The potential to manage releases of Bacillus anthracis using bioretention and a high flow media filter: Results of simulated runoff testing with tracer spores Bacillus globigii.

The threat of bioterrorism has spurred research on the decontamination and containment of different agents. Anthrax [causative agent Bacillus anthracis (Ba)] is a disease that can lead to severe infections within human and animals, particularly when inhaled. This research investigated the use of spore-contaminated simulated runoff events into stormwater control measures (SCMs), which are designed to retain and improve the quality of runoff and may have the potential to filter and contain the spores. In this study, the effectiveness of a bioretention cell (BRC) and high flow media filter (HFMF) in Huron, Ohio, were evaluated for removal of Bacillus globigii (Bg) spores (a harmless cognate of Ba). Three 4-8 mm simulated runoff events were created for each SCM using a fire hydrant and Bg spores were injected into the runoff upstream of the SCM inlets. The BRC significantly (p < 0.001) outperformed the HFMF in reducing Bg concentrations and loads, with an average load reduction of 1.9 log (∼99% reduction) compared to 0.4 (∼60% reduction), respectively. A probable critical design factor leading to these differences was the infiltration rate of the media and subsequent retention time within the filters, which was supported by similar disparities in suspended solids reductions. Differences in spore removal may also have been due to particle size distribution of the HFMF, which was more gravelly than the bioretention cell. At 3 and 6 months after the-simulated runoff tests, soil samples taken from both SCMs, yielding detectable Bg spores within the top 15 cm of media, with increased spore concentrations where ponding occurred for longer durations during the tests. This suggests that forebays and areas near inlets may be hotspots for spore cleanup in a real-world bioterrorism incident.

Monitoring spore washoff during a biological contamination incident response using automated stormwater samplers and sensors to predict contamination movement.

This study examined the washoff of Bacillus globigii (Bg) spores from concrete, asphalt, and grass surfaces by stormwater. Bg is a nonpathogenic surrogate for Bacillus anthracis, which is a biological select agent. Areas (2.74 m × 7.62 m) of concrete, grass, and asphalt were inoculated twice at the field site during the study. Spore concentrations were measured in runoff water after seven rainfall events (1.2-65.4 mm) and complimentary watershed data were collected for soil moisture, depth of water in collection troughs, and rainfall using custom-built telemetry units. An average surface loading of 107.79 Bg spores/m2 resulted in peak spore concentrations in runoff water of 102, 260, and 4.1 CFU/mL from asphalt, concrete, and grass surfaces, respectively. Spore concentrations in the stormwater runoff were greatly reduced by the third rain event after both inoculations, but still detectable in some samples. When initial rainfall events occurred longer after the initial inoculation, the spore concentrations (both peak and average) in the runoff were diminished. The study also compared rainfall data from 4 tipping bucket rain gauges and a laser disdrometer and found they performed similarly for values of total rainfall accumulation while the laser disdrometer provided additional information (total storm kinetic energy) useful in comparing the seven different rain events. The soil moisture probes are recommended for assistance in predicting when to sample sites with intermittent runoff. Sampling trough level readings were critical to understanding the dilution factor of the storm event and the age of the sample collected. Collectively the spore and watershed data are useful for emergency responders faced with remediation decisions after a biological agent incident as the results provide insight into what equipment to deploy and that spores may persist in runoff water at quantifiable levels for months. The spore measurements are also a novel dataset for stormwater model parameterization for biological contamination of urban watersheds.

Using SWMM for emergency response planning: A case study evaluating biological agent transport under various rainfall scenarios and urban surfaces.

To assist in emergency preparedness for a biological agent terrorist attack or accidental pathogen release, potential contaminant levels and migration pathways of spores spread by urban stormwater were evaluated using a Storm Water Management Model (SWMM) of U.S. Coast Guard Base Elizabeth City, North Carolina. The high temporal-spatial resolution SWMM model was built using spore concentrations in stormwater runoff from asphalt, grass, and concrete collected from a point-scale field study. The subsequent modeled contamination scenarios included a notional plume release and point releases mimicking the field study under three rainfall conditions. The rainfall scenarios included a 6-hour natural rainfall event on Dec. 8, 2021 and two design storms (2-year and 100-year events). The observed spore concentrations from asphalt and concrete from the actual field experiment were applied to calibrate the washoff parameters in the SWMM model, using an exponential washoff function. The calibrated washoff coefficient (c1) and exponent (c2) were 0.01 and 1.00 for asphalt, 0.05 and 1.45 for grass, and 2.45 and 1.00 for concrete, respectively. The calibrated SWMM model simulated spore concentrations in runoff at times and magnitudes similar to the field study data. In the point release modeled scenario, the concrete surface generated 55.6% higher average spore concentrations than asphalt. Similarly, in the field experiment, a 175% (p < 0.05) higher average spore concentration in surface runoff was observed from concrete than from asphalt. This study demonstrates how SWMM may be used to evaluate spore washoff from urban surfaces under different precipitation amounts, intensities, and durations, and how visualized spatial migration pathways in stormwater runoff may be used for emergency planning and remediation.

Evaluation of disinfection methods for personal protective equipment (PPE) items for reuse during a pandemic.

The COVID-19 pandemic resulted in many supply chain issues, including crippling of essential personal protective equipment (PPE) needed for high-risk occupations such as those in healthcare. As a result of these supply chain issues, unprecedented crisis capacity strategies were implemented to divert PPE items such as filtering facepiece respirators (FFRs, namely N95s) to those who needed them most for protection. Large-scale methods for decontamination were used throughout the world to preserve these items and provided for their extended use. The general public also adopted the use of non-specialized protective equipment such as face coverings. So, the need for cleaning, decontamination, or disinfection of these items in addition to normal clothing items became a necessary reality. Some items could be laundered, but other items were not appropriate for washing/drying. To fill research gaps in small-scale, non-commercial cleaning and disinfection, this bench-scale research was conducted using small coupons (swatches) of multiple PPE/barrier protection materials inoculated with virus (non-pathogenic bacteriophages Phi6 and MS2) and tested against a range of decontamination methods including bleach-, alcohol- and quaternary ammonium compound (QAC)-based liquid sprays, as well as low concentration hydrogen peroxide vapor (LCHPV) and bench-scale laundering. In general, non-porous items were easier to disinfect than porous items, and the enveloped virus Phi6 was overall easier to inactivate than MS2. Multiple disinfection methods were shown to be effective in reducing viral loads from PPE coupons, though only laundering and LCHPV were effective for all materials tested that were inoculated with Phi6. Applications of this and follow-on full-scale research are to provide simple effective cleaning/disinfection methods for use during the current and future pandemics.

Impact of filter material and holding time on spore sampling efficiency in water.

Bacillus anthracis and other environmentally persistent pathogens pose a significant threat to human and environmental health. If contamination is spread over a wide area (e.g. resulting from a bioterrorism or biowarfare incident), readily deployable and scalable sample collection methods will be necessary for rapidly developing and implementing effective remediation strategies. A recent surge in environmental (eDNA) sampling technologies could prove useful for quantifying the extent and levels of contamination from biological agents in environmental and drinking water. In this study, three commonly used membrane filtration materials (cellulose acetate, cellulose nitrate, and nylon) were evaluated for spore filtration efficiency, yielding recoveries from 17%-68% to 25%-117% for high and low titer samples, respectively, where cellulose nitrate filters generated the highest recoveries. A holding time test revealed no statistically significant differences between spore recoveries when analyzed at the specified timepoints, suggesting that eDNA filter sampling techniques can yield and maintain a relatively high recovery of spores for an extended period of time between filtration and analysis without a detrimental impact on spore recoveries. The results shown here indicate that emerging eDNA technologies could be leveraged for sampling following a wide-area contamination incident and for other microbiological water sampling applications.

Evaluation of Malathion, DIMP, and Strawberry Furanone as CWA Simulants for Consideration in Field-Level Interior Building Remediation Exercises.

Field-level exercises with the purpose to assess remediation following the deliberate release of a highly toxic chemical in an indoor environment can be conducted using low(er) toxicity simulants if they are closely linked to the behavior of the toxic chemical itself. Chemical warfare agent (CWA) simulants have been identified on their suitability based on chemical structural similarities and associated physical and chemical properties. However, there are no reported studies that combine measurement of simulant parameters like persistence on surfaces, ability to sample for, and capability to degrade during the decontamination phase such that the level of success of a field-level exercise can be quantified. Experimental research was conducted to assess these gaps using a select number of CWA simulants. The organophosphate pesticide malathion was found to be a suitable simulant for use in field-level exercises that simulate the release of the highly persistent nerve agent VX based on its high persistence, effective surface sampling and analysis using standard analytical equipment, and the in situ degradation in the presence of different oxidizing decontaminants.

Evaluation of sample processing methods to improve the detection of Bacillus anthracis in difficult sample matrices.

Large area sampling approaches have been developed and implemented by the US Environmental Protection Agency (EPA) to increase sample sizes, and potentially representativeness, in outdoor urban environments (e.g., concrete, asphalt, grass/landscaping). These sampling approaches could be implemented in response to an outdoor biological contamination incident or bioterrorism attack to determine the extent of contamination and for clearance following remediation. However, sample collection over large areas often contains an extensive amount of co-collected debris and native background microorganisms that interfere with the detection of biological threat agents. Sample processing methods that utilize basic laboratory equipment amenable to field deployment were selected and applied to turbid aqueous samples (TAS) to reduce particulates and native environmental organisms prior to culture and rapid viability-polymerase chain reaction (RV-PCR) analytical methods. Bacillus anthracis Sterne (BaS) spores were spiked into TAS collected by soil grab, wet vacuum collection from an outdoor concrete surface, or storm water runoff from an urban parking lot. The implementation of a sample processing method improved the sensitivity of culture and RV-PCR analytical methods for BaS spore detection in soil and wet vacuum TAS samples compared to baseline (minimal to no field processing methods applied). For soil, when the processing method was applied, samples with 15 colony forming units (CFU)/ml (60 CFU/g) and 1.5 CFU/mL (6 CFU/g) BaS spore load were detected using culture and RV-PCR, respectively. Most notably, the processing methods greatly improved the sensitivity of the RV-PCR analytical method for the wet vacuum TAS from no detection at the 1500 CFU/mL BaS spore load level to as low as 1.5 CFU/mL BaS spore load.

Determining Viral Disinfection Efficacy of Hot Water Laundering.

This protocol provides an example of a laboratory process for conducting laundering studies that generate data on viral disinfection. While the protocol was developed for research during the coronavirus disease 2019 (COVID-19) pandemic, it is intended to be a framework, adaptable to other virus disinfection studies; it demonstrates the steps for preparing the test virus, inoculating the test material, assessing visual and integrity changes to the washed items due to the laundering process, and quantifying the reduction in viral load. Additionally, the protocol outlines the necessary quality control samples for ensuring the experiments are not biased by contamination and measurements/observations that should be recorded to track the material integrity of the personal protective equipment (PPE) items after multiple laundering cycles. The representative results presented with the protocol use the Phi6 bacteriophage inoculated onto cotton scrub, denim, and cotton face-covering materials and indicate that the hot water laundering and drying process achieved over a 3-log (99.9%) reduction in viral load for all samples (a 3-log reduction is the disinfectant performance metric in U.S. Environmental Protection Agency's Product Performance Test Guideline 810.2200). The reduction in viral load was uniform across different locations on the PPE items. The results of this viral disinfection efficacy testing protocol should help the scientific community explore the effectiveness of home laundering for other types of test viruses and laundering procedures.

Influence of wash aids on Bacillus spore removal from an asphalt parking lot using two spray-based washing methods.

AIMS: The goal of this study was to measure the removal efficacy of Bacillus atrophaeus spores from a parking lot using spray-based washing methods (a pressure washer and a garden hose) and wash aids. B. atrophaeus is a commonly used nonpathogenic surrogate for B. anthracis, the causative agent of anthrax and a deadly bioterrorism agent that would cause major disruptions and damage to public health should it be disseminated over an urban area. METHODS AND RESULTS: Five wash aids (1 mM sodium chloride, an Instant Ocean® seawater solution, 0.01% Tween 20, 0.01% sodium dodecyl sulfate, and unamended tap water) were used along with two different spray sequences in this study. Across all treatment conditions, 3.7-6.4 log10  colony forming unit were recovered in the runoff water, and 0.15%-23% of spores were removed from the surface of the parking lot. CONCLUSIONS: Pressure washing removed more spores than the garden hose, and for both types of washing methods, the first pass removed more spores than the subsequent passes. The Instant Ocean and Tween 20 wash aids were found to significantly increase the percentage of spore removal when using the pressure washer, but the overall increase was only 1%-2% compared to the tap water alone. SIGNIFICANCE AND IMPACT OF STUDY: This study provides public officials and emergency responders with baseline spore physical removal information for situations where a corrosive disinfectant might have a negative impact on the environment and washing is being considered as an alternative remediation approach.

Managing and treating per- and polyfluoroalkyl substances (PFAS) in membrane concentrates.

Per- and polyfluoroalkyl substances (PFAS), which are present in many waters, have detrimental impacts on human health and the environment. Reverse osmosis (RO) and nanofiltration (NF) have shown excellent PFAS separation performance in water treatment; however, these membrane systems do not destroy PFAS but produce concentrated residual streams that need to be managed. Complete destruction of PFAS in RO and NF concentrate streams is ideal, but long-term sequestration strategies are also employed. Because no single technology is adequate for all situations, a range of processes are reviewed here that hold promise as components of treatment schemes for PFAS-laden membrane system concentrates. Attention is also given to relevant concentration processes because it is beneficial to reduce concentrate volume prior to PFAS destruction or sequestration. Given the costs and challenges of managing PFAS in membrane concentrates, it is critical to evaluate both established and emerging technologies in selecting processes for immediate use and continued research.

Emergency response to stormwater contamination: A framework for containment and treatment.

This paper presents a Stormwater Emergency Response Framework (SERF) for use in the containment and treatment of stormwater runoff following a hazardous material release. The framework consists of four high level process steps and a decision tree. These resources are intended to assist stormwater managers in fulfilling their emergency response responsibilities within the United States' National Incident Management System. Robust hydraulic and watershed modeling may take weeks to months to develop for a contaminated site, whereas decisions made in the initial hours can have a significant impact on limiting contamination spread. Many web resources are publicly available to assist responders in visualizing stormwater runoff flow paths. A case study provided in this paper also demonstrates how simple calculations may be utilized to estimate peak flows and storage volumes necessary to respond to precipitation events immediately. These calculations are useful for decision makers' allocation of containment and treatment resources within the impacted area. This includes where to deploy available resources to minimize contamination risks to downstream communities and where supplemental resources from outside partners are urgently needed.

Modeling radionuclide transport in urban overland flow: a case study.

This paper presents a case study demonstrating the process used to develop an overland flow model of radionuclide transport following an aerosol deposition from a hypothetical radiological dispersal device explosion. The process included the integration of digital elevation, building, and land cover information with hydrologic information from a calibrated Stormwater Management Model (SWMM) model. The overland flow model was used to explore the impact of washoff parameter selection and different storm events on radionuclide transport in surface flow. The range of washoff parameters used in the literature resulted in over a 7 times difference in radionuclide washoff, from a small surface removal to nearly full removal. The overland flow model illuminated the primary pathways of contaminant transport, a potentially useful tool that informs emergency response, planning, and remediation activities.

Rainfall Washoff of Spores From Concrete and Asphalt Surfaces.

After a biological terrorist attack, understanding the migration of agents such as Bacillus anthracis is critical due to their deadly nature. This is important in urban settings with higher likelihood of human exposure and a large fraction of impervious materials contributing to pollutant washoff. The study goals were to understand the removal of spores from urban surfaces under different rainfall conditions, to compare washoff of two B. anthracis surrogate spores, and to compare two empirical fits for the first flush of spores from small areas. Concrete and asphalt were inoculated with either Bacillus atrophaeus or Bacillus thuringiensis kurstaki spores and exposed to simulated rainfall. The study assessed goodness-of-fit for the Storm Water Management Model (SWMM)'s exponential washoff function compared to an alternative two-stage exponential function. The highest average washoff of spores was 15% for an hour-long experiment. Spore washoff was not significantly different for the two spore types, but there were significant differences in washoff from asphalt versus concrete with more occurring from asphalt. Average kinetic energy of the storm event impacted washoff from asphalt, but not concrete. The two-stage function had a better goodness-of-fit than the SWMM exponential function. As such, emergency responders should be aware that the spread of contamination is impacted by the droplet characteristics of the storm event and the surface material type in the contaminated area; modelers should be aware that different data-fitting approaches may be more appropriate for first-flush calculations of small washoff areas than those used for continuous long-term simulation of large subcatchments.

Decontamination of soil contaminated at the surface with Bacillus anthracis spores using dry thermal treatment.

In the event of a large, aerosol release of Bacillus anthracis spores in a major metropolitan area, soils and other outdoor materials may become contaminated with the biological agent. A study was conducted to assess the in-situ remediation of soil using a dry thermal treatment approach to inactivate a B. anthracis spore surrogate inoculated into soil samples. The study was conducted in two phases, using loam, clay and sand-based soils, as well as biological indicators and spore-inoculated stainless-steel coupons. Initial experiments were performed in an environmental test chamber with temperatures controlled between 80 and 110 °C, with and without added humidity, and with contact times ranging from 4 h to 7 weeks. Tests were then scaled up to assess the thermal inactivation of spores in small soil columns, in which a heating plate set to 141 °C was applied to the soil surface. These column tests were conducted to assess time requirements to inactivate spores as a function of soil depth and soil type. Results from the initial phase of testing showed that increasing the temperature and relative humidity reduced the time requirements to achieve samples in which no surrogate spores were detected. For the test at 80 °C with no added humidity, 49 days were required to achieve soil samples with no spores detected in clay and loam. At 110 °C, 24 h were required to achieve samples in which no spores were detected. In the column tests, no spores were detected at the 2.5 cm depth at four days and at the 5.1 cm depth at 21 days, for two of the three soils. The experiments described in the study demonstrate the feasibility of using dry thermal techniques to decontaminate soils that have been surficially contaminated with B. anthracis spores.

Laboratory results and mathematical modeling of spore surface interactions in stormwater runoff.

Development of numerical models to predict stormwater-mediated transport of pathogenic spores in the environment depends on an understanding of adhesion forces that dictate detachment after rain events. Zeta potential values were measured in the laboratory for Bacillus globigii and Bacillus thuringiensis kurstaki, two common surrogates used to represent Bacillus anthracis, in synthetic baseline ultrapure water and laboratory prepared stormwater. Zeta potential curves were also determined for materials representative of urban infrastructure (concrete and asphalt). These data were used to predict the interaction energy between the spores and urban materials using Derjaguin-Landau-Verwey-Overbeek (DLVO) modeling. B. globigii and B. thuringiensis kurstaki sourced from Yakibou Inc., were found to have similar zeta potential curves, whereas spores sourced from the U.S. military's Dugway laboratory were found to diverge. In the ultrapure water, the modeling results use the laboratory data to demonstrate that the energy barriers between the spores and the urban materials were tunable through compression of the electrical double layer of the spores via changes of ionic strength and pH of the water. In the runoff water, charge neutralization dominated surface processes. The cations, metals, and natural organic matter (NOM) in the runoff water contributed to equalizing the zeta potential values for Dugway B. globigii and B. thuringiensis kurstaki, and drastically modified the surface of the concrete and asphalt. All DLVO energy curves using the runoff water were repulsive. The highest energy barrier predicted in this study was for Dugway B. globigii spores interacting with a concrete surface in runoff water, suggesting that this would be the most challenging combination to detach through water-based decontamination.

Comparison of surface sampling methods for an extended duration outdoor biological contamination study.

Bacillus anthracis, the causative agent for anthrax, is a dangerous pathogen to humans and has a history as a bioterrorism agent. While sampling methods have been developed and evaluated for characterizing and clearing contaminated indoor sites, the performance of these sampling methods is unknown for use in outdoor environments. This paper presents surface sampling data for Bacillus atrophaeus spores, a surrogate for B. anthracis, from a 210-day outdoor study that evaluated the detection and recovery of spores using five different sampling methods as follows: sponge sticks, 37-mm vacuum filter cassettes, residential wet vacuums, robotic floor cleaners, and grab samples of soil, leaves, and grass. The spores were applied by spraying a liquid suspension onto the surfaces. Both asphalt and concrete surfaces were sampled by all the surface sampling methods, excluding grab sampling. Stainless steel coupons placed outdoors were additionally sampled using sponge sticks. Sampling methods differed in their ability to collect detectable spores over the duration of the study. The 37-mm vacuums and sponge sticks consistently detected spores on asphalt through day 37 and robots through day 99. The wet vacuums detected spores on asphalt for days 1 and 4, but not again until day 210. On concrete, all samplers detected spores until day 210 except for sponge stick samplers that detected spores only up until the day 99 time point. For all sampling methods, spore recoveries were higher from concrete than from asphalt surfaces. There was no statistically significant difference in recoveries of sponge sticks and 37-mm vacuums from either asphalt or concrete surfaces. Processing of grab samples was challenging due to non-target background microorganisms resulting in high detection limits for the samples.

Characterizing cesium sorption in freshwater settings using fluvial sediments and characteristic water chemistries.

Cesium-137 (137Cs) is a persistent contaminant that poses a significant risk to human health and the environment. Understanding the fate and transport of 137Cs following a contamination incident is necessary for effective containment and remediation. In this study, we performed experiments to investigate how Cs+ sorption processes are affected by sediment type and varying water chemistries to better understand how Cs+ is transported in freshwater settings. Sediment was collected from various river deposits along the Susquehanna River adjacent to the Safety Light Corporation United States Environmental Protection Agency (US EPA) Superfund site (Bloomsburg, PA) and characterized prior to being used in batch reactor experiments with waters characteristic of different regions in the US (Central US and Northeast US) and with three different cation types (Mg2+, Na+, and K+) over a range of ionic strengths. Greater amounts of Cs+ sorption occurred with increasing sediment mud (silt and clay) content, although no major differences in sorption between the Central and Northeast US water types were observed. At an ionic strength (I) of 10 mM, K+ inhibited Cs+ sorption most effectively, followed by Mg2+, with Na+ having little effect on Cs+ sorption over the range of ionic strengths tested (I = 0.1, 1, and 10 mM). Our findings indicate that for the representative freshwater conditions tested here, sediment type (e.g., clay fraction) has a greater influence on Cs+ sorption processes than water chemistry. Additional reactions or processes occurring in relatively fresh water could buffer cation competition for sorption sites. Conducting experiments using site-specific sediment samples and water chemistries is useful for predicting Cs+ sorption and mobility in distinct environmental settings, particularly when the level of Cs+ contamination is high and if the waste or contaminated (or receiving) waters have a relatively high ionic strength.

Perceived versus actual water quality: Community studies in rural Oaxaca, Mexico.

Compromised water quality risks public health, which becomes particularly acute in economically marginalized communities. Although the majority of the clean-water-deprived population resides in Sub-Saharan Africa and Asia, a significant portion (32 million) lives in Meso- and Latin-America. Oaxaca is one of the marginalized southern states of Mexico, which has experienced high morbidity from infectious diseases and also has suffered from a high rate of infant mortality. However, there has been a paucity of reports on the status of water quality of culturally diverse rural Oaxaca. This study follows community-based participatory research methods to address the data gap by reporting on water quality (chemical and microbiological) and by exploring social realities and water use practices within and among communities. Surveys and water quality analyses were conducted on 73 households in three rural communities, which were selected based on the choice of water sources (i.e., river water, groundwater, and spring water). Statistically significant variations among communities were observed including the sanitation infrastructure (p-value 0.001), public perception on water quality (p-value 0.007), and actual microbiological quality of water (p-value 0.001). Results indicate a high prevalence of diarrheal diseases, a desire to improve water quality and reduce the cost of water, and a need for education on water quality and health in all the surveyed communities. The complexities among the three studied communities highlight the need for undertaking appropriate policies and water treatment solutions.

Multilevel modeling of retention and disinfection efficacy of silver nanoparticles on ceramic water filters.

This research examined how variations in synthesis methods of silver nanoparticles affect both the release of silver from ceramic water filters (CWFs) and disinfection efficacy. The silver nanoparticles used were stabilized by four different molecules: citrate, polyvinylpyrrolidone, branched polyethylenimine, and casein. A multilevel statistical model was built to quantify if there was a significant difference in: a) extent of silver lost, b) initial amount of silver lost, c) silver lost for water of different quality, and d) total coliform removal. Experiments were performed on location at Pure Home Water, a CWF factory in Tamale, Ghana using stored rainwater and dugout water (a local surface water). The results indicated that using dugout vs. rainwater significantly affects the initial (p-value 0.0015) and sustained (p-value 0.0124) loss of silver, but that silver type does not have a significant effect. On average, dugout water removed 37.5µg/L more initial silver and had 1.1µg/L more silver in the filtrate than rainwater. Initially, filters achieved 1.9 log reduction values (LRVs) on average, but among different silver and water types this varied by as much as 2.5 LRV units. Overall, bacterial removal effectiveness was more challenging to evaluate, but some data suggest that the branched polyethylenimine silver nanoparticles provided improved initial bacterial removal over filters which were not painted with silver nanoparticles (p-value 0.038).

DLVO Approximation Methods for Predicting the Attachment of Silver Nanoparticles to Ceramic Membranes.

This article examines the influence of three common stabilizing agents (citrate, poly(vinylpyrrolidone) (PVP), and branched poly(ethylenimine) (BPEI)) on the attachment affinity of silver nanoparticles to ceramic water filters. Citrate-stabilized silver nanoparticles were found to have the highest attachment affinity (under conditions in which the surface potential was of opposite sign to the filter). This work demonstrates that the interaction between the electrical double layers plays a critical role in the attachment of nanoparticles to flat surfaces and, in particular, that predictions of double-layer interactions are sensitive to boundary condition assumptions (constant charge vs constant potential). The experimental deposition results can be explained when using different boundary condition assumptions for different stabilizing molecules but not when the same assumption was assumed for all three types of particles. The integration of steric interactions can also explain the experimental deposition results. Particle size was demonstrated to have an effect on the predicted deposition for BPEI-stabilized particles but not for PVP.