Thompson, Luke

Luke Thompson is a water engineer at HDR with a BS/MS and five years of experience in environmental engineering focusing on water and wastewater treatment and planning, condition assessment, hydraulic modeling, and water resources. He has worked on projects nationally but primarily has experience with projects in the pacific northwest and the desert southwest. He has applied his engineering experience as a student and professional to work with Engineers Without Borders for 8 years in Kenya and Guatemala. He is inspired to sustain our communities and environment with water engineering solutions.

Titles from this speaker

Application of Measured Rheological Data for Improved Sludge Process Design

Abstract

1.0 Purpose Wastewater sludges that contain more than 1.5 to 2 percent solids have fluid characteristics that are different than clean water. The complex non-Newtonian behavior of sludges requires more in-depth hydraulic analyses, especially when there is variability in solids concentrations. These complexities can be quantified using rheology, the study of the deformation and flow of matter. Rheology is required to appropriately design systems for non-Newtonian fluids such as primary sludge, waste-activated sludge, combined undigested sludge, thickened sludge, digester recirculation, and dewatering feed sludge. The primary goal of measuring and representing these rheological characteristics is to achieve a higher precision in hydraulic design. Rheological data was gathered for a solids improvement project at Kitsap County's Central Treatment Plant to develop hydraulic model inputs in AFT Fathom„¢ to then determine thickened sludge process design criteria. Measured rheological characteristics and updated design method findings were compared to typical rheological values and historical design methods to inform final design criteria for the thickened sludge process improvements. The measured rheological data and alternative design approach can be applied to future projects by leveraging a growing data base of rheological characteristics and alternative design approach performance data. 2.0 Rheological History and Historical Design Approaches There are typically two approaches to sizing sludge pumps. When plant data cannot be collected, it is common to use standard rheological values. A downside to this approach is that it is typically only recommended for pumping lengths of less than 100 feet. Alternatively, pump testing can be used to determine rheological characteristics but it requires a pump to already be installed and, in many situations, hydraulic analysis and design must be conducted prior to testing. It can also be difficult to estimate the pressure spike associated with pump startup to initiate sludge movement. 3.0 Rheological Experimentation An alternative approach to estimate sludge pumping hydraulics is to test plant sludge with a rotational rheometer and use that data as an input to a non-Newtonian hydraulic model. Through the use of a Brookfield DVNext rotational rheometer, rheological sampling and analysis for pumped sludges can be conducted (Ametek Brookfield Inc., 2019). This piece of equipment applies a shear force and torque to a fluid using a rotating spindle. It records the shear rate, which is a function of the spindle speed, the shear force, torque, and viscosity. Testing these values by varying the spindle speed creates a viscosity and shear stress profile for each sample. This profile characterizes the rheological properties of the fluid. The samples are also tested to determine the solids concentration so a relationship between the rheological profile and percent solids can be defined. 4.0 Application of Rheology to Modified Design Approach The purpose of these plant-specific studies is to improve hydraulic calculations using the observed rheological properties of the sludge to then establish design criteria for sludge pumping applications. AFT Fathom„¢ is a hydraulic modeling software that has capabilities to input observed rheological data and compare it with various non-Newtonian fit models to estimate the hydraulic impact of a given sludge. Such models include the standard Power Law, Bingham Plastic, and the Herschel-Buckley fits (Water Environment Federation and the American Society of Civil Engineers, 2010). AFT Fathom can then use these characteristics and fit models, along with other information such as preliminary pipe lengths and fittings, to determine the total dynamic head and other hydraulic design criteria (AFT Fathom 2023). To further improve the analysis, AFT Impulse„¢ can be used to estimate transient pressure spikes that may occur during pump startup The Fundamentals of Unfamiliar Fluids (Clark, 2021), (AFT Impulse 2023). 5.0 Case Study HDR is designing improvements for various solids treatment processes at Kitsap County's Central Treatment Plant. Amongst other miscellaneous solids improvements, new primary sludge, septage, and WAS thickening equipment and two new digesters will be designed. Equipment to support these process improvements such as thickened sludge pumps, process piping, meters, etc. are included in the design. Rheological data was collected from the plant to design new sludge pumps and ensure adequacy of existing sludge pumps for process modifications. 5.1 Experimental Approach Data was collected over four sampling events, two different seasons, and varied operational scenarios to determine a modeling and design basis for different sludge streams. Co-thickened primary sludge and septage, digested sludge, and thickened WAS samples were collected and analyzed with the rotational rheometer on site. Triplicate runs were conducted for a wide range of shear rates to collect each stream's rheological properties per testing methods recommended by the rheometer manufacturer (Ametek-Brookfield, Inc., 2017). Once trials were complete, onsite laboratory staff used standard methods to determine each sample's percent total solids and total volatile solids. 5.2 Experiment Results and Data Evaluation Test results revealed that shear stress values are, generally, positively correlated with the total solids of the samples. As anticipated, seasonal temperature impacted viscosity measurements with the colder conditions prompting more conservative design values. For each stream, shear stress and shear rate data were evaluated using the Bingham Plastic, Hershel-Buckley, and Power Law rheological fit models. Tested samples had a lower percent solids (4-6%) than the anticipated design condition after the thickener (5-8%). To address this discrepancy, measured rheological fit curves were extrapolated to estimate the properties of thickened sludge with a higher percent solids concentration than what was tested. This approach required multiple hydraulic model runs using each rheological fit model to determine the most reasonable design conditions and to avoid oversizing of the pumps. In summary, measured data for each sludge was input into the hydraulic model for each rheological fit and compared to typical design approaches to estimate the total dynamic head (TDH) that the thickened sludge pumps would experience. In some cases, typical design approaches provided more conservative TDH values as compared to the alternative design approach using measured rheological characteristics. Figure 1 depicts one example of testing results for thickened waste activated sludge (TWAS), thickened primary sludge and septage (TPSS), and digester sludge. Figure 2 depicts the rheometer on-site during a sampling event. Comparison of TDH for typical design approaches and alternative modeled design approaches based on measured data are compared in Table 1. Another rheological sampling event will be conducted in January 2024 to measure additional characteristics and seasonal variability for the sludges in question. These additional results will be compared to summer sampling data to finalize elected design criteria for the thickened sludge process improvements. 6.0 Future Development of Rheology In preparation of the aforementioned rheological testing, an internal best practice document was developed in collaboration with Matt Higgins at Bucknell University to define appropriate rheological testing criteria, data analysis methods, and design approaches using measured data. It is expected that this document will continue to be refined as more sampling events are conducted. Upon construction of each project, performance data will be evaluated to calibrate and improve the experimental criteria and alternative design approach. Rheological data sets from sludges tested at various plants can be compiled into a database to evaluate trends and consistencies in different sludges. Depending on the depth and breadth of data available and resulting findings, this comprehensive dataset may ultimately be used as a standard reference for design.

This paper was presented at the WEF Residuals and Biosolids Conference, June 18-21, 2024.

SpeakerThompson, Luke

Presentation time

14:00:00

14:30:00

Session time

13:30:00

16:45:00

SessionDewatering

Session number05

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicCo-Thickening, Dewatering, Hydraulic Model

Author(s)

Thompson, Luke

Author(s)L. THOMPSON1, E. Leonard1

Author affiliation(s)HDR 1; HDR 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159451

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count11

Elevating Sludge Process Design: The Significance of Plant-Specific Rheology Data

Abstract

RELEVANCE Wastewater sludges have fluid characteristics that differ from clean water and exhibit non-Newtonian behaviors that require specific hydraulic analyses. Rheology, the study of matter deformation and flow, can quantify rheological characteristics and improve the hydraulic design of wastewater sludge systems. A solids improvement project at Kitsap County's Central Kitsap Treatment Plant (CKTP) used onsite testing and hydraulic modeling to design various thickened sludge pumps and systems. The results from this design approach support using plant-specific rheological data when designing thickened sludge systems compared to conventional design approaches. BACKGROUND Common approaches to size sludge systems do not use plant-specific rheological testing data. Standard rheological values are typically used if plant data cannot be collected. However, this method usually only applies to systems under 100 feet in pipe length. Pump testing is another design approach but requires a constructed pump and sludge system, which must have been installed beforehand. Alternatively, a rotational rheometer can estimate sludge hydraulics by quantifying plant-specific rheological properties to develop a non-Newtonian hydraulic model. Rotational rheometers use a rotating spindle to apply shear force and torque to a fluid. A viscosity and shear stress profile can be generated by varying spindle speed to characterize the rheological properties. The solids concentrations of samples are also recorded to correlate the rheological profile with a specific percent total solids. These profiles can then be input into AFT Fathom, a hydraulic modeling software, to develop non-Newtonian hydraulic models. The Power Law, Bingham-Plastic, and Herschel-Buckly fits can be used to determine total dynamic head (TDH) for thickened sludge pumps. This hydraulic model can be used to design new thickened sludge systems or evaluate the impacts of changes to existing systems. CASE STUDY HDR is designing various solids process improvements at CKTP. New primary sludge, septage, and waste-activated sludge (WAS) thickening equipment and associated pumps, pipes, and appurtenances will be designed as part of the improvements. Rheological data collected from the plant was used to design new systems and ensure the adequacy of existing systems for process modifications. Onsite analysis of co-thickened primary sludge and septage, digested sludge, and thickened WAS were conducted using the rotational rheometer. Triplicate runs were run at various shear rates to measure each stream. In parallel, plant staff tested the total and volatile solids using standard methods. Rheological data was input into the hydraulic model, and various rheological fit curves were tested to determine design criteria for the thickened sludge systems. RESULTS Test results suggest a positive correlation between shear stress and total solids; viscosity measurement increased with colder sludge temperatures, resulting in more conservative design criteria. Figure 1 depicts shear rate and shear stress results for thickened waste activated sludge (TWAS), thickened primary sludge and septage (TPSS), and digester sludge. Figure 2 shows the rheometer during a sampling event. Sampled sludges had a lower solids (4-6%) than the design condition (5-8%) so fit curves were extrapolated to estimate sludge properties. Traditional design methods differed in modeled results as compared to this alternative approach. Table 1 compares the TDH for typical and alternative modeled design approaches. APPLICABILITY Typical design approaches use multiplication factors applied to clean water hydraulics or extrapolated data from region-specific case studies, which can result in incorrectly sizing pumps, pipes, and associated processes. For example, typical design approaches with 4-5% solids content varied by 13% between the TDH values through Kitsap's system. Alternatively, TPSS and TWAS samples had a smaller variation in total solids (0.1%) but varied in evaluated TDH by 100%. This is shown in Table 2 and reflects the point shown in Figure 1 that rheological behavior is not fully represented by solids content. Other rheological testing conducted showed up to 76% difference in TDH between similar sludges from different plants. This is also shown in Table 2. Using an alternative design approach of measuring plant-specific characteristics characterizes sludges with much more detail than typical approaches. The alternative approach mitigates inaccurate assumptions that could result in inefficient design of sludge systems. Collecting data from various plants will allow the establishment of a database to evaluate trends and consistencies in different sludges. An internal best practice document is in development with Matt Higgins at Bucknell University to develop standard testing criteria, data analysis methods, and design approaches for future applications. This effort focused on municipal sludges but could also be applied to industrial sludges and other viscous streams.

Wastewater sludges are non-Newtonian fluids requiring specialized hydraulic analyses for process design. Rheology quantifies sludge characteristics for enhanced hydraulic system design. On-site rheology testing and non-Newtonian hydraulic modeling was used to design sludge pumps and evaluate fluid property and process design impacts on pump sizing. The results from these evaluations support use of plant-specific rheology data in non-Newtonian hydraulic models as a standard design approach.

SpeakerThompson, Luke

Presentation time

08:30:00

08:50:00

Session time

08:30:00

10:00:00

SessionThickening and Dewatering: Design Considerations

Session number301

Session locationRoom 354

TopicBiosolids and Residuals

Author(s)