Ngo, Nam

Dr. Ngo is a program manager, research at DC Water who has been leading research team at DC Water day by day.

Titles from this speaker

An Evaluation of Dual External Carbon Source Strategies for the Full Denitrification Process

Abstract

Introduction Achieving low TIN levels in wastewater effluent often necessitates the addition of an electron donor (Fu et al., 2022). The selection of an appropriate carbon source is a critical decision, influenced by considerations of cost, availability, and effectiveness in terms of biomass yield (Peng et al., 2007). In the United States, methanol is a preferred choice due to its economic viability and low yield (WRF, 2019). However, recent literature suggests fermentate as a potential alternative (Ladipo-Obasa et al., 2022). One limitation of fermentate is its contribution of ammonium to the effluent. This study proposes an intermediate strategy wherein a portion of methanol is replaced with fermentate, aimed at reducing operational costs while easing the transition towards PdNA methodologies. The primary goal is to elucidate the denitrification stoichiometries under a dual carbon source, emphasising is placed on formulating operational strategies conducive to achieving desired effluent standards, along with an evaluation of reductions in methanol consumption. Methodologies A 360 L mainstream pilot system was operated for three phases. During the initial phase, methanol was utilized as the sole carbon source, with its dosing governed by a feedforward control. In the next phase, fermentate, derived from batch fermentation of primary sludge from full-scale primary clarifiers. The third phase introduced a dual carbon source strategy to facilitate a FdN process. Fermentate was dosed continuously, while methanol, serving as an additional carbon source, compensated for the remaining chemical oxygen demand necessary. Results and Discussion Phase 1: Baseline condition with methanol as external carbon source Over 153 days in this pilot operation the effluent targets were effectively met (1.91 mg N/L,Table 1). A stoichiometry factor of 4.9 g sCOD added/g NO3-N removed and a yield coefficient of 0.42 g COD/g COD were observed (Fig.1a,c); these are similar to expected literature values for methanol-driven denitrification (Mokhayeri et al., 2009). Phase 2: Nitrate removal with available primary sludge fermentate Fermentate dosed was of high quality and reached a yield of 0.21 g sCOD/g VSS (Table 2), which was on the higher end of previously reported yields (Ali et al., 2021). Throughout the operation of 125 days, a nitrate removal of 2.6 mg N/L was achieved (Table 1). The stoichiometry and yield coefficients of fermentate, recorded at 5.4 g sCOD added/g NO3-N removed and 0.47 g COD/ g COD, respectively (Fig.1a,c). Phase 3: Denitrification with dual methanol and fermentate addition a.Overall performance and impact on overall methanol needs Over a 137-day period utilizing dual external carbon sources, a feedforward control strategy was effective at achieving the average effluent TIN at only 1.91 mgN/L. (Table1). Despite significant variations in fermentate quality, particularly in terms of soluble COD due to primary sludge solids concentration variability the strategic incorporation of methanol to address these variations ensured the attainment of favorable TIN levels in the effluent (Table 1&2). It was observed that employing both carbon sources concurrently did not modify their individual behaviour. This was evident by the predicted nitrate removal using the stoichiometries from phase 1 and 2 being similar to the observed nitrate removal (Fig.1a). Even though the predicted nitrate removal showed a slightly improved efficiency of carbon use in phase 3, this was not statistically significant, as shown in (Fig.1b). The amount of external MeOH needed in this phase was 3.2+/-1.4 g sCOD added/gNO3-N removed or showed a MeOH saving of 35% compared to phase 1. b.Microbial selection and functionality under dual substrate addition Even though overall N removal was as expected under dual substrate dosing, a change in kinetic behavior was observed (Fig.2). Nitrite accumulation was observed in denitrification activity tests, irrespective of whether fermentate or methanol was the carbon source. Nitrite accumulation was never observed when doing activity tests with full-scale MeOH adapted biomass or during phase 1 (Fig.2a,d,e). The nitrite accumulation behaviour was also confirmed in the reactor by profiling tests (Fig. 3). Notably, the PdN efficiency was higher with fermentate at 76% and methanol at 52 % (Fig. 2b,c), mirroring findings from the pilot profiling experiment, which reported a PdN efficiency of 47%, as shown in (Fig.3). This result was surprising as methylotrophs do not tend to accumulate nitrite easily. The extended 262-day period of employing fermentate as a carbon source in the reactor potentially enhanced the diversity of nirS type denitrifiers, consequently altering the community-level dynamics in response to different electron donors (Hallin et al., 2006). Nitrate levels needed to be pushed below 1.97 mg N/L to avoid nitrite coming out of the denitrification zone. Conclusions This study at the Blue Plains AWTP underscores the efficacy of dual carbon sources-methanol and fermentate-in enhancing TIN removal in wastewater treatment. Employing a sequential methodology, the research highlighted the stoichiometric and operational efficiency of combining these carbon sources. These findings provide a strategic pathway for the implementation PdNA processes, signifying a substantial advancement in cost-effective and efficient nitrogen removal strategies.

This study assesses the effectiveness of using methanol and fermentate as dual carbon sources for Total Inorganic Nitrogen (TIN) removal in wastewater treatment. Findings show that combining these sources enhances nitrate removal efficiency and reduces methanol consumption, facilitating the transition towards Partial Denitrification- Anammox (PdNA) methodologies.

SpeakerLee, Chengpeng

Presentation time

15:30:00

16:00:00

Session time

15:30:00

17:00:00

SessionEnhancing Nitrogen Removal: Insights Into Carbon Sources and Mechanisms

Session number420

Session locationRoom 340

TopicAdvanced Level, Facility Operations and Maintenance, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)

Lee, Chengpeng, Ngo, Nam, Islam, M.A. Sadikul, Hatcher, Jacob, Riffat, Rumana, Azam, Hossain, Wells, George, De Clippeleir, Haydee

Author(s)C. Lee1, N. Ngo2, M. Islam3, J. Hatcher4, R. Riffat5, H.M. Azam6, G. Wells7, H. De Clippeleir8

Author affiliation(s)1Northwestern University, VA, 2DC Water, VA, 3University of the District of Columbia, 4The George Washington University, MD, 5George Washington University, VA, 6University of the District of Columbia, DC, 7, IL, 8DC Water & Sewer Authority, VA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159619

Volume / Issue

Content sourceWEFTEC

Word count14

Determining Activated Sludge Characteristics Impacting Clarifier Capacity and Performance through Two Simple Measurements

Abstract

Introduction Improving settleability and clarifier capacity is an important driver in current technology innovations (Sturm & De Clippeleir, 2020). To date, sludge volume index (SVI) is still a standard settling measurement method to determine settleability. However, SVI measurements are not sensitive enough to detect small differences in settling behavior. SVI just describes non-stokesian settling (hindered and compression settling zone), while there has been strong evidence that flocculent settling (stokesian settling) is the main settling regime in clarifiers and hindered settling only occurs during clarifier failure (Kinnear, 2002). Therefore, an alternative measurement, the 'threshold of flocculation (TOF)' method (Mancell-Egala et al. 2017a) to quantify the stokesian settling (flocculant settling). TOF describes collision efficiency particles and is thus dependent on the non-settling fraction, particle charge, particle density, particle size, extracellular polymeric substances (EPS) characteristics etc. Initial work has shown a direct correlation between TOF and effluent TSS (Ngo et al., 2021a) and showed high sensitivity detecting small changes in behavior. On a more fundamental level, increased collision efficiency (lower TOF) was directly linked with increased EPS-TKN/COD ratios and introduced as a parameter to improve clarifier models (Ngo et al., 2021b). In addition, based on the wide range of systems studied so far (Table 1), more insights have been gathered on how a combination of TOF and SVI data can provide a better interpretation of sludge settling, sludge characteristics and system behavior. This paper compiles the current lessons learned and demonstrates the power of knowing both settling parameters which can potentially avoid the need for more complicated measurements such as particle size, EPS etc. Methodological Approach A throughout literature review of reported combinations of SVI30 (7 to 1051 mg L/g TSS) and TOF (11 to 1500 mg TSS/L) under various configurations, operational conditions, and wastewater characteristics were summarized in Figure 1 and Table 1. This captured a wide range of different sludge morphologies, settling characteristics, wastewater types and operational conditions. TOF and SVI method are described in Mancell-Egala et al. 2017a. Results & Discussion Flaws of only focusing on SVI (non-stokesian settling) or TOF (stokesian settling) Most systems presented in Figure 1 showed good hindered settling behavior with only a few examples with SVI> 100 mL/g TSS (Fig. 1). When looking into a narrow range of SVI of 50-100 mL/g TSS, a wide range of systems and system behaviors can be found (Fig. 1, Table 1). One can understand that these sludge types have vastly different morphologies resulting in difference in clarifier performance. Effluent quality in this narrow SVI range was at a minimum 2 mg TSS/L and at maximum 87 mg TSS/L (Table 1). When looking into a good flocculation behavior range described by TOF < 300 mg TSS/L (Ngo et al., 2021a), a vastly different behavior in SVI within the same TOF range can also be observed (Figure 1). Also, here a wide range of systems and sludge morphologies fell within this TOF ranges (Fig. 1, Table 1). This implies that relying solely on TOF may lead to encountering clarifier capacity limitations. Power of combining TOF and SVI for interpretation of sludge characteristics Figure 2 illustrates floc morphology, drawing insights from the patterns observed in Figure 1 across various system types. TOF is more directly linked to particle size with decreasing TOF with increasing floc or particle size. SVI is more directly linked to density with higher density and more compacted flocs leading to lower SVI. Combining the 2 characteristics leads to an overall morphology assessment (Fig. 2). Case study 1: Optimization of high-rate activated sludge systems Overall, one can see the importance of substrate and feast-famine management in high-rate systems and how these impacts settling behavior and settling limitations. EX: Increase TOF within the same SVI range typically occurs when switching to an A-stage system versus a contact stabilization (CS) system [Fig.3, arrow A, (Rahman et al., 2019)]. More details are described in figure 3. Case study 2: Cyclone selection for densification (inDENSE and DEMON example): With the hydrocyclone one selected for denser and larger particles and thus improved SVI and TOF, while one wasted out the smaller and more fluffy flocs with increased TOF and increased SVI (Figure 4A). For activated sludge systems applying cyclone wasting the differences are smaller and the wasted fraction is mostly defined by increased TOF (lower collision efficiency) rather than a true SVI and potentially density difference (Figure 4B). This example demonstrates the benefit of being able to quantify the selection over a cyclone in more detail and describe what might be limited and reported in Avila et al. (2021). Conclusion Overall, this paper provides a framework for interpretation and quantification of settling within activated sludge systems. It shows the power of using two practical measurements, SVI and TOF, to describe sludge characteristics and to help optimizing systems as shown in the case study examples. With further adoption of the TOF combined with SVI measurements, the proposed framework will be further enhanced.

The paper addresses the limitations of the traditional Sludge Volume Index (SVI) in measuring wastewater settleability and introduces the 'threshold of flocculation' (TOF) as a sensitive alternative, correlating with effluent TSS. Combining SVI and TOF offers a comprehensive understanding of sludge characteristics, optimizing system performance. Case studies on high-rate activated sludge systems and cyclone densification demonstrate the practical benefits of this approach.

SpeakerAhmad, Sakib

Presentation time

13:30:00

14:00:00

Session time

13:30:00

15:00:00

SessionInnovative Approaches to Address Traditional Operational Challenges

Session number211

Session locationRoom 344

TopicFacility Operations and Maintenance, Intermediate Level, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Ahmad, Sakib, De Clippeleir, Haydee, Ngo, Nam, Riffat, Rumana, Gu, April, Li, Yuang

Author(s)S. Ahmad1, H. De Clippeleir2, N. Ngo3, R. Riffat4, A.A. Gu5, Y. Li6

Author affiliation(s)1George Washington University, DC, 2DC Water & Sewer Authority, VA, 3DC Water, VA, 4George Washington University, VA, 5, NY, 6Cornell University

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159614

Volume / Issue

Content sourceWEFTEC

Word count14

Description: Developing Approaches for Achieving Biological Phosphorous Removal and Improved...

Developing Approaches for Achieving Biological Phosphorous Removal and Improved Settleability in High-rate Activated Sludge Systems

Abstract

This study focuses on determining the minimum SRT maintaining significant bio-P activity, quantifying phosphorus removal methods, and evaluating sludge settling. This paper offers practical guidance on the implementation of HRAS systems for determining the actual bio-P phosphate removal through parallel contact stabilization assimilation reactors.

This work demonstrates that bio-P activity washed out of aerobic SRT of 1.2-1.8 day. Overall, about 56% of P removal was achieved through bio-P while the rest was achieved through assimilation. This study showed the need for developing strategies for SRT uncoupling to selectively retain PAOs in high-rate system to potentially achieve P removal and improved overall capacity of high-rate system through improving settling.

SpeakerNgo, Nam

Presentation time

11:30:00

12:00:00

Session time

10:30:00

12:00:00

SessionHealthy As A Horse? Assessing Bio-P Stability

Session locationRoom S403a - Level 4

TopicFacility Operations and Maintenance, Intermediate Level, Municipal Wastewater Treatment Design, Nutrients

Author(s)

Ngo, Khoa Nam

Author(s)K. Ngo 1; C. Lee 2 ; H. Truong 3; E. Kin 2; S. Fuentes 4; C, Chen 3 ; G. Wells 5; H. De Clippeleir 6; C. Lee 2;

Author affiliation(s)District of Columbia Water and Sewer Authority 1; District of Columbia Water and Sewer Authority, Northwestern University 2 ; District of Columbia Water and Sewer Authority, Northwestern University 3; District of Columbia Water and Sewer Authority, Northwestern University 2; District of Columbia Water and Sewer Authority 4; District of Columbia Water and Sewer Authority 3 ; District of Columbia Water and Sewer Authority 5; 6; 2;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159176

Volume / Issue

Content sourceWEFTEC

Word count16

Evaluating the Potential of Recovering Vivianite for Phosphorus Removal and Improving Class A Biosolids Applications

Abstract

INTENDED OBJECTIVE: Biosolids from water resource recovery facilities (WRRFs ) are increasingly used for agricultural and recreational land purposes due to their sustainable means to replenish macronutrients. However, the relatively high phosphorous content of biosolids limits certain applications. This study aims to identify optimal locations for recovering vivianite and subsequently phosphorus, to allow class A biosolids reach ideal phosphorus levels. INTRODUCTION: Global consumption rates of synthetic fertilizers per unit of cropland have increased 3 to 8 times over the past half century (Lu et al. 2017). Class A biosolids are increasingly explored as an alternative to commercial fertilizers due to their effective means to replenish carbon and macronutrients (Gilmour et al. 2013). However, the N:P ratio of biosolids is typically lower than commercial fertilizers which can cause an accumulation of phosphorus when applied to soil, increasing risk for eutrophication (Penn et al. 2002). Therefore, it is critical to implement efficient phosphorus-removal technologies/techniques within the biosolids treatment train to improve the N:P ratio and limit the amount of phosphorus that result in the cake. Therefore, this study aims to analyze the P mass balance of the Blue Plains advanced wastewater treatment plant in Washington, DC as well as its vivianite characterization in full-scale. The process sampling, modelling and analysis led to identification of potential locations for vivianite recovery, and initial estimations on how much the P content in our class A biosolids might be reduced by recovering vivianite upfront. MATERIALS AND METHODS: Sampling campaign: Samples were collected in DC Water Blue Plains over a 3-month period (Mid-February to Mid-May 2022). Quantitative analysis: Phosphorus is measured by the EPA 365.1 method. Scanning Electron Microscopy with Energy Dispersive and Mossbauer Spectroscopy: Prepared by method in Prot et al. 2021. Modelling method: Visual Minteq version 3.3 with DOC SHM model RESULTS & DISCUSSION P mass balance at Blue Plains and P content in biosolids product Blue Plains advanced WWRF achieved a 98% incoming TP removal over its primary (enhanced-chemical phosphorus removal) and secondary systems through iron dosing. The removed P is diverted to the solids fraction and results in a Class A biosolids product (BLOOM) with 2.88% P (dry weight basis) and 28-32%TS (Fig.1A). The P:N ratio of our product is 1:1 and thus higher in P content than the target of 1:2 P:N for typical fertilizers. Decreasing P content in BLOOM by 50% or thus recovery 60% of vivianite would increase the value and applicability of BLOOM. Vivianite formation and formation potential along the Solids Treatment Train A total Fe/P molar ratio of 1.5 or greater allows for optimal vivianite precipitation (Cong et al. 2017) which is reflected in DC Water treatment flow diagram (Figu 1). Vivianite was detected in primary thickened sludge, blend of thickened primary (PS) and waste activated sludge (WAS), and digested sludge b ased on sequential extraction method in Wang et al. 2021. This was also further supported by the clear co-location of Fe and P in SEM images (Figure 2A and 2B). These locations are consistent with the vivianite scaling seen in primary sludge gravity thickening lines and centrifuge lines in the facility. Through quantitative analysis, the vivianite mass flow in thickened primary sludge, blended PS/WAS and digested solids accounted for 8%, 52%, and 49% of the incoming P to the plant (Fig. 1). These vivianite ranges are like those reported by iron-dosing plants in Prot et al. 2021 and Wilfert et al. 2016. Estimation of P recovery potential needed to impact Class A biosolids P content Based on the current vivianite-P levels in the three identified locations (Fig. 1), sludge after anaerobic digestion contained the highest level of vivianite-P. This is likely due to higher orthophosphorus levels after thermal hydrolysis treatment which allows for additional vivianite formation with Fe(II). This notion is supported by the low levels of Fe(II) concentrations after anaerobic digestion indicating that most of it is bound (Fig. 1). We estimated how much vivianite recovery efficiency we might need to decrease the P content in the BLOOM with an ideal target of ~0.014 kg P/kg TS and acceptable target of 0.022 kg P/kg TS. Given the highest vivianite levels in digested sludge, a recovery efficiency of at least 40% with ideally 70% is sufficient to meet our targets (Fig. 3). Utilizing vivianite recovery technologies such as magnetic separation (80% of vivianite recovery in digestates according to Wijdeveld et al. 2022), and other alternative options could provide the potential recovery target needed to improve BLOOM. CONCLUSIONS Based on current vivianite-removal technology efficiencies, removing vivianite will significantly impact the phosphorus levels in BLOOM. Results suggest that after anaerobic digestion is a preferred and feasible option to implement recovery technology due to its high vivianite content as well as the opportunity to recover vivianite in a fraction of the digestate to produce low P BLOOM rather than the whole biosolids treatment train. Future testing will explore recovery efficiencies of P and vivianite to confirm feasibility and setup a path towards pilot testing approaches.

Biosolids from water resource recovery facilities (WRRFs) are increasingly used for agricultural and recreational land purposes due to their sustainable means to replenish macronutrients. However, the relatively high phosphorous content of biosolids limits certain applications. This study aims to identify optimal locations for recovering vivianite to manage phosphorous levels in class A biosolids.

SpeakerGuo, Peibo

Presentation time

08:30:00

08:50:00

Session time

08:30:00

10:00:00

SessionEnhancing Digestion to Improve Operations and Resource Recovery: Capture of Control

Session number501

Session locationRoom 256

TopicBiosolids and Residuals, Energy Production, Conservation, and Management, Facility Operations and Maintenance, Intermediate Level

Author(s)

Guo, Peibo, Yan, Yuan, Ngo, Nam, Peot, Chris, Gu, April, Reid, Matthew, Bollmeyer, Melissa, De Clippeleir, Haydee

Author(s)P. Guo1, Y. Yan2, N.H. Ngo3, C.J. Peot4, A.A. Gu5, M. Reid2, M. Bollmeyer2, H. De Clippeleir6

Author affiliation(s)1Brown and Caldwell, VA, 2Cornell University, NY, 3, CA, 4DC Water & Sewer Authority, DC, 5, NY, 6DC Water & Sewer Authority, VA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159698

Volume / Issue

Content sourceWEFTEC

Word count16

Description: Harnessing Machine Learning for Enhanced A-Stage Process Efficiency: A Pioneering...

Harnessing Machine Learning for Enhanced A-Stage Process Efficiency: A Pioneering Full-Scale Study

Abstract

Introduction The shift towards energy- and resource-efficient WWTPs is no longer a privilege. For this reason, the A/B scheme is attracting substantial industrial and scientific interest in which the A-stage role is to maximize carbon diversion to the recovery streams and maintain stable low carbon influent to the B-stage. This is attained by operating the process in a very dynamic manner where high mass and volumetric loading rates are applied. As a result, a key challenge in the A-stage process is sludge settleability and the associated maintenance of effluent quality, particularly effluent suspended solids (ESS) [1]. In an operational-related context, it was reported that return streams can have a noticeable effect on A-stage performance [5]. It was found that bio-augmenting the A-stage process with waste nitrification sludge (WNS) may positively influence process performance, whereas supernatant return flow from solids processing (SPB) may negatively influence process stability [5]. However, this was never quantified or transformed into a control strategy for the return streams This is particularly of operational significance because such variables (WNS and SPB flows) are the key manipulated variables, given that solids wastage in Blue Plains is highly dependent on the capacity of the solids processing facilities rather than process performance. Hence, there is a need to develop a robust control strategy for ESS minimization, based on WNS and SPB. The bottleneck for implementing such a control strategy is to develop a model that can overcom the complex and dynamic nature of A-stage process. To this end, this study presents two data-driven modelling approaches to predict ESS of the full scale HiCS system operating at Blue Plains WWTP. This is the first machine learning (ML) model to be developed for an A-stage process. Methodology Modeling are based on a 2-year dedicated data effort from the WEST train of full-scale HiCS system at Blue Plains advanced WWTP. In addition to primary effluent, HiCS handles return flows such as SPB and WNS. Process parameters that are routinely measured include suspended solids, COD fractions, environmental and operational conditions (i.e., SRT, SOR, SLR, MLSS), advanced settleability measurements (i.e., TOF, and EPS TKN). Such variables represent possible model features (inputs), whereas the output (target) is process ESS, which was consistently monitored. Findings The data considered for this project were collected from Online sensors, DC Water Lab, and Research team. As shown in Figure 1, the obtained features have significant variation in frequency (how frequent these features are measured) and consistency (consistency in measuring features at the suggested frequency). This can be referred to the complexity of the process, which necessitates the consideration of sophisticated parameters like TOF, and LOSS [1]. In addition, sensing associated challenges have a key role to play [3]. To address challenges with the data, two modelling approaches are presented: (1) high frequency features classification (HF-C) model, and (2) all features regression (AF-C) model. In the HF-C model, the problem was approached as a classification problem where ESS was classified into three classes (good: <25 mg/L, action needed: >25 mg/L & 35 mg/L <, and bad: >35 mg/L). In this model, only features with high frequency were considered. Such features are mostly the flow-based features such influent, return streams, and wastage flow rates. AUC-ROC and F1 score along with accuracy were used to assess model performance which considered the effect of the less represented classes. Among different algorithms tested, the performance of four algorithms stands out, as shown in Figure 2a. When further evaluated based on the recall of the minor classes and extent of overfitting, it can be seen from Figure 2b that the support vector machine with radial basis function (SVM-rbf) is the best performing model. For the AF-R, the framework, demonstrated in Figure 3, was developed to circumvent the challenges of predicting dynamic and highly non-linear targets, significant variations in features availability, A-stage complexity, and data imbalance. A three-step data imputation approach where adopted to alleviate the effects of the high missingness in the data. Figure 4 shows the resulting outcome of the target and other features after outlier removal, and imputation. Subsequently, the model was developed in a multi-step fashion where the 7-day and 3-day moving average (MA) were first estimated and used as inputs to predict the Raw ESS. Figure 5 shows the effect of optimizing model architecture. These optimizations included the utilization of a weighted loss function to count for data imbalance and stratified cross validation to equally sample from different periods over the 866 days. These modifications resulted in an R2 of 0.72 and 48% reduction in RMSE (in comparison with average) using RF. This is compared to R2 of 0.2 to 0.3 for the model before optimization. Finally, it was observed that the integration of settling features (TOF, LOSS, EPS COD, and SVI) and operational parameters (SRT, WAS solids, and MLSS), and WNS characteristics (WNS COD fractions) significantly improved model performance. Figure 6 shows an example of the results when such features are introduced to the model where R2 above 0.85 was observed with more than 65% reduction in RMSE.

We explore the use of machine learning (ML) to enhance the efficiency of High-rate Contact Stabilization in the A-stage process of Blue Plains Advanced WWTP. By analyzing 2 years of operational data, research develops ML models to predict effluent suspended solids, incorporating high-frequency flow-based features & advanced settleability parameters. Optimized models significantly improve predictive accuracy, highlighting ML's potential for process control, stabilization, & resource recovery.

SpeakerAlSayed, Ahmed

Presentation time

16:00:00

16:30:00

Session time

15:30:00

17:00:00

SessionApplication of Machine Learning and Modeling in Carbon Diversion Technologies

Session number419

Session locationRoom 243

TopicAdvanced Level, Facility Operations and Maintenance, Intelligent Water

Author(s)

AlSayed, Ahmed, Ngo, Nam, Khan, Usman, De Clippeleir, Haydee, Wells, George

Author(s)A. AlSayed1, K. Nam Ngo2 U. Khan3, H. De Clippeleir, 4, G. Wells5

Author affiliation(s)1, 5Department of Civil and Environmental Engineering, McCormick School of Engineering, Northwestern University, <sup2, 4> District of Columbia Water and Sewer Authority 3Department of Civil Engineering, Lassonde School of Engineering, York University; District of Columbia Water and Sewer Authority; Department of Civil and Environmental Engineering, McCormick School of Engineering

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159678

Volume / Issue

Content sourceWEFTEC

Word count13

Improving Clarifier Models by Describing Extracellular Polymeric Substances

Abstract

Improved settleability in activated sludge processes is an essential feature of new innovations. To accelerate the adoption of such technologies, the ability to link operational conditions with settling characteristics is needed to support process design and prediction of improvements in settleability. The previous works indicated that the threshold of flocculation (TOF) (Mancell-Egala et al., 2017a), which describes the collision efficiency of particles, was successfully introduced as a simple experimental method to calculate the flocculent settling coefficient (rp) in 1-D clarifier models and to enhance the ability to predict clarifier effluent solids. TOF also showed to have a clear relationship with effluent quality making it a useful operational parameter to detect flocculation limitations. In addition, extracellular polymeric substances (EPS) quality, most often expressed as a protein over polysaccharides ratio has been linked to flocculation behavior, densification and granulation (McSwain et al., 2005). This knowledge was used to develop an empirical function between the composition of (EPS) expressed as EPS-TKN/COD and TOF. This relationship between EPS composition and TOF was introduced as a means of linking biological process models (i.e. Sumo2C model) and 1-D clarifier models (Ngo et al., 2021b). Essential for this approach is the prediction of EPS amounts and quality from process models as a function of feast-famine, and other operational conditions as this defines settling behavior. This paper discusses three approaches for EPS prediction from process models and will provide insights on 2 which type of EPS modeling might be needed for different purposes. While this abstract describes different datasets tested for the different models, the full paper will provide a full comparison of the three models on the full-scale dataset collected at Blue Plains

This paper discusses three approaches for EPS prediction from process models and will provide insights on which type of EPS modeling might be needed for different purposes. With optimized EPS quality prediction, it is possible to simulate settling improvements based on changes in operational conditions both based on a wide range of SRT as well as based on feast-famine driver. The latter will help to accelerate the adoption of intensification technologies.

SpeakerNgo, Nam

Presentation time

10:35:00

10:50:00

Session time

10:30:00

12:00:00

SessionPushing the Boundaries of Our Biological Models

Session locationRoom S404a - Level 4

TopicFacility Operations and Maintenance, Intermediate Level, Municipal Wastewater Treatment Design, Research and Innovation

Author(s)

Ngo, Khoa Nam

Author(s)N. Khoa Nam 1; T. Wadhawan 2 ; B. Sturm 3; J.P. Boltz 4; J. Hinojosa 5; A.N. Massoudieh 6; I. Takacs 7; J. Jimenez 8; H. De Clippeleir 9;

Author affiliation(s)District of Columbia Water and Sewer Authority 1; Dynamita SARL, France 2 ; University of Kansas 3; Woodard & Curran Arizona State University, USA 4; District of Columbia Water and Sewer Authority 5; Catholic University of America 6; Dynamita SARL, France 7; Brown and Caldwell, USA 8; District of Columbia Water and Sewer Authority, USA 9;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159190

Volume / Issue

Content sourceWEFTEC

Word count9

Description: Improving Clarifier Performance and Capacity through Full-scale Implementation of...

Improving Clarifier Performance and Capacity through Full-scale Implementation of High-rate Contact Stabilization

Abstract

When combined with carbon efficient nutrient removal systems (short-cut nitrogen removal), high-rate activated sludge (HRAS) systems provide a potential pathway towards energy neutrality at Water Resource Recovery Facilities (WRRFs) (Rahman et al., 2020). In well operated HRAS systems, 50-60% of influent wastewater COD can be captured and sent to anaerobic digestion through carbon redirection and enhanced settling in clarifiers. Carbon redirection depends on short solids retention time (SRT) to minimize aerobic oxidation while solids capture in clarifiers is a function of bioflocculation (Jimenez et al., 2015; Rahman et al., 2016). However, the operational conditions of HRAS system can lead to a very dynamic process resulting in inconsistent clarifier performance and poor effluent quality, which in turn, reduces the net COD captured and energy recovery through anaerobic digestion (Miller et al., 2016). The secondary treatment or HRAS system at Blue Plains Advanced WWTP in Washington, DC operates at 1to 3 days SRT. The secondary clarifier performance is positively impacted when the HRAS system is bioaugmented with waste sludge from the downstream, enhanced nitrogen removal (ENR) system, and negatively impacted by recycle from the solids thickening and dewatering processes. Bioaugmentation with ENR sludge allows for better settling characteristics through improved bioflocculation (Mancell-Egala et al., 2017b; Van Winckel et al., 2019) and reduced energy demand through increased oxygen transfer efficiency (Garrido-Baserba et al., 2020). On the other hand, the solids recycle flow (solids processing building return flow, or SPB) has high levels of colloidal material that cannot settle without being adsorbed onto flocs and thus increases fines in the secondary effluent (Mancell-Egala et al., 2017b; Van Winckel et al., 2019). Previous research at Blue Plains showed that biofloculation in HRAS systems is the limiting factor in achieving good effluent quality, especially with high colloidal loads coming from the solids recycle flow (Mancell-Egala et al., 2017b; Van Winckel et al., 2019). The same studies showed that extraccellular polymeric substances (EPS) production was the critical factor impacting flocculation properties and settling characteristics. High-rate Contact Stabilization (CS) or RAS aeration has shown to enhance EPS production and bioflocculation by imposing a feast-famine regime (Rahman et al., 2016). It was therefore suggested that a high-rate CS system rather than a high-rate step-feed system (current configuration) should allow for enhanced bioflocculation within the Blue Plains secondary treatment system. Full-scale CS implementation was easy to implement to the current existing infrastructure at Blue Plains as it only required to bypass feed flow to the later stages to allow for a RAS aeration zone or stabilization zone to be created (Figure 1). Overall, this study focused on evaluating the impact and potential benefits of full-scale high-rate CS implementation, including the complexities of bioaugmentation and SPB flows on settling behavior and clarifier performance.

The following conference paper was presented at WEFTEC 2021, October 16-20, 2021. To read the full abstract, see "Abstract" tab below.

SpeakerNgo, Nam

Presentation time

16:00:00

16:20:00

Session time

16:00:00

17:30:00

SessionSecondary Clarifier Treatment Performance

Session number117

TopicFacility Operations and Maintenance, Municipal Wastewater Treatment Design

Author(s)

Nam Ngo

Author(s)N. Ngo1,2; M. Sabur1; A. Massoudieh2; B. Wett4; C.B. Bott3; N.J. Passarelli1; A. Tesfaye1; R. Suzuki1; C. deBarbadillo1; H. De Clippeleir1;

Author affiliation(s)District of Columbia Waterand Sewer Authority, DC1Department of Civiland EnvironmentalEngineering, Catholic University of America, DC2Hampton Roads Sanitation District3ARA consult GmbH, AU4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2021

DOI10.2175/193864718825158017

Volume / Issue

Content sourceWEFTEC

Word count13

Description: Mitigating Volatile Sulfur Compound Emission From Primary and Secondary Activated...

Mitigating Volatile Sulfur Compound Emission From Primary and Secondary Activated Sludge Systems Using New Low-Cost Operational Strategies

Abstract

INTRODUCTION
Since the early twentieth century, treatment plants have typically been located at remote locations on the outskirts of the cities they serve. Due to an increase in population size, urbanization, life standard and irrigation needs, the demand for water and wastewater treatment plants (WWTP) has been rising rapidly (Estrada et al., 2011). As a result, large WWTPs are often found near main metropolitan areas, so the need for odor prevention increased accordingly. A critical factor in facilitating the integration of intensified WWTP within urbanized regions is cost-effective and efficient odor emissions prevention, control, and treatment. For decades, research and technologies have been focused on the treatment of foul air from treatment processes providing end-of-pipe solutions for volatile sulfur compound (VSC) removal that results in higher capital and operational costs to utilities (Giri et al., 2014). Technologies developed include physical-chemical approaches that can remove H2S as well as biological approaches (i.e. biofilters and trickling filters) that can also remove volatile organic sulfur compounds (VOSCs) (Camp Dresser & McKee, 2003). Treatment and cost-effectiveness of these end-of-pipe approaches are mainly dependent on the ease to capture the foul air and, therefore mostly applied for sewer networks, screening and grit removal facilities, and biosolids storage facilities. However, one of the significant sources of nuisance odor emission within WWTP is the primary and secondary treatment system, which is mainly caused by VOSC emission rather than H2S (Sekyiamah et al., 2008). Due to the low odor threshold of VOSCs such as methyl mercaptan (MM), dimethyl sulfide (DMS), dimethyl disulfide (DMDS) compared to H2S (Estrada et al., 2011), the smaller fluxes observed within WWTP and in particular within secondary systems can have a significant impact on the overall nuisance odor emission. Due to its large surface area, the end-of-pipe odor treatment technologies often require significant capital investment and are often impractical.
In this project, we proposed new operational strategies for low-cost odor mitigation in both primary treatment systems and secondary activated sludge systems based on a better understanding of odor production kinetics. For the primary treatment system, a new sludge pumping mode was proposed to minimize compression and retention of sludge blankets. For the secondary system, a switch was made from a step feed mode with anaerobic selectors to a high-rate contact stabilization mode with aerobic stabilizer and contactor with anaerobic selectors. The achieved odor reduction through these approaches is presented in this paper.
MATERIALS AND METHODS
Sampling campaign: An AC'SCENT surface Emission Isolation Flux Chamber (Bazemo et al., 2021) was used for gas phase sampling at the surface of primary clarifiers and the different passes and zones in secondary reactor system. The VOSCs off-gas samples were sent to ALS Environmental Laboratory to be analyzed for MM, DMS, and DMDS (ALS, USA). H2S measurements were carried out using an electrochemical sensor (Odalog, USA). The influent and sludge characterizations were captured. Historical measurements using the same sampling methods were used as a baseline for the secondary system, while different operational modes were compared side by side for the primary system. Developing and evaluating new operational mode for primary clarifier: Three modes were tested at different underflow rates detailed in Figure 1. It should be noted that mode 1 and mode 3A & 3B alternated every two cycles on one clarifier for short-term testing and were tested side by side during steady-state period. As both modes ran in parallel on the same day, the impacts of wastewater characteristics and temperature on odor production outcomes between modes were minimized. Full-scale high-rate CS implementation in secondary system: West and East secondary full-scale activated sludge systems at Blue Plains were switched from stepfeed to CS configuration on April 7th, 2020 and August 1st, 2020 respectively (Figure 1B & 1C). More details on how this switch improved secondary performance can be found in Ngo et al., 2021.
RESULTS & DISCCUSIONS
Primary system odor production decreased by more than a half using a new pumping strategy: The proposed strategy was based on the reports from Bazemo et al. (2021), showing 64% of H2S and 89% VOCS emissions were produced in the sludge blankets. Figure 2A & 2B indicated that mode 3A and 3B resulted in significantly lower H2S and VOSC emissions compared to mode 1. Minimizing the sludge buildup time was more important than increasing the sludge pump flow rate, as no clear differentiation between mode 3A and 3B was observed. Thus, the total primary sludge pump flow rates from each house could be maintained while minimizing potential odor generation from further thickening. The steady-state operation showed that with this low-cost operation change, a reduction of 57% of H2S and 63% of VOSC was feasible (Figure 2C and 2D). In addition, this new mode maintains H2S levels under 1.6 ppm (2.2 ppm baseline) and 46 ppbv VOSC (111 ppbv baseline). Bioaugmentation and Contact stabilization (CS) mode decreased VSC emission by 23% and 81%, respectively: In secondary treatment, VOSC is the main contributor of odor and the only H2S emitted comes from primary effluent stripping (Bazemo et al., 2021). In addition, off-gas testing during baseline testing showed that 78% of odor emission in secondary was related to the first pass and production of odor compounds in sludge blankets and anaerobic zones. In addition, kinetic experiments using batch testing showed an evident inhibition of VOSC production due to nitrate (Figure 3A) or oxygen (Figure 3B) presence. Bioaugmentation using biological nutrient removal (BNR) sludge into secondary systems has been demonstrated to improve nutrient removal, oxygen transfer efficiencies, and settleability (Ngo et al., 2021). Due to the nitrate production of 0.43 mg/L-N, when one of the secondary systems receives all BNR sludge during the summer months, VOCSs emission was reduced by 23% with double bioaugmentation scenario (Fig. 3C). When both secondary systems receive each half of the BNR sludge, such levels of nitrate cannot be achieved and VOSCs emission increased again, while benefits of oxygen transfer and settleability were maintained (Fig.3C). When CS mode was applied, and bioaugmentation was maintained at 50%, VOSC reduced by 83% (Figure 3C) and H2S production decreased by 75%, despite the lack of net nitrate production. As larger part of the sludge inventory is stored under aerobic conditions rather than under anaerobic conditions, overall emission was clearly reduced.
CONCLUSION
This study developed new operational strategies in primary and secondary systems to mitigate the VSC emissions by minimizing the anaerobic sludge inventory without impacting performance in the primary or even improving overall system performance in the secondary Ngo et al. (2021). By understanding odor production kinetics, low-cost operational strategies can offer an alternative to end-of-pipe odor treatment technologies with significant capital investment costs.

Intensified WWTP within urbanized regions is cost-effective and efficient odor emissions prevention, control, and treatment. This study developed new operational strategies in primary and secondary systems to mitigate the VSC emissions by minimizing the anaerobic sludge inventory without impacting performance. By understanding odor production kinetics, low-cost operational strategies can offer an alternative to end-of-pipe odor treatment technologies with significant capital investment costs.

SpeakerNgo, Nam

Presentation time

09:00:00

09:15:00

Session time

08:30:00

10:00:00

TopicIntermediate Level, Facility Operations and Maintenance, Odors and Air Quality, Sustainability and Climate Change

Author(s)

Ngo, Nam

Author(s)Khoa Nam Ngo1,2; Margaret Lan-Anderson1,3; William Albrittain1; Chris J. Reilly1; Ryu Suzuki1; Arash Massoudieh2; Nicholas Passarelli1; Aklile Tesfaye1; George Wells3; Haydée De Clippeleir1

Author affiliation(s)District of Columbia Water and Sewer Authority, Washington, DC1; The Catholic University of America, Washington, DC2; Northwestern University Library, Evanston, IL3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158520

Volume / Issue

Content sourceWEFTEC

Word count18

Optimizing Side Impacts of Using Primary Sludge Fermentate for Shortcut N removal in Chemical P Removal Facilities

Abstract

Introduction Traditionally, primary sludge fermentate has been utilized in biological-P removal plants to stabilize and enhance P removal (WRF Project 4975 Report, 2023). However, there is an emerging interest in employing fermentate in chemically enhanced P removal plants to support nitrogen removal and decrease the dependency on external carbon. Especially with the development of novel nitrogen removal systems such as partial denitrification anammox (PdNA), the use of fermentate can result in significant carbon removal savings (Ali et al., 2021; Ladipo-Obasa et al., 2022). It was estimated that for a plant like Blue Plains that relies on methanol (MeOH) as an external carbon source for N removal, the use of primary sludge fermentate can replace 15% of MeOH when deployed for full denitrification or 30-40% of MeOH when deployed for PdNA. To maximize N removal with fermentate, the fermentation yield in terms of volatile fatty acids or overall soluble COD yields plays a big role. This yield is dependent on the operational conditions of the fermenter with solids retention time (SRT) being one of the most important factors. The relationship between SRT and sCOD or VFA yields is shown in Figure 1A & 1B. Typically, an SRT of 3 days is needed to maximize yields (Fig. 1A & 1B). However, it should be noted that nutrients (NH4, OP) are also released (Fig 1C & 1D). Typically, in a non-chemical P plant, a yield of around 0.0055 gNH4-N/gVSS and 0.000842 gPO4-P/gVSS is expected (Fig 1C & 1D). However, when relying on ferric dosing, it is expected that enhanced P release will be observed due to the iron reduction in the fermenter (Fig 1D). This could cause a challenge as now P first bound with Fe, needs to be recaptured to meet discharge limits. This paper provides an assessment of primary sludge fermentation side impacts that need to be accounted for fermentate use for N removal in chemical-P plants. This includes impact of P recycles loads, solids load due to settling changes and odor emissions. Material and methods: Primary sludge was collected from Blue Plains Advanced Wastewater Treatment Plant. Fermentation tests were conducted in batches during different seasons. The last two seasons (Spring and Summer) results will be included in the full paper. Fermentate underwent characterization in terms of chemical composition and was tested for settling parameters (Ngo et al., 2021). Additionally, a full-scale batch fermentation was conducted in the gravity thickener during winter conditions. Results and discussion: Side impact 1: P release yields in chemical P removal plants All tests of Blue Plains primary sludge yielded consistent results in terms of sCOD and NH4 yields. Overall, these yields were a little lower than reported literature (Fig. 1A & 1C), most likely due to the long sewer systems and significant fermentation and loss of soluble organics before the sewage reaches the plant. For P yields, a larger variability existed (Fig. 1D), which might be related to the fermentation conditions (pH variability) or Fe dosing rates in the plant. Overall, the P concentration expected in the fermentate is about 30.9+/-12.6 mg P/L or 0.74+/-0.3 mg Peq/L in the mainstream. Given our TP limit of 0.18 mg TP/L, this contribution is significant and needs to be addressed. Potential avenues to look into to resolve this are optimization of fermentation conditions, potentially operating under pH <5 (Ali et al., 2021). A second avenue is to re-oxidize fermentate from ferrous to ferric and bind this back to FePO4. Current measurements show the availability of 0.72 mol Fe/P, which would allow us to decrease P content to 0.21 mg Peq/L in mainstream/L theoretically or 0.38 mg Peq in mainstream/L at current plant stoichiometries. Side impact 2: Settling changes during fermentation Spring and summer tests show a deterioration in flocculation behavior (Fig. 2A). Even though threshold of flocculation value was different, the trends were consistent. The decreased collision efficiency resulted in increased turbidity and non-settling fraction in the fermentate. This was consistent with observations from literature (Bouzas et al., 2007). It should also be noted that TOF reached the higher levels at the highest sCOD yields and thus we need to anticipate an increase in particulates at increased yields. Typically, we are seeing solids levels of 325+/-230 mg TSS/L in fermentate. While flocculation deteriorated, hindered settling properties improved with the decrease trend of SVI30 (Fig. 2B). This illustrated the interpretation of floc morphology and behavior between flocculation and hindered settling properties (Fig. 3). Side impact 3: Odor formation During fermentation, odor is formed and its composition under current gravity thickener operation and fermentation is showed on table 1. Increased odor is a result of microbial reactions under deep anaerobic conditions. Hydrogen sulfide formation remained low due to the presence of ferrous. Understanding the odor compounds can support evaluation of odor treatment and mitigation strategies. Conclusions Overall, this study quantified the expected increase in P loading coming from fermentate, the expected impacts on settling and odor formation. These three factors must be taken into account when considering primary sludge fermentate for N removal.

This study investigates using primary sludge fermentate in CEPT plants to support N removal and reduce using external carbon. At Blue Plains AWWTP, fermentate can replace 15% of methanol for full denitrification or 30-40% for PdNA. SRT correlates with sCOD and VFA yields, peaking at 2-3 days. The research also explores side effects like P loading, altered settling behavior, and odor formation, emphasizing the need to optimize fermentation conditions and implement effective odor treatment.

SpeakerIslam, Shafkat

Presentation time

16:00:00

16:30:00

Session time

15:30:00

17:00:00

SessionEnhancing Nitrogen Removal: Insights Into Carbon Sources and Mechanisms

Session number420

Session locationRoom 340

TopicAdvanced Level, Facility Operations and Maintenance, Municipal Wastewater Treatment Design, Nutrients, Research and Innovation

Author(s)

Islam, Shafkat, Ngo, Nam, Lapidus, David, Mendoza, Sara, Pathak, Bipin, Kozeracki, Emilia, Riffat, Rumana, Azam, Hossain, Massoudieh, Arash, De Clippeleir, Haydee

Author(s)S. Islam1, N. Ngo2, D. Lapidus3, S. Mendoza4, B. Pathak5, E. Kozeracki6, R. Riffat7, H.M. Azam3, A.N. Massoudieh8, H. De Clippeleir9

Author affiliation(s)1The George Washington University, DC, 2DC Water, VA, 3University of the District of Columbia, DC, 4Carollo Engineers, VA, 5DC Water & Sewer Authority, DC, 6The Catholic University of America, CT, 7George Washington University, VA, 8Catholic University of America, DC, 9DC Water & Sewer Authority, VA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159525

Volume / Issue

Content sourceWEFTEC

Word count18

Description: Towards More Reliable Dewatering Performance by Optimizing Polymer Dose...

Towards More Reliable Dewatering Performance by Optimizing Polymer Dose Decision-making

Abstract

Blue Plains Advanced wastewater treatment plant (AWWTP) was the first utility in the USA to install Cambi thermal hydrolysis process (THP) together with anaerobic digester (AD) to reduce solids production, increase energy resource recovery and produce class A biosolids. The new facilities were commissioned at the Blue Plains Advanced Wastewater Treatment Plant (AWTP) in 2015. The technology choice provided a major benefit on dewatering process by improving the cake TS, which has a large economic impact on treatment operations by decreasing the hauling costs, and by improving the quality of the "Bloom” biosolids product that is regionally marketed (Li, 2021). Dynamic changes in operational condition of the THP and AD process, sludge characteristics, and seasonal impacts (Li, 2021) result in high variety of cake TS (%) from 24 to 38% TS and filtrate TSS from 50 to 1530 mg TSS/L at the final dewatering belt filter presses. Poor cake TS causes higher hauling costs, while unreliable filtrate TSS significantly impacts the filtrate treatment facility. In addition, the polymer cost also may increase year by year depending on the market price, so picking the right optimal polymer dose range can optimize operational cost. In practice, the polymer dose is set manually by the operator and requires constant attention to minimize polymer dose while maintaining good operational throughput. Polymer dose decision making is thus mainly driven by human factors. Therefore, this study focused on investigating if the polymer dosing decision made by operators is adequate or if there is room to improve dewatering performance, which helps to define research development needs for helping optimizing polymer costs at the plant.

Our team finished a first evaluation of the full-scale final dewatering process at Blue Plains and found that currently about 30% of the time the operator is overdosing polymer. Operating the system at the Eco-PD will allow for polymer dose savings while stabilizing cake and filtrate quality. In addition, acoustic signals before and after polymer dose and flocculation will be used to develop a feedforward feedback polymer dose control. Current development is ongoing.

SpeakerNgo, Nam

Presentation time

14:30:00

14:50:00

Session time

13:30:00

15:00:00

SessionUpgrading and Optimizing Thickening and Dewatering

Session locationRoom S401a - Level 4

TopicIntermediate Level

Author(s)

Ngo, Khoa

Author(s)K. Ngo 1; T. Nguyen 2 ; H. Nguyen 3; D. Dao 2; J. Proctor 3; A. Tesfaye 4; D. Adalian 4; A. Massoudieh 5; N. Passarelli 4; H. De Clippeleir 6; K. Ngo 1;

Author affiliation(s)DC Water 1; Catholic University of America 2 ; Catholic University of America 3; Catholic University of America 2; DC Water 3; DC Water 4; DC Water 4; DC Water 5; DC Water 4; DC Water 6; DC Water 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159234

Volume / Issue

Content sourceWEFTEC

Word count11

Description: Validation Of The Novel Settling Prediction Model Framework For Various Full-Scale...

Validation Of The Novel Settling Prediction Model Framework For Various Full-Scale Systems

Abstract

INTRODUCTION
A clear trend towards intensified and resource-efficient technologies is observed as wastewater treatment plants are moving towards resource recovery facilities. Given that current secondary clarifiers are often the largest footprint bottleneck to achieve intensification, improving settleability, clarifier capacity, and effluent quality have become an essential feature of new technologies (Ekama et al., 1997). Recently, Ford et al. (2018) and Sturm & De Clippeleir (2020) described different degrees of settling improvements using the inDENSE technology based on a combination of physical (cyclones) and microbial selection (Bio-P and plug flow configurations). However, it was unclear how easily transferrable the latter observations were to other plants as the effects of operational conditions on settleability are challenging to estimate and extrapolate to new systems. Unlike the use of physical and microbial selection for shortcut nitrogen removal, where kinetic measurements or molecular tools help to quantify selection or selective wasting (Van Winckel et al., 2019), no clear quantification for settling selection is available, and thus transferability of results is challenging.
In previous work, the threshold of flocculation (TOF) (Mancell-Egala et al., 2017a), describing the collision efficiency of particles, was successfully introduced as a simple experimental method to calculate the flocculent settling coefficient (rp) in one-dimensional (1D) clarifier models and enhanced the ability to predict clarifier effluent solids (Ngo et al., 2021a; Figure 1). TOF also showed to have a clear relationship with effluent quality making it a useful operational parameter to detect flocculation limitations. Besides that, a strong correlation was found between the composition of extracellular polymeric substances (EPS) expressed as EPS-TKN/COD and TOF. The relationship between EPS composition and TOF was introduced as a means of linking biological process models (Sumo2C model) and 1D clarifier models (Ngo et al., 2021b; Figure 1). The latter model framework (Figure 1) shows the potential to predict settling behavior from operational conditions and would open up opportunities to extrapolate concepts from one facility to another. Preliminary validation using literature data showed settling trends related to solids retention time changes well. However, full validation using full-scale wastewater, process, and settling data was missing. In this study, we are filling this gap by detailed monitoring of three activated sludge systems at Blue Plains (two secondary contact stabilization systems, one biological nutrient removal system). In addition, sampling at five additional full-scale locations is initiated and will be added to the full paper to gain confidence that the proposed model framework is generally applicable. Two major validations are aimed for (1) validation of the two empirical equations (Figure 1) and (2) validation that process models can predict settling changes in full-scale systems based on operational conditions.
MATERIALS AND METHODS
Two high-rate secondary systems and one biological nutrient removal systems were samples for at least six months consisting of wastewater characteristics, flocculation settling, Vesilind parameters, and sludge composition including EPS. Similar measurement at five additional full-scale systems is initiated to generate similar data set for a broader range of operational conditions and systems. At least two of the full-scale systems include hydrocyclone selection. Empirical equations were validated directly from data (EPS~TOF) or using steady-state clarifier modeling (rp~TOF). Data gathered was then used to set up and calibrate the Sumo2C model (Hauduc et al., 2019) and validate predicted TOF and clarifier performance with the observed dataset. The latter action is ongoing and will be fully reported in the full paper.
RESULTS AND DISCUSSIONS
Validation of empirical equations A wide range of full-scale activated sludge systems was selected for validation to test the potential global applicability. Two years of validation data (2020 and 2021) from EAST and WEST secondary systems at Blue Plains were sampled (Figure 2 and Table 1). In addition, each secondary system was operated under different configurations including stepfeed (SF) and contact-stabilization mode (feast-famine) mode. Besides that, another five new full-scale WWTPs are sampled later this year to include larger variability in SRT, effluent quality, organic loading, and reactor configurations. Initial testing results are presented in figure 1B and 1D. Despite the significant differences in operational conditions of the systems, all validation data fell well within 95% prediction interval of the training data that was established based on stepfeed secondary system and BNR systems at Blue Plains systems (Figure 1). This confirmed that the developed equations are valid and transferrable. Process model-based prediction of settling behavior The overall model concept and an example of the model setup for the two secondary systems at Blue Plains are shown in Figure 1. This step included a detailed and longer-term sampling of full-scale systems, including detailed wastewater characterization (Table 1) to allow dynamic process models of the latter systems, in addition to the settling behavior and EPS (Figure 3). First, a steady-state model run will be aimed to get a sense of TOF prediction of the model, and this phase will be followed by dynamic modeling of the more than six-month period to see how well the model can pick up changes in settling over time. Both the stepfeed mode and contact stabilization mode will be simulated, which in practice resulted in improved settling behavior (Figure 2). The latter is a good example of operational condition change within one system. In addition to that, sampling campaigns within five additional full-scale systems are ongoing, which will provide a broader view of the applicability of the modeling framework. We believe that this work can be a gamechanger in approaching settleability and settling predictions.
CONCLUSION
This is the first time that process conditions were directly linked to settleability in a way model prediction of settling improvements based on changes in operational conditions are made possible. The power of the proposed settling prediction model is being validating this study based on eight full-scale systems. It brings us one step closer to a practical approach for enhancing the ability to predict clarifier effluent quality and performance as a result of operational and wastewater changes.

To accelerate the adoption of new innovations, the ability to link operational conditions with settling characteristics is needed to support process design. This study is the first time that process conditions were directly linked to settleability in a way model prediction of settling improvements based on changes in operational conditions are made possible. It brings us one step closer to a practical approach for enhancing the ability to predict clarifier effluent quality and performance.

SpeakerNgo, Nam

Presentation time

14:30:00

14:55:00

Session time

13:30:00

15:00:00

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

Author(s)

Ngo, Nam

Author(s)Khoa N. Ngo1,2; Jose Jimenez3; Tanush Wadhawan4; Arash Massoudieh2; Aklile Tesfaye1; Imre Takács4; Haydée De Clippeleir1

Author affiliation(s)District of Columbia Waterand Sewer Authority, Washington, DC1; Catholic University of America2; Brown and Caldwell, Florida3; Dynamita SARL, Sigale,France4

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158670

Volume / Issue

Content sourceWEFTEC

Word count13