Ram Mohan, Gayathri, Ram Mohan

Gaya is a professional engineer with significant experience in applied research, commissioning and operating pilot-scale water and wastewater...

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About Ram Mohan, Gayathri

Gaya is a professional engineer with significant experience in applied research, commissioning and operating pilot-scale water and wastewater treatment technologies, and leading full-scale field process optimization efforts. Over the course of her career, Gaya has led operations and maintenance staff to develop capital projects, optimize existing processes, investigate new technologies, and perform research on a wide variety of advanced and innovative wastewater treatment, biosolids, water reuse and resource recovery projects.

Ram Mohan, Gayathri

Titles from this speaker

Description: Adapting to What Flows Down the Pipe: Full-scale Bio-P Optimization Following...

Adapting to What Flows Down the Pipe: Full-scale Bio-P Optimization Following Changes in the Collection System

Abstract

The F. Wayne Hill Water Resources Center (FWHWRC) is Gwinnett County’s largest and most advanced wastewater treatment facility with a capacity of 60 MGD (maximum month). The FWHWRC utilizes enhanced biological phosphorus removal (EBPR) and chemical trim to meet a stringent effluent TP limit of 0.08 mg/L. This paper will discuss details of efforts undertaken to address impacts on full-scale plant operations, primarily resulting from changes in the collection system related to odor and corrosion control chemicals, that further influenced raw wastewater characteristics.

The F. Wayne Hill WRC is Gwinnett County's largest, most advanced wastewater treatment facility with a capacity of 60 MGD. FWHWRC utilizes EBPR and chemical trim to meet a stringent effluent TP limit of 0.08 mg/L. This paper will discuss efforts undertaken to address impacts on full-scale plant operations (Bio-P, nutrient recovery), primarily resulting from changes in the collection system related to odor and corrosion control chemicals that led to changes in wastewater characteristics.

SpeakerRam Mohan, Gayathri

Presentation time

11:00:00

11:30:00

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)

Ram Mohan, Gayathri

Author(s)G. Ram Mohan 1; R. Latimer 2 ; P. Pitt 3; C. Yi 1; J. Garmon 4; R. Harris 5; G. Ram Mohan 1;

Author affiliation(s)Hazen and Sawyer, Atlanta, GA 1; Hazen and Sawyer 2 ; Hazen and Sawyer 3; Hazen and Sawyer 1; Gwinnett County Department of Water Resources 4; Gwinnett County Department of Water Resources 5; Hazen and Sawyer 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159175

Volume / Issue

Content sourceWEFTEC

Word count17

Description: Beyond the PFAS treatment Barrier: Key Lessons from an 18-Month Pilot on PFAS...

Beyond the PFAS treatment Barrier: Key Lessons from an 18-Month Pilot on PFAS removal from Wastewater

Abstract

At the intersection of water reuse and PFAS regulatory pressure, Western Municipal Water District in southern California has embarked on one of the first full-scale PFAS adsorption installations for municipal wastewater prior to aquifer recharge. For Western, the complexity of PFAS impacts proved to be far beyond those observed in drinking water matrices with PFAS concentrations greater than 1,000 ng/L coupled with concentrations of effluent organic matter approaching 6 mg/L of total organic carbon (TOC). With this challenging water quality coupled with tightening PFAS regulations in wastewater discharges, direct adsorptive treatment from their tertiary treated wastewater was expected to yield rapid changeout intervals and subsequently higher cost. As water reuse treatment applications become more common in the United States, PFAS treatment will become a critical driver of process selection and operating cost. Tasked with developing a robust PFAS treatment scheme for aquifer recharge of wastewater effluent in southern California, this presentation will focus on the outcomes from an 18-month PFAS wastewater treatment investigation with bench and pilot scale results related to the feasibility of granular activated carbon (GAC) and ion exchange resin (IX) coupled with extensive pretreatment to meet newly released PFAS MCLs in wastewater treatment applications.

Bench scale rapid small scale column tests (RSSCTs) were used to screen adsorbents and operational conditions that subsequently informed the development of a pilot study to investigate adsorbent treatment effectiveness. RSSCTs were conducted for GAC, IX, and novel sorbents at a variety of empty bed contact times (EBCT). The best performing PFAS adsorbents from the RSSCTs were initially piloted for 1 month directly on the tertiary treated wastewater before bio-fouling and high concentrations of effluent organic matter quickly exhausted the adsorbents necessitating a pretreatment step to prolong PFAS adsorption performance and sustain operability. In this first phase of PFAS adsorption piloting, PFOA breakthrough occurred in less than 20 days with GAC operated at 20 minutes EBCT while biological fouling contributed to excessive head loss accumulation and inhibited pilot operation. After an unsuccessful direct adsorption pilot, a pretreatment piloting campaign comprised of conventional coagulation, flocculation, sedimentation, and cloth filtration was instituted to reduce concentrations of competitive adsorbates (i.e. TOC) and algal cells that were inhibiting adsorption effectiveness.

This conventional pretreatment train was selected to utilize existing full-scale infrastructure at the WWRF which could be optimized in this application upstream of PFAS adsorption. Other pretreatment configurations were also considered including direct filtration schemes eliminating the sedimentation phase and media filtration schemes omitting the cloth filtration step. Optimization of the piloted pretreatment train was conducted through a series of jar testing experiments to determine adequate pH and coagulant dose as well as piloting trials to modify floc particle sizes for better removal in downstream sedimentation and filtration processes. Pretreatment was able to reduce TOC levels by 30% and turbidity levels by 90% to sustain a paired adsorption train with both GAC and IX in series to treat PFAS concentrations greater than 1,000 ng/L down to non-detect for more than 100 days. Comparison of adsorption longevity of the pretreated wastewater effluent to direct adsorption treatment suggested that adsorption performance improved by a factor of 3 yielding considerable savings associated with adsorbent changeout. Results of the pilot study and coupled cost estimates and facility layouts served as the basis for treatment selection and full-scale design.

The implications of this pilot study highlight the decreased PFAS treatment longevity and subsequently higher changeout costs that are anticipated in water reuse applications. Analysis of PFAS changeout intervals revealed that there was cost incentive to invest in optimizing adsorption pretreatment, as was done in this study, to prolong adsorbent treatment effectiveness. This presentation will summarize bench and piloting results used to optimize TOC removal in adsorption pretreatment that ultimately contributed to improved PFAS treatment longevity for downstream GAC and IX. Piloting nuances associated with PFAS adsorption from treated wastewater including how to mitigate biological fouling and necessary water quality targets for pretreatment will also be shared. As one of the earliest pilot studies evaluating adsorption technologies for PFAS removal from wastewater, this presentation will highlight results that can be used to better inform treatability evaluations in other water reuse applications demonstrating the cost savings and operational benefits of adsorption pretreatment and hybrid adsorbent orientations.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

14:30:00

14:45:00

Session time

13:30:00

15:00:00

SessionTackling the PFAS Puzzle: Addressing Wastewater Effluent Concerns for Reuse

Session locationMcCormick Place, Chicago, Illinois, USA

TopicContaminants of Emerging Concern & Trace Organics

Author(s)

MURRAY, CONNER, Ram Mohan, Gayathri

Author(s)C. MURRAY1, G. Ram Mohan1

Author affiliation(s)Hazen and Sawyer1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825159930

Volume / Issue

Content sourceWEFTEC

Word count17

Cost Effective Approaches for Control of Multiple Constituents of Emerging Concern (CECs): WRF #5171

Abstract

Summary: With rapidly evolving regulatory drivers, the geographical diversity in state-level limits imposed, and lack of information on holistic management strategies there exists a critical need to develop an integrated risk-based CEC management framework to guide both watershed managers and regulators with quantitative data to help make informed decisions. This Water Research Foundation-funded study aims to elucidate the impacts of various CEC management approaches, typically implemented in potable reuse schemes, on ecological and human health-related risk reduction. This goal will be achieved by developing a decision framework for utilities aimed at identifying holistic, watershed-wide, cost-effective approaches to address multiple CECs. A summary of the comprehensive literature review on 'state of knowledge' on emerging trends related to CEC monitoring and treatment, as well as evolving regulatory drivers in the US will be presented. Additionally, trends related to CEC management from meta-analysis of data gathered from nation-wide practitioner surveys will be shared with the audience. Lastly, a comprehensive treatability database under development will watershed-wide CEC management. Learning objectives: The following are some key learning objectives: 1.Summary of existing federal and state-specific regulations/guidelines in the US for CEC management in drinking water, wastewater and water reuse applications. 2.Discussion on gaps in existing regulatory framework and future recommendations. 3.Overview of risk-based screening protocols for selection of candidate CECs, and, 4.Review of removal efficiencies (biological and physio-chemical) for established treatment barriers commonly incorporated in conventional (baseline) and advanced wastewater treatment and reuse applications. Full presentation description: Detection of contaminants of emerging concern (CECs) in impacted drinking water supplies in various parts of the world has triggered efforts to establish and prioritize regulatory frameworks that improve CEC monitoring and control in watersheds. This study aims to elucidate the impacts of various management approaches such as industrial source tracking and control, advanced wastewater treatment, advanced drinking water treatment, stormwater, and focused agricultural run-off best management practices on ecological and human health-related risk reduction. The research team is partnering with multiple municipalities, academicians, regulators, and industry leaders across the country to document existing drivers, practices, and outcomes related to the management of multiple CECs in watersheds. The proposed technical approach consists of the following tasks: (1) extensive literature review for state of knowledge assessment on monitoring and treatment of CECs and evolving regulatory drivers, (2) conducting national utility surveys to qualitatively and quantitatively assess watershed-wide CEC monitoring efforts in the US, (3) development of a risk-based framework using CEC occurrence data, treatment barriers and water quality end goals, and, (4) utilizing stakeholder-driven multi-criteria decision analysis to develop quantitative metrics to guide utilities towards selection of most efficient and cost-effective alternatives for the management of CECs in watersheds. Utilities are often faced with budgetary constraints with capital improvements related to rehab of aging infrastructure which often supersede research initiatives in the absence of well-structured and transparent decision frameworks. This study aims to identify gaps and address roadblocks in current and future regulatory drivers related to CEC management. The resulting risk registry and quantitative metrics will provide information to our targeted audience; WRF utility subscribers, watershed managers and regulators, to enable informed decision-making on how best to utilize a risk-based framework to determine viable and most cost-effective approaches to manage CECs. This presentation will provide a comprehensive evaluation of the impacts of various management approaches such as industrial source tracking and control, advanced wastewater and drinking water treatment, stormwater, and focused agricultural run-off best management practices on ecological and human health-related risk reduction. Through this presentation, an overview of the findings on existing CEC occurrence and treatment, screening protocols, management strategies and evolving regulatory drivers will be provided. In particular, this proposed presentation will cover an extensive literature review conducted on state of knowledge assessment on monitoring and treatment of CECs and evolving regulatory drivers. The roadblocks identified in current and future regulatory drivers related to CEC management will be outlined and addressed.

As population growth and climate change continue to strain water supplies, utilities face challenges related to potable water. With rapidly evolving regulatory drivers, and a lack of information on CECs, there exists a need to develop risk-based CEC management framework to help with informed decision making and long-term planning. The WRF 5171 team is collaborating with municipalities, and industry leaders to document drivers, practices, and outcomes related to managing CECs across watersheds.

SpeakerRam Mohan, Gayathri

Presentation time

13:30:00

14:00:00

Session time

13:30:00

14:30:00

SessionNon-PFAS Up and Coming Concerns

Session number604

Session locationRoom 346

TopicFacility Operations and Maintenance, Intermediate Level, Microconstituents and Contaminants of Emerging Concern (Non-PFAS), Research and Innovation

Author(s)

Ram Mohan, Gayathri, Owen, Christine, Murray, Conner

Author(s)G. Ram Mohan1, C.A. Owen2, C. Murray3

Author affiliation(s)1Hazen and Sawyer, GA, 2Hazen and Sawyer, FL, 3Hazen and Sawyer, CO

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159709

Volume / Issue

Content sourceWEFTEC

Word count15

Densification Specific Considerations for Secondary Clarifier Assessments

Abstract

Intensification is a major innovation for water resource recovery facilities (WRRFs) to realize cost-effective use and deployment of infrastructure. One of the promising technologies and approaches for process intensification is densified activated sludge (DAS). Secondary clarifiers are a key unit process to ensure retention of the solids inventory and permit compliance. The performance of clarifiers depends on several interrelated processes and factors including hydrodynamics, settling, turbulence, flocculation, sludge rheology, atmospheric conditions, tank geometry, internal features and loading conditions. Several tools and design “rules of thumb” are available from regulatory loading guidelines such as Ten State Standards, sludge specific assessment tools such as state point analysis, and calibrated, site-specific tools such as 2D and 3D computational fluid dynamics (CFD) modeling. These tools have been in use for decades with traditional sludge settling characteristics. However, the industry is still working through methods and procedures to assess the impacts of DAS settling characteristics on traditional secondary clarifier operations and loading guidelines. This paper will highlight the use of clarifier evaluation tools for DAS applications, including key considerations, observed performance, potential loading rates, and other relevant properties. Case studies are highlighted to demonstrate potential impacts at full-scale WRRF sites.

This paper was presented at WEFTEC 2023 in Chicago, IL.

SpeakerMartin, Will

Presentation time

11:30:00

12:00:00

Session time

10:30:00

12:00:00

SessionSecondary Clarification Advancements

Session locationRoom S401d - Level 4

TopicAdvanced Level, Municipal Wastewater Treatment Design

Author(s)

Martin, William

Author(s)W. Martin 1; A. Griborio 2 ; R. Latimer 3; R. Vandermeulen 4; G. Ram Mohan 5; W. Martin 1;

Author affiliation(s)Hazen and Sawyer, St. Paul, MN 1; Hazen and Sawyer, Hollywood, FL 2 ; Hazen and Sawyer, Atlanta, GA 3; Hazen and Sawyer 4; Hazen and Sawyer 5; Hazen and Sawyer 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159196

Volume / Issue

Content sourceWEFTEC

Word count8

Description: Evaluation Of Two-Phase Anaerobic Co-Digestion Of Wastewater Sludge With...

Evaluation Of Two-Phase Anaerobic Co-Digestion Of Wastewater Sludge With High-Strength Waste To Increase Solids Processing Capability At The F. Wayne Hill Water Resources Center

Abstract

The F. Wayne Hill Water Resources Center (FWHWRC) in Gwinnett County, GA, currently uses five egg-shaped mesophilic anaerobic digesters for wastewater sludge stabilization and receives high-strength waste such as fats, oils, and grease (FOG) that is co-digested with sludge. A future need for an increase in solids handling capacity is anticipated that warrants intensification of sludge management including the anaerobic digestion (AD) process. The purpose of this study was to evaluate the potential transitioning of the current digesters to two-phase AD, to determine if lower solids retention times (SRT), and thus a possible increase in the solids handling capacity of the plant could be achieved, as well as assess operational stability of the modified digestion process. This study evaluated the efficacy of two-phase AD in terms of methane production, and COD and solids reduction for FWHWRC. This was done through experiments conducted in two different phases of bench-scale work listed as follows: - Phase I - Biomechanical methane potential (BMP) tests to evaluate the effect of volumetric FOG/HSW loading on the performance of co-digestion. - Phase II - An extended trial with six semi-continuous bench scale digesters operated to investigate the impacts of single-phase compared to two-phase digestion under a range of loading conditions for municipal sludge and FOG/HSW. Phase I â€“ BMP Testing Biochemical methane potential tests (BMP) tests were performed with feed collected from FWHWRC to evaluate the effect of volumetric FOG/HSW loading on the performance of co-digestion. One of the main goals of this approach was to determine the FOG/HSW loading at which methane production could be impacted and to identify bottlenecks that cause the limitation. BMP tests were performed with 5-20% FOG/HSW feed by volume for co-digestion and compared against control BMP tests without FOG/HSW addition. Methane yields increased from 0.25 L/g VS for the control tests to >0.4 L/g VS for tests where FOG/HSW was added at 10% of the feed volume. As can be seen in Figure 1, higher FOG/HSW additions led to significant lag phases in methane production, even though the eventual methane yields were higher than the control. Analysis of long-chain fatty acids (LCFAs) and short-chain fatty acids (SCFAs) showed that palmitic and stearic acids accumulated under higher FOG/HSW volumetric loadings as shown in Figure 2, and concurrent observation of a lack of acetate accumulation suggests that the bottleneck in inhibited digesters co-digesting FOG/HSW with sludge is likely to be the conversion of LCFAs to acetate and not direct complete inhibition of methanogenesis. These results also provide an indication that for adopting two-phase AD, it would be critical to ensure the conversion of LCFAs to acetate in the acidogenic phase. Phase II â€“ Bench Scale Digester Trials Six semi-continuously fed digesters â€“ R1 through R6 â€“ were set up and operated in the laboratory for a duration of 300 days. Two digesters, R1 and R2, served as controls, with R1 representing a non-co-digesting single-phase digester, and R2 a co-digesting single-phase digester. R3 and R4 represented a two-phase system with no FOG/HSW addition, while R5 and R6 represent a two-phase system with FOG/HSW addition. Full details of the reactor configurations, operating conditions and results from microbial community analysis will be provided in the final paper.
Key Outcomes The results from operating these six digesters over a series of conditions including various FOG/HSW loadings, SRTs, and buffering regimes, provided several key observations:
1. Two-phase AD was found to provide no added benefits in increasing solids handling or methane production when not co-digesting FOG/HSW. This is contrary to the argument that two-phase AD provides kinetic advantages for acidogenesis and methanogenesis and could here be a result of thermodynamic limitations governing overall methane yields and thus COD and solids reduction.
2. Successful co-digestion, even in single-phase operation, as currently practiced at FWHWRC, required operating conditions (particularly pH) that support a microbial community that allows for the conversion of LCFAs such as palmitic and stearic acids to acetate, and further to methane. Although it is common to classify co-digestion performance for a given FOG/HSW loading, this observation along with the results from the BMP tests supports the use of LCFA concentrations as a more accurate parameter to classify FOG/HSW loading with.
3. Two-phase AD with co-digestion failed to achieve the desired outcome because of a lack of LCFA conversion in the acidogenic phase. This is because the low pH in acidogenic digesters likely inhibited the growth of syntrophic bacteria responsible for beta-oxidation of LCFAs. Considering the above results, it was concluded that two-phase AD, especially, when co-digesting with FOG/HSW provides no notable advantage over single phase digestion. One additional benefit of the study was a deeper understanding of factors that affect successful co-digestion with FOG/HSW in single-phase operation. Most plants that incorporate co-digestion with FOG/HSW do not have set metrics for how much FOG/HSW loading is acceptable. We identified here the components of FOG/HSW, viz., LCFAs, and particularly individual LCFAs such as palmitic and stearic acid, which we recommend be tracked in full-scale digesters to ensure optimum performance during co-digestion with FOG. Such tracking at a regular frequency of 1-2 times per SRT using techniques described in this report would allow identifying overloaded conditions well in advance of deteriorating digester performance and could signal the need for operational adjustments that would allow syntrophic LCFA degrading bacteria to grow and thrive in the digesters. In addition to further results from the BMP testing, the final paper will provide full results from the bench scale digester trials including methane production, COD and VS conversion, pH, VFA and LCFA concentrations. This will be supplemented by analysis of the microbial community undertaken using 16s rRNA sequencing which led to a deeper understanding of the role of microorganisms involved and the impact of operating conditions on the requirements for LCFA conversion.
Learning Outcomes: This paper will provide valuable information for utilities who are considering or currently operating co-digestion with FOG/HSW in either a single-phase or two-phase configuration. In particular, the improved understanding of the operational impact of LCFA conversion (or lack thereof) and the conditions required to achieve this provides a useful insight into the underlying mechanisms of digester operating issues that may be experienced by utilities. The poor performance of two-phase digestion with FOG/HSW could be critical information for utilities who are potentially considering this solution for co-digestion systems.

The F. Wayne Hill Water Resources Center (FWHWRC) in Gwinnett County, GA, uses mesophilic anaerobic digesters for sludge stabilization and receives high-strength waste (FOG) that is co-digested with sludge. The purpose of this study was to evaluate the potential transitioning of the current digesters into two-phase anaerobic digesters, to determine if lower solids retention times (SRT), and thus a possible increase in the solids handling capacity of the plant could be achieved.

SpeakerRam Mohan, Gayathri

Presentation time

13:55:00

14:05:00

Session time

13:30:00

15:00:00

TopicIntermediate Level, Biosolids and Residuals, Energy Production, Conservation, and Management, Research and Innovation

Author(s)

Ram Mohan, Gayathri

Author(s)Gayathri Ram Mohan1; Greg J. Knight2; Sudeep Popat3; Julia Ann Funk3; Jessica Deaver3

Author affiliation(s)Hazen and Sawyer, Atlanta, GA1; Black & Veatch, Atlanta, GA2; Clemson University, Clemson, SC3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2022

DOI10.2175/193864718825158616

Volume / Issue

Content sourceWEFTEC

Word count25

Description: Innovative Carbon-based Advanced Treatment in Action: Unveiling Key Lessons Learned...

Innovative Carbon-based Advanced Treatment in Action: Unveiling Key Lessons Learned from Pilot Demonstrations

Abstract

Introduction
As population growth, urbanization, and climate change place burdens on existing water supplies, water resource recovery facilities (WRRFs) are required to meet increasingly stringent discharge requirements, that are beyond the capabilities of conventional treatment, prompting the adoption of advanced treatment. In parallel, utilities are increasingly faced with low quality and limited quantity of potable water supplies. Recovery and reuse of treated wastewater effluent (i.e., water reuse) has emerged as a key strategy for meeting future water demand and water management needs. Treatment to achieve reuse requirements and/or nutrient reductions can be achieved using membrane based advanced treatment (mBAT), e.g., reverse osmosis; however, mBAT can be capitally and energetically intensive. Alternative carbon-based advanced treatment (CBAT) schemes employing multiple processes like coagulation/flocculation/sedimentation, ozonation, biofiltration and granular activated carbon (GAC) continue to be explored as an alternative to mBAT since they can reduce capital costs and energy requirements. However, data documenting the ability of these alternative treatment trains to concurrently and effectively remove organics, nutrients, and CECs to meet stringent treated water targets is limited. This work showcases two distinct case studies that demonstrate the effective removal of organics, nutrients, and CECs through the integration of multiple unit processes within multi-barrier CBAT trains. The following are some key learning objectives:
Treatment Process Requirements to achieve specific end-use goals in two distinct cases: a drinking water and a wastewater perspective.
Comparison of Organic and Contaminants of Emerging Concerns (CECs) Removal Performance: Understand capability of a CBAT train to concurrently treat and remove organics and CECs.
Summary of key lessons learned from each study to offer insights and guidance for future full-scale implementations.

Materials and methods
Case study 1
A CBAT train was piloted downstream of a WRRF in Tennessee to meet multiple fit-for-purpose objectives, that were primarily driven by a need to treat the wastewater effluent to meet stringent nutrient standards. This objective aligned well and paved path for other applications such as river and reservoir augmentation. The WRRF employed a three-stage biological nutrient removal (BNR) configuration with denitrification filters. The CBAT train (Figure 1) consists of membrane filtration (Suez ZW500D, Veolia, Boston, MA), ozonation (Intuitech Z400), Intuitech F1200 filtration unit filled with acclimated GAC media (F820) for BAC filtration, and Calgon GAC skid filled with Filtrasorb 300 (F300) type media. The membrane filtration unit was installed to remove total suspended solids (TSS) and simulate the performance of a full scale MBR system. The Ozone skid (Z400) included two, over-under baffled ozone contactors with a nominal hydraulic retention time of 20 minutes each. The F1200 BAC filters were operated in aerobic and anoxic modes to investigate the impacts on nitrogen removal. The pilot was operated for 9 months.

Case study 2
In this study, a CBAT train was piloted for 6 months to evaluate the level of treatment needed to treat groundwater impacted by rapid infiltration basins with and without ozonation (Intuitech Z400) prior to carbon treatment (Intuitech F1200), as well as testing carbon in both adsorptive (GAC) and biological mode (BAC). The configuration for the CBAT is shown in Figure 2.

Results and discussion
Total organic carbon (TOC) removal. Figure 3 illustrates the evolution of TOC concentrations along the different stages of the CBAT process in Case Study 1. The TOC concentration remains relatively stable after ozonation but begins to decline remarkably after passing through the aerobic BAC and GAC, demonstrating its effectiveness in adsorbing organic compounds. Figure 4 illustrates the TOC concentration trends across multiple CBAT scenarios over time in case study 2. Across all scenarios, a general downward trend in TOC concentration is observed. Ozonation provides a moderate reduction, while BAC and GAC stages contribute further TOC removal. The GAC consistently demonstrates significant TOC adsorption capacity, helping achieve TOC levels below the treatment target. To sum up, these results underscore the multi-barrier CBAT system's ability to incrementally and effectively remove organic contaminants. Constituents of Emerging Concern (CECs. Figure 5 presents the concentrations of PFAS various PFAS compounds (e.g., PFBS, PFHxS, PFNA, PFOA, and PFOS) across different scenarios for BAC and GAC stages. The BAC effluent (Figure 6a) shows moderate removal of PFAS compounds. The GAC effluent (Figure 6b) demonstrates more substantial reductions in PFAS concentrations compared to BAC. To sum up, these results also emphasize the need for multi-stage treatment to address both short- and long-chain PFAS effectively.

This paper was presented at WEFTEC 2025, held September 27-October 1, 2025 in Chicago, Illinois.

Presentation time

13:30:00

13:45:00

Session time

13:30:00

15:00:00

SessionInnovative Carbon-Based Advanced Treatment Solutions: Transforming Water Reuse

Session locationMcCormick Place, Chicago, Illinois, USA

TopicContaminants of Emerging Concern & Trace Organics

Author(s)

Ram Mohan, Gayathri, Wang, Jiefu, Khunjar, Wendell

Author(s)G. Ram Mohan1, J. Wang2, W. Khunjar1

Author affiliation(s)Hazen and Sawyer1, Virginia Tech2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Sep 2025

DOI10.2175/193864718825160150

Volume / Issue

Content sourceWEFTEC

Word count14

Description: Optimizing Dissolved Organic Nutrient Management: Exploring Carbon-Based Advanced...

Optimizing Dissolved Organic Nutrient Management: Exploring Carbon-Based Advanced Treatment Strategies

Abstract

Introduction As population growth, urbanization, and climate change intensify pressures on water resources, utilities are faced with an increased urgency for advanced water treatment (AWT) solutions and a need to enhance resilience against evolving climatic conditions. Concurrently, wastewater resource recovery facilities (WRRFs) are faced with increasingly stringent nutrient discharge limits that surpass the capabilities of conventional treatment methods. Consequently, utilities are compelled to adopt innovative approaches to address the quality and quantity of water supplies while ensuring regulatory compliance and sustainability. In this work, we highlight case studies of two forward-thinking utilities, distinguished by geographical contexts and unique drivers, yet united by a commitment to advance climate change adaptation strategies, achieve ultra-low nutrient limits, and integrate holistic one water initiatives. Metro Water Recovery (Denver, CO): Upcoming Colorado water quality regulations are set to impose stringent stream standards, notably 2.01 mg/L for total nitrogen (TN) and 0.10 mg/L for total phosphorus (P) on WRRFs, including Metro Water Recovery's Robert W. Hite Treatment Facility (RHWTF) and Northern Treatment Plant (NTP). AWT technologies like carbon-based advanced treatment (CBAT) schemes (e.g., coagulation/flocculation/sedimentation (floc/sed), ozone (O3), biofiltration (BAF), and granular activated carbon (GAC)) may address stringent nutrient limits while also aligning with Direct Potable Reuse (DPR) requirements. A study was initiated to: 1) assess the treatability of dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and soluble non-reactive phosphorus (sNRP) using CBAT technologies; and 2) discern the capabilities of CBAT in concurrently achieving nutrient limits and DPR compliance. Evaluation of nutrient removal through tertiary CBAT processes spanned full-scale applications (floc/sed at NTP and BAF/floc/sed at RHWTF's Denver Water Recycling Plant (DWRP)) and pilot-scale (O3 only, BAF only, and O3/BAF at RHWTF), supplemented by bench-scale floc/sed (jar testing) and GAC evaluations (rapid small-scale column tests). Parameters such as O3 dose and empty bed contact times aligned with potable reuse standards. While full-scale floc/sed/filtration at NTP (Figure 1; Figure 2) and DWRP (Figure 3, Figure 4) (~20 mg/L alum) effectively managed particulate P and sNRP removal, it did not meet DOC and DON targets for Direct Potable Reuse (DPR) applications. CBAT testing showed potential for control of DOC and DON, albeit with the need for multiple potentially costly unit processes. The GAC runtime (up to 3,500 Bed Volumes for DOC and DON targets) was notably extended through enhanced upstream treatment. While floc/sed processes achieved comparable DOC and DON removal rates (up to 40% each) at the expense of elevated coagulant doses (80 mg/L Ferric chloride), O3/BAF treatments realized a modest 26% reduction in DON. Future pilot efforts aim to assess the efficacy of a comprehensive CBAT treatment train, inclusive of tertiary denitrifying BAF, to fulfill TN requirements and optimize DPR suitability. AWT Utility (Midwest): A midwest AWT utility has seen significant population growth in recent years and is estimated to double by 2040. Rapid growth and a desire improve the health of the receiving water body have urged the utility to consider alternative water supplies. Subsequently, the utility commissioned a CBAT pilot consisting of O3, two-stage BAF, GAC, and UV advanced oxidation process (UVAOP). The objective of this study was to pilot CBAT technologies to demonstrate the ability of AWT process trains to produce high quality finished water that meets stringent water quality targets. This study utilized a multi-barrier scheme of O3/two-stage BAF (aerobic/anoxic) to meet low TN limits. Filters were operated in several phases (Table 1) until effluent quality targets were met (TOC < 3 mg/L, TN < 2 mg/L, contaminants of emerging concern (CECs)- meet MCLs) and steady-state was achieved. Select operational parameters were varied during each phase and the resulting water quality surrounding the first anoxic BAF (BAF 3) is shown in Figure 8. Table 2 shows the effluent DO, nitrate (NO3-N) concentrations and corresponding % NO3-N removal achieved across each anoxic BAF. Results indicate that when supplemental carbon and upstream feed DO levels were controlled, anoxic BAF 1 established and maintained anoxic conditions and achieved NO3-N removals up to 60% with anoxic BAF 2 acting as a polishing biofilter (%NO3-N removal ~30%). When supplemental carbon and upstream DO quenching chemical doses were reduced, anoxic BAF 1 turned into a sacrificial BAF, consuming excess DO and displaying poor nitrate removals (~15%), while anoxic BAF 2 became the dominant anoxic biofilter (> 60% NO3-N removal). Piloting efforts demonstrate how a modified CBAT train may simultaneously meet low TN targets (< 2 mg/L) and produce high quality product water. Conclusion Case studies at Metro Water Recovery and a midwest AWT utility demonstrate CBAT's potential for improving finished water quality for reuse and meeting ultra-low nutrient discharge requirements. Project findings provide first guidance on how WRRFs can adjust operational setpoints using CBAT process infrastructure to meet DPR or discharge water quality requirements in ecologically sensitive and drought-prone watersheds.

This study explores carbon-based advanced treatment (CBAT) as an alternative to reverse osmosis for removing dissolved organics and nutrients. Case studies at the Franklin Water Reclamation Facility in Tennessee and the Metro Water Recovery Robert W. Hite Treatment Facility in Colorado evaluated CBAT pilots. Using various configurations, the study measured the removal efficiency of dissolved organic carbon, dissolved organic nitrogen, dissolved organic phosphorus, and total inorganic nitrogen.

SpeakerHlad, jeffrey

Presentation time

11:00:00

11:30:00

Session time

10:30:00

12:00:00

SessionAdvancements in Non-RO Treatment for IPR/DPR: Exploring Cutting-Edge Solutions

Session number530

Session locationRoom 235

TopicIntermediate Level, Microconstituents and Contaminants of Emerging Concern (Non-PFAS), Sustainability and Climate Change, Water Reuse and Reclamation

Author(s)

Hlad, jeffrey, Freedman, Daniel, Ram Mohan, Gayathri, Khunjar, Wendell, Scopp, Anna, Peterson, Eric, Rauch-Williams, Tanja, Wang, Jiefu

Author(s)J. hlad1, D. Freedman1, G. Ram Mohan2, W. Khunjar3, A. Scopp4, E. Peterson4, T. Rauch-Williams1, J. Wang5

Author affiliation(s)1Metro Water Recovery, 2Hazen and Sawyer, 3Hazen and Sawyer, VA, 4Hazen and Sawyer, 5Virginia Tech, VA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159696

Volume / Issue

Content sourceWEFTEC

Word count11

Base text size -

Ram Mohan, Gayathri

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