Gerges, Hany

Dr. Gerges has more than 34 years of experience in wastewater engineering. Dr. Gerges experience has included evaluation, optimization, and design of more than 90 wastewater treatment plants worldwide.He is also the developer of many software packages which have been successfully used for evaluation and rerating of primary and secondary clarifiers that resulted in millions of dollars in savings to clients. Hany's experiecne include the optimization of grit removal systems. Dr. Gerges is one of the lead authors of the recent WEF manual on grit sampling and characterization.

Titles from this speaker

Innovative Baffle System Tripling Primary Sedimentation Capacity and Saving Millions

Abstract

Learning Objective - To provide insight and share the experience of using an innovative baffle system in the primary sedimentation process at Dublin San Ramon Services District (DSRSD) to enhance the total suspended solids (TSS) and biochemical oxygen demand (BOD) removal efficiencies and increase capacity. Results of the stress testing indicated that PSTs equipped with baffle system achieved a total suspended solids removal of 46 percent at overflow rate of 8000 gpd/ft2 which is more than the triple the original capacity of the PSTs. Background The DSRSD operates a 17 MGD wastewater treatment plant in Dublin, California. The wastewater treatment plant had four primary sedimentation tanks (PSTs). Additional BOD5 removal in the primaries reduces loading to the secondary process thus reducing aeration demand as well as capital costs of new infrastructure for potential future nutrient removal requirements. Therefore, DSRSD initiated a project to increase the capacity and improve performance of the primary process. Feld testing and preliminary modeling was conducted to identify potential structural improvements. The study indicated that by optimizing the existing four tanks (with internal baffles) and adding one new tank, DSRSD would be able to achieve the goal. Objectives The objectives are threefold: 1.To introduce an innovative baffle system to increase the capacity and improve suspended solids and biochemical oxygen demand capture in conventional primary treatment. Such baffle systems could be applied at many conventional primary treatment plants leading to significant savings in downstream secondary treatment capital and operational costs. 2.To present the baffle systems as a potential replacement of chemically enhanced primary treatment as means of increasing solids capture. 3.To present DSRSD experience and lessons learned during the design, testing and construction of the baffle system. Status In 2017, DSRSD initiated an optimization study as part of the design project to investigate the potential of optimizing the existing PSTs. The study indicated that optimizing existing tanks and adding one more tank will achieve DSRSD goal. Since finishing the bulk of construction (2021), the primaries have exceeded the anticipated primary solids capture (upwards of 70 percent) under normal flow conditions. Stress testing indicated that the PSTs equipped with the baffle system was capable of achieving TSS removal efficiency of 46 percent at overflow rates as high as 8000 gpd/ft2. This overflow rate is almost triple the original flow rate that could have been sustained in the past (before installing the baffle system) by the PSTs while maintaining reasonable performance. A co-benefit of increasing the solids capture across the primaries is an increase in biogas production. Biogas production has increased approximately 20 percent. This increase is attributed to a combination of higher solids/organics capture across the primaries and primary solids having higher BTU content than waste activated sludge. Methodology Using CFD, an influent flocculation baffle, two mid-tank baffles , and a sludge protector canopy were modeled. Modeling results predicted that the preferred design would increase TSS and BOD5 removal efficiencies by increasing flocculation, improving the flow regime inside the tanks, decreasing short-circuiting, and decreasing sludge re-suspension. Field Testing and Data Analysis: Table 1 shows the sequence of the testing activities. PST#4 is one of the old tanks with deeper side water depth than PSts # 1, 2 and 3. As part of this project, internal baffles and transversal launders were installed into tank #4. PST # 5 is a completely new tank. For the stress testing, the old PSTs were taken offline to increase the loadings on the new PSTs. Effluent suspended solids and sludge density samples were collected as part of the stress testing. Figure 1 shows the results of the stress testing with both PSTs # 4 and 5 online. Table 2 summarizes the results of the testing. It is clear from the data that PSTs were able to achieve TSS removal efficiency as high as 59 percent at over flow rate of approximately 4100 gpd/ft2. On the second day of stress testing, PST# 4 was taken offline and the whole plant flow of approximately 15.75 mgd (average) was diverted to PSTs #5, during the testing, the effluent launders of PSTs # 5 were flooded indicating exceeding the hydraulic capacity of the tank. However, TSS removal efficiency was still satisfactory exceeding 46 percent. Conclusions 1.The new baffle system improved PSTs performance by increasing the TSS removal rate from 38 to 65 percent. 2.The new baffle system increased the process capacity of the PSTs and enables the PSTs of achieving TSS removal efficiency of 46 percent at over flow rate higher than 8000 gdp/ft2. 3.The new baffle system increased the TSS captured in the PST leading to increase ion biogas production. Significance: The baffle systems described herein improved TSS capture and allowed the PSTs to operate at much higher overflow rate than typically applied at conventional primary treatment. Such baffle systems could be applied at many primary treatment in many plants leading to significant savings in downstream secondary treatment capital and operational costs. Also, the baffle systems could be used in lieu of chemically enhanced primary treatment as means of increasing solid capture

An innovative baffle system has been utilized in the primary sedimentation process at Dublin San Ramon Services District (DSRSD) to enhance total suspended solids (TSS) and biochemical oxygen demand (BOD) removal efficiencies and increase capacity. Stress testing indicated that PSTs equipped with new baffle system achieved TSS removal of 46 percent at overflow rate of 8000 gpd/ft2 which is more than the triple the original capacity. Such a baffle system could be potential replacement of CEPT.

SpeakerGerges, Hany

Presentation time

11:00:00

11:30:00

Session time

10:30:00

12:00:00

SessionThree Different Flavors of Improvement for Preliminary/Primary Treatment

Session number522

Session locationRoom 349

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

Author(s)

Gerges, Hany, Yee, Jackie, Delight, Steve, Schilling, Bill, Falk, Michael, Greenfield, David

Author(s)H. Gerges1, J. Yee2, S. Delight2, B. Schilling3, M.W. Falk4, D. Greenfield5

Author affiliation(s)1HDR, CA, 2, CA, 3West Yost, CA, 4HDR Inc, CA, 5HDR, SC

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159546

Volume / Issue

Content sourceWEFTEC

Word count11

Maximizing the Treatment Potential of Secondary Clarifier Using CFD

Abstract

Objective Computational
Fluid Dynamics (CFD) has proven to be a reliable and effective method for modeling secondary clarifiers in wastewater treatment plants. By simulating flow dynamics and solids distribution, CFD provides a detailed understanding of clarifier performance under various operational and structural configurations. This powerful tool enables plant operators and engineers to identify targeted solutions that enhance treatment efficiency and optimize plant operations.

Background
The Pomona Water Reclamation Plant (PWRP), operated by the Los Angeles County Sanitation District (LACSD), has encountered challenges related to its secondary clarifiers over the past decade. With the application of CFD the HDR team conducted a comprehensive optimization study to identify cost-effective modifications to improve flow and solids distribution in the mixed liquor (ML) channel and enhance clarifier performance, leading to higher treatment capacity.

Methodology
This study developed both two-dimensional (2D) and three-dimensional (3D) CFD models that reflect the physical characteristics and current performance of the clarifiers through calibration based on historical and field data. 2D CFD model, also known as HDR's high-accuracy clarifier model (HACM©), replicates the physical processes in the clarifiers using mathematical relationships to understand clarifiers performance impact from various modifications, such as flocculation baffle, mid-tank baffle, transversal launders, and channel baffle system. 3D CFD modeling was used in evaluation of hydraulic flow distributions among clarifiers, as well as solids concentration distributions.

2D Process Model Findings
A preliminary 2D HACM© CFD model has been developed using the plant's historical MLSS and flow data and refined through the effluent suspended solids (ESS) data collected in the field. The model provided insights of solids distribution in the clarifier (Figure 1), enabling the team to evaluate various modifications on clarifier performance (Table 1). In the base case with the existing configuration, the secondary clarifier has an ESS concentration of 39 mg/L. The preliminary modeling results indicate that replacing the existing 82ft-long launder with a combination of a 50ft longitudinal launder and five 18ft transversal launders could lead to a 33% reduction in ESS concentrations. Figure 1(b) shows that the shorter launder remediates the end wall effect, reducing turbulences caused by the wall and promotes a more effective settling zone. The proposed modifications, such as the combination of perforated flocculation baffle and mid-tank baffle, could further improve clarifier performance. As shown in Figure 1(c), the flocculation baffle and mid-tank baffle create a zone that promote solids settling and minimize resuspension of settled solids, resulting in a significant ESS concentration of 72% (Table 1).

Figure 1. Flow And Solids Concentration Distributions in Secondary Clarifiers Under Various Modifications

Table 1. Optimization Results with Various Secondary Clarifier Modifications

3D Model Findings
Results from the 3D CFD analysis indicated that solids distribution in the ML channel could be significantly improved with modifications such as a channel baffle. A critical component for satisfactory secondary clarifier performance is even solids distribution to the clarifiers. Under the base case scenario with existing configuration and without air additions in the secondary treatment system, the difference between the highest and lowest solids loadings across clarifiers is around 7%. In addition, as shown in Figure 2(a), the tracer response curve for clarifier 6 has a delayed time to peak and lower peak concentration, likely due to low velocity zones in the ML channel towards clarifier 6 (Figure 3(a)). The channel baffle provides an effective remediation by inducing additional mixing and enhanced local turbulence inside the channel (Figure 3(b)), which result in more uniform tracer responses (Figure 2(b)). The modeling results suggest that installing a baffle inside the ML channel can reduce the variation between the highest and lowest solids loadings from 7% to 2.5%.

Figure 2. Tracer Response Curves in (a) base case; (b) channel baffle case

Figure 3. Cross-sectional Views of the ML channel before Clarifier 6: Velocity Magnitude Distributions in (a) base case; (b) channel baffle case

Significance
The findings from this study highlight the potential for targeted modifications to significantly enhance secondary clarifier performance at the Pomona Water Reclamation Plant. By leveraging CFD modeling, the team identified and evaluated cost-effective solutions that address existing challenges, improve flow and solids distribution, and optimize clarifier efficiency. These proposed improvements not only enhance the plant's ability to manage higher hydraulic and solids loadings but also demonstrate the value of advanced modeling techniques in achieving operational excellence. This approach provides a replicable framework for similar facilities facing comparable challenges, supporting the long-term sustainability and reliability of wastewater treatment systems.lity and reliability of wastewater treatment systems.

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

Presentation time

13:30:00

13:45:00

Session time

13:30:00

15:00:00

SessionInnovative Applications of Computational Fluid Dynamics Modeling

Session locationMcCormick Place, Chicago, Illinois, USA

TopicProcess Control and Modeling

Author(s)

Xu, Arthur, Weiland, Thomas, Ackman, Philip, Wu, Arista, Gerges, Hany, McCorquodale, J