Parmenter, Adam

Adam is a biosolids process design engineer and project manager with 20-years of service at HDR. His biosolids expertise comes from design, construction, operation, and troubleshooting of biosolids facilities around the United States.

Titles from this speaker

Flux Capacity: Screw Press Sizing Of The Future

Abstract

The most common technologies for sludge dewatering in wastewater treatment plants include belt filter presses, centrifuges, and screw presses, with the latter known for their significant advantages in low power consumption and high efficiency during the dewatering process. Various manufacturers supply screw presses to wastewater treatment plants, offering pilot testing to assess the performance, throughput capability, and feasibility of dewatering units in diverse practical and controlled environments. However, unlike centrifuges and belt filter presses, the capability to compare the throughput of screw presses throughput between manufacturers is lesser known. While the throughput equipment capacity comparisons for centrifuges and belt filter presses are well-established through G-Volumes and filter areas, respectively, a similar standardization for screw presses is not widely recognized. The Tres Rios Water Reclamation Facility, owned by The Pima County Regional Wastewater Reclamation Department, serves as the centralized sludge handling and solids treatment system for the entire county, offering a treatment capacity of 50 MGD and over 180 WTPD of solid dewatering. Currently utilizing three centrifuges for sludge dewatering, the facility faces challenges related to high polymer and power usage. In response, as part of the county's transition from achieving Class B to Class A biosolids, a new dewatering facility employing screw presses was proposed aimed to reduce energy costs and enhance the efficiency and reliability of the dewatering process, ultimately supplying future solar dryers. During the summer and fall of 2023, three screw press pilots, and one volute press pilot were conducted in collaboration with various equipment manufacturers. The primary objective of these pilots was to verify and evaluate dewatering performance and ultimate equipment selection using digested sludge from the Tres Rios WRF. A new approach was implemented when comparing pilot test results relative to full-scale equipment selection. The approach is to compare 'flux' of each machine at its best performance point. The machine's flux is the rate of liquid and/or solids flow rate per surface area of the machine. In doing this analysis, full-scale equipment is sized relative to the pilot test's best performance at a proven flux rate. An equal flux rate from pilot to full-scale equipment will help ensure similar and expected performance at full-scale operation. To compare performance of the screw press units during the pilot testing, liquid and solids flux rates were calculated for each manufacturer. The liquid flux rate results of the three screw press manufacturers are shown in Table 1. The volute press manufacturer was not included in the evaluation due to the poor pilot test results compared with the other manufacturers. The lower flux rate, indicative of a higher dewatering capability, signifies superior dewatering through an extended residence. Manufacturer 2 and 3 out-performed Manufacturer 1 by providing higher filtration area. Manufacturer 1 was not recommended for further consideration due to small full-scale equipment size options, resulting in the preferred maximum liquid flux rate of 0.31 gpm/sf for best performance. The results from the pilot testing aided in identifying the required flux rate achieve best performance, and ultimately confirms full-scale equipment sizing for a range of operating conditions. Table 2 shows that both manufacturers required five installed units dewater the design load, and a throughput derating of up to 75% is needed compared with the listed manufacturer nameplate. In contrast to using screw press volume, relying on manufacturer recommendations, or arbitrary derating of equipment as a metric for performance comparison among different manufacturers, the presentation will present findings showing that flux rate calculation during pilot units provides fair and more realistic results. Larger screw presses are noted to lose efficiency as the ratio of surface area to volume decreases with the growth in diameter and length of the screw. This claim can be better studied with a flux rate that remains constant regardless of the equipment size due to the solids retention time being equal, which this pilot study investigated. Attendees of this presentation will gain valuable insights into the comparative performance of screw presses from different manufacturers post-pilot testing. This knowledge will aid in establishing informed selection criteria for optimizing dewatering solutions in wastewater treatment plants.

The paper evaluates screw presses for sludge dewatering at the Tres Rios WRF. Four pilot tests in 2023 assessed different manufacturers using "flux"—the liquid/solids flow rate per unit surface area. Superior dewatering occurred at lower flux rates, indicating higher capabilities with extended residence time. The study concluded that liquid flux rate is a more accurate performance metric than manufacturer recommendations or arbitrary derating.

SpeakerFraijo, Alejandra

Presentation time

09:00:00

09:20:00

Session time

08:30:00

10:00:00

SessionThickening and Dewatering: Design Considerations

Session number301

Session locationRoom 354

TopicBiosolids and Residuals

Author(s)

Fraijo, Alejandra, Parmenter, Adam, Prevatt, Jeff

Author(s)A. Fraijo1, A. Parmenter2, J. Prevatt3

Author affiliation(s)1HDR Engineering, AZ, 2HDR, MN, 3PIMA COUNTY WASTEWATER, AZ

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159520

Volume / Issue

Content sourceWEFTEC

Word count9

Description: The Results of Replacing a Class A Biosolids Stabilization Technology to Gain...

The Results of Replacing a Class A Biosolids Stabilization Technology to Gain Capacity and Save Money

Abstract

INTRODUCTION Due to historical and continued population growth, the Town of Erie Colorado's North Water Reclamation Facility (NWRF) needed to expand. The NWRF's existing solids treatment process utilized an alkaline biosolids stabilization process to achieve Class A cake. Frequent shutdowns of the dewatering system occurred due to significant scaling in its screw press, caused by the high dosage of lime. Acid addition was consequently introduced as a permanent solution to reduce scaling, but as a result, the stabilized solids did not meet Class A fecal coliform reduction requirements. Due to expansion needs and the current system issues, a new or greatly modified system was required. The Town became interested in evaluating a new solids processing system that would both meet the requirements of the desired Class A end-product, as well as reduce the total annual operating and maintenance costs. HDR was tasked with a comprehensive alternatives evaluation for several biosolids stabilization technologies to determine which option would best suit the Town. The evaluation included establishing design conditions, analyzing the existing system's capacity, performing a preliminary screening of all alternatives, conducting a non-economic evaluation for the narrowed alternatives, and developing an economic evaluation including capital and operation and maintenance costs. This approach incorporated both monetary and non-monetary considerations to ensure that the selected technology would meet the Town's short-term and long-term interests. APPROACH The initial step was to compare the capacity of the existing biosolids handling system against the projected 10- and 20-year solids flows and loads, and determine the scope of expansion required to keep the existing system in operation. The next step in the evaluation process was to perform a screening level alternatives analysis for other biosolids stabilization technologies. Several considerations were included in the analysis including the number of installations of each technology within the United States, feasibility of construction, extensive annual costs for operation or maintenance, and process safety. After completing the preliminary screening of biosolids stabilization alternatives, HDR and the Town eliminated multiple technologies from further consideration. The following stabilization systems were shortlisted for further evaluation: - Alkaline Biosolids Stabilization: Existing System Expansion - Autothermal Thermophilic Aerobic Digestion (ATAD) - BCR Neutralizer System The first alternative, which is to expand the existing lime stabilization system, assumed no changes to the plant's current biosolids stabilization process other than increased capacity. The second alternative, Autothermal thermophilic aerobic digestion (ATAD), examined changing the process to a two-step aerobic digestion system patented by Thermal Process Systems (TPS) that utilizes high temperatures to trigger microbial activity by high carbon consumption thermophiles. The last alternative, the BCR Neutralizer system, is a process in which sodium chlorite and sulfuric acid are combined to make chlorine dioxide, which is then added to thickened WAS. It is a batch process rather than a continuous flow process, and it uses three additional chemicals to obtain Class A biosolids: sodium nitrate, ferric sulfate, and sodium hydroxide. The non-economic evaluation played a key role in the selection process. The non-economic factors included: - Operator Attention - Operator Familiarity - Maintenance Requirements/Complexity - Flexibility to meet Future Flows and Loads - Footprint - Implementation - Redundancy - Sustainability - Safety The last step in further evaluating the three alternatives was to conduct a monetary comparative analysis by developing the opinion of probable construction costs and a net present value (NPV) analysis using labor, energy, and chemical costs for a 10-year and 20-year evaluation. RESULTS The non-economic evaluation demonstrated that the ATAD alternative was preferred to the BCR Neutralizer alternative following the non-economic evaluation. After operating a chemical lime system for biosolids stabilization and handling several operational and maintenance-related difficulties associated with it, the Town favored a treatment process that did not require heavy chemical use. Additionally, the Town preferred an alternative that would be easily implemented within the plant's existing process, and that would sustainably and reliably produce a desirable biosolids end-product, so that they could reduce their dependence on third-party hauling companies. The figure below shows ATAD alternative as the favorable stabilization process versus the BCR Neutralizer. Figure 1: Non-Economic Evaluation of Narrowed Alternatives (Town of Erie NWRF Expansion Preliminary Design Report, HDR, 2019) The economic evaluation showed that the ATAD alternative was twice the capital cost of the other two alternatives, however, after review of the 10 and 20 year net present values, the ATAD alternative was the most favorable. Table 1 below provides a summary of those costs. Table 1: NPV Analysis for Keep Existing and ATAD Alternatives (Town of Erie NWRF Expansion Master Plan, HDR, 2019) Construction started towards the end of 2020 and the ATAD process was in operation by the start of 2023. The biosolids system is currently processing an average of 2800 PPD. With a design capacity of 11,700 PPD, the treatment system will have capacity to meet future growth. By year end of 2023, the new ATAD process has provided annual cost savings to the Town including a reduction in chemical cost by $75,000, reduction in hauling costs by $100,000, 10% reduction in electrical costs and $40,000 reduction in gas usage compared to previous years using the existing lime stabilization system. CONCLUSION After the evaluation was completed, the ATAD alternative was selected by both non-economic and economic selection criteria. The selection would provide the Town with a more sustainable biosolids stabilization process and the best value given review of the NPV analysis. As a result of this decision, design and construction of a new ATAD solids treatment facility was built. The Town is currently producing Class A Biosolids consistently. Actual cost savings have been apparent compared to the existing system, with first year annual cost savings equaling nearly a quarter million dollars. The outcome of this analysis highlights the importance of reviewing the big picture and not just the initial capital cost for selecting a biosolids stabilization process. This approach can be implemented for facilities looking to improve their solids handling system by applying a similar evaluation process to ultimately achieve their goals.

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

SpeakerParmenter, Adam

Presentation time

10:45:00

11:15:00

Session time

08:30:00

11:15:00

SessionProgram Drivers: Economics, Regulatory, and Market Considerations

Session number24

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

Topicbiological stabilization, Biosolids Management Planning, Class A biosolids