Oza, Shubhashini

Shubha Oza is a Process Engineer for Research & Innovation group at Brown and Caldwell. She has over 20 years of experience in applied research...

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About Oza, Shubhashini

Shubha Oza is a Process Engineer for Research & Innovation group at Brown and Caldwell. She has over 20 years of experience in applied research and development. She has a Ph.D. in Environmental Systems from University of North Carlia at Charlotte. She leads research projects related to reuse, and biosolids at Brown and Caldwell. She currently serves as the Vice-Chair for AWWA Membrane Committee and National Representative for State of South Carolina's on the Water Reuse Board

Oza, Shubhashini

Titles from this speaker

A Surveillance Study: Per-and polyfluoroalkyl Substances (PFAS) in Biosolids

Abstract

This surveillance study was aimed at understanding concentrations of PFAS in biosolids. To address this objective, samples were collected from of twenty-five wastewater resource recovery facilities (WRRFs) throughout North America over a six-month period. A minimum of two samples were collected from each WRRF: Location A – sludge entering the stabilization process, and Location B – biosolids (post-stabilization sludge). Modified EPA Method 537.1 was used to analyze 40 PFAS compounds in these samples by Eurofins Laboratories. Only 20% of the measured PFAS compounds were detected in the biosolids samples. Three major solid stabilization methods were evaluated, anaerobic digestion, incineration, and chemical stabilization. Anaerobic digestion and chemical stabilization indicated increases in PFAS in Location B in comparison to Location A, except for in the case of incineration, where ash samples (Location B) did not contain any of the measured PFAS compounds above the method detection limit.

Per-and polyfluoroalkyl Substances (PFAS) are being extensively studied in all the matrices due to their ubiquitous presence in the environment and negative human health impacts. This study conducted a survey of twenty-five wastewater resource recovery facilities (WRRF) throughout North America over a six-month period to evaluate for PFAS other emerging contaminants in biosolids. Among the 40 PFAS compounds evaluated, only 20% were detected in biosolid samples. Concentrations of the detected PFA

SpeakerOza, Shubhashini

Presentation time

13:30:00

13:55:00

Session time

13:30:00

15:00:00

SessionUnderstanding and Addressing PFAS in Biosolids

Session locationRoom N426b - Level 4

TopicMunicipal Wastewater Treatment Design, PFAS

Author(s)

Oza, Shubhashini

Author(s)S. Oza 1; S. Estahbanati 2 ; J. Norton 3; N. Hontoria 4; X. Fonoll Almansa 5; M. Khan 6; C. Muller 7; K. Bell 8; J. Hatfield 4; S. Oza 1;

Author affiliation(s)Brown & Caldwell 1; Brown & Caldwell 2 ; Great Lake Water Authority 3; Brown & Caldwell 4; Great Lake Water Authority 5; Great Lake Water Authority 6; Brown & Caldwell 7; Brown & Caldwell 8; Brown & Caldwell 4; Brown & Caldwell 1;

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2023

DOI10.2175/193864718825159011

Volume / Issue

Content sourceWEFTEC

Word count10

Comparing Modeling Tools Visual MINTEQ and OLI Studio to Evaluate Scaling Tendency of Aerated Anaerobically Digested Solids: A Pilot Study

Abstract

Common phosphate minerals in wastewater treatment plants such as struvite (MAP, MgNH4PO4*6H2O), calcium phosphates such as amorphous calcium phosphate (ACP, Ca3(PO4)2), and iron salt precipitates such as vivianite (Fe3(PO4)2*8H2O) have been recognized as a maintenance and operational nuisance for their tendency to scale and deposit within anaerobic digesters, in pipe bends, and on dewatering equipment downstream of anaerobic digesters. Precipitation of these minerals occur if the concentrations of the ionic constituents exceed the solubility product (Ksp) of the solid which is measured as scaling tendency (ST) or scaling index (SI). The solubility of these precipitates is dependent on factors such as pH, temperature, other competing ions, and nucleation sites. Chemical thermodynamic modeling could be used in evaluating the parameters that contribute to scaling and, thereby, safeguard process equipment from scaling-induced damage, improve treatment efficiency, and regulate phosphorus sequestration to produce nutrient rich biosolids. In this study two commercially available models were evaluated: (i) Visual MINTEQ Version 4.0 and (ii) OLI Studio. The model inputs were gathered at a pilot-scale experimental setup at Hampton Roads Sanitation District's (HRSD) Atlantic Treatment Plant (ATP), Virginia Beach, VA. The pilot evaluates the impact of aeration, mixing, and chemical addition of thermally hydrolyzed pretreated, anaerobically digested solids on scaling tendency. Critical parameters such as pH, temperature, alkalinity, orthophosphate (OP), ammonia (NH3), and major cations and anions concentrations were measured as model inputs. The solids formed during these evaluations were characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM)/Energy Dispersive X-Ray Spectroscopy (EDS), and Raman Spectroscopy analysis to validate prediction by the two models. The pilot set up at ATP consists of four tanks (Figure 1). Each tank is 11 feet tall and can hold up to about 63 gallons of digestate. The tanks are operated as daily batch fed continuously stirred tank reactors maintained by pump recirculation at a 3-day solids retention time (SRT). The tanks are aerated with fine bubble diffuser membranes which can be operated at constant or intermittent air flow rates, via dissolved oxygen (DO) or pH set points. Chemical injection lines will be added to measure the effects of calcium hydroxide [Ca(OH)2] and magnesium hydroxide [Mg(OH)2] at varying dosages. The modelling process was based on the pilot influent solution compositions depicted in Table 1 of anaerobic digestate. In both modeling programs, anaerobically digested solids at a temperature of 30 degrees C, a pH of 7.4, and initial parameters from Table 1 were analyzed to determine the pilot influent potential precipitate formation. Figure 2 represents the fractions of solids predicted to form at equilibrium in Visual MINTEQ and Figure 3 displays similar results produced from OLI, both in mg/L. The two model predictions are closely related, listing siderite, struvite, and calcite as the top three controlling precipitates, respectively. This is a prediction of what is forming currently in the digesters, prior to manipulation in the pilot from aeration or chemical addition. A pH sweep from 7 to 8.5 as well as a temperature sweep from 20 degrees C to 40 degrees C were also analyzed in both modeling programs to understand the effects of aeration within the pilot on pH, biological activity, and how the solubility of scaling precipitates were affected. These results, as well as future work that includes modeling the effects of chemical addition in the pilot, will be presented. Precipitate Characterization was conducted in a contract laboratory for XRD, SEM/EDS, and Raman Spectroscopy to determine precipitate identification. The major peaks in XRD patterns produced likely matched with struvite. Further testing will be completed and presented to validate the solids predicted to form by the models. The presentation will showcase the outcomes derived from each model, offering insights into their respective abilities to predict the potential precipitation of controlling solids. The precipitate characterization analysis will also be compared to determine the validity of results and to further optimize both modeling software.

Two models were evaluated: (i) Visual MINTEQ and (ii) OLI Studio. A pilot study assessed the impact of aeration and mixing of thermally hydrolyzed pretreated, anaerobically digested solids on scaling tendency and measured pH, temperature, orthophosphate, ammonia, and major cations and anions concentrations as model inputs. Sensitivity analyses for pH and temperature were conducted for both unaerated and aerated anaerobic digestate in each model.

SpeakerHarris, Caitlyn

Presentation time

13:30:00

14:00:00

Session time

13:30:00

15:00:00

SessionInnovations in Phosphorus Management: From Models to Solutions

Session number603

Session locationRoom 340

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

Author(s)

Harris, Caitlyn, Oza, Shubhashini, Nicholson, Jeffrey, Matel, Holly Anne, Ward, Barbara, Bell, Katherine, Muller, Christopher, Wilson, Christopher, Bott, Charles

Author(s)C.A. Harris1, S. Oza2, J.D. Nicholson3, H. Matel3, B.J. Ward3, K.Y. Bell4, C. Muller5, C. Wilson1, C.B. Bott3

Author affiliation(s)1HRSD, VA, 2Brown and Caldwell, NC, 3Hampton Roads Sanitation District (HRSD), VA, 4Brown and Caldwell, CA, 5Brown and Caldwell, MA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159528

Volume / Issue

Content sourceWEFTEC

Word count21

Description: Comparing Modeling Tools Visual MINTEQ and OLI Studio to Evaluate Scaling Tendency...

Comparing Modeling Tools Visual MINTEQ and OLI Studio to Evaluate Scaling Tendency of Aerated Anaerobically Digested Solids: A Pilot Study

Abstract

Purpose: Common phosphate minerals in wastewater treatment plants, such as struvite/magnesium ammonium phosphate (MAP, MgNH4PO4- 6H2O), calcium phosphates such as amorphous calcium phosphate (ACP, Ca3(PO4)2), and iron salt precipitates such as vivianite (Fe3(PO4)2 8H2O), are known for their tendency to scale and deposit within anaerobic digesters, pipe bends, and dewatering equipment downstream of anaerobic digesters. These deposits pose maintenance and operational challenges. Precipitation of these minerals occurs when the concentrations of ionic constituents exceed the solubility product (Ksp) of the solid, measured as scaling tendency (ST) or saturation index (SI). The solubility of these precipitates depends on factors such as pH, temperature, competing ions, and nucleation sites. Chemical thermodynamic modeling can evaluate the parameters contributing to scaling and, thereby, safeguard process equipment from scaling-induced damage, improve treatment efficiency, and regulate phosphorus sequestration to produce nutrient-rich biosolids. This modeling work could benefit the wastewater treatment industry by providing rapid optioneering for solutions limiting and targeting scaling mineral deposition and assessing various process optimizations for new pilot technologies. In this study, two chemical thermodynamic models were evaluated: (i) Visual MINTEQ Version 4.0 and (ii) OLI Studio. Model inputs were gathered from a pilot-scale experimental setup at Hampton Roads Sanitation District's (HRSD) Atlantic Treatment Plant (ATP), in Virginia Beach, VA. The pilot evaluated the impact of aeration, mixing, and chemical addition on the scaling tendency of thermally hydrolyzed, pretreated, anaerobically digested solids. Critical parameters such as pH, temperature, alkalinity, orthophosphate (OP), ammonia (NH3), and major cations and anions concentrations were measured as model inputs. The solids formed during these evaluations were characterized by: X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM)/Energy Dispersive X-Ray Spectroscopy (EDS), and Raman Spectroscopy analysis to validate predictions of the two models. Methods: The pilot setup at ATP consisted of four tanks (Figure 1), each 11 feet tall and capable of holding about 45 gallons of digestate. These tanks operated as daily batch fed continuously stirred tank reactors, maintained by pump recirculation at a 3-day solids retention time (SRT). Aeration was provided using fine bubble diffuser membranes, operated either at a constant airflow rate or via a dissolved oxygen (DO) set point. The effects of chemical injection of magnesium hydroxide [Mg(OH)2] and calcium hydroxide [Ca(OH)2] were also studied at various Ca+Mg:OP ratios of 0 (control), 0.25:1, 0.5:1, and 1:1. The modeling process was based on pilot operational conditions: anaerobic digestate (pilot influent), aerated anaerobic digestate constantly at 5 LPM, and aerated anaerobic digestate on a DO setpoint of 0.2 mg/L. Inputs for these operational conditions were collected during pilot tests and averaged for model insertion. For each model run, pH and temperature sensitivity analyses were conducted from pH 7-9, and temperatures 20 - 40°C to determine effects on precipitate formation according to Visual MINTEQ and OLI Studio. Experiments with Mg(OH)2 and Ca(OH)2 were conducted in both models for the aerated cases to simulate chemical injection and evaluate the effectiveness of each chemical in OP removal, as well as the accuracy of each model in predicting mineral formation. Results: Both Visual MINTEQ and OLI Studio effectively predicted mineral formation in anaerobic digestate under varying conditions. Initially, both models predicted the formation of metal phosphates (Mg, Ca, Fe) in anaerobic digestate. Upon aeration at 5 LPM, both models identified struvite as the dominant mineral formed in the pH sensitivity analysis, though they differed in predicting other compounds. Visual MINTEQ predicted the formation of calcite and vivianite, while OLI Studio predicted tricalcium phosphates, calcite, and siderite. In the temperature sensitivity analysis, both models yielded consistent results for calcite and struvite formation, suggesting that temperature has a less significant impact on mineral precipitation than pH. In the aerated run targeting a DO setpoint of 0.2 mg/L with Mg(OH)2, both models accurately predicted struvite as the dominant mineral, with its formation increasing alongside the chemical dose, as depicted in Figures 2 and 3. Table 1 compares the OP removal predicted by each model to the measured pilot results for the same test. Both models closely aligned with the measured OP removal via struvite formation, and solid-phase characterization confirmed struvite as the major compound, as indicated by XRD pattern peaks. The presentation will showcase the outcomes derived from each model, offering insights into their respective abilities to predict the potential for the precipitation of controlling solids. The precipitate characterization analysis will also be compared to determine the validity of results and to further optimize both modeling software. The results of this study will enhance our understanding regarding scaling minerals likely to form within anaerobic digestion pretreated with a thermal hydrolysis process, post anaerobic digestion, and on downstream equipment, as well as in a potential post aerobic digestion setup. A validated model could then be used to predict scaling potential and characterize minerals formed at other WRRFs to better treat these nuisance scaling minerals and determine their potential for harvesting/sequestration as a nutrient rich product.

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

SpeakerHarris, Caitlyn

Presentation time

15:45:00

16:05:00

Session time

15:45:00

16:45:00

SessionAdvances in Process Modeling: Aeration, Scaling, and Anaerobic Digestion Dynamics

Session number20

Session locationBaltimore Convention Center, Baltimore, Maryland, USA

TopicChemical Treatment, Modeling, Phosphorus Removal and Recovery, Specific Methanogenic Activity Test

Author(s)

Harris, Caitlyn, Oza, Shubhashini, Nicholson, Jeffrey, Ward, BJ, Matel, Holly Anne, Bott, Charles, Muller, Christopher, Wilson, Christopher

Author(s)C. Harris1, S. Oza1, J. Nicholson2, B. Ward2, H. Matel2, C. Bott2, C. Muller1, C. Wilson2

Author affiliation(s)Brown and Caldwell, 1Brown and Caldwell, 1Hampton Roads Sanitation District (HRSD), 2Hampton Roads Sanitation Department, 2Hampton Roads Sanitation District (HRSD), 2Hampton Roads Sanitation District (HRSD), 2Brown and Caldwell, 1

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date May 2025

DOI10.2175/193864718825159765

Volume / Issue

Content sourceResiduals and Biosolids Conference

Word count21

Reliable Wastewater Disinfection with Peracids: Integrating Batch Kinetics and Hydrodynamics

Abstract

INTRODUCTION Concerns related to the formation of disinfection byproducts (DBPs) during chlorine disinfection of wastewater and other safety concerns regarding chlorine operation initiated a great interest in alternative chemical disinfectants. For example, peracetic acid (PAA) received significant attention due to its minimal aquatic toxicity and efficacy in reducing regulated fecal indicator bacteria (FIB) (Antonelli et al., 2006; Manoli et al., 2019; WEF, 2020). The generally low efficacy of PAA in inactivating viruses in wastewater along with the ongoing discussions about revision of the United States Environmental Protection Agency Ambient Water Quality Criteria to include a viral indicator (Dunkin et al., 2017), led to a strong interest in another peracid, performic acid (PFA), which its bacterial and viral inactivation capacity usually outperforms PAA (Ragazzo et al., 2020). The objective of this study was to establish efficacy of PFA as a disinfectant compared to PAA and sodium hypochlorite for secondary effluent wastewater applications. The inactivation of indigenous FIB by PFA has been evaluated and compared with PAA and sodium hypochlorite under identical conditions. The disinfection data were interpreted using the concept of integral CT (ICT) and modeled by an ICT-based double-exponential microbial inactivation kinetic model to develop ICT-response data. This abstract presents the initial results of the Water Research Foundation Project #5219 titled 'Performic Acid Disinfection in Wastewater Effluent and CSOs In Context of Disinfection By-Products and Future Ambient Water Quality Criteria for Viruses', with the participation of more than 10 wastewater treatment plants (WWTPs) across the United States and Canada. Similar experiments with the ones presented herein for the first WWTP will be performed for all participating utilities, thus the results of this project may have a significant impact on disinfection practices in North America. Additional to FIB experiments, disinfection tests on viral indicators inactivation and DBPs formation will also be performed in the framework of this project. METHODS Secondary effluent wastewater was collected from a WWTP in ON, Canada (activated sludge-based processes). Its basic water quality characteristics were: pH=7.6, TSS=7.7 mg/L, BOD=10.8 mg/L, COD=13.5 mg/L, TN=18.6 mg/L, and TP=0.4 mg/L. Disinfection bench tests were performed in 2 L of wastewater at 2 disinfectant concentrations (1 and 2 mg/L for PFA and chlorine; 2 and 3 mg/L for PAA). Samples were collected at 6 contact times (0, 1, 3, 5, 10 and 30 min) and analyzed for disinfectant concentration (Chemetrics and Hach methods) and E. coli, fecal coliforms, total coliforms and enterococci (standard membrane filtration methods) (GAP EnviroMicrobial Services, London, ON, Canada). RESULTS The residual disinfectant concentration data were used to calculate exposure to chemical disinfectant (i.e., integral CT) by fitting initial demand (D, mg/L) and decay (k, 1/min) (Eq. 1): ICT=((C0-D)/k)âˆ™(1-e^(-kâˆ™t))(1) where ICT is the integral estimate of the time-dependant residual disinfectant concentration (mg min/L), C0 is the initial concentration of disinfectant (mg/L) and t is the contact time (min). The FIB inactivation data were plotted as a function of integral CT (Figures 1-4) and modeled by a double-exponential inactivation kinetic model in the domain of ICT (Eq. 2): N=N0âˆ™(1-β)âˆ™e^(-kdâˆ™ICT^m )+N0âˆ™(β)âˆ™e^(-kpâˆ™ICT)(2) where N0 and N are the initial and after treatment concentration of bacteria (CFU/100 mL), β is the fraction of particle-associated bacteria, m is a parameter that describes initial resistance of bacteria to disinfectant, and kd and kp are the ICT-based inactivation rate constants for dispersed (free) and particle-associated bacteria, in (L/(mg min))m and L/(mg min), respectively. PFA exhibited the highest inactivation efficiency for all studied indigenous FIB, followed by chlorine and PAA (Figures 1-4). For example, model-predicted integral CT requirements for 1-log reduction of total coliforms and enterococci were determined as 3-4 mg min/L, 8-10 mg min/L and 40-45 mg min/L for PFA, chlorine and PAA respectively (Figures 3 and 4). Based on model predictions, to achieve a 2-log reduction of both commonly regulated E. coli and fecal coliforms, PFA required ~10 times lower ICT than both PAA and chlorine (Figures 1 and 2). We also present an advanced disinfectant dosing control strategy that accounts for changes in wastewater quality and quantity, together with the hydrodynamics of the contact chamber. Bench test results of PFA (Eqs. 1 and 2) were integrated into a process model to evaluate four dosing strategies, namely, flow pacing, constant ICT, constant ICT advanced demand, and constant ICT advanced demand/decay. Figure 5 and Table 1 show that the advanced control strategy achieves consistent performance and optimizes disinfectant dosage. CONCLUSIONS Results show that PFA was superior to both PAA and chlorine. Although the PFA pricing estimates are currently higher than that of hypochlorite, the lower ICT requirements of PFA may result in a competitive cost compared to chlorine. This indicates the need for site-specific testing to better understand disinfection efficiency and cost benefits of PFA as a wastewater disinfectant.

The objective of this study was to establish disinfection efficacy of performic acid (PFA) compared to peracetic acid and sodium hypochlorite, for secondary effluent wastewater applications. The disinfection data were interpreted and modeled using the concept of integral CT, leading to the development of an advanced dose control strategy. PFA was the most effective disinfectant, and when combined with advanced process control, a consistent performance throughout the operation was achieved.

SpeakerManoli, Kyriakos

Presentation time

09:30:00

10:00:00

Session time

08:30:00

10:00:00

SessionPeracids Challenge Traditional Disinfectants

Session number503

Session locationRoom 338

TopicDisinfection and Public Health, Intermediate Level, Research and Innovation

Author(s)

Manoli, Kyriakos, Jang, Eunkyung, Mitobe, Sierra, Parra, Anggy, Diaz Rangel, Carlos, Bell, Katherine, Da Silva, Allegra, Oza, Shubhashini, Norton, John, Tikariha, Lomesh, Lawryshyn, Yuri, Santoro, Domenico

Author(s)K. Manoli1, K.Y. Bell2, E. Jang2, J. Norton3, S. Mitobe1, A. Parra4, C.A. Diaz Rangel1, A.K. Da Silva5, S. Oza6, L. Tikariha7, Y. Lawryshyn7, D. Santoro8

Author affiliation(s)1Lambton Water Center, Research & Innovation, Lambton College, Ontario, 2Brown and Caldwell, CA, 2, 3Great Lakes Water Authority, IL, 4Lambton Water Center, Research & Innovation, Lambton College, 5Brown and Caldwell, CO, 6Brown and Caldwell, NC, 7University of Toronto, 8USP Technologies, GA

SourceProceedings of the Water Environment Federation

Document typeConference Paper

PublisherWater Environment Federation

Print publication date Oct 2024

DOI10.2175/193864718825159567

Volume / Issue

Content sourceWEFTEC

Word count11

Base text size -

Oza, Shubhashini

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