Griborio, Alonso

Dr. Griborio is Hazen and Sawyer Director of Clarification Technology. He is an internationally recognized expert in clarifier modeling and optimization and is co-developer of the 2D hydrodynamic clarifier model “2Dc”. Dr. Griborio has served as speaker at numerous workshops related to wastewater treatment plant design and optimization, has authored more than 60 conference and peer-reviewed publications and has completed more than 50 clarifier design, stress testing and CFD modeling projects. Dr. Griborio has participated in projects in the United States, Canada, Japan, Korea, Australia, Israel, Colombia, Ecuador, Panama and Venezuela.

Titles from this speaker

Description: Can Anyone in California Make a Circle? Case Studies from Unique Clarifier...

Can Anyone in California Make a Circle? Case Studies from Unique Clarifier Assessments at California WRFs

Abstract

Many WRFs in California were built with investment following the Clean Water Act of the 1970’s. As such, many of the assets in these WRFs are now reaching the end of their useful life. Faced with aging infrastructure, new regulatory pressures, and increasing loads, these WRFs have had to realize more capacity from the same infrastructure. Computational fluid dynamics (CFD) modeling has been an indispensable tool in the evaluation, retrofit/design of clarifiers at numerous facilities in California. In many of these evaluations, careful consideration of the geometry of the clarifier is needed to understand the true capacity of the unit process. This paper will review case studies of unique. applications of CFD 2D and 3D modeling to assess clarifier improvements and design at three WRFs.

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

SpeakerChu, Irene

Presentation time

10:30:00

11:00:00

Session time

10:30:00

12:00:00

SessionSecondary Clarification Advancements

Session locationRoom S401d - Level 4

TopicAdvanced Level, Municipal Wastewater Treatment Design

Author(s)

Chu, Irene

Author(s)I. Chu 1; P. Pitt 2 ; A. Griborio 3; C. Portner 2; M. Ahmad 4; J. Desai 5; J. Wang 2; G. Warren 6; R. Pipkin 7; A. Lopez 7; I. Chu 1;

Author affiliation(s)Hazen and Sawyer, San Francisco, CA 1; Hazen and Sawyer, San Francisco, CA 2 ; Hazen and Sawyer, San Francisco, CA 3; Hazen and Sawyer 2; San Francisco Public Utilities Commission 4; San Francisco Public Utilities Commission 5; East Bay Municipal Utility District 2; East Bay Municipal Utility District 6; Union Sanitary District 7; Union Sanitary District 7; Hazen and Sawyer 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159194

Volume / Issue

Content sourceWEFTEC

Word count17

Combining Metabolic, Kinetic and Physical Selection to Achieve Full-Scale Continuous Flow Densified Activated Sludge and Nutrient Removal at Robert W. Hite Treatment Facility

Abstract

Introduction: Metro Water Recovery's (Metro) Robert W. Hite Treatment Facility (Hite) in Denver, CO is permitted for a maximum month (MM) flow of 220 mgd and has two parallel liquids treatment trains including the North Secondary (NSEC). The NSEC utilizes a modified Ludzack Ettinger (MLE) process with a sidestream anaerobic reactor (SAR) to achieve nutrient removal. In 2018, Metro's facility plan identified a need for increased aerobic solids retention time (aSRT) to meet future potential total nitrogen (TN) and total phosphorus (TP) regulations (Colorado Regulation 31). To avoid costly expansion, Metro commissioned a full-scale demonstration train (NAB2) to trial densified activated sludge (DAS). This work documents findings from the full-scale demonstration facility and discusses how Metro is translating DAS into a full-scale solution at the RWHTF. Specifically, this paper will discuss factors that have led to the development and long-term operation of DAS with biological and physical selection, as well as provide insights into how particle size distribution (PSD) may be impacted by operational parameters and influence nutrient removal. Materials and Methods: DAS facility: The DAS demonstration facility (denoted as NAB2) consisted of an isolated, paired aeration basin and secondary clarifier from NSEC. Description of the facility is provided elsewhere (Avila et al., 2021). Metro operated NAB2 to test multiple distinct metabolic and kinetic selector configurations, with two primary configurations, Fig 1. A 'control' train was also operated without physical and biological selection. Routine influent/eff concentrations of organics, solids and nutrient content were determined using Standard Methods for the Examination of Water and Wastewater. PSD of the MLSS, hydrocyclone UF, and hydrocyclone OF were routinely characterized. Settling Column Testing: Settling column testing of bulk DAS ML was conducted on multiple occasions to determine the Vesilind equation settling coefficients (V0 & k) as well as the PSD. Additionally, settling properties for particle size fractions: <200µm, 200-600µm, and >600µm were characterized across a concentration range of approximately 1,500 mg/L to 6,000 mg/L. Activity Testing: Batch scale activity testing of bulk mixed liquor and three particle size fractions was used to evaluate nutrient removal rates of activated sludge in 5-gallon reactors. Analytes (NH4, NO3, NO2, and PO4) were measured with HACH TNT kits. Hydrocyclone Nozzle Testing: Hydrocyclone UF nozzle sizes ranging from 15 to 25 mm were individually tested at a target pressure of 30 psi. Flow measurements from the hydrocyclone feed and OF were recorded via flow meter. Total suspended solids (TSS) and PSD samples were collected from the RAS, OF, and UF. Process and Capacity Modeling - Data from NAB2 testing were used to develop, calibrate, and validate AB2 specific and a whole plant process model in BioWinTM and computational fluid dynamics (CFD) models of the NSEC secondary clarifiers. These models establish system capacity of existing infrastructure and design criteria for full-scale implementation. Results and Discussion: Impact of biological selection on densification: PSD of NAB2 biomass during configuration 1 (SAR-MLE) mode) stabilized into a uni-modal distribution, with median size increasing from 100 to 200 um respectively (Fig 2A). The average SVI30 for the NAB2 versus control basins were 102 mL/g and 153 mL/g respectively. PSD of NAB2 biomass during configuration 2 (SAR-A2O) mode reflected a bi-model distribution (Fig 2B). The average SVI30 for the test versus control basins were 81 mL/g and 173 mL/g respectively. Cumulatively, results suggest that improved settleability is observed when the mass fraction of granules (particles >212 um) in the sludge exceeds 15%. This was observed on multiple occasions when NAB2 operated in SAR-A2O mode with anaerobic food to microorganism ratio (F/M) being sustained between 1.0 and 3.0 lb sCOD/lb MLVSS-day. Impacts on PSD on Settling Performance and Biomass Activity: Settling velocity and compressibility were observed to increase as the particle size fraction increased (Table 1). Biomass activity results indicated that larger particle size fractions had lower denitrification and nitrification rates versus smaller particle size fractions while Bio-P activity was highest in particles greater than 200 um. These results indicate that minimizing particles sizes greater than 600 um may allow Metro to exploit high nitrification/denitrification/Bio-P rates and with superior settling and compressibility (Quoc et al., 2021). Influence of Physical Selective Pressures on PSD in NAB2 (Fig 3): Results indicated that mass flow through the UF could be reduced when the nozzle size decreases (Fig 2). This phenomenon can potentially be exploited to craft a wasting strategy focused on developing and keeping a target PSD. DAS impacts on Capacity: Stress testing indicated that NAB2 could be loaded at surface overflow rates (SORs) >700 gpd/sf and solids loading rates (SLRs) >60 pounds per day per square foot (ppd/sf) while still maintaining reliable blanket control and stable effluent TSS (Fig 4). Whole plant process and CFD modeling indicated that the densified scenario could allow Metro to successfully treat 2040 flows without needing to invest in additional aeration basins or secondary clarifiers, allowing for savings of $50 million dollars.

To meet future nitrogen and phosphorus regulations without constructing new infrastructure, Metro Water Recovery conducted a full-scale demonstration of densified activated sludge (DAS) at its Robert W. Hite Treatment Facility. This study evaluated the DAS system, focusing on metabolic and kinetic selector configurations, particle size distribution, and nutrient removal efficiency. Results include impacts of configurations, particle size, and nozzle size and projected capital cost savings.

SpeakerMaltos, Rudy

Presentation time

09:00:00

09:30:00

Session time

08:30:00

10:00:00

SessionFull-scale Intensification Experience

Session number510

Session locationRoom 343

TopicFacility Operations and Maintenance, Intermediate Level, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)

Maltos, Rudy, Rauch-Williams, Tanja, Freedman, Daniel, Cavanaugh, Liam, Scopp, Anna, Priest, Ryan, Griborio, Alonso, Mayer, Alyssa, Noteboom, Haley, Latimer, Ron, Sun, Yewei, Khunjar, Wendell

Author(s)R. Maltos1, T. Rauch-Williams1, D. Freedman1, L.M. Cavanaugh1, A. Scopp2, R. Priest2, A. Griborio3, A.J. Mayer4, H. Noteboom5, R.J. Latimer6, Y. Sun7, W. Khunjar8

Author affiliation(s)1Metro Water Recovery, CO, 2Hazen and Sawyer, CO, 3Hazen & Sawyer, FL, 4Hazen & Sawyer, OH, 5Hazen & Sawyer, NY, 6Hazen and Sawyer, GA, 7Hazen and Sawyer, VA, 8Hazen & Sawyer PC, VA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159645

Volume / Issue

Content sourceWEFTEC

Word count24

Description: Computational Fluid Dynamics Modeling and Validation Testing of Peripheral Feed...

Computational Fluid Dynamics Modeling and Validation Testing of Peripheral Feed Peripheral Overflow Clarifiers at the East Bay Municipal Utility District Main Wastewater Treatment Plant

Abstract

The East Bay Municipal Utility District (EBMUD) owns and operates the Main Wastewater Treatment Plant. The plant has twelve 140-ft diameter peripheral feed peripheral overflow (PFPO) secondary clarifiers. EBMUD is in the process of rehabilitating these clarifiers and worked with Hazen to define optimization opportunities that would result in improved performance. This paper presents the application of a CFD model for the evaluation and optimization of the EBMUD PFPO clarifiers; and the validation testing performed to confirm the successful implementation of the proposed modifications. While there is minimal literature on CFD modeling of PFPO clarifiers, the study demonstrates that it can be done with great success. The original modeling resulted in recommended modifications to the existing clarifiers and predicted improvements of 25% in effluent quality. Validation testing after two clarifiers were modified, proved the modifications were valuable and confirmed over 30% improvement in effluent quality.

EBMUD owns and operates the Main WWTP. The plant has twelve 140-ft diameter peripheral feed peripheral overflow (PFPO) secondary clarifiers. EBMUD is in the process of rehabilitating these clarifiers and worked with Hazen to define optimization opportunities that would result in improved performance. This paper presents the application of a CFD model for the evaluation and optimization of the EBMUD PFPO clarifiers; and the validation testing performed to confirm the successful implementation of the proposed modifications. Field testing conducted after the clarifier rehabilitation demonstrated the effectiveness of the clarifier modifications and confirmed over 30% improvement in effluent quality.

SpeakerGriborio, Alonso

Presentation time

17:05:00

17:25:00

Session time

16:00:00

17:30:00

SessionSecondary Clarifier Treatment Performance

Session number117

TopicFacility Operations and Maintenance, Municipal Wastewater Treatment Design

Author(s)

Alonso Griborio

Author(s)J. Wang1;A. Griborio2;P. Pitt2;I. Chu2;C. Portner2;

Author affiliation(s)East Bay Municipal Utility District, Oakland, CA1Hazen and Sawyer, P.C., San Francisco, CA2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2021

DOI10.2175/193864718825158172

Volume / Issue

Content sourceWEFTEC

Word count25

Densification Specific Considerations for Secondary Clarifier Assessments

Abstract

Intensification is a major innovation for water resource recovery facilities (WRRFs) to realize cost-effective use and deployment of infrastructure. One of the promising technologies and approaches for process intensification is densified activated sludge (DAS). Secondary clarifiers are a key unit process to ensure retention of the solids inventory and permit compliance. The performance of clarifiers depends on several interrelated processes and factors including hydrodynamics, settling, turbulence, flocculation, sludge rheology, atmospheric conditions, tank geometry, internal features and loading conditions. Several tools and design “rules of thumb” are available from regulatory loading guidelines such as Ten State Standards, sludge specific assessment tools such as state point analysis, and calibrated, site-specific tools such as 2D and 3D computational fluid dynamics (CFD) modeling. These tools have been in use for decades with traditional sludge settling characteristics. However, the industry is still working through methods and procedures to assess the impacts of DAS settling characteristics on traditional secondary clarifier operations and loading guidelines. This paper will highlight the use of clarifier evaluation tools for DAS applications, including key considerations, observed performance, potential loading rates, and other relevant properties. Case studies are highlighted to demonstrate potential impacts at full-scale WRRF sites.

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

SpeakerMartin, Will

Presentation time

11:30:00

12:00:00

Session time

10:30:00

12:00:00

SessionSecondary Clarification Advancements

Session locationRoom S401d - Level 4

TopicAdvanced Level, Municipal Wastewater Treatment Design

Author(s)

Martin, William

Author(s)W. Martin 1; A. Griborio 2 ; R. Latimer 3; R. Vandermeulen 4; G. Ram Mohan 5; W. Martin 1;

Author affiliation(s)Hazen and Sawyer, St. Paul, MN 1; Hazen and Sawyer, Hollywood, FL 2 ; Hazen and Sawyer, Atlanta, GA 3; Hazen and Sawyer 4; Hazen and Sawyer 5; Hazen and Sawyer 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159196

Volume / Issue

Content sourceWEFTEC

Word count8

Optimizing Suspended Solids Removal in Secondary Clarifiers from DAS Systems

Abstract

Introduction:
Metro Water Recovery's Robert W. Hite Treatment Facility (Hite) in Denver, CO, is permitted for a maximum month flow (MMF) of 220 mgd and an average daily flow (AADF) of 130 mgd. Hite includes the North Secondary (NSEC) treatment train, rated at 106-mgd MMF and 94-mgd AADF, which utilizes an MLE process with a sidestream anaerobic reactor (SAR) for nutrient removal. In 2018, Metro's facility plan highlighted the need for increased aerobic solids retention time (aSRT) to comply with potential future total nitrogen and total phosphorus regulations. Metro commissioned a full-scale demonstration train (NAB2) to test densified activated sludge (DAS) to avoid costly expansion.

While DAS is effective at improving settleability and increasing treatment capacity, it can also lead to higher secondary clarifier effluent suspended solids (ESS) (Figure 1). This study investigates the causes for elevated ESS from DAS and identified strategies for improving ESS by modifying existing clarifiers utilizing comprehensive field sampling and an updated 2Dc computational fluid dynamics (CFD) model.

Secondary Clarifier Capacity Evaluation:
This study builds on previous 2Dc modeling efforts evaluating the capacity of NSEC's secondary clarifiers under projected future flows and loads with DAS implementation. Stress testing of the NAB2 DAS pilot indicates that NAB2 could be loaded at surface overflow rates (SORs) > 700 gpd/sf and solids loading rates (SLRs) > 60 pounds per day per square foot (ppd/sf) while still maintaining reliable blanket control and stable ESS (Figure 2). Whole plant process and 2Dc modeling indicate that DAS could provide Metro sufficient capacity to address design flows/loads at the NSEC while also meeting stringent nutrient limits without new basins or clarifiers (1).

Weir Sampling to Inform Modeling:
The NSEC clarifiers have inboard (two weirs) and outboard (one weir) launders, and different effluent quality associated with each weir. In both the conventional activated sludge (CAS) control and NAB2 DAS pilot systems, the narrow space between the inboard and outboard launder is believed to create a higher velocity current up the side wall of the clarifier where approximately 2/3 of the effluent flow leaves the clarifier. In the DAS system, this effect may be exacerbated by the unique properties of the densified particles, including higher settling velocities and reduced agglomeration as indicated by increased dispersed suspended solids (DSS) (Figure 3) (2).

To support this investigation, comprehensive field sampling was performed on the NAB2 DAS pilot to gather ESS data from each weir across four clarifier quads (Figure 4). The data confirm higher ESS associated with the outboard launder and support updated 2Dc model calibration to evaluate potential clarifier modifications to reduce ESS.

Modeling Approach and Key Findings:
The updated 2Dc modeling code was enhanced to depict a more accurate representation of NSEC's dual launder system and the ability to report ESS per weir (including blocking flow from individual weirs). This enhanced model was used to perform a sensitivity analysis including weir blocking, center well extensions, and addition of a Stamford baffle. The alternative improvements were evaluated under the following NSEC design conditions: MMF (106 mgd) and load, AADF (94 mgd) and load, and peak flow (150 mgd) with annual average load. Results indicate that multiple alternatives may significantly reduce ESS:

Alt 1: Block Weir 3: Blocking the outboard launder weir is a simple, low-cost modification, and is predicted to reduce ESS by 25-50% through addressing uneven solids distribution identified in field data.

Alt 2: Block Weir 3 + Center Well Extension: Extending the center well by 2' is predicted to reduce ESS by 30-70%; however, structural modifications to the mechanism arm and center well would be required.

Alt 3: Block Weir 3 + Stamford Baffle: Adding a Stamford baffle is predicted to reduce ESS by 40-70%, with improvements attributed to better sludge blanket stability and optimized flow patterns.

Alt 4: Combine All Modifications: Integrating all strategies is predicted to have the highest ESS reduction (45-75%), but careful sludge blanket monitoring and return activated sludge (RAS) flow control would be required to keep the blanket below the Stamford baffle (Figure 5).

Predicted ESS improvements were applied to historic NAB2 ESS data to determine the anticipated ESS ranges for each alternative (Table 1).

Conclusion:
This study showcases an enhanced 2Dc modeling approach for optimizing ESS in DAS systems. For DAS systems experiencing ESS challenges, utilities may consider clarifier modifications such as blocking specific weirs, extending the center well, and adding a Stamford baffle to help address uneven solids distribution, mitigate density currents, and optimize clarifier performance. These modifications show potential ESS reductions ranging from 25-75%, offering practical, site-specific solutions. 2Dc modeling is a valuable tool for diagnosing elevated ESS issues and identifying opportunities to reduce variability, helping utilities make informed decisions to optimize clarifier performance. By combining advanced modeling tools with targeted clarifier improvements, utilities can effectively reduce ESS variability and position themselves to meet future regulatory requirements.

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

Presentation time

16:00:00

16:30:00

Session time

15:30:00

17:00:00

SessionUnderstanding Clarifier Settleability from Fundamental to Intensification Process

Session locationMcCormick Place, Chicago, Illinois, USA

TopicLiquid Stream Treatment Technology - Secondary & Tertiary Treatment

Author(s)

Scopp, Anna, Maltos, Rudy, Priest, Ryan, Freedman, Daniel, Rauch-Williams, Tanja, Griborio, Alonso, Khunjar, Wendell, Martin, Will, McCorquodale, J

Author(s)A. Scopp1, R. Maltos2, R. Priest1, D. Freedman2, T. Rauch-Williams2, A. Griborio1, W. Khunjar1, W. Martin1, J. McCorquodale3

Author affiliation(s)Hazen and Sawyer1, Metro Water Recovery2, University of New Orleans Jets3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825160004

Volume / Issue

Content sourceWEFTEC

Word count11