Viswanathan, Sudhakar

Sudhakar (Sunny) Viswanathan is Vice President at 374Water, a global cleantech, social impact company based in Durham, NC. He has a bachelors and a masters degree in environmental engineering, he is a Syracuse University alumnus with 25 years of industry experience including leadership positions at Suez and Veolia; He has authored over 35 technical papers and currently spearheads the commercialization and business development of the Supercritical Water Oxidation technology. Sunny has presented at hundreds of regional, national and international conferences.

Titles from this speaker

Adopting Emerging PFAS Destruction Technologies: The Orlando SCWO Case Study

Abstract

Motivation & Goals
The City of Orlando, Florida is a large, fastest growing, progressive, and sustainability minded community. Orlando's Water Reclamation Division of the Public Works Department provides wastewater collection and treatment services to the City's businesses and residents through the Iron Bridge Water Reclamation Facility, a 40 MGD plant, and the Conserv I Water Reclamation Facility, a 7.5 MGD plant. Currently, biosolids from each of the plants are dewatered, stabilized and hauled to land application sites or landfills for disposal. Regulations established by SB 712 restrict this practice during wet weather (when groundwater is within 2 feet of the surface), and landfills are often hesitant to accept biosolids during these periods. This has necessitated on-site dewatering and storage of sludge-a practice the City aims to minimize through the adoption of technologies that can reduce sludge volumes and eliminate reliance on land application.

As a proactive measure, the City is also seeking solutions to address contamination issues, specifically concerning per- and polyfluoroalkyl substances (PFAS), to safeguard water sources potentially impacted by biosolids disposal. After evaluating various management strategies, including composting, incineration, and drying, the City identified supercritical water oxidation (SCWO) as an innovative and cost-effective solution for both biosolids volume reduction and contaminant elimination.

The overarching project goal was to install, commission, and test a SCWO system at the City of Orlando's Iron Bridge Water Reclamation Facility. The measures of success for the project included (1) ensuring the timely preparation of the site and delivery/installation of the SCWO unit, (2) passing functional tests, and (3) continuously processing biosolids that meet volume and organics/PFAS reduction targets.

Methods
The SCWO system used converts organic-rich waste into clean vent gas and liquid effluent composed solely of water, inert inorganics and minerals. During the SCWO process, waste is heated and pressurized above the critical point of water (374°C, 221 bar), allowing it to enter a supercritical state. In this state, organics become highly soluble, facilitating the mineralization of persistent organic compounds like PFAS. The oxidation of organic matter generates energy in the form of heat, which is recycled within the process.

Samples were collected prior to influent wastewater screening, between the end of sludge handling and the SCWO system inlet, at the effluent of the SCWO unit, at the effluent of the plant's wastewater treatment process, and at the air emissions outlet of the SCWO system. At each sampling point, relevant parameters including flowrate, chemical oxygen demand, and PFAS were assessed and used to evaluate the performance. This sampling was conducted at baseline, during system startup, and at regular monthly intervals during system operation.

Results
The City received a grant from the Florida Department of Environmental Protection through the Clean Water State Revolving Fund in February 2024 for upwards of $800,000 (Table 1). After four months of site evaluation and planning, the SCWO provider mobilized the SCWO system to Orlando's Ironbridge facility and completed installation and start-up (including functional tests) within three months. At present, the SCWO system is in its third month of operation and has run multiple types of PFAS wastes including biosolids. Testing is expected to continue through February 2025 at which point an evaluation of whether to demobilize the unit or continue operation will be made (Figure 1). Results from initial PFAS testing reinforce previous research that showcase the ability of SCWO to non-selectively destroy >99% of PFAS analytes (Table 2) of different classes and chain length. Results are repeatable, as shown by data in Table 3 that was collected when treating the same PFAS waste through SCWO the following week.

Significance
This talk will explore the opportunities and challenges of conducting an on-site demonstration of emerging PFAS technologies, using the implementation of SCWO at Orlando's Ironbridge Facility as a case-study. The presentation will highlight key project enablers, including how funding was sourced, to inspire other facilities to support the adoption of emerging PFAS technologies.

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

Presentation time

11:30:00

11:45:00

Session time

10:30:00

12:00:00

SessionThermal Treatment of PFAS in Biosolids

Session locationMcCormick Place, Chicago, Illinois, USA

TopicContaminants of Emerging Concern & Trace Organics

Author(s)

Senehi, Naomi, Viswanathan, Sudhakar, Garb, David

Author(s)N. Senehi1, S. Viswanathan2, D. Garb2

Author affiliation(s)University Of California Irvine1, 374Water Inc.2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2025

DOI10.2175/193864718825160135

Volume / Issue

Content sourceWEFTEC

Word count11

Description: Case study of Pennsylvania's first net positive resource recovery facility...

Case study of Pennsylvania's first net positive resource recovery facility â€“ The Hermitage Success Story

Abstract

In the past two decades, wastewater treatment plants (WWTP) have been undergoing a dramatic transformation from solely focusing on wastewater treatment to resource recovery of valuable byproducts from waste. Utilities are increasingly realizing the benefits of biofertilizer production, nutrient recovery, energy production, and water conservation and the value it brings to the overall bottom-line for the end user. Wastewater utilities are also uniquely positioned to bridge the demands of renewable energy production as well as reducing organic solid waste from ending up in landfill, both regulated in many states in the US. The US EPA has identified more than 1,300 facilities in the US that rely on anaerobic digestion to reduce organics from wastewater, however, per the American Biogas Council, an estimated 40% of all anaerobic digesters in the US are being underutilized. Digesters with excess capacity are energy sinks, requiring just as much heat and electricity when operated at under capacity as they do while fully optimized, but with very little return in the form of energy production (as biogas). This unused digester capacity can be utilized to anaerobically codigest landfill diverted organics to produce biogas, which in turn can be converted to biomethane or heat and electricity using a combined heat and power system. Increased biogas production is just one of the many benefits of introducing high strength biodegradable wastes from commercial and industrial establishments into municipal anaerobic digestion systems. Digestion systems can also be designed to produce Class A or exceptional value (EQ) biosolids that is returned to the market as biofertilizer or soil amendment. In anticipation of an upgrade from 5.0 to 7.7 MGD, Hermitage Municipal Authority in Pennsylvania undertook a major upgrade of their solids handling facility to increase treatment capacity. The facility only has secondary treatment, meaning there is no easy-to-digest, high calorific value primary sludge as a feed to the new anaerobic digesters. As part of the upgrade, one of the goals was to boost biogas generation and use it as the primary fuel in a combined heat and power (CHP) cogeneration system to offset process heat and generate renewable electricity. This lead to a solids management plan specifically design to address high strength codigestion of source separated organic (SSO) wastes imported to the facility, mostly focused on pre-consumer expired or contaminated food waste, all while still able to produce a US EPA approved Class A biofertilizer. A new two phased digestion system was built using two existing anaerobic concrete tanks on site and one new steel tank. This system includes a first stage thermophilic hydrolysis reactor to acidify high strength waste, followed by high rate mesophilic digesters. A new biogas collection and treatment system and a combined heat and power unit was installed. Subsequently, a second CHP system was installed to maximize biogas utilization with minimal downtime. A new depackaging system, capable of handling dairy/liquid waste was included as part of this initial upgrade. This limited use process justified the needs of the time since only one regional dairy had agreed to divert their pre-packaged, expired dairy waste to the wastewater plant for organics recovery. Subsequently, a second depackaging system was installed to widen the imported source separated organics profile, specifically to include the capabilities to extract organics from various packaged solid food waste. The design of the facility also include a staging area to receive imported packaged organic waste from grocers, large food manufacturers, dairy and other organic waste generators. More recently, a new innovative depackaging process was installed to improve organics removal efficiencies, reduce contaminant level in extracted organic slurry, and manage increased throughput of imported waste at the facility. The three depackaging units are now capable of handling both solids and liquid waste effectively. Since January of 2013, the facility has grown from having just one dedicated organics waste supplier to now receiving food waste from over a dozen major sources. The facility has since processed over 8,000 dry tons of solid waste and over 12 million gallons of high strength liquid waste. The facility utilizes a custom organics feed staging strategy in the advanced anaerobic digestion system, that allows an applied organics loading rate (OLR) in excess of 12 kg/m3 (0.75 lb/ft3) in the first stage thermophilic acid digester. The second stage mesophilic gas digester is fed at a rate of 3 kg/m3 (0.19 lb/ft3), which is typical of conventional digesters, but is capable of higher OLR input. The phased digester feed is a combination of secondary municipal sludge and depackaged organic high strength slurry, in some instances pre-heated prior to introducing it to the thermophilic digesters. The organics loading ratio on a mass basis for municipal sludge to imported waste ranges between 1 to 0.6 and 1 to 1, with 20 tons of municipal sludge for every 12 to 20 tons of organic slurry. The phased digestion system is a US EPA's Process to Further Reduce Pathogens (PFRP) equivalent process, designed to achieve Class A biofertilizers as the final product. The current bioenergy system is capable of treating over 125,000 cubic feet of biogas and generates up to 13,400 kilowatts hour of power. The goal is to convert the biogas into compressed natural gas (CNG) to capitalize on the renewable energy credits to improve the cities renewable energy portfolio. In addition to increasing the bioenergy and biofertilizer production, the authority collects tipping fees from food waste generators that offsets ratepayer contributions. Renewable bioenergy production using landfill diverted organics all occurs within this resource recovery facility. This synergistic approach will benefit the solid waste industry from having to find new ways to manage organic food waste, the energy industry from having to build new renewable energy facilities, and most critically the wastewater industry in maximizing existing infrastructure to produce biofertilizer, recovery nutrients, produce bioenergy, and conserve water all while generating revenue from tipping fees. The paper offers a concise methodology that illustrates this synergetic approach to a growing problem. The paper aims to cover the nuances of source separated organics pretreatment, anaerobic codigestion and related processes.

The following conference paper was presented at Residuals and Biosolids 2021: A Virtual Event, May 11-13, 2021.

SpeakerViswanathan, Sudhakar

Presentation time

11:30:00

11:45:00

Session time

11:00:00

12:15:00

SessionOptimizing Digestion and Co-Digestion

Session number3

Session locationSimu-Live

Topicanaerobic co-digestion, biomethane, lipids/proteins/carbohydrates ratio, TWAS, Manure, SSO, business case evaluation, food waste

Author(s)

S. ViswanathanT. DarbyJ. Wert

Author(s)S. Viswanathan1; T. Darby2; J. Wert3

Author affiliation(s)Veolia Water Technologies 1; City of Hermitage 2; Rettew 3;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2021

DOI10.2175/193864718825157953

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count16

Description: PFAS Elimination Rates in Sludge, Ion Exchange Resin, and Aqueous Film Forming Foam...

PFAS Elimination Rates in Sludge, Ion Exchange Resin, and Aqueous Film Forming Foam Using Supercritical Water Oxidation: A Quantitative Review

Abstract

Rising concern of Perfluorinated alkylated substances (PFAS) contamination of our ecosystem has sparked interest in this class of pollutants as it pertains to water and waste management. While PFAS sources are numerous, it is widely believed that firefighting foam and extensive industrial uses are common pathways for PFAS compounds to proliferate into our ecosystem. In an attempt to better understand the fate and transport of PFAS compounds undergoing supercritical water oxidation (SCWO), a one (1) wet ton per day scale SCWO system was employed to study the treatment efficiencies of this process. There is a pressing need to develop and validate advanced treatment technologies that can destroy PFAS in a variety of substrates. In this paper, we report on how three distinct PFAS containing wastes from three different sources were treated using SCWO process. The waste includes lime stabilized sludge from a municipal wastewater resource recovery facility; aqueous film forming foam (AFFF) from a DoD facility; and spent ion exchange resin from a ‘pump and treat’ water treatment facility. Supercritical water oxidation or SCWO for short, is a physicalthermal process that relies on the unique reactivity and transport properties of water above its critical point of 374 °C and 218 atm. At these conditions, organic compounds and oxygen are highly soluble and often completely miscible in supercritical water (Phillip E. Savage 1999), and with the addition of oxygen, they rapidly and completely oxidized to form carbon dioxide, clean water, and inorganic salts (Thomason, T.B. et al., 1984)( Marrone, P.A. et al., 2004). The studies examined a variety of PFAS compounds, both targeted and non-targeted, but most specifically focused on PFOA and PFOS. These two compounds are the most studied PFAS compounds, they are highly toxic and most commonly detected in our ecosystem (McCarthy, C. et al., 2017). SCWO, on average, was able to eliminate 99.95% of PFOA and 99.99% of PFOS across all waste substrates, and greater than 99.9% elimination of all other PFAS compounds combined. Non-targeted PFAS were accounted for using laboratory scale verification tests by employing fluorine mass balance. No hydrogen fluoride was found in the effluent gas, and all the fluorine from the destroyed PFAS was accounted for as fluoride in the effluent water, with no low molecular weight or volatile PFAS compounds in the emission. This paper will cover the pre-treatment, pre-preparation and supercritical water oxidation requirements for the various waste inputs to ensure complete destruction of recalcitrant wastes without producing any undesired byproducts. The studies produced valuable data and design parameters to support design and deployment of SCWO for real world applications.

This paper details the use of a 3rd generation supercritical water oxidation (AirSCWO) system for the elimination of recalcitrant wastes like PFAS sequestered within sludge, adsorbed on ion exchange resin, and as a major ingredient of synthetic Class B aqueous film forming foam (AFFF). The study shows that waste destruction is possible without producing any undesired byproducts. The studies produced valuable data to support design and deployment of full-scale application.

SpeakerViswanathan, Sudhakar

Presentation time

14:00:00

14:20:00

Session time

13:30:00

15:00:00

SessionBehavior of Emerging Contaminants in Thermal Treatment Processes

Session locationRoom S503 - Level 5

TopicIntermediate Level, Microconstituents and Contaminants of Emerging Concern (Non-PFAS), PFAS

Author(s)

Viswanathan, Sudhakar

Author(s)S. Viswanathan 1; S. Viswanathan 1 ; K. Nagar 3; S. Viswanathan 1;

Author affiliation(s)374Water 1; 374Water 1 ; 374Water 3; 374Water 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159082

Volume / Issue

Content sourceWEFTEC

Word count21

Description: Quantifying Supercritical Water Oxidation Efficiency Treating PFAS Laden Sludge, Ion...

Quantifying Supercritical Water Oxidation Efficiency Treating PFAS Laden Sludge, Ion Exchange Resin and Aqueous Film Forming Foam

Abstract

Abstract Rising concern of Perfluorinated alkylated substances (PFAS) contamination of our ecosystem has sparked interest in this pollutant as it pertains to water and waste management. While PFAS sources are numerous, it is widely believed that firefighting foam and extensive industrial uses are common pathways for PFAS compounds to proliferate into our ecosystem. In an attempt to better understand the fate and transport of PFAS compounds undergoing supercritical water oxidation (SCWO), a one (1) wet ton per day scale SCWO system was employed to study the elimination efficiencies of this process. There is a pressing need to develop and validate advanced treatment technologies that can destroy PFAS in a variety of substrates. In this paper, we report on how three distinct PFAS waste substrates from three different sources were treated using SCWO process. The waste includes lime stabilized sludge from a municipal wastewater resource recovery facility; aqueous film forming foam (AFFF) from a DoD facility; and spent ion exchange resin from a 'pump and treat' water treatment facility. Supercritical water oxidation or SCWO for short, is a physical-thermal process that relies on the unique reactivity and transport properties of water above its critical point of 374 °C and 218 atm. At these conditions, organics are fully soluble in supercritical water, and with the addition of oxygen, all organics rapidly and completely oxidized to form carbon dioxide, clean water, and inorganic salts. The studies examined a variety of PFAS compounds, both targeted and non-targeted, but most specifically focused on PFOA and PFOS. These two compounds are the most studied PFAS compounds, they are highly toxic and most prolific in our ecosystem. SCWO, on average, was able to eliminate 99.95% of PFOA and 99.99% of PFOS across all waste substrates, and greater than 99.9% elimination of all other PFAS compounds combined. Non-targeted PFAS was accounted for using laboratory scale verification tests by employing fluorine mass balance. No hydrogen fluoride was found in the effluent gas, and all the fluorine from the destroyed PFAS was accounted for as fluoride in the effluent water, with no low molecular weight or volatile PFAS compounds in the emission. This paper will cover the pre-treatment, pre-preparation and supercritical water oxidation requirements for the various waste inputs to ensure complete destruction of recalcitrant wastes without producing any undesired byproducts. The studies produced valuable data and design parameters to support design and deployment of SCWO for real world applications. Introduction - Section removed to fit 9,000 character count - Material and Method An AirSCWO 1 system was used for these studies, this system is the smallest in scale, and designed to continuously treat aqueous waste of about 1 m3 or 1 wet ton of sludge at 10-20% dry solids content per day (Figure 2). The system consists of a 25-gallon feed hopper integrated with a homogenization tank with internal recirculation to keep the slurry in suspension. A high-pressure pump transfers the homogenized waste to the SCWO reactor via a heat exchanger, to preheat the incoming slurry. A high-pressure compressor provides air, also preheated using a heat exchanger, followed by a plug flow once through SCWO reactor. Three cooling heat exchangers and depressurizing equipment bring the outputs to near ambient conditions. For treatability studies, a minimum of 5 gallons is required for a representative run, but larger volumes of wastes are needed to simulate real world operating conditions. A typical run lasts about 12-36 hours, during which the process operates at different conditions, until steady state performance is established, at which point samples of all effluents (liquid, gaseous, solids) are collected and analyzed to determine treatment performance, including fate of N, P, organics and key metals. Most operating parameters are monitored in real time while others, such as trace and emerging contaminants are analyzed off-line using grab sampling. Process operating parameters were monitored for energy balances and energy recovery, these data are used to develop detailed modeling for scaled systems. In an effort to demonstrate the efficacy of SCWO for PFAS elimination for varied input slurries, three wastes from three different sources were selected for the studies. The three wastes are (i) municipal wastewater sludge, which was stabilized using lime but contained high concentrations of PFAS; (ii) full strength aqueous film forming foam (AFFF) and (iii) ion exchange (IX) resin from a pump and treat system, which is sequestering PFAS compounds in the adsorption media. These wastes all pose different challenges, for example, the need for AFFF to be diluted, making it calorie poor and requiring cofuel; or IX wastes being generated once every 6 months or so, requiring the waste to be stored and processed over the period between changes. Results The first study was treating PFAS laden lime stabilized sludge, results for which show that greater than 99% conversion of Chemical Oxygen Demand (COD) to energy, and elimination of 99.95% for PFOA and 99.99% for PFOS. Table 1 shows that the removal across all carboxylic acid (PFCAs) compounds was greater than 99.9%, and across all sulfonic acid (PFSA's) compounds was greater than 99.99%. This waste had no detectable precursors and SCWO demonstrated excellent elimination rates for short chained (6 Carbon and less) PFAS compounds. The process achieved greater than 99.99% elimination across other 24 derivatives of PFAS found in the sludge. In this study, PFOS was the predominant compound and constituted 88% of the influent PFAS but only 3% of the effluent concentration. In the second study, the AirSCWOTM process treated AFFF, diluted down to about 30 times. About 25 L of dilute AFFF was processed (Krause, M. et al., 2022), only 9 compounds of the 28 analyzed were detected in the influent. PFOS was reduced over 99.99%, and PFOA nearly complete at 100%. Table 2 shows that the removal across all carboxylic acid (PFCAs) compounds was greater than 99.9%, and across all sulfonic acid (PFSA's) compounds was greater than 99.99%. This waste had detectable precursors and greater than 99.9% removal was achieved. Greater than 99.99% elimination rates were demonstrated for short chained PFAS compounds. Total targeted PFAS elimination was established at 99.99% over the course of the experiment. In this study, PFOS was again the predominant compound, and constituted 72% of the influent PFAS and 45% of the effluent concentration. The third study was a demonstration aiming to process spent ion exchange resin, a waste byproduct of water treatment, specifically targeting PFAS compounds. The results from the study treating IX demonstrated that PFOS was reduced over 98%, and PFOA nearly complete at 100%. Table 3 shows that the removal across all carboxylic acid (PFCAs) compounds was greater than 99.9%, and across all sulfonic acid (PFSA's) compounds was greater than 99%. This waste had detectable precursors and nearly 99% removal was achieved. Greater than 99.9% elimination rates were demonstrated for short chained PFAS compounds . Total targeted PFAS elimination was greater than 99.5% over the course of the experiment. In this study, both PFHXS and PFOS were the predominant compounds, and constituted 71% of the influent PFAS and 90% of the effluent concentration. The reactor residence time within the SCWO reactor ranged between 68 seconds for all the studies. Greater destruction of PFAS can be achieved by extending the reaction time (e.g., to greater than 10 seconds) to the desired log-reduction of specific PFAS compounds, especially in highly concentrated wastes such as aqueous film forming foam and ion exchange. The non-targeted PFAS elimination was verified at laboratory scale at Duke University by employing fluorine mass balance. No hydrogen fluoride was found in the effluent gas, and all the fluorine from the destroyed PFAS was accounted for as fluoride in the effluent water with no low molecular weight or volatile PFAS emission. (Deshusses, M.A., 2020) Summary As the studies demonstrate, supercritical water oxidation using the AirSCWOTM system can be effectively and efficiently utilized to achieve near complete PFAS elimination in various PFAS contaminated substrates, rendering the process outputs - i.e., water and air free of contaminants. Other studies involving aqueous slurries including pharmaceuticals, PFAS concentrates and microplastic have been successfully treated using AirSCWOTM, demonstrating the versatility of the process to treat and eliminate recalcitrant wastes. With full scale units being implemented, these studies offer valuable insights to further optimize the process and achieve even greater performance and cost effectiveness.

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

SpeakerViswanathan, Sudhakar

Presentation time

8:30:00

9:00:00

Session time

8:30:00

11:45:00

SessionSession 10: PFAS Challenges and Treatment

Session number10

Session locationCharlotte Convention Center, Charlotte, North Carolina, USA

TopicEmerging Issues (PFAS, Microplastics, Covid, etc.)

Author(s)

S. Viswanathan

Author(s)S. Viswanathan1, M. Deshusses2, D. Hatler3, K. Nagar4,

Author affiliation(s)374Water Inc.1; Duke University;2; 374Water Inc.3

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2023

DOI10.2175/193864718825158774

Volume / Issue

Content sourceResiduals and Biosolids

Word count18

Description: Regional Supercritical Water Oxidation Facility for PFAS-laden Industrial...

Regional Supercritical Water Oxidation Facility for PFAS-laden Industrial Pretreatment Wastes

Abstract

A regional super critical water oxidation (SCWO) facility has the potential to provide an economically viable, energy-neutral destruction alternative for per- and polyfluoroalkyl substances (PFAS) able to accept multiple concentrated waste streams. SCWO is a physicalthermal process capable of destroying PFAS with the ability to capture energy from the destruction process for energy production, providing the opportunity to turn PFAS destruction from a huge user of electricity to an energy-neutral or even energy-positive endeavor. Energy production is fueled by high-energy waste streams, which could include granular activated carbon (GAC) media, and anion exchange resins (AER), and biosolids. This desktop study outlines conceptual design and economic analysis for regional SCWO infrastructure to handle spent media and foamate from industrial pretreatment systems.

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

SpeakerLing, Alison

Presentation time

08:35:00

09:05:00

Session time

08:30:00

10:00:00

SessionApproaches to PFAS Destruction and Centralized Treatment

Session locationRoom S401d - Level 4

TopicPFAS

Author(s)

Ling, Alison

Author(s)A. Ling 1; A. McCabe 2 ; D. Garb 3; S. Viswanathan 4;

Author affiliation(s)Department of Civil Engineering, University of St. Thomas 1; Barr Engineering 2 ; 374Water 3; 374Water 4;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159143

Volume / Issue

Content sourceWEFTEC

Word count11

Description: SCWO for Orlando: A Case Study on Commissioning Supercritical Water Oxidation for...

SCWO for Orlando: A Case Study on Commissioning Supercritical Water Oxidation for the Treatment of Biosolids to Eliminate PFAS and Reduce Reliance on Biosolids Land Application

Abstract

The City of Orlando, Florida is home to 312,000 people and is one of the fastest growing cities in the U.S. The City is recognized as a progressive, sustainability minded community and has a Water Reclamation Division of the Public Works Department that provides wastewater collection and treatment services to the City's businesses and residents. The Water Reclamation System has historically been divided into the easterly and westerly subsystems. The easterly subsystem is served by the Iron Bridge Water Reclamation Facility, a 40 million gallon per day ('MGD') plant, and the Conserv I Water Reclamation Facility, a 7.5 MGD plant. The westerly subsystem is served by the Conserv II Water Reclamation Facility, a 25 MGD plant. Currently, biosolids from each of the plants are dewatered, stabilized and hauled to land application sites or landfills for disposal. Due to concerns of nutrient contamination of both surface and groundwaters, regulations established by SB 712 restrict this practice during wet weather. Presently, biosolids cannot be applied to land when groundwater is within 2 feet of the surface, and landfills are often hesitant to accept biosolids during these periods. Considering Florida's seasonal pattern of thunderstorm activity and exposure to tropical weather, this happens with regularity, necessitating on-site dewatering and storage of sludge-a practice the City aims to minimize through the adoption of technologies that can reduce sludge volumes and eliminate reliance on land application. As a proactive measure, the City is also seeking solutions to address contamination issues, specifically concerning per- and polyfluoroalkyl substances (PFAS), to safeguard water sources potentially impacted by biosolid disposal. After evaluating various management strategies, including composting, incineration, and drying, the City identified supercritical water oxidation (SCWO) as an innovative and cost-effective solution for both biosolids volume reduction and contaminant elimination. With support from the Bipartisan Infrastructure Law emerging contaminant funding, the City received a grant from the Florida Department of Environmental Protection (FDEP) through the Clean Water State Revolving Fund to pilot test a SCWO system capable of processing 6 wet tons of biosolids per day developed by the technology provider 374Water. If the pilot test proves to be successful, FDEP has committed to provide an additional grant to the City for the purchase and installation of a 30 ton per day unit at the City's Conserv I plant. SCWO is a waste treatment technique that converts organic-rich waste into clean vent gas and liquid effluent composed solely of water, inert inorganics and minerals. During the SCWO process, waste is heated and pressurized above the critical point of water (374°C, 221 bar), allowing it to enter a supercritical state. In this state, organics become highly soluble, facilitating the mineralization of persistent compounds like PFAS. The oxidation of organic matter generates energy in the form of heat, which is recycled within the process. The outcome is a treatment technology that transforms biosolids into a contaminant-free, mineral-rich effluent and clean vent gas. 374Water's AirSCWO system utilizes ambient air to supply oxygen, enhancing oxidation efficiency while reducing costs and risks associated with the handling of compressed gases such as pure oxygen or hydrogen peroxide. Its innovative reactor design promotes high velocity to prevent clogging, enhances corrosion protection, and allows for a more compact system. Additionally, the modular, containerized design fits within a 40-foot shipping container, ensuring safety and ease of transport and installation. Pilot-scale demonstrations and numerous lab-scale studies have confirmed AirSCWO's capability to eliminate emerging contaminants like PFAS with over 99.9% efficiency, generating no harmful by-products in the liquid effluent or vent gas. These advancements provide confidence that 374Water's technology is well-suited to meet the biosolids management goals of Orlando's Iron Bridge Water Reclamation Facility. The overarching project goal was to install, commission, and test one of 374Water's AirSCWO 6 units at the City of Orlando's Iron Bridge Water Reclamation Facility. The measures of success for the project included (1) ensuring the timely preparation of the site and delivery/installation of the AirSCWO 6 unit, (2) passing functional tests, and (3) continuously processing biosolids that meet volume and organics/PFAS reduction targets. To do so, samples were collected prior to influent wastewater screening, between the end of sludge handling and the AirSCWO 6 inlet, at the effluent of the AirSCWO 6 unit, and at the effluent of the wastewater treatment process (see Figure 1). At each sampling point, relevant parameters including flowrate, chemical oxygen demand, and PFAS (via EPA Method 1633) were assessed and used to evaluate the performance. The extensive sampling plan (Table 1) included baseline testing, system startup testing, and monthly testing. This presentation will explore the opportunities and challenges of conducting an on-site demonstration of an emerging technology, using the implementation of 374Water's AirSCWO 6 at the City of Orlando's Iron Bridge Water Reclamation Facility as a case-study. The discussion will outline the project's background, the City's motivations and planning processes, as well as expectations, risk analysis/mitigation strategies, timelines, and budgeting. 374Water will provide updates on progress toward meeting project goals, address past, present, and upcoming risks, and offer insights on navigating flexible timelines to ensure the successful commercialization of new technologies.

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

SpeakerSenehi, Naomi

Presentation time

10:15:00

10:35:00

Session time

10:15:00

11:45:00

SessionAdvanced Thermal Processes for Sustainable Biosolids Management: Case Studies and Innovations

Session number25

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicBiosolids treatment, business case evaluation, Hydrothermal Liquefaction, Innovative Technology, PFAS/Emerging Contaminants, Sludge treatment

Author(s)

Senehi, Naomi, Viswanathan, Sudhakar, Saba, Matt, Schlageter, Jackie, Suits, Daniel, Oyler, Alan

Author(s)N. Senehi1, S. Viswanathan1, M. Saba1, J. Schlageter1, D. Suits1, A. Oyler2

Author affiliation(s)374Water, 1The City of Orlando, 2

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159747

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count27

Spent Media Management Options for Industrial PFAS Treatment Applications

Abstract

Introduction Many municipal WRRFs are evaluating upstream per- and polyfluoroalkyl substance (PFAS) sources and requiring industrial pretreatment in response to regulatory drivers and public scrutiny. While the technology space for PFAS separation and destruction is experiencing rapid acceleration in development and scale-up, the gold standard for removing both long- and short-chain PFAS removal from water remains sorption media and ion exchange due to high achievable effluent water quality and concentration factors. Several good reviews have highlighted design and operation considerations for sorption and ion exchange removal of PFAS (1—5). In addition, other reviews have addressed the growing suite of PFAS destruction technologies available (6—8). However, there is a lack of targeted guidance for how facilities can manage spent media and incorporate operational considerations into facility design. Most spent media is currently routed to disposal via either landfilling, hazardous waste incineration, or GAC reactivation, but emerging technologies have the potential to reduce costs and energy usage associated with media management. Objective and Significance This project addresses this gap by outlining status and outlook for spent media disposal options, including their full management pathway, design and planning considerations, and comparative energy usage of each option. With the increasing implementation of PFAS removal in industrial wastewater systems, this will support planning and decision making both for existing and future treatment systems. Figure 1 illustrates different pathways currently available or expected to be available in the near future, while Table 1 presents a comparison of different spent media management options. Results Options to regenerate media onsite include regenerable ion exchange resin or GAC. Onsite regeneration removes PFAS from media in place, producing a concentrated PFAS waste stream that can be destroyed using any number of offsite or onsite liquid destruction technologies (Figure 1). Thus, onsite media regeneration as a system acts as a liquid-liquid concentration step comparable to reverse osmosis or foam fractionation. IX media specifically designed for regeneration has been developed for PFAS. This resin can be regenerated onsite using brine and solvent, then returned to service. Regeneration cycles need to occur more often than changeout for single-use resins, due to lower PFAS removal capacity. Regenerable resin significantly reduces the volume of waste generated requiring disposal. When PFAS concentrations are in the low ppb and operational timeframes for remediation are 10 years or longer, regenerable resin often makes economic sense and should be considered. While regenerable ion exchange is most effective with specific, regenerable media, GAC regeneration can be implemented with standard bituminous carbon and thus can be retrofit into an existing GAC treatment system. Revive Environmental's GAC RENEWTM technology enables on-site GAC regeneration that optimizes for time, resources, and energy. This technology utilizes extraction-based, non-thermal technology to further concentrate and destroy PFAS in GAC used to treat groundwater and drinking water. Offsite thermal GAC reactivation is commercially available, with regional facilities operated by GAC vendors. Thermally reactivated GAC has demonstrated comparable PFAS removal performance to virgin GAC when returned to the same site for reuse (3). GAC reactivation facilities typically only enter site-specific reactivation contracts with facilities exceeding 80,000 pounds carbon per changeout, so effective use of thermal reactivation is limited to large facilities (at least 1-5 MGD, depending on concentrations and water quality). This option also requires transportation to and from the facility. Existing disposal options for single-use media include landfilling and hazardous waste incineration. Landfilling has the issue of not destroying PFAS and serving as a medium-term sink and source of PFAS. The ability of hazardous waste incineration to fully defluorinate PFAS remains uncertain, and its ongoing use for PFAS disposal is challenged by regulatory uncertainty and limited capacity. An alternate disposal option for single-use media is supercritical water oxidation (SCWO), which has demonstrated high destruction efficiencies (9). Disposal of spent media via SCWO also carries the potential for significant energy recovery, as both GAC and IX resin are high-energy feedstocks and current operating data suggests that ongoing operation would not require external fuel. Table 2 summarizes initial estimates for energy use and costs for options presented above. GAC regeneration offers lower operating costs per mass of media regenerated or changed out than single-use media options with offsite disposal, but potential savings will depend on how regeneration frequencies compare to changeout and disposal frequencies. When considering life-cycle energy usage, the energy used to produce virgin carbon to replace single-use GAC systems is the most significant factor. Site-specific factors that influence which management options are most practical include facility size and location, influent water quality, and type of media used (if already determined).

This work addresses industrial wastewater facilities treating PFAS and summarizes status and outlook for spent media disposal options, including technology readiness levels, energy usage, and operating costs. Onsite IX and GAC regeneration options have the potential to significantly reduce operating costs, especially in high-concentrations applications. Supercritical water oxidation (SCWO) is an emerging offsite management option with the potential to be energy neutral or positive.

SpeakerLing, Alison

Presentation time

16:30:00

17:00:00

Session time

15:30:00

17:00:00

SessionRevolutionizing PFAS Treatment: Harnessing the Power of Media Technologies

Session number230

Session locationRoom 338

TopicIntermediate Level, Microconstituents and Contaminants of Emerging Concern (Non-PFAS), PFAS, Research and Innovation

Author(s)