Andrea Silverman

Andrea Silverman
Andrea Silverman

Assistant Professor of Environmental Public Health Sciences

Professional overview

The goal of Dr. Andrea Silverman’s work is to develop sustainable and appropriate wastewater treatment systems, in an effort to protect public health and the environment. Within the topics of water quality and wastewater treatment, she focuses on the detection and control of waterborne pathogens, the design of disinfection processes in natural wastewater treatment systems (e.g. treatment ponds and constructed wetlands), and the safe reuse of human waste.

Dr. Silverman has conducted research in Accra, Ghana on the use of untreated wastewater for vegetable irrigation. In Nairobi, Kenya, she worked with Sanergy, a social enterprise that composts human waste for reuse in agriculture, to ensure effective quality control and safety of the end product. Her ongoing research includes the study of how sunlight kills microorganisms in water (i.e., sunlight disinfection) and the use of this information to create numerical models that predict disinfection rates, which can then be used for the design of natural wastewater treatment systems.

As a professor, Dr. Silverman teaches courses at the Tandon School of Engineering and the School of Global Public Health that address environmental contaminants and appropriate interventions reduce their public health impact, including removal and transformation processes in natural and engineered systems. Courses taught include Introduction to Environmental Engineering, Environmental Health in a Global World, and the Detection and Control of Waterborne Pathogens.

Education

BS, Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA
MS, Environmental Engineering, University of California Berkeley, Berkeley, CA
PhD, Environmental Engineering, University of California Berkeley, Berkeley, CA

Honors and awards

Outstanding Graduate Student Instructor Award, UC Berkeley (2011)
Chang-Lin Tien Fellowship, UC Berkeley (2011)
Science and Engineering for Global Health Fellowship, The Center for Emerging and Neglected Diseases, UC Berkeley (2009)
Chancellor’s Fellowship, UC Berkeley (2007)

Areas of research and study

Environmental Interventions
Environmental Public Health Services
Sanitation systems
Sustainability
Waterborne pathogens

Publications

Publications

Assessment of Commonly Measured Wastewater Parameters to Estimate Sewershed Populations for Use in Wastewater-Based Epidemiology: Insights into Population Dynamics in New York City during the COVID-19 Pandemic

Hoar, C., Li, Y., & Silverman, A. I. (n.d.).

Publication year

2022

Journal title

ACS Environmental Science and Technology Water

Volume

2

Issue

11

Page(s)

2014-2024
Abstract
Abstract
Understanding per capita rates of disease incidence or prevalence from wastewater surveillance data requires an estimate of the population contributing to wastewater samples, given that populations in large urban areas are dynamic, especially if major events, such as the onset of the COVID-19 pandemic, cause large population shifts. To assess whether commonly measured wastewater parameters can be used to estimate sewershed populations, we used wastewater data collected from New York City's (NYC) 14 wastewater treatment facilities to evaluate the relationship between influent loads of four wastewater parameters-ammonia, total Kjeldahl nitrogen, total suspended solids, and five-day carbonaceous biochemical oxygen demand-and census-based population estimates of the corresponding sewersheds during 2019, when populations were assumed to be relatively stable. Ammonia mass load had the most consistent relationship with sewershed population, regardless of wet weather contributions to NYC's predominantly combined sewer system. Changes in ammonia loads due to COVID-19 restrictions enacted in March 2020 generally reflected population shifts in sewersheds serving areas of Manhattan and Brooklyn, for which previous studies report decreased commuter mobility and residential populations. Our findings highlight the utility of ammonia mass load in influent wastewater as a population indicator to normalize wastewater-based epidemiology data and track sewershed population dynamics.

Effect of pH on endogenous sunlight inactivation rates of laboratory strain and wastewater sourced E. coli and enterococci

Chiyenge, M., & Silverman, A. I. (n.d.).

Publication year

2022

Journal title

Environmental Science: Processes and Impacts

Volume

24

Issue

11

Page(s)

2167-2177
Abstract
Abstract
Understanding the influence of environmental factors like pH on solar disinfection in sunlight-dependent wastewater treatment systems can aid in improving their design. Previous research found pH to influence the solar disinfection rates of bacteria in water containing exogenous photosensitizers that facilitate photo-oxidative inactivation. However, limited research has been conducted on the role of external pH on endogenous solar inactivation processes that occur independent of exogenous photosensitizers. As such, we studied the inactivation rates of laboratory-cultured and wastewater-sourced E. coli and enterococci in sensitizer-free matrices with pH ranging from 4 to 10 under full-spectrum and UVB-filtered simulated sunlight. Elevated solar inactivation rates were observed at pH 4 for all bacterial populations evaluated, and at pH 10 for laboratory-cultured and wastewater-sourced E. coli. Dark inactivation was observed at the pH extremes for some bacteria, but did not contribute significantly to the increased inactivation rates observed under simulated sunlight at these pH, except for laboratory-cultured E. coli at pH 10. UVB light was found to play an important role in sunlight inactivation, albeit the contribution of UVB light to solar inactivation observed for Enterococcus spp. diminished at pH 4 and 5, suggesting that indirect endogenous inactivation pathways facilitated by longer wavelength light were enhanced under acidic conditions. Our findings demonstrate that external pH affects the kinetics of endogenous sunlight inactivation processes, and the results have potential to be integrated into models for predicting inactivation kinetics in sunlight-mediated treatment systems that operate over a range of pH conditions.

Interlaboratory performance and quantitative PCR data acceptance metrics for NIST SRM® 2917

Sivaganesan, M., Willis, J. R., Karim, M., Babatola, A., Catoe, D., Boehm, A. B., Wilder, M., Green, H., Lobos, A., Harwood, V. J., Hertel, S., Klepikow, R., Howard, M. F., Laksanalamai, P., Roundtree, A., Mattioli, M., Eytcheson, S., Molina, M., Lane, M., Rediske, R., Ronan, A., D’Souza, N., Rose, J. B., Shrestha, A., Hoar, C., Silverman, A. I., Faulkner, W., Wickman, K., Kralj, J. G., Servetas, S. L., Hunter, M. E., Jackson, S. A., & Shanks, O. C. (n.d.).

Publication year

2022

Journal title

Water Research
Abstract
Abstract
Surface water quality quantitative polymerase chain reaction (qPCR) technologies are expanding from a subject of research to routine environmental and public health laboratory testing. Readily available, reliable reference material is needed to interpret qPCR measurements, particularly across laboratories. Standard Reference Material® 2917 (NIST SRM® 2917) is a DNA plasmid construct that functions with multiple water quality qPCR assays allowing for estimation of total fecal pollution and identification of key fecal sources. This study investigates SRM 2917 interlaboratory performance based on repeated measures of 12 qPCR assays by 14 laboratories (n = 1008 instrument runs). Using a Bayesian approach, single-instrument run data are combined to generate assay-specific global calibration models allowing for characterization of within- and between-lab variability. Comparable data sets generated by two additional laboratories are used to assess new SRM 2917 data acceptance metrics. SRM 2917 allows for reproducible single-instrument run calibration models across laboratories, regardless of qPCR assay. In addition, global models offer multiple data acceptance metric options that future users can employ to minimize variability, improve comparability of data across laboratories, and increase confidence in qPCR measurements.

Making waves: Uses of real-time, hyperlocal flood sensor data for emergency management, resiliency planning, and flood impact mitigation

Silverman, A. I., Brain, T., Branco, B., Challagonda, P. S. V., Choi, P., Fischman, R., Graziano, K., Hénaff, E., Mydlarz, C., Rothman, P., & Toledo-Crow, R. (n.d.).

Publication year

2022

Journal title

Water Research

Volume

220
Abstract
Abstract
Flooding is expected to increase due to intensification of extreme precipitation events, sea-level rise, and urbanization. Low-cost water level sensors have the ability to fill a critical data gap on the presence, depth, and duration of street-level floods by measuring flood profiles (i.e., flood stage hydrographs) in real-time with a time interval on the order of minutes. Hyperlocal flood data collected by low-cost sensors have many use cases for a variety of stakeholders including municipal agencies, community members, and researchers. Here we outline examples of potential uses of flood sensor data before, during, and after flood events, based on dialog with stakeholders in New York City. These uses include inputs to predictive flood models, generation of real-time flood alerts for community members and emergency response teams, storm recovery assistance and cataloging of storm impacts, and informing infrastructure design and investment for long-term flood resilience project planning.

Monitoring SARS-CoV-2 in wastewater during New York City's second wave of COVID-19: sewershed-level trends and relationships to publicly available clinical testing data

Hoar, C., Chauvin, F., Clare, A., McGibbon, H., Castro, E., Patinella, S., Katehis, D., Dennehy, J. J., Trujillo, M., Smyth, D. S., & Silverman, A. I. (n.d.).

Publication year

2022

Journal title

Environmental Science: Water Research and Technology

Volume

8

Issue

5

Page(s)

1021-1035
Abstract
Abstract
New York City's wastewater monitoring program tracked trends in sewershed-level SARS-CoV-2 loads starting in the fall of 2020, just before the start of the city's second wave of the COVID-19 outbreak. During a five-month study period, from November 8, 2020 to April 11, 2021, viral loads in influent wastewater from each of New York City's 14 wastewater treatment plants were measured and compared to new laboratory-confirmed COVID-19 cases for the populations in each corresponding sewershed, estimated from publicly available clinical testing data. We found significant positive correlations between viral loads in wastewater and new COVID-19 cases. The strength of the correlations varied depending on the sewershed, with Spearman's rank correlation coefficients ranging between 0.38 and 0.81 (mean = 0.55). Based on a linear regression analysis of a combined data set for New York City, we found that a 1 log10 change in the SARS-CoV-2 viral load in wastewater corresponded to a 0.6 log10 change in the number of new laboratory-confirmed COVID-19 cases per day in a sewershed. An estimated minimum detectable case rate between 2-8 cases per day/100 000 people was associated with the method limit of detection in wastewater. This work offers a preliminary assessment of the relationship between wastewater monitoring data and clinical testing data in New York City. While routine monitoring and method optimization continue, information on the development of New York City's wastewater monitoring program may provide insights for similar wastewater-based epidemiology efforts in the future.

Escherichia coli and Enterococcus spp. Indigenous to Wastewater Have Slower Free Chlorine Disinfection Rates than Their Laboratory-Cultured Counterparts

Mwatondo, M. H., & Silverman, A. I. (n.d.).

Publication year

2021

Journal title

Environmental Science and Technology Letters

Volume

8

Issue

12

Page(s)

1091-1097
Abstract
Abstract
Most published data on chlorine disinfection of bacteria are from experiments conducted using reference-strain bacteria cultured in a laboratory. However, indigenous environmental bacteria, such as those in wastewater, can be more resistant to disinfection than their laboratory-cultured counterparts. To investigate this phenomenon, we conducted controlled experiments to systematically quantify and compare free chlorine inactivation kinetics of laboratory-cultured Escherichia coli and Enterococcus faecalis to corresponding E. coli and enterococci sourced from wastewater, without confounding factors related to the sample matrix. To allow direct comparison between bacterial populations, dissolved and particulate constituents of the sample matrices that could influence disinfection kinetics were removed using sequential centrifugation steps prior to disinfection experiments. The first-order chlorine inactivation rate constants of laboratory-cultured E. coli (k = 18.6 L mg-1min-1) and E. faecalis (k = 12.7 L mg-1min-1) were over an order of magnitude greater than those of wastewater-sourced E. coli (k = 0.65 L mg-1min-1) and enterococci (k = 0.18 L mg-1min-1) in PBS. These results indicate that wastewater bacteria were less susceptible to free chlorine inactivation than corresponding laboratory-cultured bacteria. Results from control experiments suggest that the observed differences in disinfection rates were due to cell-related differences between the bacterial populations and not caused by matrix effects, aggregation, or purification procedures utilized.

SARS-CoV-2 wastewater surveillance for public health action

McClary-Gutierrez, J. S., Mattioli, M. C., Marcenac, P., Silverman, A. I., Boehm, A. B., Bibby, K., Balliet, M., De Los Reyes, F. L., Gerrity, D., Griffith, J. F., Holden, P. A., Katehis, D., Kester, G., LaCross, N., Lipp, E. K., Meiman, J., Noble, R. T., Brossard, D., & McLellan, S. L. (n.d.).

Publication year

2021

Journal title

Emerging Infectious Diseases

Volume

27

Issue

9

Page(s)

E1-E9
Abstract
Abstract
Wastewater surveillance for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has garnered extensive public attention during the coronavirus disease pandemic as a proposed complement to existing disease surveillance systems. Over the past year, methods for detection and quantifi cation of SARS-CoV-2 viral RNA in untreated sewage have advanced, and concentrations in wastewater have been shown to correlate with trends in reported cases. Despite the promise of wastewater surveillance, for these measurements to translate into useful public health tools, bridging the communication and knowledge gaps between researchers and public health responders is needed. We describe the key uses, barriers, and applicability of SARS-CoV-2 wastewater surveillance for supporting public health decisions and actions, including establishing ethics consideration for monitoring. Although wastewater surveillance to assess community infections is not a new idea, the coronavirus disease pandemic might be the initiating event to make this emerging public health tool a sustainable nationwide surveillance system, provided that these barriers are addressed.

Scaling of SARS-CoV-2 RNA in settled solids from multiple wastewater treatment plants to compare incidence rates of laboratory-confirmed COVID-19 in their sewersheds

Wolfe, M. K., Archana, A., Catoe, D., Coffman, M. M., Dorevich, S., Graham, K. E., Kim, S., Grijalva, L. M., Roldan-Hernandez, L., Silverman, A. I., Sinnott-Armstrong, N., Vugia, D. J., Yu, A. T., Zambrana, W., Wigginton, K. R., & Boehm, A. B. (n.d.).

Publication year

2021

Journal title

Environmental Science and Technology Letters

Volume

8

Issue

5

Page(s)

398-404
Abstract
Abstract
Published and unpublished reports show that SARSCoV- 2 RNA in publicly owned treatment work (POTW) wastewater influent and solids is associated with new COVID-19 cases or incidence in associated sewersheds, but methods for comparing data collected from diverse POTWs to infer information about the relative incidence of laboratory-confirmed COVID-19 cases, and scaling to allow such comparisons, have not been previously established. Here, we show that SARS-CoV-2 N1 and N2 concentrations in solids normalized by concentrations of PMMoV RNA in solids can be used to compare incidence of laboratory confirmed new COVID-19 cases across POTWs. Using data collected at seven POTWs along the United States West Coast, Midwest, and East Coast serving ∼3% of the U.S. population (9 million people), we show that a 1 log change in N gene/PMMoV is associated with a 0.24 (range 0.19 to 0.29) log10 change in incidence of laboratory confirmed COVID-19. Scaling of N1 and N2 by PMMoV is consistent, conceptually, with a mass balance model relating SARS-CoV-2 RNA to the number of infected individuals shedding virus in their stool. This information should support the application of wastewater-based epidemiology to inform the response to the COVID-19 pandemic and potentially future viral pandemics.

Sunlight Photolysis of Extracellular and Intracellular Antibiotic Resistance Genes tetA and sul2 in Photosensitizer-Free Water

Dunn, F. B., & Silverman, A. I. (n.d.).

Publication year

2021

Journal title

Environmental Science and Technology

Volume

55

Issue

16

Page(s)

11019-11028
Abstract
Abstract
Antibiotic resistance genes (ARGs; the genetic material in bacteria that encode for resistance to antibiotics) have been found in the aquatic environment, raising concerns of an environmental transmission route. In an effort to contribute to models predicting the fate of ARGs in the environment - to design control measures, predict health risks, inform ARG surveillance activities, and prioritize policy interventions - and given the importance of sunlight in damaging DNA, we evaluated the sunlight photolysis kinetics of antibiotic-resistant bacteria (ARB) and ARGs under laboratory conditions, focusing on Escherichia coli SMS-3-5 and its ARGs tetA and sul2. Experiments were conducted in the absence of photosensitizers, and ARG decay rates were quantified by quantitative polymerase chain reaction (qPCR) with short and long amplicon targets. Long amplicon qPCR targets quantified greater photolysis rate constants, due to greater ARG coverage. After a lag phase, intracellular ARG had faster decay rates than extracellular ARG, likely due to the contribution of intracellular indirect photolysis processes. Furthermore, all ARG decay rates were significantly slower than those of E. coli. Decay rate constants and quantum yields are presented as foundational work in the development of models to describe the persistence of ARGs in sunlit, environmental waters.

Systematic Review and Meta-Analysis of the Persistence of Enveloped Viruses in Environmental Waters and Wastewater in the Absence of Disinfectants

Silverman, A. I., & Boehm, A. B. (n.d.).

Publication year

2021

Journal title

Environmental Science and Technology

Volume

55

Issue

21

Page(s)

14480-14493
Abstract
Abstract
Enveloped viruses are characterized by a lipid-containing envelope that encapsulates the virion, and they have been the cause of major outbreaks and pandemics. Some enveloped viruses are excreted in feces and other bodily fluids of infected people and animals, raising the question of their fate in the aquatic environment. Consequently, we conducted a systematic review and meta-analysis of the decay rate constants (k) of enveloped viruses from 12 families (i.e.,Coronaviridae,Cystoviridae(specifically Phi6),Filoviridae,Hepadnaviridae,Herpesviridae,Orthomyxoviridae,Paramyxoviridae,Pneumoviridae,Poxviridae,Retroviridae,Rhabdoviridae,Togaviridae) in environmental waters and wastewater to evaluate their decay kinetics and identify the environmental and virus characteristics that influencek. A total of 812kthat met inclusion criteria were identified in the literature, with the number ofkfor each family ranging from 0 to 560, and the virus family averaged values ofkranging from 0.11 d-1and 1.85 d-1. Virus type (i.e., genus, species, subspecies, or subtype), method of virus enumeration (i.e., culture-based or (RT-)QPCR), and experimental water matrix type, temperature and sterility were found to have significant effects onk. Additionally, enveloped viruses were found to have statistically significantly greaterkthan nonenveloped viruses. Multiple linear regression models that allow prediction of log10kas a function of virus type, enumeration method, water temperature, and water type are provided for six virus families that had sufficient data available for model fitting (i.e.,Coronaviridae, Phi6,Herpesviridae,Orthomyxoviridae,Rhabdoviridae,Togaviridae). Compiled log10kand multiple regression models can be used to inform management of human and animal waste, operation of water and wastewater facilities, and exposure risks to treatment plant workers and communities living in regions that lack treatment facilities. Given limited data available for some enveloped virus families with a potential water-related transmission route, there is need for additional data collection to aid academic researchers, public health agencies, and water and wastewater professionals involved in outbreak response.

Systematic review of the relative concentrations of noroviruses and fecal indicator bacteria in wastewater: considerations for use in quantitative microbial risk assessment

Hamadieh, Z., Hamilton, K. A., & Silverman, A. I. (n.d.).

Publication year

2021

Journal title

Journal of Water and Health

Volume

19

Issue

6

Page(s)

918-932
Abstract
Abstract
Human noroviruses are a leading cause of food- and water-borne disease, which has led to an interest in quantifying norovirus health risks using quantitative microbial risk assessment (QMRA). Given the limited availability of quantitative norovirus data to input to QMRA models, some studies have applied a conversion factor to estimate norovirus exposure based on measured fecal indicator bacteria (FIB) concentrations. We conducted a review of peer-reviewed publications to identify the concentrations of noroviruses and FIB in raw, secondary-treated, and disinfected wastewater. A meta-analysis was performed to determine the ratios of norovirus-FIB pairs in each wastewater matrix and the variables that significantly impact these ratios. Norovirus-to-FIB ratios were found to be significantly impacted by the norovirus genotype, month of sample collection, geographic location, and the extent of wastewater treatment. Additionally, we evaluated the impact of using a FIB-to-virus conversion factor in QMRA and found that the choice of conversion ratio has a great impact on estimated health risks. For example, the use of a conversion ratio previously used in the World Health Organization Guidelines for the Safe Use of Wastewater, Excreta and Greywater predicted health risks that were significantly lower than those estimated with measured norovirus concentrations used as inputs. This work emphasizes the gold standard of using measured pathogen concentrations directly as inputs to exposure assessment in QMRA. While not encouraged, if one must use a FIB-to-virus conversion ratio to estimate norovirus dose, the ratio should be chosen carefully based on the target microorganisms (i.e., strain, genotype, or class), prevalence of disease, and extent of wastewater treatment.

Engineering an Interdisciplinary Connection: Bridging Gaps between Chemical, Electrical, and Environmental Engineers

Dvorkin, Y., Modestino, M. A., & Silverman, A. I. (n.d.).

Publication year

2020

Journal title

iScience

Volume

23

Issue

7

Global Sensitivity Analysis of Environmental, Water Quality, Photoreactivity, and Engineering Design Parameters in Sunlight Inactivation of Viruses

Zhang, X., Lardizabal, A., Silverman, A. I., Vione, D., Kohn, T., Nguyen, T. H., & Guest, J. S. (n.d.).

Publication year

2020

Journal title

Environmental Science and Technology

Volume

54

Issue

13

Page(s)

8401-8410
Abstract
Abstract
Sunlight-mediated inactivation of microorganisms is a low-cost approach to disinfect drinking water and wastewater. The reactions involved are affected by a wide range of factors, and a lack of knowledge about their relative importance makes it challenging to optimize treatment systems. To characterize the relative importance of environmental conditions, photoreactivity, water quality, and engineering design in the sunlight inactivation of viruses, we modeled the inactivation of three - human adenovirus and two bacteriophages - MS2 and phiX174 - in surface waters and waste stabilization ponds by integrating solar irradiance and aquatic photochemistry models under uncertainty. Through global sensitivity analyses, we quantitatively apportioned the variability of predicted sunlight inactivation rate constants to different factors. Most variance was associated with the variability in and interactions among time, location, nonpurgeable organic carbon (NPOC) concentration, and pond depth. The photolysis quantum yield of the virus outweighed the seasonal solar motion in the impact on inactivation rates. Further, comparison of simulated sunlight inactivation efficacy in maturation ponds under different design decisions showed that reducing pond depth can increase the log inactivation at the cost of larger land area, but increasing hydraulic retention time by adding ponds in series yielded greater improvements in inactivation.

Photocatalytic hydrogels for removal of organic contaminants from aqueous solution in continuous flow reactors

Katzenberg, A., Raman, A., Schnabel, N. L., Quispe, A. L., Silverman, A. I., & Modestino, M. A. (n.d.).

Publication year

2020

Journal title

Reaction Chemistry and Engineering

Volume

5

Issue

2

Page(s)

377-386
Abstract
Abstract
Light-driven degradation of organic contaminants by photocatalytic nanoparticles has attracted significant attention for wastewater treatment applications. However, implementation of these approaches has been limited by challenges in reactor design, which often require post-treatment separation of nanoparticles or exhibit low reactivity owing to immobilization of particles at the surface of heterogeneous supports. In this work, we present a material design strategy that circumvents these challenges by encapsulating photocatalytic particles in three-dimensional polymer networks, leading to structurally-stable photocatalytic hydrogels that were used as the walls of a flow reactor. This design leverages the volumetric reactions of commonly-implemented slurry reactors but circumvents the need for downstream separation of photocatalytic particles. A two-step soft lithography technique was used to fabricate a patterned poly(hydroxyethyl methacrylate-co-acrylic acid) hydrogel composite with embedded titanium dioxide (TiO2) nanoparticles that were employed as a photocatalyst. In this configuration, contaminant molecules introduced via a flow channel were absorbed into the hydrogel, and subsequently diffused to the surface of the embedded photocatalyst particles where they were oxidized upon light irradiation. Using reactor configurations with low residence times (15 seconds) and moderate UV irradiation (0.28 mW cm-2 at 365 nm), we demonstrated removal of up to 33% of model contaminant methylene blue (MB) and 13% of the antibiotic norfloxacin, both of which were introduced at a concentration of 3 mg L-1. The influence of molecular design parameters, such as hydrogel ionic strength, crosslinking density, and photocatalyst loading on transport and reactor performance were investigated and shown to have a strong influence on the transport properties of the hydrogels, providing options for optimizing the material to enhance treatment efficiency.

Systematic Review and Meta-Analysis of the Persistence and Disinfection of Human Coronaviruses and Their Viral Surrogates in Water and Wastewater

Silverman, A. I., & Boehm, A. B. (n.d.).

Publication year

2020

Journal title

Environmental Science and Technology Letters

Volume

7

Issue

8

Page(s)

544-553
Abstract
Abstract
A systematic review and meta-analysis was conducted to identify decay rate constants (k) of human coronaviruses and their viral surrogates (i.e., animal coronaviruses and the enveloped bacteriophage Phi6) in water and wastewater and disinfection rates with exposure to free chlorine and germicidal ultraviolet light (UV254). Here, 73 k were identified, with only 12 for human coronaviruses, as opposed to animal coronaviruses or Phi6. In the absence of disinfectants, k increased with temperature. Between 22 and 25 °C, mean k for coronaviruses ranged from 0.19 ± 0.06 d-1 in laboratory buffer (n = 4) to 2.9 ± 0.03 d-1 in sterilized wastewater (n = 3), which are within the ranges observed for Phi6 and nonenveloped viruses. No free chlorine or UV254 disinfection studies for coronaviruses were identified that met the systematic review inclusion criteria, although evidence from the literature suggests that coronaviruses would be inactivated if disinfectant doses recommended for nonenveloped viruses were applied. Three disinfection experiments were identified for Phi6. However, given different genome compositions and virion structures between coronaviruses and Phi6, it is not clear whether Phi6 should be used as a surrogate for evaluating free chlorine or UV254 k. Therefore, there is a critical need for additional studies that specifically evaluate disinfection kinetics of coronaviruses in the aqueous environment.

Comparison of biological weighting functions used to model endogenous sunlight inactivation rates of MS2 coliphage

Silverman, A. I., Tay, N., & Machairas, N. (n.d.).

Publication year

2019

Journal title

Water Research

Volume

151

Page(s)

439-446
Abstract
Abstract
Sunlight inactivation is important for disinfection of viruses in sunlit waters. As such, attempts have been made to predict the endogenous photoinactivation rate of bacteriophage MS2 using biological weighting functions, which describe microorganism sensitivity to sunlight inactivation as a function of wavelength. In this study, four biological weighting function models were compared to assess their ability to predict endogenous inactivation rates (kendo) of MS2. Previously-published and newly-collected datasets consisting of an incident irradiance spectrum (used as an input to the model) and a measured inactivation rate (kobs) were used for model validation and comparison. kendo values predicted by each model were compared with measured kobs to evaluate the ability of each biological weighting function to predict endogenous sunlight inactivation rates. A model previously developed by Mattle et al. (Env. Sci. Technol. 49, 334–342) over-predicted inactivation rates, whereas the other three models – a model from Fisher et al. (Env. Sci. Technol. 45, 9249–9255), a new model developed in this study, and a modification of the model by Mattle et al. (developed as part of this study) – were better able to estimate inactivation rates. The biological relevance of the spectral shape of each biological weighting function is discussed.

Simplified process to determine rate constants for sunlight-mediated removal of trace organic and microbial contaminants in unit process open-water treatment wetlands

Silverman, A. I., Sedlak, D. L., & Nelson, K. L. (n.d.).

Publication year

2019

Journal title

Environmental Engineering Science

Volume

36

Issue

1

Page(s)

43-59
Abstract
Abstract
Unit process, open-water (UPOW) treatment wetlands are a unique type of constructed wetlands that are designed to promote photo- A nd microbiologically mediated natural water treatment processes. A mechanistic understanding of the removal processes for nitrate, trace organic contaminants (TrOCs), and microbial contaminants in UPOW wetlands has been established, and equations have been previously developed to describe removal kinetics. However, the numerical models developed to predict photodegradation rate constants for the removal of TrOC and microbial contaminants involve too many steps to facilitate a practical design approach. In this article, we present a method for predicting rates of phototransformation of representative TrOCs (atenolol, propranolol, sulfamethoxazole, and carbamazepine) and inactivation of microbial indicator organisms (Escherichia coli and MS2) that allows a user to readily design UPOW wetlands to meet different performance goals. Photodegradation rate constants were determined for a range of conditions that influence treatment efficacy (i.e., time of year, pH, latitude, and dissolved organic carbon concentration), and are presented in a series of figures. We illustrate the use of these figures for UPOW wetland design with a representative example of the design process. A spreadsheet containing sample calculations is included in the Supplementary Data.

Systematic review and meta-analysis of decay rates of waterborne mammalian viruses and coliphages in surface waters

Boehm, A. B., Silverman, A. I., Schriewer, A., & Goodwin, K. (n.d.).

Publication year

2019

Journal title

Water Research

Volume

164
Abstract
Abstract
Surface waters are essential natural resources. They are also receiving waters for a variety of anthropogenic waste streams that carry a myriad of pollutants including pathogens. Watershed and fate and transport models can help inform the spatial and temporal extent of microbial pollution from point and non-point sources and thus provide useful information for managing surface waters. Viruses are particularly important water-related pathogens because they often have a low infectious dose, which means that ingestion of even a small volume of water containing a low concentration of virions has the potential to cause disease. We conducted a systematic review of the literature, following best practices, to gather decay rate constants (k) of mammalian waterborne viruses (enteroviruses, adenoviruses, noroviruses, astroviruses, rotaviruses, and hepatitis A viruses) and coliphages in raw surface waters to aid in the parameterization of virus fate and transport models. We identified 562 k values from the literature, with the largest number identified for enteroviruses and coliphages and the smallest for astrovirus, hepatitis A virus, and norovirus. Average k values for each virus varied from 0.07 to 0.9 per day, in order from smallest to largest: Norwalk virus (i.e., noroviruses) < Human astrovirus < Mastadenovirus (i.e., adenoviruses) < Hepatovirus A (i.e., hepatitis A viruses) < Rotavirus A < coliphages < Enterovirus. A meta-analysis investigated how k varied among viruses for experiments conducted with different virus serotypes or species at different temperatures, salinities, and sunlight exposures, and for experiments that enumerated viruses using different methodologies. Virus species or serotype did not affect k among decay experiments. k values were generally larger for experiments conducted at higher temperatures, in sunlight, and in estuarine waters, and enumerated using culture methods. k values were statistically different between virus types with Norwalk virus, Hepatovirus A, and Mastadenovirus having smaller k values than other viruses, controlling for experimental condition and enumeration method. While F+ coliphage k values were similar to those of Enterovirus, Human astrovirus, and Rotavirus A, they were different from those of the other mammalian viruses. This compilation of coliphage and mammalian virus k values provides essential information for researchers and risk assessors who model virus fate and transport in surface waters and identifies avenues for future research to fill knowledge gaps.

Sunlight-mediated inactivation of health-relevant microorganisms in water: a review of mechanisms and modeling approaches

Nelson, K. L., Boehm, A. B., Davies-Colley, R. J., Dodd, M. C., Kohn, T., Linden, K. G., Liu, Y., Maraccini, P. A., McNeill, K., Mitch, W. A., Nguyen, T. H., Parker, K. M., Rodriguez, R. A., Sassoubre, L. M., Silverman, A. I., Wigginton, K. R., & Zepp, R. G. (n.d.).

Publication year

2018

Journal title

Environmental Science: Processes and Impacts

Volume

20

Issue

8

Page(s)

1089-1122
Abstract
Abstract
Health-relevant microorganisms present in natural surface waters and engineered treatment systems that are exposed to sunlight can be inactivated by a complex set of interacting mechanisms. The net impact of sunlight depends on the solar spectral irradiance, the susceptibility of the specific microorganism to each mechanism, and the water quality; inactivation rates can vary by orders of magnitude depending on the organism and environmental conditions. Natural organic matter (NOM) has a large influence, as it can attenuate radiation and thus decrease inactivation by endogenous mechanisms. Simultaneously NOM sensitizes the formation of reactive intermediates that can damage microorganisms via exogenous mechanisms. To accurately predict inactivation and design engineered systems that enhance solar inactivation, it is necessary to model these processes, although some details are not yet sufficiently well understood. In this critical review, we summarize the photo-physics, -chemistry, and -biology that underpin sunlight-mediated inactivation, as well as the targets of damage and cellular responses to sunlight exposure. Viruses that are not susceptible to exogenous inactivation are only inactivated if UVB wavelengths (280-320 nm) are present, such as in very clear, open waters or in containers that are transparent to UVB. Bacteria are susceptible to slightly longer wavelengths. Some viruses and bacteria (especially Gram-positive) are susceptible to exogenous inactivation, which can be initiated by visible as well as UV wavelengths. We review approaches to model sunlight-mediated inactivation and illustrate how the environmental conditions can dramatically shift the inactivation rate of organisms. The implications of this mechanistic understanding of solar inactivation are discussed for a range of applications, including recreational water quality, natural treatment systems, solar disinfection of drinking water (SODIS), and enhanced inactivation via the use of sensitizers and photocatalysts. Finally, priorities for future research are identified that will further our understanding of the key role that sunlight disinfection plays in natural systems and the potential to enhance this process in engineered systems.

Modeling the endogenous sunlight inactivation rates of laboratory strain and Wastewater E. coli and enterococci using biological weighting functions

Silverman, A. I., & Nelson, K. L. (n.d.).

Publication year

2016

Journal title

Environmental Science and Technology

Volume

50

Issue

22

Page(s)

12292-12301
Abstract
Abstract
Models that predict sunlight inactivation rates of bacteria are valuable tools for predicting the fate of pathogens in recreational waters and designing natural wastewater treatment systems to meet disinfection goals. We developed biological weighting function (BWF)-based numerical models to estimate the endogenous sunlight inactivation rates of E. coli and enterococci. BWF-based models allow the prediction of inactivation rates under a range of environmental conditions that shift the magnitude or spectral distribution of sunlight irradiance (e.g., different times, latitudes, water absorbances, depth). Separate models were developed for laboratory strain bacteria cultured in the laboratory and indigenous organisms concentrated directly from wastewater. Wastewater bacteria were found to be 5-7 times less susceptible to full-spectrum simulated sunlight than the laboratory bacteria, highlighting the importance of conducting experiments with bacteria sourced directly from wastewater. The inactivation rate models fit experimental data well and were successful in predicting the inactivation rates of wastewater E. coli and enterococci measured in clear marine water by researchers from a different laboratory. Additional research is recommended to develop strategies to account for the effects of elevated water pH on predicted inactivation rates.

Sunlight inactivation of viruses in open-water unit process treatment wetlands: Modeling endogenous and exogenous inactivation rates

Silverman, A. I., Nguyen, M. T., Schilling, I. E., Wenk, J., & Nelson, K. L. (n.d.).

Publication year

2015

Journal title

Environmental Science and Technology

Volume

49

Issue

5

Page(s)

2757-2766
Abstract
Abstract
Sunlight inactivation is an important mode of disinfection for viruses in surface waters. In constructed wetlands, for example, open-water cells can be used to promote sunlight disinfection and remove pathogenic viruses from wastewater. To aid in the design of these systems, we developed predictive models of virus attenuation that account for endogenous and exogenous sunlight-mediated inactivation mechanisms. Inactivation rate models were developed for two viruses, MS2 and poliovirus type 3; laboratory- and field-scale experiments were conducted to evaluate the models' ability to estimate inactivation rates in a pilot-scale, open-water, unit-process wetland cell. Endogenous inactivation rates were modeled using either photoaction spectra or total, incident UVB irradiance. Exogenous inactivation rates were modeled on the basis of virus susceptibilities to singlet oxygen. Results from both laboratory- and field-scale experiments showed good agreement between measured and modeled inactivation rates. The modeling approach presented here can be applied to any sunlit surface water and utilizes easily measured inputs such as depth, solar irradiance, water matrix absorbance, singlet oxygen concentration, and the virus-specific apparent second-order rate constant with singlet oxygen (k2). Interestingly, the MS2 k2 in the open-water wetland was found to be significantly larger than k2 observed in other waters in previous studies. Examples of how the model can be used to design and optimize natural treatment systems for virus inactivation are provided.

On-farm treatment of wastewater used for vegetable irrigation: Bacteria and virus removal in small ponds in Accra, Ghana

Silverman, A. I., Akrong, M. O., Drechsel, P., & Nelson, K. L. (n.d.).

Publication year

2014

Journal title

Journal of Water Reuse and Desalination

Volume

4

Issue

4

Page(s)

276-286
Abstract
Abstract
Many urban farmers in Accra collect irrigation water from streams and open drains, which they store in small, on-farm ponds before use. Given that this water can be highly contaminated with wastewater, another potential role of the ponds is to disinfect irrigation water prior to use. To better understand the factors influencing bacteria and virus removal in these small ponds, we investigated the removal of culturable fecal indicator bacteria (Escherichia coli and enterococci) and coliphage (F+ and somatic coliphage) in a single batch of water stored for 3 days. Sunlight exposure was found to be important for removal. Bacteria and coliphage removal rates were faster in shallow sun-exposed water than in deeper water, due to sunlight attenuation with depth. Bacteria removal rates varied depending on solar irradiation, and correlations between total daily UVB fluence and bacteria removal rates were observed. Coliphage removal was observed in sun-exposed water but not in dark controls that allowed for sedimentation, further highlighting the importance of sunlight-mediated processes. These small ponds appear to have similar disinfection processes to larger-scale waste stabilization ponds, but can have more efficient inactivation due to their shallow depth and operation as batch reactors. Design and management recommendations for on-farm ponds are discussed.

Quality of irrigation water used for urban vegetable production

Keraita, B., & Silverman, A. (n.d.). In Irrigated urban vegetable production in Ghana: characteristics, benefits and risk mitigation (2nd ed.).

Publication year

2014

Page(s)

62

Sunlight inactivation of ms2 coliphage in the absence of photosensitizers: Modeling the endogenous inactivation rate using a photoaction spectrum

Nguyen, M. T., Silverman, A. I., & Nelson, K. L. (n.d.).

Publication year

2014

Journal title

Environmental Science and Technology

Volume

48

Issue

7

Page(s)

3891-3898
Abstract
Abstract
The endogenous sunlight inactivation rates of MS2 coliphage in photosensitizer-free water were measured (kobs) under different light conditions and compared to modeled inactivation rates (kmod) computed using a previously published action spectrum. Experiments were conducted under simulated and natural sunlight there was generally good agreement between modeled and observed MS2 sunlight inactivation rates in the summer and winter, suggesting that the action spectrum can be used to predict changes in the inactivation rate caused by diurnal and seasonal changes in natural sunlight irradiance. However, we show that a major source of uncertainty in the predictions is the ability to accurately measure or model the comparatively weak and highly variable solar irradiance between 280 and 300 nm, a range to which the inactivation rate is very sensitive the action spectrum was also used to predict the endogenous inactivation rates of MS2 at different depths in a column of strongly humic-colored [i.e., solar ultraviolet (UV)-attenuating] wetland water under simulated sunlight; we observed fairly good agreement between kobs and kmod, suggesting that the action spectrum can be used to estimate the decrease in the endogenous inactivation rate caused by spectrally selective sunlight attenuation in the water column.

Quantification of human norovirus GII, human adenovirus, and fecal indicator organisms in wastewater used for irrigation in Accra, Ghana

Silverman, A. I., Nelson, K. L., Akrong, M. O., Amoah, P., & Drechsel, P. (n.d.).

Publication year

2013

Journal title

Journal of Water and Health

Volume

11

Issue

3

Page(s)

473-488
Abstract
Abstract
Quantitative microbial risk assessment (QMRA) is frequently used to estimate health risks associated with wastewater irrigation and requires pathogen concentration estimates as inputs. However, human pathogens, such as viruses, are rarely quantified in water samples, and simple relationships between fecal indicator bacteria and pathogen concentrations are used instead. To provide data that can be used to refine QMRA models of wastewater-fed agriculture in Accra, stream, drain, and waste stabilization pond waters used for irrigation were sampled and analyzed for concentrations of fecal indicator microorganisms (human-specific Bacteroidales, Escherichia coli, enterococci, thermotolerant coliform, and somatic and F coliphages) and two human viruses (adenovirus and norovirus genogroup II). E. coli concentrations in all samples exceeded limits suggested by the World Health Organization, and human-specific Bacteroidales was found in all but one sample, suggesting human fecal contamination. Human viruses were detected in 16 out of 20 samples, were quantified in 12, and contained 2-3 orders of magnitude more norovirus than predicted by norovirus to E. coli concentration ratios assumed in recent publications employing indicator-based QMRA. As wastewater irrigation can be beneficial for farmers and municipalities, these results should not discourage water reuse in agriculture, but provide motivation and targets for wastewater treatment before use on farms.

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