Assistant Professor of Environmental Public Health Sciences
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.
BS, Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MAMS, Environmental Engineering, University of California Berkeley, Berkeley, CAPhD, Environmental Engineering, University of California Berkeley, Berkeley, CA
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)
Environmental InterventionsEnvironmental Public Health ServicesSanitation systemsSustainabilityWaterborne pathogens
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
Escherichia coli and Enterococcus spp. Indigenous to Wastewater Have Slower Free Chlorine Disinfection Rates than Their Laboratory-Cultured Counterparts
SARS-CoV-2 wastewater surveillance for public health action
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
Sunlight Photolysis of Extracellular and Intracellular Antibiotic Resistance Genes tetA and sul2 in Photosensitizer-Free Water
Systematic Review and Meta-Analysis of the Persistence of Enveloped Viruses in Environmental Waters and Wastewater in the Absence of DisinfectantsSilverman, A. I., & Boehm, A. B.
Journal titleEnvironmental Science and Technology
Page(s)14480-14493AbstractEnveloped 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
Engineering an Interdisciplinary Connection: Bridging Gaps between Chemical, Electrical, and Environmental EngineersDvorkin, Y., Modestino, M. A., & Silverman, A. I.
Global Sensitivity Analysis of Environmental, Water Quality, Photoreactivity, and Engineering Design Parameters in Sunlight Inactivation of VirusesZhang, X., Lardizabal, A., Silverman, A. I., Vione, D., Kohn, T., Nguyen, T. H., & Guest, J. S.
Journal titleEnvironmental Science and Technology
Page(s)8401-8410AbstractSunlight-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 reactorsKatzenberg, A., Raman, A., Schnabel, N. L., Quispe, A. L., Silverman, A. I., & Modestino, M. A.
Journal titleReaction Chemistry and Engineering
Page(s)377-386AbstractLight-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 WastewaterSilverman, A. I., & Boehm, A. B.
Journal titleEnvironmental Science and Technology Letters
Page(s)544-553AbstractA 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 coliphageSilverman, A. I., Tay, N., & Machairas, N.
Journal titleWater Research
Page(s)439-446AbstractSunlight 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 wetlandsSilverman, A. I., Sedlak, D. L., & Nelson, K. L.
Journal titleEnvironmental Engineering Science
Page(s)43-59AbstractUnit 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 watersBoehm, A. B., Silverman, A. I., Schriewer, A., & Goodwin, K.
Journal titleWater Research
Volume164AbstractSurface 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 approachesNelson, 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.
Journal titleEnvironmental Science: Processes and Impacts
Page(s)1089-1122AbstractHealth-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
Sunlight inactivation of viruses in open-water unit process treatment wetlands: Modeling endogenous and exogenous inactivation ratesSilverman, A. I., Nguyen, M. T., Schilling, I. E., Wenk, J., & Nelson, K. L.
Journal titleEnvironmental Science and Technology
Page(s)2757-2766AbstractSunlight 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
Quality of irrigation water used for urban vegetable productionKeraita, B., & Silverman, A. In Irrigated urban vegetable production in Ghana: characteristics, benefits and risk mitigation (2nd ed.).
Sunlight inactivation of ms2 coliphage in the absence of photosensitizers: Modeling the endogenous inactivation rate using a photoaction spectrum
Quantification of human norovirus GII, human adenovirus, and fecal indicator organisms in wastewater used for irrigation in Accra, Ghana
Sunlight inactivation of human viruses and bacteriophages in coastal waters containing natural photosensitizers
Comparison of enterovirus and adenovirus concentration and enumeration methods in seawater from Southern California, USA and Baja Malibu, Mexico
Human virus and bacteriophage inactivation in clear water by simulated sunlight compared to bacteriophage inactivation at a Southern California beachLove, D. C., Silverman, A., & Nelson, K. L.
Journal titleEnvironmental Science and Technology
Page(s)6965-6970AbstractFew quantitative data exist on human virus inactivation by sunlight and the relationship between human and indicator viruses under sunlit conditions. We investigated the effects of sunlight on human viruses (adenovirus type 2, poliovirus type 3) and bacteriophages (MS2, Q-Beta SP, Fi, M13, PRD1, Phi-X174, and coliphages isolated from Avalon Bay, California). Viruses were inoculated into phosphate buffered saline or seawater, exposed to a laboratory solar simulator for ≤12 h, and enumerated by double agar layer or cell culture to derive first-order inactivation rate constants (kobs, h -1). The viruses most resistant to sunlight were adenovirus type 2 (kobs= 0.59 ± 0.04 h-1) and bacteriophage MS2 (kobs= 0.43 ± 0.02 h-1), which suggests MS2 may be a conservative indicator for sunlight resistant human viruses in clear water when sunlight inactivation is the main removal mechanism. Reasonable agreement was observed between somatic coliphage inactivation rates measured in the solar simulator (kmean = 1.81 h-1) and somatic coliphages measured in the surf zone during a field campaign at Avalon Bay during similar sunlight intensity (k = 0.75 h-1 at log-RMSE minimum; k range = 0.54 h-1 to >1.88 h-1; Boehm, A. B. et al. Environ. Sci. Technol. 2009, 43, (21), 8046-8052). Hence, measuring sunlight inactivation rates of viruses in the laboratory can be used to estimate inactivation in the environment under similar sunlight and water quality conditions.