ammonia (ABAC) or the ratio of ammonia to nitrate/nitrite (AvN) are becoming more common in WRRFs, the biological mechanisms of low DO operation are still not well documented. Low DO is generally referred to as operating below 0.5 mg/L but more specifically at a DO concentration that results in conditions that promote simultaneous nitrification and denitrification or SND, which can vary based on loading rates, process configuration, temperature, and floc morphology. Operating at low DO and achieving SND provides the opportunity for several process improvements in addition to achieving 10-30% aeration savings compared to conventional DO control. It can simplify operations and save additional energy by eliminating the need for multiple mixed liquor recycles and reduce supplemental carbon requirements. SND has also been shown to improve biological phosphorus removal. It is only when these mechanisms are understood can they be fully exploited to intensify treatment. This presentation will cover the current state of the industry as well as recent findings from an ongoing Water Research Foundation study (WRF 5083) investigating the benefits and mechanisms of low DO operation. The overarching research questions of this study that will be addressed are: 1. What setpoints represent low DO? 2. How are nitrification, denitrification, and phosphorus removal kinetics impacted by low DO operation? 3. What role does carbon cycling play in successful low DO BNR systems? 4. How do we maintain good settleability in low DO BNR systems?
Participating Facilities
The WRF study includes several participating facilities and pilot plants that are at different stages of planning, construction, or operation. The following facilities are either in operation or nearing the end of a demonstration phase. Rochester, MN: The Rochester WRF consists of a two-stage high purity oxygen plant and an activated sludge system operated in parallel. The activated sludge plant was operated in an A2O configuration and low DO operation was achieved by inputting low DO setpoints in the DO controllers and adjusting the DO setpoints as needed to prevent excessive ammonia bleed through. Hydrocyclone based wasting was also investigated to improve settling. City of Pueblo, CO: The James R. Dilorio WRF consists of a 19-MGD secondary facility using the Johannesburg BNR process. Aeration is controlled using a continuous AvN controller that results in an average low DO concentration of 0.2-0.5 mg/L. The facility has been achieving about 11 mg/L TIN and 0.6 mg/L TP with little chemical addition. Hydrocyclone based wasting is used at this facility to promote sludge densification. Operating at low DO has resulted in $150k/year in aeration savings and $300k/year in chemical savings. City of St. Petersburg, FL: The Southwest WRF is a 20-MGD A/O plant treating primary effluent. The plant operates at low DO concentrations and low SRT conditions to control nitrification and effluent N and P concentrations. Low DO operation has resulted to poor sludge settling affecting secondary clarifier capacity during the wet weather season. To improve the settling characteristics, hydrocyclone based wasting was recently implemented.
Results and Discussion
Using mixed liquor samples from the St. Petersburg facility, the specific denitrification rate was measured at different DO concentrations and the results are presented in Figure 1. As shown in this figure, denitrification was not measured until the DO concentration was less than 1 mg/L, but the rate was only approximately 20% of the maximum denitrification rate. It was not until the DO was lowered to 0.5 mg/L that the denitrification rate increased to about 70% of the maximum rate. Although denitrification at low DO was observed in the St. Petersburg batch tests and full-scale plant, at the Rochester WRF demonstration facility, SND was typically only observed in the first aerobic zone and not in the proceeding zones even though the DO was maintained at 0.3-0.4 mg/L as shown in profile in Figure 2. This was likely due to the type of substrate available after the first aerobic zone. An example of the impact of substrate type on denitrification is shown in Figure 3 where lower denitrification rates were measured after the readily biodegradable COD was consumed. These observations suggest that even lower DO concentrations are required in downstream zones that lack sufficient rbCOD and may rely on hydrolysis of slowly degradable COD. Testing at several facilities indicate that the maximum nitrification rates are not significantly reduced when adapted for low DO operation, but there is clear increase in the oxygen affinity. This results in higher nitrification rates at lower DO concentrations compared to conventional DO systems. The maximum nitrification rate is reduced by approximately 20-30% and apparent half saturation coefficient decreases to approximately 0.1 to 0.2 mg/L as shown in Figure 4 for the St. Petersburg facility. Overall, this only results in about 40% reduction of the nitrification rate at 0.2 mg/L DO. However, this rate can be increased by increasing the DO without losing a lot of overall nitrification capacity. Another observation in facilities operating at low DO concentrations is improved and more stable biological P removal. For example, the Rochester WRF had consistently lower OP concentrations as demonstrated in Figure 2. Lower nitrate in the RAS and more efficient use of influent carbon were obvious contributing factors, but higher P-uptake rates were also observed in low DO batch activity tests as shown in Figure 5. It is still unclear at this time what the mechanisms are, but it is hypothesized that low DO concentrations result in lower aerobic utilization rates of internally stored carbon that promotes higher P-uptake rates. These tests will be repeated at other facilities and the mechanisms investigated further in the pilot facilities. Poor settleability has often been associated with low DO operation, but these observations were from oxidation ditch plants that typically have poor settleability due to lack of proper selectors and plug flow conditions. As shown in Figure 6, if a process has well designed selectors that adequately reduce the influent rbCOD before the first low DO zone, the settleability remains good. Settling will be documented for the participating facilities.

Although advanced aeration controllers are becoming more common, the mechanisms of low DO operation are still not well documented. Operating at low DO provides the opportunity for several process improvements in addition to achieving 10-30% aeration savings. This paper elucidates the biological mechanisms of low DO operation based on observations at several WRRFs as part of an ongoing Water Research Foundation study (5083).

SpeakerMiller, Mark

Presentation time

13:35:00

13:50:00

Session time

13:30:00

15:00:00

TopicAdvanced Level, Energy Production, Conservation, and Management, Facility Operations and Maintenance, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Miller, Mark

Author(s)Mark Miller1; Varun Srinivasan2; Ahmed Al-Omari3; Don Esping4; Pusker Regmi5; Kayla Bauhs6; Belinda Sturm7; Leon Downing8; Jose Jimenez9

Author affiliation(s)Brown and Caldwell, Charlotte, NC1; Brown and Caldwell, Boston, MA2; Brown and Caldwell, Alexandria, VA3; Brown and Caldwell, St. Paul, MN4; Brown and Caldwell, Beltsville, MD5; Brown and Caldwell, Nashville, TN6; University of Kansas, Lawrence, KS7; Black & Veatch, Madison, WI8; Brown and Caldwell, Maitland, FL9

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158603

Volume / Issue

Content sourceWEFTEC

Word count13

The Savings are in the Details: Fundamentals of ABAC Design

Abstract

The use of advanced aeration controls in WRRFs, particularly ammonia-based aeration control (ABAC), is becoming more widespread in North America. Compared to conventional dissolved oxygen (DO) control, ABAC utilizes all the available aeration tank capacity more efficiently by only nitrifying the influent ammonia necessary to obtain a desired effluent ammonia concentration. However, existing aeration systems are rarely capable of meeting equipment turndown requirements of ABAC since they were not originally designed to do so. This means that certain design parameters must be considered not only for existing systems but also for new facilities and aeration systems. The objective of this paper is to cover the fundamentals of designing around and implementing ABAC.

The following conference paper was presented at WEFTEC 2021, October 16-20, 2021. To read the full abstract, see "Abstract" tab below.

SpeakerMiller, Mark

Presentation time

16:00:00

16:15:00

Session time

16:00:00

17:30:00

SessionAmmonia-based Aeration Control: How to Make it Work

Session number313

TopicFacility Operations and Maintenance, Intelligent Water, Research and Innovation, Resilience, Disaster Planning and Recovery

Author(s)