CFD Modeling and Process Testing

Tangential Inlet Velocity PlanMr. Samstag was an early adopter of computational fluid dynamics (CFD) for application to wastewater processes. He is the author of the Fortran program TANKXZ which solves for solids settling and transport with density couple in a two dimensional Cartesian coordinate domain. TANKXZ incorporates a k-epsilon turbulence model and uses the SIMPLE method of Patankar for resolution of pressure in solving for the fluid velocity field. For the past ten years he has been a user of the commercial CFD software Fluent and open source software, OpenFOAM. He is the secretary for the Management Team for the IWA working group for CFD and the manager of the LinkedIn Group “CFD for Wastewater.”



• Consultant for an Australian equipment manufacturer on the optimum geometry for a small rectangular sedimentation tank for a remote treatment facility. Modelling completed in OpenFOAM.

Tangential Inlet Velocity PlanPrincipal author and project manager for an internal clarifier optimization project. In this project Mr. Samstag evaluated the major geometric elements of the radial flow (circular) secondary clarifier using field-calibrated three dimensional (3D) CFD models. Elements investigated: inlet geometry, feed well diameter and depth, effluent geometry, and tank depth. The work recommended a standard geometry for Carollo-design activated sludge clarifiers.

IR Velocity Plot City of Daytona Beach, Florida – Process subconsultant for field testing of solids and velocity profiles and modelling consultant for optimization of aeration in a 15 mgd Bardenpho wastewater reclamation plant.

Solids Profile 10 mgd 3520 ppm 150 SVI Existing Depth Longmont Clarifier Capacity Analysis, Longmont, CO – Prepared three dimensional CFD analyses of alternative inlet configurations for capacity analysis and potential modification of existing activated sludge clarifiers. The investigation compared the performance of three different inlet configurations – target baffle, tangential energy dissipating inlet (EDI), and a concentric tub EDI. The target baffle and concentric tub EDI provided the best performance.

Philadelphia 092512 EDCOrange County Utilities, Orlando, Florida – Process engineer for field testing of five different types of vertical-shaft mixing impellers for activated sludge mixing: three hydrofoil and two hyperboloid mixers. For each mixing impeller three kinds of field test was accomplished: solids profile, velocity profile, and hydraulic residence time (HRT). The impellers were ranked in terms of coefficient of variation (CoV) for solids distribution.

Flluent nEW Tank Mesh (Figure 9)Sedimentation Tank Capacity Analysis, West County Wastewater District, Richmond, CA – Process engineer and author of a technical memorandum evaluating the capacity of activated sludge sedimentation tanks using a two-dimensional CFD model in Fluent based on user defined functions for solids settling and density couple. Mr. Samstag prepared protocols for field tests for calibration of the modeling. The modeling established the safety factor over state point analysis required to determine capacity as a function of overflow, mixed liquor solids concentration, and sludge settleabilty.

Solids  Profile 2.5 mps 1500sBlacks Ford SBR Mixing Evaluation, JEA Utility, Jacksonville, Florida – Process engineer and principal author of a report evaluating mixing efficiency of a jet-aeration and pumped mixing system for this 5 mgd (19,000 m3/day) capacity sequencing batch reactor (SBR) WWTP. In this study field solids profile measurements were used to calibrate a Fluent 3-dimensional CFD model using user defined functions (UDF) for solids settling, transport, and density couple. Results of the study indicated that the pumped mix system was significantly undersized to meet a conventional mix criterion of less than 10 percent variation of solids concentrations over the cross section of the tank. Follow-up studies showed that neutral density CFD studies significantly over-predict the degree of mixing of activated sludge in moderate concentration ranges.

• Process Engineer for field testing of primary clarifiers at the Orange County Sanitation District’s main plant in Fountain Valley California. Testing included settling rate tests, solids profile measurement, and mass balance monitoring to determine the cause of less-than expected underflow solids concentration.

fig_1Project manager for computational fluid dynamics (CFD) modeling of proposed lamella rectangular activated sludge sedimentation tanks for an extension to the Sonam WWTP in Seoul, Korea. Managed and directed CFD modeling and reviewed the final report.

• Rock Creek Facilities Plan, Clean Water Services – As part of this facilities plan, Mr. Samstag conducted field tests of secondary clarifiers at this WWTP including solids profile and sludge settling velocity tests. This test work was used in evaluation of the capacity of these clarifiers for future loading.

Solids ProfileProcess engineer for secondary sedimentation evaluations for the North San Mateo Water and Sewer District WWTP in Daly City, California. Responsible for analysis of process data, field testing including residence time distribution (RTD) dye testing, solids profile modeling, settling velocity testing, drogue and acoustic Doppler velocimeter (ADV) testing of square, center-feed activated sludge sedimentation tanks, review and presentation of three-dimensional CFD modeling, and final report authorship.

Velocity ProfileTest manager for secondary sedimentation evaluations for the Clark County, Nevada WWTP. Mr. Samstag led a field team in tests of existing radial flow secondary sedimentation tanks. Work included residence time distribution dye testing, solids profiling, velocity profiling using drogue and acoustic Doppler velocimeters, and modeling using a custom two-dimensional CFD model.

Renton RTD Test Curve• Process engineer for evaluation of the aeration system for the South Plant at Renton operated by King County Department of Natural Resources and Parks, Wastewater Treatment Division. The South Plant is an activated sludge plant with a capacity of 110 mgd (416,000 m3/day) using fine bubble aeration. In this project, Mr. Samstag directed dye testing in the aeration tanks to determine their hydraulic characteristics and used commercial and custom models to test the efficiency of different strategies for control of dissolved oxygen.

Andre Settling TestComprehensive Sewage Facilities Plan, City of Aberdeen, Washington – Project manager and process engineer for field-testing of sludge settling velocity and clarifier solids profile, CFD and process modeling, and capacity evaluation as part of a project to upgrade the plant to meet the terms of a consent decree.

Clarity Velocity Profile• Secondary Clarifier Rehabilitation, Olympus Terrace Sewer District, Mukilteo, Washington – Project manager and partial author of a report recommending the appropriate geometry for equipment replacement for a 58-foot diameter secondary sedimentation tank at a 2.2 mgd (8,300 m3/day) oxidation ditch wastewater treatment plant. The evaluation included computer simulation using a 2-dimensional, turbulent flow, density-sensitive, solids transport CFD model which predicted solids profiles and effluent solids concentrations for different geometry for the tank inlet and outlet zones. The report recommended a dual-feed well inlet arrangement based on the modeling. The modeling also predicted better performance for a Stamford baffle over a straight sidewall configuration in the effluent zone of the tank.

• Lagoon Biosolids Investigation, City of Oak Harbor, Washington – Project manager and process engineer for evaluation of operation of the Seaplane Lagoon Wastewater Treatment Plant. As part of the project, he evaluated the performance of an aerated lagoon treatment works. The evaluation emphasized interference with treatment performance by accumulations of lagoon biosolids and the impact of nitrogen transformations in the lagoons on effluent disinfection. The evaluation included solids deposition testing using test protocols developed by Mr. Samstag.

• Secondary Treatment Facilities Upgrade and Expansion, Allegheny County Sanitary Commission (ALCOSAN), Pittsburgh, Pennsylvania – Process engineer for evaluation of primary treatment facilities for combined sewer flows up to 625 mgd and expansion of the 200 mgd (750,000 m3/day) secondary treatment capacity to 275 mgd (1,0410,000 m3/day). Mr. Samstag served as process engineer for plant testing to confirm hydraulic and process characteristics of primary treatment facilities with loading rate as high as 4000 gallons per day per square foot (163 m/day). Dye, solids profile, and long-column settleability tests were conducted to establish capacity under high flows. Mr. Samstag developed the mass balance for the upgraded plant and evaluated aeration system requirements. New fine bubble aeration disc diffusers were evaluated to supplement existing tubular diffusers.

• Wastewater Facilities Plan Update, Spokane Advanced Wastewater Treatment Facility, Spokane, Washington – On the Spokane project Mr. Samstag served as process consultant for evaluation of requirements for effluent toxicity control and nitrification for this 40 mgd (151,000 m3/day) facility. He directed settling column tests as a part of evaluation of operation of the plant in a contact / re-aeration mode. Evaluations were also conducted into the feasibility of nitrification to a high degree to meet changing regulatory requirements.

lott_first_anoxic• Nitrogen Removal Facilities, LOTT Wastewater Treatment Plant, Olympia, Washington – Performed process evaluation and design for new aeration and biological nitrogen removal (BNR) tanks for conversion of a 22 million gallon per day high purity oxygen (HPO) activated sludge facility. The LOTT project was Washington’s second plant designed for nitrogen removal with its most severe effluent standard of 3 mg/l total nitrogen. The design for LOTT used the four-stage Bardenpho™ process. Mr. Samstag led a team in field dye and solids testing of existing sedimentation tanks to establish their capacity under future design loads. Testing was also conducted at the Kelowna, British Columbia Bardenpho™ facility as a part of the work.

• Wastewater Reclamation Facilities Design, City of Fontana, California – Process specialist for preliminary design of anoxic / aerobic suspended growth biological nitrogen removal processes for this 8 mgd (30,000 m3/day) capacity plant. For this project, Mr. Samstag led a team in field testing of a plant currently serving the Fontana drainage to establish design sludge settleability characteristics.

• TF/SG Test Facility, Municipality of Metropolitan Seattle, Seattle, Washington – Process engineer for design of a 25-gpm test facility for the TF/SG process constructed at the West Point Treatment Plant. Prepared process drawings and participated in progress meetings during operation of the facility.

• High Purity Oxygen Test Facility, Municipality of Metropolitan Seattle, Seattle, Washington – Project manager for modification of the TF/SG test facility to serve as a test facility for high purity oxygen (HPO) activated sludge. Mr. Samstag was chairman of the technical review committee for operation of the facility and partial author of the final report. The testing program operated over a period of one year and proved the feasibility of contact / re-aeration operation of the HPO process at West Point at solids residence times as low as 0.75 days and plug flow operation as low as 0.5 days. An anaerobic selector configuration was tested for two months without success.

• West Point Treatment Plant Expansion, Secondary Sedimentation Investigations, Municipality of Metropolitan Seattle, Seattle, Washington – Project manager for a series of full-scale, field and laboratory-scale tests and numerical modeling of sedimentation tanks as a part of preliminary design of primary and secondary sedimentation tanks for Seattle Metro’s largest wastewater treatment plant. As part of the program, full-scale sedimentation tanks were field tested at four sites and physical model testing and CFD modeling was conducted by Professor J. A. McCorquodale. The investigations concluded that either circular or rectangular tank designs could be used for effective secondary sedimentation up to hydraulic loading rates of 1500 gallons per day per square foot if aeration tanks are appropriately sized.

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