Machado, Chris

Chris is one of Stantec's wastewater practice leaders with 22 years of experience. His work includes wastewater treatment process design, facility...

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About Machado, Chris

Chris is one of Stantec's wastewater practice leaders with 22 years of experience. His work includes wastewater treatment process design, facility assessment and planning, process optimization, design management, engineering services during construction, research, and development. Chris specializes in biological nutrient removal (BNR) and has participated in many BNR design, planning, and evaluation projects involving nitrogen and phosphorus removal and recovery. Chris provided technical leadership to plan, assess, and design processes for over fifty treatment facilities in the United States.

Machado, Chris

Titles from this speaker

Description: Bringing It All Together: Designing a Densified AO/SND Process for Efficient...

Bringing It All Together: Designing a Densified AO/SND Process for Efficient Biological Nutrient Removal

Abstract

ABSTRACT: This study presents the design, challenges, and process control strategy for low DO BNR facility with DAS in cold climate using ABAC. The advantages of this design include simplification of a 4-stage Bardenpho process to an A/O configuration with EBPR, reducing operational complexity and air demand while still maintaining effective nitrogen removal. This is the first application of low DO process in cold climate with daily effluent ammonia limit using DAS and ABAC. The full-scale construction began in the third quarter of 2023 and will be completed by May 2025. Start-up activities and process changes to low DO will begin in January 2025.

FACILITY BACKGROUND: The secondary process at Boulder WRRF includes anoxic/aerobic/post-anoxic zones followed by Solids Contact Tanks (SCTs). BWRRF is currently under construction to upgrade the secondary process with DAS, low DO A/O configuration to promote SND with inDENSE™ to meet regulation-driven targets of 0.75 mg/L-P and 9.0 mg/L-N.

PROCESS DESIGN: The process design includes upgrades for A/O SND process with ABAC to meet daily effluent ammonia and TIN limits. Installation of supplemental mixing, replacing all remaining ceramic disc membranes with membrane discs, and incorporating inDENSE™ are also included in the design.

Basis of Design: The basis of design for the selector is presented in Table 1. The selector has an important role in densification, filaments control, and EBPR. Key design considerations for feast and famine ratio, F/M ratio, HRT, and SRT are noted in Table 1. Zone 4 is designed as a swing zone to augment anaerobic volume if needed. The F/M and feast and famine ratios selected for design for this project is consistent with other similar applications (Strum, 2020). Feast/famine ratio for this application is at 20% (for three selector zones). The criterion used for determination of feast/famine was provided in Sun et al. (2022).

Mixing System: Dynamic modeling was used to develop minimum airflows to maintain ML suspension. Typically, 0.05 to 0.09 SCFM/SF is used for facilities with primary clarification. Design guidelines for mixing requirements for DAS is lacking; however, it is assumed that DAS biomass is similar to CAS. Table 2 compares the minimum airflow with model results. Given the concerns over potentially overaerating, and the importance of maintaining a suspended biomass during periods of low load, a supplemental large bubble mixing system was included in Zones 4 and 8, and the SCTs (Figure 2). The large bubble mixing system compressors were retrofitted into an existing, unused blower room and include desiccant dryers. The dried airstream is then delivered by exposed piping to the aeration basins and SCT.

Densification Technology Design: Physical selection is important for accumulation of granules (Roche et al., 2022). For this project, hydrocyclones will be used in an effort to improve settleability and low DO process performance. The hydrocyclones have the flexibility to pull either ML from the ML channel or RAS and includes the ability to remotely add or remove hydrocyclones from operation. These design features provide additional flexibility to control wasting. The design criteria for the hydrocylones are presented in Table 3. Figure 3 shows the full range of wasting capacity. Biological selection which is exposing specific bacteria to alternating cycles of feast and famine is critical (WRF, 2024). The alternating A/O condition is intended to promote the growth of PAO and retention by hydrocyclone to increase granule density and settling velocity.

Aeration Blowers: The process air blowers provide oxygen to BNR process and a sidestream Post-Aerobic Digester. The existing blowers were oversized, difficult to turndown, and reaching their end of useful life. Two of the existing blowers will be replaced with dual-core turbocompressors to improve flexibility and turndown. Additionally, a common header was bisected to allow for blowers to be dedicated to a single aerobic process, allowing for additional energy savings due to lower header pressures.

Process Modeling: A calibrated dynamic process model was developed in BioWin, SUMO, and SIMBA#. Table 4 compares the process performance in BioWin and SUMO. Details of process modeling is presented in another paper. Modeling was conducted with default and adjusted kinetics. For kinetics adjustments, KDO of AOB and NOB of 0.4 and 0.2 mg O2/L were used, respectively. The model with default kinetics provided slightly better nitrogen removal performance. Sensitivity analysis was also conducted in BioWin by including hydrocyclones with specified removal for PAO of 1.5 to study the impact on EBPR. Modeling was conducted with ABAC feedback strategy in BioWin and feedback and feedforward (step gain) in SIMBA#. Both models showed that the proposed design is able to consistently meet effluent ammonia of <1 mg/L. The advantages and disadvantages of each control strategy are discussed.

SUMMARY: With this upgrade, BWRRF will convert a complex 4-stage Bardenpho process to an A/O configuration, and this shift not only simplifies the treatment process but also eliminates the need for internal ML recycle. Advantages are reducing operational complexity and air demand while still maintaining effective nitrogen removal. This is the first application of low DO in cold climate with daily effluent ammonia limit with DAS and ABAC.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

09:30:00

10:00:00

Session time

08:30:00

10:00:00

SessionDensified Activated Sludge: Practical Design and Modeling Experiences Converge

Session locationMcCormick Place, Chicago, Illinois, USA

TopicLiquid Stream Treatment - Nutrient Removal and Recovery

Author(s)

Arabi, Sara, Marks, Christopher, Sigmon, Cole, Charnas, Cody, Brown, Nathan, Trujillo, Shelley, Machado, Chris

Author(s)S. Arabi1, C. Marks2, C. Sigmon2, C. Charnas1, N. Brown1, S. Trujillo1, C. Machado1

Author affiliation(s)Stantec Inc.1, City of Boulder2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2025

DOI10.2175/193864718825159911

Volume / Issue

Content sourceWEFTEC

Word count15

Incorporating Asset Management Reliability Elements in Water Resource Recovery Facility Design: A Case Study

Abstract

Background and Objectives The Clark County Water Reclamation District (CCWRD) collects and reclaims water from over 240,000 business and residential accounts in Southern Nevada. CCWRD's main treatment facility, the Flamingo Water Resource Center (FWRC), has the capacity to treat 492 megaliters/day MLD (130 million gallons/day MGD) and is being expanded to 567 MLD (150 MGD) to accommodate growth. Project 19007 Secondary Treatment Aeration Basins and Secondary Clarifiers (Project) is part of this expansion. It entails the first phase of a new 190 MLD (50 MGD) secondary treatment complex, the West Secondary Treatment (WST). The first phase of the new WST facilities has a design capacity of 95 MLD (25 MGD) and includes three biological nutrient removal (BNR) trains. The design of the WST is complete, and the facilities are currently under construction. CCWRD and the WST design team developed and implemented a Reliability Centered Design (RCD) methodology for the Project with the following objectives: 1) Identify one-time opportunities to improve the design, 2) Produce a robust design that meets CCWRD's reliability requirements and risk tolerance, 3) Verify design adequacy to meet O&M needs, 4) Quantify system risk by identifying the consequences and likelihood of failure, The RCD enabled the design to be optimized and asset management reliability elements to be incorporated at early stages. It also informed stakeholders and prepared the ground for future reliability centered maintenance (RCM) activities. Methodology The RCD methodology integrated reliability with risk-based solutions from the beginning of the Project. It aligned reliability with CCWRD's risk management profile (Figure 1). CCWRD, the design team, and the Construction Manager at Risk (CMAR) contractor held several workshops to conduct the RCD process through four distinct steps: 1) Design and Operation Philosophy - The basis of design was used for the RCD process as it defined the functional requirements, operating context, and baseline design. The team reviewed design and operation philosophies to document and consolidate O&M staff input. CCWRD's risk matrix scoring was reviewed and adopted as a basis for RCD. 2) Failure Mode Effects and Criticality Analysis (FMECA) - FMECA workshops were held to review the individual systems, validate the operating requirements, provide feedback on design alternatives, discuss one-time opportunities, identify the potential failure modes, and assign consequences of failure to each system. A key goal was to identify design improvements to manage or eliminate failure modes through implementation of one-time opportunities. 3) Reliability Block Diagram (RBD) Modeling - The information gathered in steps 1 and 2 was used to create an RBD model and estimate the availability, costs, and risks. A logical representation of the different process areas was created. Failure modes and consequences of failure were entered for the various systems. Maintenance, including spares, was assigned to the failure blocks, representing failure management strategies for the different failure modes. The simulation was then developed for a 40-year life cycle. 4) Model Validation, Optimization, and Recommendations — The final RCD workshops validated the model assumptions and presented preliminary results. CCWRD provided feedback on the model results based on their experience with similar equipment and the operation of existing facilities. Model adjustments were made based on this feedback, and the RCD process was completed. Conclusion Overall, the RDC effort was successful and identified 95 one-time opportunities through the collaborative workshops and discussions with CCWRD's O&M staff, design consultant, and contractor. Many of these opportunities were included in the design and will enhance O&M conditions in future operations. The RBD model's main insights were availability, annual costs, and risk (Table 1). The model showed that availability reductions were mainly due to planned maintenance (PM) rather than random outages (Figures 2 and 3). The results indicate that the WST design will achieve full capacity almost ninety-four percent of the time. If more availability is required, an optimization of the duration or interval of the PMs can be considered. The model estimated labor, spare parts, and equipment costs over the lifetime of the assets. The estimates covered corrective, planned, and inspection activities (Figure 4). Labor costs were stable from year to year. Nevertheless, relatively high spare parts costs appeared beginning around year ten and then again approximately ten years later which were primarily due to diffuser replacements. According to the RBD model results all risk scores were under the criticality threshold, so the model showed that the WST design meets the risk criteria (Figure 5). The model indicated that highly critical systems such as the blower and electrical systems have enough redundancy and do not affect the overall risk profile. The main contributors to criticality included systems like diffusers, actuators, clarifier drives, or sludge mechanisms that do not have redundancies and impact the overall system when they fail. However, the risk profiles of these systems were low. Significance This presentation provides an RCD methodology that can be used by WRRFs to incorporate asset management reliability elements at the design stage.

The Clark County Water Reclamation District (CCWRD) Flamingo Water Resource Center 567 MLD (150 MGD) expansion design used a Reliability Centered Design (RCD) methodology to assess failure modes, consequences of failures, and how best to prevent them while mitigating risk. The Project's RCD had the following outcomes: Identified one-time opportunities, produced a design that met CCWRD's reliability requirements and risk tolerance, verified design adequacy to meet O&M needs, and quantified system by identifying the consequences and likelihood of failure.

SpeakerMachado, Chris

Presentation time

15:30:00

16:00:00

Session time

15:30:00

16:30:00

SessionIntegrated Resilience and Reliability Planning

Session number223

Session locationRoom 335

TopicAsset Management, Facility Operations and Maintenance, Intermediate Level, Resilience, Safety, and Disaster Planning

Author(s)

Machado, Chris, Marelli, Jared, Zhang, Katherine, Hahn, Kristopher, Alfaqih, Laith, Basson, Marius

Author(s)C. Machado1, J. Marelli2, K. Zhang2, K.H. Hahn3, L. Alfaqih4, M. Basson5

Author affiliation(s)1Stantec, CO, 2Clark County Water Reclamation District, NV, 3Aladon, FL, 4Stantec, OH, 5Aladon

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159592

Volume / Issue

Content sourceWEFTEC

Word count15

Description: OPERATIONS, PERFORMANCE, COSTS: OPTIMIZING CHEMICAL PHOSPHORUS REMOVAL THROUGH...

OPERATIONS, PERFORMANCE, COSTS: OPTIMIZING CHEMICAL PHOSPHORUS REMOVAL THROUGH COLLABORATIVE IMPLEMENTATION

Abstract

Background: South Platte Renew (SPR) is the third largest WRRF in Colorado, with a capacity of 50 MGD. SPR has implemented a chemical phosphorus (Chem-P) removal process to achieve effluent TP below 1.0 mg/L for regulatory compliance. The SPR Engineering and Operations teams took a holistic and collaborative approach from design to operation for optimum Chem-P implementation with the following core objectives:
1) Operations: Assess plant operation impacts and implement a treatment process with operation flexibility designed for optimization.
2) Performance: Evaluate and select chemical addition strategies for reliability and optimum performance.
3) Costs: Minimize chemical addition costs while achieving optimum performance.

Relevance and Status: This manuscript presents methodology and lessons learned that WRRFs can use to implement chemical P removal with flexibility for optimization targeting operations, performance, and costs. It also offers insight into potential optimization measures that WRRFs can implement on existing systems that rely on chemical P removal. The project is complete and full-scale results are presented.

Methodology: The collaborative implementation approach adopted by SPR spans from the pre-design to post-commissioning phases of the project, including the following:

Pre-design phase: The project team, including engineering, operations, maintenance, and laboratory staff, conducted a bench-scale testing campaign to define potential chemicals for design through Jar-Testing. SPR completed the Jar-Testing at multiple sampling locations using ferric sulfate (or ferric chloride) and alum.

Design phase: The next steps included process modeling and a full-scale pilot study. The team shortlisted three dosing points for consideration and finalized two chemicals. The process modeling effort evaluated these points, including one upstream of the primary clarifier (PC) at the headworks, and the other at the influent of the solids contact tanks (SCT). The goal was to define the optimal dosing strategy by adjusting dosage distributions between headworks and SCTs. The pilot study used existing odor control chemical storage and dosing facilities to validate the modeling effort and assess plant operational impacts using a single dosing point. The design adopted a dual point strategy and incorporated flexibility for dosing two chemicals in the two selected locations.

Operation phase: After commissioning, the team conducted a full-scale optimization study using dual dosing points for two scenarios. For scenario 1, a fixed minimum ferric sulfate dose of 13.5 mg/L was set at the headworks, and a variable alum dose at the SCTs. For scenario 2, the doses were varied in both points. The goal was to determine the optimum chemical combination, dosage, and dose location to meet the target effluent concentrations of 1.0 mg/L and 0.7 mg/L. In addition, the study investigated optimal removal, operation impacts, chemical volumes, delivery schedules, and costs for forecasting and budgeting.

Results: The key results of this project are summarized as follows:
Pre-design and Design Phases: The full-scale piloting demonstrated that a Ferric Sulfate dose of 35 mg/L and 40 mg/L at the headworks are required to reach effluent TP concentrations of 1.0 mg/L and 0.7 mg/L, respectively (Figure 1). However, process modeling indicated that applying different dosing combinations between the headworks and SCTs with a higher dose at the SCTs would be more effective. The advantages of dosing more to the SCTs include reducing overall chemical dosage requirement (Figure 2), less alkalinity consumption, less primary sludge production, and less solids loading to the digester.

#Operation Phase: The optimization study included a systematic approach to testing dosing strategies for target effluent TP of 0.7 and 1.0 mg/L. Figures 3 and 4 show the optimization study results for scenarios 1 and 2. For scenario 1, alum dosage to the SCT increased stepwise to 35 mg/L to achieve a TP level below 0.7 mg/L. For scenario 2, when ferric dosage was increased to 19 mg/L at the headworks and alum dosage was reduced to 15 mg/L at the SCTs, the effluent TP increased to above the target. Further stepwise reductions to both coagulants resulted in effluent TP concentrations higher than 1.0 mg/L. The results confirmed the design hypothesis that applying different dosing combinations between headworks and SCTs with a higher dose at the SCTs is more effective in terms of chemical use.

#Costs: A cost analysis was conducted primarily considering the cost of chemicals used. Table 1 shows the cost analysis and cost efficiency per unit mass of P removed for each P target and scenario. For the effluent TP target of 0.7 mg/L, a higher cost was observed for similar dosage of the chemicals for the dual point chemical dosing strategy (scenario 2) compared with higher coagulant dosage in SCT influent (scenario 1). On the contrary, for the effluent TP goal of 1.0 mg/L, the dual point dosing of similar dosage of coagulants (scenario 2) resulted in a lower cost than higher dosage at SCT influent (scenario 1). Overall, the dual dosing strategy resulted in 25% to 29% chemical costs savings in comparison with the single point dosing piloted during the design phase.

Summary: SPR successfully used a holistic and collaborative approach to design, implement, and optimize its chemical P removal process that showed important operational impacts.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

13:30:00

14:00:00

Session time

13:30:00

15:00:00

SessionFundamentals of Physical and Chemical Phosphorus Removal

Session locationMcCormick Place, Chicago, Illinois, USA

TopicOptimization of Municipal Facility Operations

Author(s)

Williss Kohr, Zeena, Arabi, Sara, Machado, Chris, Trujillo, Shelley, Fang, Yuan

Author(s)Z. Williss Kohr1, S. Arabi2, C. Machado2, S. Trujillo2, Y. Fang2

Author affiliation(s)South Platte Water Renewal Partners1, Stantec Inc.2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825159973

Volume / Issue

Content sourceWEFTEC

Word count11

Description: Process Modeling and Aeration Control Design with ABAC for A/O SND Process with...

Process Modeling and Aeration Control Design with ABAC for A/O SND Process with Densification

Abstract

ABSTRACT: Boulder WRRF is under construction for upgrades for DAS with inDENSE™ and low DO A/O to promote Simultaneous Nitrification Denitrification (SND). Given the first-of-its-kind application of A/O SND in a cold climate with a daily effluent ammonia limit, detailed process modeling was conducted using BioWin, SUMO, and SIMBA#. Sensitivity analysis was conducted to assess the impact of kinetics on biological performance for the design. Aeration control using ABAC was modeled with feedback and feedforward strategies in BioWin and SIMBA#. Modeling showed this design can meet all the anticipated permit requirements for N and P. The ABAC strategy provided 3-13% energy saving compared with constant low DO operation. The models and aeration control approach will be validated with full scale data as part of BWRRF start up in early 2025.

PROCESS MODELING
BioWin Modeling: Calibrated and validated dynamic process models were developed in BioWin and SUMO to confirm performance. SIMBA# was used to support fine tuning of aeration control design. All platforms provided consistent results for the preliminary modeling efforts for using constant low DO approach. Table 1 compares the average effluent quality in BioWin and SUMO using default kinetics. Compared with BioWin, SUMO overpredicted denitrification and resulted in lower effluent TIN. For the permitting application, BioWin model (Figure 1) was used because it provided more reasonable performance. Key aeration design parameters for the DAS process, additional model scenarios and dynamic modeling graphs with BioWin and SUMO will be presented in the full paper. Process modeling was conducted using adjustments in kinetics (Table 2). For the model runs with adjusted kinetics, KDO of AOB and NOB were adjusted to 0.4 and 0.2 mg O2/L. The model with default kinetics provided slightly better N removal performance. Sensitivity analysis was conducted to assess the performance of the Aeration Basins (ABs) and Solids Contact Tanks (SCTs) with default and adjusted kinetics at high (1 mg/L) and low DO (0.3 mg/L) set points (DOSP) in SCTs. Figure 2 shows results from sensitivity analysis. With default kinetics, NOB concentrations drop significantly in SCTs (suggesting nitrite shunt) when reducing DO levels in SCTs while the NOB population remains the same with adjusted kinetics and provides more reasonable performance of the proposed process. Sensitivity analysis was also conducted in BioWin by including hydrocyclones with an assumed specified removal for Phosphate Accumulating Organism (PAO) of 1.5 to study the impact on EBPR (in full paper).

SIMBA# Modeling: Constant low DO and ABAC control strategies were used in SIMBA#. The ABAC strategy in SIMBA is presented in Figure 3. The location of the ammonia probes is shown in Figure 4. The scenario matrix used for SIMBA# modeling is presented in Table 3.

RESULTS Control Objectives: The design intent for aeration control included ABAC using conventional PI loops for feedback control with the following goals: Daily effluent ammonia limit of 1.0 mg N/L, TIN of 11 mg/L, and TP < 1 mg/L. Model calibration was conducted for the number and type of diffusers in each basin. Constant low DO strategy was also modeled in exploratory runs.

Modeling Results with SIMBA# ABAC Modeling with Feedback Control Strategy: Figures 5 and 6 compare air flows with constant low DO and ABAC for the existing system and the future A/O SND process (with valves and diffusers and new dual core blowers), respectively. Figures 7 and 8 compare the energy use with constant DO and ABAC for existing and future upgrades, respectively. Comparing the two control strategies, on average, ABAC consumes less energy than constant low DO strategy. Although differences in energy consumption are less than 5-6 % during high loading, the energy consumption under low loading can reach 13%. Energy consumption varies over a wider range for ABAC compared with low DO due to DO changes ranging from 0.1 to 3 mg/L. For all the high loading condition modeling scenarios, effluent ammonia and TP targets were met but effluent TIN was slightly elevated from target values at 11.3 C and 13.5 C. Under the low loading conditions, effluent targets for ammonia, TP, and TIN were met at all three temperatures.

ABAC Modeling with Feedback in BioWin: ABAC was modeled in BioWin using BioWin Controller using the distribution tool and default kinetics.

Comparison of Models for ABAC Modeling with Feedback Strategy: Though differences exist between the models in BioWin and SIMBA# for ABAC modeling with feedback strategy for DOSP in each aerobic zone, both showed that the proposed process can consistently meet the effluent daily ammonia goal of 1 mg N/L. Figure 9 compares the ammonia profile in the aerobic zones for BioWin and SIMBA with feedback control strategy. While BioWin uses a tapered aeration mode with the air distribution tool, SIMBA# uses the same DOSP in each of the aerobic zones. Figure 10 compares the DO profile with SIMBA# and BioWin.

ABAC Modeling with Feedback and Feedforward Step Gain in SIMBA#: A feedforward step gain (for DO) based on ammonia ranges in Zone 7 was developed during this project in SIMBA#, using default kinetics. The resulting DOSP was fed to all DO controllers in all basins. The advantages and disadvantages are discussed in the full paper.

SUMMARY: Modeling showed that the design can meet all the anticipated permit requirements.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

08:30:00

08:45:00

Session time

08:30:00

10:00:00

SessionOvercoming Challenges to Implement Advanced Aeration

Session locationMcCormick Place, Chicago, Illinois, USA

TopicProcess Control and Modeling

Author(s)

Patel, Vrunda, Arabi, Sara, Marks, Christopher, Sigmon, Cole, Charnas, Cody, Brown, Nathan, Trujillo, Shelley, Machado, Chris, Patel, Vrunda, Zamanzadeh, Mirzaman

Author(s)V. Patel1, S. Arabi1, C. Marks2, C. Sigmon2, C. Charnas1, N. Brown1, S. Trujillo1, C. Machado1, V. Patel1, M. Zamanzadeh3

Author affiliation(s)Stantec Inc.1, City of Boulder2, inCTRL Solutions3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825159912

Volume / Issue

Content sourceWEFTEC

Word count15

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