Steele, Muriel

Muriel has a BS in Civil Engineering from Arizona State University and an MS and PhD from Clemson University in Environmental Engineering. She worked...

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About Steele, Muriel

Muriel has a BS in Civil Engineering from Arizona State University and an MS and PhD from Clemson University in Environmental Engineering. She worked in consulting before joining Charlotte Water in 2019. In her time with Charlotte Water, Muriel has served as Water Quality Program Specialist and Senior Engineer supporting the WWTPs before becoming Charlotte Waters first in-house Process Engineer and now leads the newly formed Research and Development group within the Environmental Management Division, Charlotte Waters wastewater operations division.

Steele, Muriel

Titles from this speaker

Description: Dewatering Benefits of SLG Technology at the McDowell Creek Water Resource Recovery...

Dewatering Benefits of SLG Technology at the McDowell Creek Water Resource Recovery Facility

Abstract

Dewatering Benefits of SLG Technology at the McDowell Creek Wastewater Treatment Plant Anish Luthra, PE, PMP, CDM Smith Kathryn Quaid, CDM Smith Muriel Steele, PhD, PE, Charlotte Water Charlotte Water's McDowell Creek Wastewater Treatment Plant (WWTP) has historically faced biosolids dewatering challenges related to achieving typical industry cake dryness for belt filter press dewatering of anaerobically digested biosolids. This presentation will discuss the dewatering benefits experienced by the plant by piloting a solids-liquid-gas (SLG) pretreatment process ahead of belt filter press dewatering. The plant's processes include screening, grit removal, primary clarification, 5-stage BNR for nitrogen and phosphorus removal, secondary clarification, deep-bed sand filters, UV disinfection, cascade aeration, gravity belt WAS thickening, mesophilic anaerobic digesters, and dewatering belt filter presses. Anaerobically digested solids from four primary digesters overflow into a single, common secondary digester. From the secondary digester, digested solids are pumped to the dewatering facility for final dewatering via Ashbrook belt filter presses. Dewatered cake is conveyed by a belt conveyor to a covered storage area before being loaded onto hauling trucks typically for land application, or alternatively landfill disposal. In recent years, the plant has struggled to produce dewatered cake total solids concentrations above 12.5% on average. In early 2023, Charlotte Water elected to pilot the solids-liquid-gas (SLG) pretreatment process offered by Orege to optimize the dewatering operations at the McDowell Creek WWTP. The SLG technology is composed of three parts - the SLG skid, an air compressor, and a deaerator. The SLG technology uses compressed air to modify the rheology of the digested sludge upstream of belt filter press. Low pressure compressed air is injected into the digested sludge, creating a floating emulsion sludge. Polymer is then added to the emulsion to complete the flocculation process ahead of dewatering. The emulsion's larger solids surface area improves polymer adherence, resulting in better water release and higher cake dryness. Before the pilot was commissioned, Charlotte Water developed pilot evaluation criteria containing a variety of measurable and subjective goals to determine pilot success. Pilot logistics were then established through a collaboration between Charlotte Water, CDM Smith, and Orege. It was determined that the plant's existing digested sludge pumps that normally feed the belt filter presses would not have enough head to overcome the pressure of the SLG unit. As such, a temporary 1000-gallon sludge buffer tank and additional sludge pump were provided. Temporary piping was installed to feed the buffer tank, sludge pump, SLG skid, deaerator, and belt filter press. A variety of polymer selections were also evaluated as part of the pilot to determine compatibility with the SLG emulsion. Once the pilot was commissioned, the baseline verification period began. The project team observed Charlotte Water's operation of the belt filter press under typical operating conditions and collected and analyzed baseline samples to compare against historical data. After a week of baseline verification, the pilot moved into the optimization period. During this period the belt filter press was started under typical operating conditions by Charlotte Water and baseline samples were collected before the SLG unit was started up for the day. During the three months of optimization, the project team made process adjustments to the SLG unit and belt filter press to determine the optimal operating parameters for pilot operation. Once the optimal pilot operating parameters were determined, the field staff performed a two-week field test. During the field test, the belt filter press was started under normal operating conditions and baseline samples were collected and analyzed. Then, the SLG unit was started up and optimal pilot operating parameters were set. Multiple samples were taken throughout the SLG run time before the unit was shut down and the belt filter press was adjusted back to normal parameters for a second round of baseline sampling. This process was repeated for 10 days, during which baseline parameters remained consistent and SLG parameters remained consistent. The pilot results suggested the SLG pretreatment process improved cake dryness by an average of approximately 2% total solids concentration. This is a significant improvement from the historical performance of McDowell Creek WWTP's dewatering operations. Polymer treatment rate and filtrate quality remained similar to baseline conditions. Table 1 contains average field test results and historical data. Figures 1-3 present daily average cake, filtrate, and polymer treatment rate results from the field test period. The project team is currently performing a lifecycle cost analysis to evaluate the capital cost investment of the SLG pretreatment process and the annual cost savings associated with the operational improvements of the SLG process, which will be ready for presentation by the time of the 2024 Water Environment Federation (WEF) Residuals and Biosolids Conference.

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

SpeakerLuthra, Anish

Presentation time

13:30:00

14:00:00

Session time

13:30:00

16:45:00

SessionDewatering

Session number05

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicDewatering, Dewatering Optimization, Dewatering Pretreatment

Author(s)

Luthra, Anish

Author(s)A. Luthra1, K. Quaid1, M. Steele2

Author affiliation(s)CDM Smith Inc. 1; Charlotte Water 2;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159432

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count14

Pilot-Scale Anaerobic Digestion and Dewatering of Aerobic Granular Sludge

Abstract

Charlotte Water (CLTWater) has 123 MGD of capacity between five major wastewater treatment plants (WWTPs) and is interested in sustainable and cost-effective technologies that may be selected for future WWTP expansions or for replacement of existing treatment infrastructure. Aerobic granular sludge (AGS) is an innovative secondary wastewater treatment technology that can achieve biological nutrient removal (BNR). Aqua-Aerobic Systems, Inc (AASI) is the vendor for AquaNereda, the patented AGS system that utilizes specific biological and hydraulic selection pressures to produce and maintain the AGS in a sequencing batch reactor (SBR). CLTWater elected to pilot AquaNereda to understand how it might be used to expand the capacity of our overall system, either at an existing plant or in place of another BNR technology at our new plant under design, the Stowe Regional Water Resource Recovery Facility (SRWRRF). An AGS pilot was performed at McDowell Creek WWTP from June 2019 to February 2020 to determine its viability as a treatment for CLTWater. Before starting the AquaNereda pilot, CLTWater developed a list of objectives to achieve during the piloting process with actionable and achievable goals defined for each objective. These objectives included 1. Evaluating simulated performance representing treatment with and without primary clarifiers 2. Observing development of granules from flocculant sludge 3. Evaluating solids characteristics 4. Evaluating process control and operability 5.Involving State regulatory agencies to facilitate potential future permitting processes To address the objective of evaluating solids characteristics, a separate solids study was conducted at Bucknell University to provide insight on solids handling and treatment impacts for potential full-scale Nereda implantation. CLTWater wanted to assess impacts to digestion performance, dewatering, and recycle streams when aerobic granular sludge (AGS) and conventional activated sludge (CAS) are treated concurrently. During the study, Bucknell operated four lab-scale digesters that were fed several solids blends (Table 1) including two 100% thickened waste activated sludge (WAS) digesters to demonstrate differences between AGS and CAS WAS and two 60% primary sludge (PS)/40% WAS digesters to simulate McDowell's current digestion process and the expected maximum contribution of AGS to any digestion process at CLTWater. Waste solids from the Nereda pilot reactor treating primary effluent were thickened to ‰¥5% using gravity belt thickening and shipped to Bucknell with thickened PS and CAS-WAS from McDowell's full scale processes. Bench-scale 20-day HRT mesophilic anaerobic digesters were fed daily. Biogas production was monitored throughout the trial, but other analyses were performed after 71 days (~3.5 SRTs) to ensure results were representative of steady-state conditions. Results include quantified metrics and other observations related to 1) digester performance VS destruction, biogas production; 2) solids handling sludge viscosity, polymer demand, cake solids, cake metals content and odor production; and 3) recycle streams digestate nutrient concentrations. For digester performance, results showed that volatile solids reduction (VSR) for AGS-WAS was comparable to CAS-WAS with slightly different methane yields between Digesters 3 and 4 (60% PS/40% WAS). Minor differences in solids handling parameters were observed including marginally higher viscosity and polymer demand for digested solids that included AGS, but these differences were more pronounced in the digestate from Digesters 1 and 2 (100% WAS). Recycle stream soluble TKN concentrations were similar regardless of WAS source; however, recycle streams from reactors including AGS-WAS were characterized by markedly lower soluble TP concentration. The finding of much lower soluble TP concentration for AGS-WAS was surprising given that the Nereda process includes enhanced biological phosphorus removal (EBPR) and the pilot reactor performed comparable EBPR as the full-scale mainstream conventional BNR process. Unfortunately, the pilot timeline did not allow for additional investigation into the cause of this observation, but further research may be warranted in this area. This presentation will discuss high-level results from each of the objectives targeted during the AquaNereda pilot but will focus mainly on the solids-related findings. We will present overall conclusions from the pilot as well as lessons learned related to implementing a pilot for a process that has broad reaching implications across a wastewater treatment plant. Finally, the future of AGS implementation at CLTWater will be discussed.

This paper was presented at the WEF/IWA Residuals and Biosolids Conference, May 16-19, 2023.

SpeakerSteele, Muriel

Presentation time

8:30:00

Session time

8:30:00

11:45:00

SessionSession 12: Innovative Processes in Anaerobic Digestion

Session number12

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicResearch & Innovations

Author(s)

M. Steele

Author(s)M. Steele1, B. Figdore2, M. Higgins3,

Author affiliation(s)Charlotte Water1; HDR2; Bucknell University3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158775

Volume / Issue

Content sourceResiduals and Biosolids

Word count10

Description: Troubleshooting VSR: A Multi-Approach Strategy Towards Significant Operational...

Troubleshooting VSR: A Multi-Approach Strategy Towards Significant Operational Savings

Abstract

Charlotte Water (CLT Water) is the largest public water and wastewater utility in the Carolinas, serving more than a million customers in the City of Charlotte and greater Mecklenburg County. CLT Water owns and operates five major wastewater treatment plants (WWTPs) with an average treated flow of 78.1 million gallons per day (mgd). Additionally, CLT Water oversees one of the largest class B biosolids programs in the southeastern United States, operating with 17,000 acres of permitted agricultural land in both North and South Carolina and producing over 100,000 wet tons (WT) of biosolids annually. CLT Water's largest WWTP is McAlpine Creek Wastewater Management Facility (McAlpine Creek), with an average treated flow of 41.3 mgd and 60,000 WT of biosolids produced annually. There are three major regulatory categories that are required in order to meet the Class B land application biosolids standards: (1) metals concentrations, (2) vector attraction reduction, and (3) pathogen reduction. This paper will focus on volatile solids reduction (VSR) - the vector attraction reduction alternative CLT Water uses to meet land application standards, the financial impact of a sudden failure to meet the VSR requirements, and the troubleshooting and optimization steps taken to address the issue experienced and to improve the overall solids treatment process. McAlpine Creek is a regional solids processing facility, which in addition to treating the solids produced at the plant, it also receives primary sludge (PS) and waste activated sludge (WAS) from the Sugar Creek WWTP (Sugar Creek) for treatment. McAlpine Creek is designed to receive primary solids from Sugar Creek through a dedicated force main, which connects to McAlpine Creek's primary solids gravity thickeners (GTs), while WAS from Sugar Creek, also designed to be pumped through a dedicated force main, connects to a combined WAS well at McAlpine Creek. Even though the infrastructure exists for Sugar Creek PS and WAS to enter directly into McAlpine's solids treatment train, due to a history of hydraulic overloading of the GTs, Sugar Creek's PS and WAS were being sent through gravity sewer lines and entering McAlpine Creek through the influent flow. McAlpine Creek solids treatment train currently consists of primary clarification, primary sludge gravity thickening, WAS centrifuge thickening, anaerobic digestion of thickened primary sludge (TPS) and thickened waste activated sludge (TWAS), and finally centrifuge dewatering of digested sludge. CLT Water meets the vector attraction reduction requirement by achieving a minimum of 38% VSR through the anaerobic digestion calculated on a monthly basis. Typically, McAlpine Creek achieves the minimum VSR requirement with a comfortable buffer, achieving around 45% VSR, without any major issues. In July 2022, operational staff became alarmed when they noticed a trending decline in VSR results prompting the need for immediate operational changes to be made. The efforts however were not enough to avoid a VSR failure of 36% in July 2022, which prevented CLT Water from land applying the biosolids. Instead, CLT Water had to landfill the entire July biosolids production, totaling over 4,000 WT which cost the City approximately $500,000. Operational efforts to troubleshoot the problem continued for several months past July 2022 with improved success later in the fall and through the same summer period of 2023. The main strategies implemented were: (1) digester feed optimization by improving performance of gravity thickeners, (2) VSR calculation method evaluation, and (3) data tracking and proactive sampling. Improving GT performance included adjusting pumping flow rates, throttling existing valves, and replacing malfunctioning valves from primary clarifiers to GTs to improve PS % solids from <0.5% to 1.0-1.5%. Another significant change was reverting the Sugar Creek PS and WAS transport and tie in points to their original design (PS connected to GTs and WAS connected to a combined WAS well), Sugar Creek's solids were no longer going to McAlpine Creek's influent. Additional optimization trials included actions related to polymer use, configuration of duty/standby GTs, and installation of TSS probes and VFDs on Sugar Creek's PS pumps to McAlpine Creek. While a few of the optimization trials did not cause any improvements, several of the strategies yielded positive results and improvements of PS thickening, digestion, and consequently, volatile solids reduction. CLT Water staff went beyond operational changes and started evaluating the VSR calculation method used by the CLT Water biosolids program for many years. There are two main allowable VSR calculation methods including, approximate mass balance and Van Kleeck. CLT Water uses the latter method. After initial research, staff learned the Van Kleeck calculation underestimates the VSR whenever there is grit accumulation inside digesters. Several digester cleanout projects at various WWTPs were performed over the last ten years including at McAlpine Creek confirming that significant grit accumulation does occur inside CLT Water's digesters. With this information, CLT Water started calculating VSR using both methods and tracking the results side by side. The evaluation showed that the approximate mass balance method yields a slightly higher VSR result and proved to be more representative of CLT Water's process due to the proven grit accumulation. Finally, based on the VSR calculation method evaluation, CLT Water decided to more closely monitor percent solids going into the digesters to predict any potential issues sooner, giving staff adequate time to make operational changes to avoid future failures. Additionally, CLT Water found it to be beneficial to run an EPA-approved alternative test (40-day anaerobic digestion bench test) during months that the percent solids based on historical trends were expected to decline. The 40-day digestion bench test was performed in August 2022, as an immediate response to the July 2022 VSR failure, and proactively conducted in the Summer of 2023. By continuing to perform the alternative test early in the months known to suffer from percent solids falling-off, if by the end of the month the calculated VSR results do fail, staff can use the results from the 40-day digestion bench test to meet the EPA requirements and potentially not interrupt any land application operations and incur unexpected landfill costs. This paper will detail out the multi-approach strategy taken by CLT Water staff to troubleshoot and optimize processes around thickening, anaerobic digestion, and VSR calculation which resulted in many lessons learned, benefits around the overall solids treatment processes, and significant cost savings in the biosolids beneficial reuse program.

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

SpeakerPortiolli, Giovanna

Presentation time

08:30:00

11:15:00

Session time

08:30:00

11:15:00

SessionTroubleshooting & Optimization

Session number26

Session locationOklahoma City Convention Center, Oklahoma City, Oklahoma

TopicClass B Biosolids, thickening, Volatile Solids Reduction

Author(s)

Portiolli, Giovanna

Author(s)G. Portiolli1, M. Steele1

Author affiliation(s)Charlotte Water1; Charlotte Water 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Jun 2024

DOI10.2175/193864718825159456

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count10

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Steele, Muriel

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