Devitt, Dillon

Dillon is a Project Manager and Wastewater Process Engineer with design and management experience in chemical and biological wastewater treatment for municipal and industrial facilities. Dillon combines his technical skills with client relations to successfully execute projects and provide efficient and effective operations to help clients achieve their objectives.

Titles from this speaker

Getting a Grip on AGS Waste Solids: Settleability and Phosphorus Release

Abstract

INTRODUCTION The Aerobic Granular Sludge (AGS) and other densified processes offer the promise of biomass intensification with the added benefit of nutrient removal. A key element needed to support AGS is the selective wasting of flocculant biomass and particles from the process. Wasting occurs from the top of the settled solids or by other physical methods (e.g. hydrocyclones). While this wasting approach is essential to the AGS process, it results in waste solids (WAS) streams that differ from conventional activated sludge (CAS) with higher flow rates, lower total suspended solids (TSS) concentrations, and biological nutrient removal (BNR) activity. Therefore, the AGS WAS must be managed in a completely different way from CAS WAS. Two key WAS management challenges need to be considered. The first challenge is managing intermittent AGS WAS flows, which are on the order of 5 to 15 times higher than CAS WAS flow rates on average and approaching 100 times higher for instantaneous flow rates. The second challenge for AGS WAS management is understanding the impact of the phosphorus accumulating organisms (PAOs) on the solids handling system and managing the potential for struvite formation. The objectives of the project work are the following: *Define AGS WAS settleability characteristics *Expand the understanding of phosphorus release potential (total OP release) and rates METHODS & APPROACH Solids Settling Characterization All WAS samples were taken directly from the pipe that transfers WAS from the AGS reactors to the solids buffer tank (Figure 1). Settlability was evaluated using a 5.5-inch diameter column settler (Figure 2). The settling column was filled with 10 L of WAS sample for each test. Sample ports, located every 2 L and at the bottom of the column, were used to collect supernatant and settled solids samples. Settled WAS and supernatant samples were taken and TSS was measured in both samples. Sludge volume index (SVI) values were also estimated. Phosphorus Release Rates and Potential Phosphorus release testing has been conducted using gang stirrer apparatuses with 1.5 L samples (Figure 3) and low-rate mixing (30-50 s-1). A carbon source was added to 10 of the samples giving F:M ratios ranging from 0.0 to 0.5 g-COD/g-VSS. Additionally, the initial TSS concentration was varied by providing some initial thickening in some samples resulting in a range from 1,500 to 5,000 mg/L. The initial total phosphorus and phosphate concentrations were measured in the raw WAS sample. Samples were subsequently taken from the release tests through a 34 h time period. Samples were filtered and phosphate measured. Results & Discussion AGS WAS Settling Rates The WAS volume was recorded as a function of time by measuring the depth of the sludge layer in two separate test batches. Initial WAS concentrations were 2,500-5,000 mg/L and thickened to 8,500-10,000 mg/L by the end of the test period. The final settled volume was reached within 4-12 minutes. The maximum settling velocity was 3.9-11.9 m/hr at time 2-4 minutes and decreasing over time (Figure 4). SVI5 values were estimated in the range 110-200 mL/g, and SVI30 values were calculated in the range 100-120 mL/g. The TSS concentration in the supernatant was 8-40 mg/L. Evaluation of modeled settling in a clarifier was conducted using a BioWin simulator based on the calculated Vesilend model clarifier coefficients. Model sludge blanket height and effluent suspended solids remained within the desired range, even with the additional solids. A state point analysis from BioWinTM indicated that the AGS WAS operating condition was within the solids-flux limitation of the clarifier (Figure 5). Phosphorus Release Rates and Potential Phosphorus release testing showed phosphorus release rates varied initially in response to carbon dosing with higher short-term release rates followed by reduced long-term release rates (Figure 7). Short-term (or initial) release rates varied from 0.4 mg-P/g-TSS/h for no carbon addition to 4.0 mg-P/g-TSS/h for carbon addition (acetic acid with F:M of ~ 0.4 g/g). The long-term release rates varied from 0.1 to 0.7 mg-P/g-TSS/h for initial TSS concentrations in the range 1,500-5,000 mg/L (Table 1 and Figure 8). The effect of starting TSS concentration was more important than carbon addition for this test batch with rates normalized to volume increasing exponentially as shown in Figure 8. The overall phosphorus released varied in the range 7-22% of the initial TP measured. A follow-up test was conducted showing a release of 25-30% of the initial TP over a 72-h release period. A phosphorus mass balance on the plant aligns with maximum releasable TP observed based on the phosphorus removed from the liquid stream. An evaluation of the settling characteristics of AGS WAS showed high settling velocities resulting in WAS TSS concentrations similar to CAS WAS TSS concentrations with low DSS concentrations. Based on the results of phosphorus release testing, struvite mitigation is recommended for anaerobic digestion of AGS WAS.

The aerobic granular sludge (AGS) process offers strong potential for both incorporating nutrient removal and process intensification for wastewater treatment. Some outstanding research needs have come to the forefront. This paper seeks to address questions that have arisen regarding waste solids. In particular, the work evaluated the settleability and phosphorus release potential of AGS waste solids.

SpeakerEvans, Eric

Presentation time

14:00:00

14:30:00

Session time

13:30:00

15:00:00

SessionEvaluating Plantwide Impacts of AGS and DAS

Session number606

Session locationRoom 343

TopicIntermediate Level, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)

Evans, Eric, Geesman, Ashley, Devitt, Dillon, Thompson, Matthew, Sova, Ronald, Kigin, Abby

Author(s)E.A. Evans1, A. Geesman2, D. Devitt3, M.J. Thompson4, R.J. Sova5, A. Kigin5

Author affiliation(s)1HDR, IA, 2, IA, 3HDR ENGINEERING, INC., NE, 4, NE, 5HDR Inc, NE

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159522

Volume / Issue

Content sourceWEFTEC

Word count12

Description: Innovations in Biogas Management: Overcoming Challenges in the Anaerobic Lagoon...

Innovations in Biogas Management: Overcoming Challenges in the Anaerobic Lagoon Startup in South Sioux City

Abstract

The City of South Sioux City (SSC), Nebraska, faced a pivotal challenge in wastewater management when the Sioux City, IA Wastewater Treatment Plant (SCWWTP) announced its decision to cease acceptance of wastewater from local heavy industries (e.g., meat packing) . This was compounded by significant flooding in 2019 that damaged local infrastructure, prompted the city to accelerate plans for constructing its own wastewater treatment facility (WWTF). Anaerobic treatment is an ideal fit for high strength wastewaters, and with anaerobic systems comes the need for biogas handling. The City of SSC planned to utilize this resource beneficially, however sulfur quickly became a problem. The City of SSC embarked on constructing a covered anaerobic lagoon (CAL) system integrated with Nebraska's first Aerobic Granular Sludge (AGS) system to effectively manage its industrial wastewater. A site layout illustrated in (Figure 1). The lagoons where to provide pretreatment to the high strength wastewater. Lagoon discharge would then be collected in a wet well and pumped to an aerobic granular sludge system for final treatment, UV disinfection, then finally sent to the Missouri River. The anaerobic pretreatment would generate biogas that could be used beneficially in the WWTF boilers, with future plans to augment the City's natural gas by cleaning the biogas to a renewable natural gas level for injection. During the startup phase of the anaerobic lagoon, biogas was generated with unexpectedly high levels of hydrogen sulfide (H2S), reaching concentrations as high as 2.5% by volume, shown in (Figure 2). These elevated H2S levels overwhelmed the biogas H2S removal system, which utilized a proprietary activated carbon vessel designed to manage lower concentrations. The initial biogas management strategy intended for this gas was to supplement natural gas in a boiler system for heating the anaerobic lagoons, but the challenges presented by the high H2S levels made the biogas unusable in the boilers without a removal system capable of treatment. This led to the question of 'where is the sulfur coming from?'. The background water quality in the area was known to have a high sulfate concentration, and the industries were known to discharge elevated sulfur, however these two sources could only account for approximately 50% of the Sulfur coming into the facility. A sulfur balance was performed, and modeling was done to estimate the fate of the sulfur once it entered the WWTF. A simplified figure shows this balance in (Figure 3). The results lead to discussions with local industries, and the discovery of increased sulfuric acid usage at the industries on site pretreatment to meet the Cities new WWTF's influent FOG limits. HDR worked with the City, the industry, and the Nebraska Department of Environment and Energy to implement a pilot study at the industries pretreatment system. The intent was to reduce sulfuric acid usage to find a reasonable balance between acid usage and FOG discharge limits. Although the results of the pilot study succeeded in reducing sulfur to the WWTF it consequently generated colloidal none settling solids. These colloidal solids were not removed in either the anaerobic or AGS system and cause strain on both the WWTF's UV disinfection system, by reducing UVT, and effluent TSS limits. photos of the settleability testing and Reduced UVT effluent quality are shown in (Figure 4) and (Figure 5). The pilot study was immediately ceased, and the industry agreed to explore alternative acid sources in the future. In response to these challenges, SSC implemented immediate operational adjustments while exploring the economic feasibility of on-site sulfur management strategies. Both liquid phase and gas phase sulfur management strategies were evaluated, resulting in the decision to pursue installation of a more robust biogas chemical scrubber system. This planned upgrade aims not only to improve biogas quality but also to enhance the economic viability of the biogas produced. Future plans include integrating the upgraded biogas treatment system with a third-party renewable natural gas (RNG) facility, enabling further purification and injection into the natural gas grid. This strategic pivot highlights SSC's commitment to sustainability and innovation in its wastewater management practices. This presentation will delve into the technical specifications of the anaerobic lagoon design, the challenges encountered during the startup phase, and the innovative strategies employed to manage biogas quality effectively. It will also provide insights into the operational adjustments made to mitigate the high H2S levels. Additionally, facility operating data is being used to help develop and calibrate a desktop model of the overall sulfur balance around the facility including gas and liquid phase dynamics with variable loadings and operating conditions. This work will contribute to the broader discourse on effective sustainable biogas and sulfur management practices and innovative approaches in wastewater treatment facilities dealing with similar challenges. This study serves as a case study for other treatment facilities aiming to optimize their biogas management strategies while ensuring compliance with environmental standards and promoting sustainable practices in wastewater treatment.

This paper was presented at the WEF Residuals & Biosolids and Innovations in Treatment Technology Joint Conference, May 6-9, 2025.

SpeakerDevitt, Dillon

Presentation time

16:25:00

16:45:00

Session time

15:45:00

16:45:00

SessionOptimizing Biogas Production and RNG: Microaeration and Sulfur Management

Session number19

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicAnaerobic Digestion, Biogas Cleaning, Biogas desulfurization, Biogas Utilization, Chemical Treatment, Industrial Dischargers, Renewable Natural Gas, Sulfur