Viswanathan, Sudhakar

Sudhakar (Sunny) Viswanathan is Vice President at 374Water, a global cleantech, social impact company based in Durham, NC. He has a Masters in Environmental Engineering from Syracuse University and over 23 years of industry experience; He has authored over 30 technical papers and currently spearheads the commercialization and business development of the Supercritical Water Oxidation technology.

Titles from this speaker

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)