Log Removal Values Research Articles

Longitudinal Surveillance of Antibiotic Resistance in Escherichia coli and Enterococcus spp. from a Wastewater Treatment Plant and Its Associated Waters in KwaZulu-Natal, South Africa.

We assessed the prevalence, distribution, and antibiotic resistance patterns of Escherichia coli and Enterococcus spp. isolated from raw and treated wastewater of a major wastewater treatment plant (WWTP) in KwaZulu-Natal, South Africa and the receiving river water upstream and downstream from the WWTP discharge point. Escherichia coli and enterococci were isolated and counted using the Colilert®-18 Quanti-Tray® 2000 and Enterolert®-18 Quanti-Tray 2000 systems, respectively. A total of 580 quantitative PCR-confirmed E. coli and 579 enterococci were randomly chosen from positive samples and tested for in vitro antibiotic susceptibility using the disk diffusion assay against 20 and 16 antibiotics, respectively. The removal success of the bacterial species through the treatment procedure at the WWTP was expressed as log removal values (LRVs). Most E. coli were susceptible to meropenem (94.8%) and piperacillin-tazobactam (92.9%), with most Enterococcus susceptible to ampicillin (97.8%) and vancomycin (96.7%). In total, 376 (64.8%) E. coli and 468 (80.8%) Enterococcus isolates showed multidrug resistance (MDR). A total of 42.4% (246/580) E. coli and 65.1% (377/579) enterococci isolates had multiple antibiotic resistance indices >0.2. The LRV for E. coli ranged from 2.97 to 3.99, and for enterococci the range was observed from 1.83 to 3.98. A high proportion of MDR E. coli and enterococci were present at all sampled sites, indicating insufficient removal during wastewater treatment. There is a need to appraise the public health risks associated with bacterial contamination of environmental waters arising from such WWTPs to protect the health of users of the receiving water bodies.

Silver and zinc oxide nanoparticle disinfection in water treatment applications: synergy and water quality influences

Abstract The synergistic potential of silver and zinc oxide nanoparticles for water disinfection was investigated herein. By causing cell death through membrane interactions, oxidative killing, and DNA deactivation, metallic nanoparticles may be integrated with point-of-use water treatment systems for applications in rural and remote geographies. Disinfection efficacy was evaluated in batch-phase experiments under both synthetic and real water conditions, where synthetic water was varied by pH and dissolved oxygen levels. Ceramic pot filters with comparative nanoparticle concentrations were also investigated. In all cases, combinations of silver and zinc nanoparticles resulted in improved disinfection in comparison to either metal in isolation. In batch experiments, dissolved oxygen proved to be particularly impactful, with kinetic rates reducing approximately 45% when in low oxygen environment (<3 mg/L) versus high oxygen (>8 mg/L). Log removal values (LRVs) were further, on average, 31% lower in real water than synthetic water after 300 min, though silver–zinc combinations were still superior to either metal alone. In filters, those impregnated with 67% silver and 33% zinc achieved average LRVs of 2.7 and 2.9 after 60 min of filtration and 24 h of storage, respectively, while those with only silver achieved average LRVs of 2.0 and 3.1 at those same times.

Fabrication, tuning and performance analysis of polyacrylonitrile (PAN)-derived microfiltration membranes for bacteria removal from drinking water

Removal of bacterial contaminations from water using advanced technologies is one of the essential steps in improving human health. The present study’s aim was to develop high performance microfiltration membranes from polyacrylonitrile (PAN) for bacteria removal from drinking water. The characteristics and performance of membranes were tuned through exploring the variation of prominent fabrication and operating parameters. The findings reveal that increasing PAN concentration in dope and addition of citric acid were successful in tailoring membrane microstructure. Bacteria rejection in modified membranes improved by exhibiting high log removal values (LRV) ranging from 3.92 (99.87%) to 5.57 (99.99%) while permeate fluxes were in the range of 35.83–58.62 L·m−2·h−1. The trends are explained by taking into account the structural characteristics of bacterial strains. Exploring the effect of operating parameters on the performance of membranes revealed that increase in feed concentration from 103 to 107 cfu·ml−1 improved membrane rejection. The largest rejection (5.57) was observed toward Staphylococcus aureus at feed concentration of 107 cfu·ml−1. Similarly, rejection improved upon reducing operating pressure from 3.5 to 1.5 bar. Also, shifting of feed pH to 7.4 and 9.4 enhanced membrane rejection to as high as 4.60 and 5.66 toward E. coli and Staphylococcus aureus, respectively. This was attributed to the zeta potential and isoelectric point values of the membranes and involved strains. Overall, the findings revealed that the developed PAN membranes are more effective in removal of gram-positive strains and their rejection is strongly dependent on the peptidoglycan layer of strains.

Determination of log removal values of bacteria by spiral-wound reverse osmosis modules and a hollow fiber ultrafiltration module using Escherichia coli and indigenous heterotrophic bacteria as indicators.

The use of reverse osmosis (RO) membranes has been expanding not only to medical applications but also to water supply and reclaimed water applications due to its strong ability to remove a wide range of contaminants. Many researchers reported RO performance as a barrier against waterborne viruses; however, there are limited reports on its ability to remove bacteria from water. This investigation evaluated the removal performances of several spiral-wound RO modules and a hollow fiber ultrafiltration (UF) module in two different ways: dosing tests in batch-wise mode operation and in continuous-mode operation. The dosing tests of Escherichia coli using RO modules confirmed that E. coli could leak from the feed-side into the permeate. The log removal values (LRVs) (4.21- to >7.44-log10) by the RO modules from different production lots were found to vary greatly. In continuous-mode operation of the RO module, the LRVs for indigenous heterotrophic bacteria decreased over the operation period. These results clearly illustrate that bacteria, which originate on the feed-side, can leak into the permeate-side and then begin to proliferate in the permeate. On the other hand, using a UF module, E. coli was not detected in the permeate regardless of the operation mode.

Biosand Filter as a Point-of-Use Water Treatment Technology: Influence of Turbidity on Microorganism Removal Efficiency

The number of people living without access to clean water can be reduced by the implementation of point-of-use (POU) water treatment. Among POU treatment systems, the domestic biosand filter (BSF) stands out as a viable technology. However, the performance of the BSF varies with the inflow water quality characteristics, especially turbidity. In some locations, people have no choice but to treat raw water that has turbidity above recommended levels for the technology. This study aimed to measure the efficiency with which the BSF removes microorganisms from well water and from fecal-contaminated water with turbidity levels of 3, 25, and 50 NTU. Turbidity was controlled by the addition of kaolin to water. Turbidity removal varied from 88% to 99%. Reductions in total coliform (TC) and Escherichia coli ranged from 0.54–2.01 and 1.2–2.2 log removal values (LRV), respectively. The BSF that received water with a higher level of turbidity showed the greatest reduction in the concentration of microorganisms. Additional testing with water contaminated with four bacterial pure cultures showed reductions between 2.7 and 3.6 LRV. A higher reduction in microorganisms was achieved after 30–35 days in operation. Despite the filter’s high efficiency, the filtrates still had some microorganisms, and a disinfection POU treatment could be added to increase water safety.

Disinfection enhancement of single ozonation by combination with peroxymonosulfate salt

Controlling pathogens and undesired biofouling in aquaculture or shipping activities is important due to the related potential economic and public health impacts. Accordingly, the treatment of seawater has increased interest in the maritime industry. Advanced Oxidation Processes are promising techniques for the treatment of different aqueous matrices. In this context, sulfate radical-based AOPs appear to be a good alternative for seawater applications. Consequently, the goal of this study is to evaluate the disinfection efficacy of combining the peroxymonosulfate salt ([PMS] = 1 and 5 mg L−1) with an ozonation treatment. Different inactivation processes (O3, PMS, and O3/PMS) have been investigated with Vibrio alginolyticus as a target microorganism. In comparison with single ozonation, kinetic rates have been accelerated by 65 % and 123 % with the addition of 1 and 5 mg L−1 of PMS, respectively. It results in a synergistic effect for the O3/PMS combination. The transferred ozone dose is also notably reduced for reaching the 4 Log-removal value (O3: 1.53 mg O3 ·L−1; O3/PMS: 0.87 mg O3 ·L−1 (1 mg PMS·L−1), and 0.59 mg O3 ·L−1 (5 mg PMS·L−1)). O3/PMS treatment also presents a greater residual effect and higher acute toxicity of the treated effluent. Results obtained suggest the peroxymonosulfate as a good promoter of disinfection in the presence of O3, not only by increasing the inactivation rate but also in minimizing bacterial regrowth, which implies greater cell damage during treatment processes. Thus, the O3/HSO5- process deserves further research as an alternative to traditional techniques for water treatment.

Contribution of biofilm layer to virus removal in gravity-driven membrane systems with passive fouling control

Passive gravity-driven membrane (PGM) filtration is a type of gravity-driven membrane (GDM) filtration operated with passive physical fouling control measures that add limited to no complexity to the system (e.g. permeate flux interruptions, gravity-driven air scouring, system draining), allowing a greater permeate flux to be sustained. A key aspect of PGM/GDM systems is the development of a structurally loose and permeable biofilm layer on the membrane that enables a sustainable flux to be achieved and has also been associated with improved removal of humic acids, polysaccharides, proteins, assimilable organic carbon and microcystins. The present study investigated if the biofilm layer of PGM systems also contributes to virus removal, for both intact and breached PGM systems. Breach sizes considered ranged from 20 to 180 µm. Challenge tests (CTs) identified an increase of 2.0+ in the log removal value (LRV) for viruses in both intact and breached PGM systems when a biofilm layer was present, suggesting that the biofilm layer is capable of bridging the gap over integrity breaches, acting as a secondary barrier to contaminants that would otherwise bypass treatment by flowing through the breach. Pressure decay tests (PDTs), however, did not identify the same increase in LRVs as that of CTs, suggesting that the standard PDT approach cannot consider the contribution of the biofilm layer to the removal of small material such as viruses. An alternative integrity testing protocol for PGM systems was developed using a modified PDT approach that takes into account the additional removal provided by the biofilm layer. This alternative protocol is also simpler and requires less frequent testing, contributing to the simplification of overall operation of PGM systems in small/remote communities and decentralized applications.

Performance Evaluation of Water Filter Made from Oyong (<i>Luffa сylindrica</i>) Fiber Coated with Silver Nano Particles for Coliform Bacteria Removal in Wastewater

Oyong fiber (OF) is widely available natural fiber, the material characteristics and porosity make it a suitable alternative for filtration media. Accordingly, to investigate the potential use of OF as filter material in the wastewater disinfection process, this study applied different silver nanoparticles coating onto OF and proposed a new filter structure at lower cost. The OF coated AgNPs and OF coated Ag-GO were successfully synthesized following the chemical reduction methods as reported in the literature. SEM image shown that silver nanoparticles were randomly distributed on the surface of OF. Both OF coated AgNPs and Ag-GO exhibited a good disinfection capability for Total Coliform removal from wastewater. The OF coated Ag-GO have better Total Coliform Log Removal Value (LRV) of 3.3 and still maintain stable disinfection ability even at high filtration rate.

Solar Powered Microplasma-Generated Ozone: Assessment of a Novel Point-of-Use Drinking Water Treatment Method.

Ozonation is widely used in high-income countries for water disinfection in centralized treatment facilities. New microplasma technology has reduced the energy requirements for ozone generation dramatically, such that a 15-watt solar panel is sufficient to produce small quantities of ozone. This technology has not been used previously for point-of-use drinking water treatment. We conducted a series of assessments of this technology, both in the laboratory and in homes of residents of a village in western Kenya, to estimate system efficacy and to determine if the solar-powered point-of-use water ozonation system appears safe and acceptable to end-users. In the laboratory, two hours of point-of-use ozonation reduced E. coli in 120 L of wastewater by a mean (standard deviation) of 2.3 (0.84) log-orders of magnitude and F+ coliphage by 1.54 (0.72). Based on laboratory efficacy, 10 families in Western Kenya used the system to treat 20 L of household stored water for two hours on a daily basis for eight weeks. Household stored water E. coli concentrations of >1000 most probable number (MPN)/100 mL were reduced by 1.56 (0.96) log removal value (LRV). No participants experienced symptoms of respiratory or mucous membrane irritation. Focus group research indicated that families who used the system for eight weeks had very favorable perceptions of the system, in part because it allowed them to charge mobile phones. Drinking water ozonation using microplasma technology may be a sustainable point-of-use treatment method, although system optimization and evaluations in other settings would be needed.

Removal of MS‐2 coliphage in full‐scale reverse osmosis systems

AbstractRecent activity in the potable reuse field will incorporate reverse osmosis (RO) processes that will be required to provide pathogen removal. The California State Water Resources Control Board has implemented a 12‐10‐10 log removal value (LRV) requirement for viruses, Giardia, and Cryptosporidium for groundwater recharge projects. Depending on the details of a Surface Water Source Augmentation Project, new regulations in 2018 specify an additional log reduction requirement up to a total of 14‐12‐12. Regulatory requirements that specify a treatment technique (e.g., RO) and establish log removal requirements for treatment trains are being implemented. Surrogate indicators such as electrical conductivity (EC) and total organic carbon (TOC) reduction are currently being used as online indicators to determine compliance of RO systems. The actual virus removal through a full‐scale operating system is something that has not been extensively characterized. Most of the information that exists for testing with viruses is associated with bench‐ or pilot‐scale evaluations. Evaluations of permeate from full‐scale RO systems operating with wastewater effluent as the source water indicate that viruses are not present; however, concerns remain about the potential loss of integrity through the RO system. Under the regulatory criteria established in the US Environmental Protection Agency Membrane Filtration Guidance Manual for drinking water, bulk surrogate indicators such as EC or TOC lack the sensitivity to accurately measure the actual log reduction for pathogens. It is generally recognized that the feed water quality matrix can be variable in composition, which can also affect the measurement. Bulk surrogate indicators do not satisfy the criteria for being discretely quantifiable, a term that is synonymous with the indicator having a specific molecular weight or defined composition. While alternative chemical markers such as fluorescence compounds, sulfate, or strontium yield higher LRVs, the methods are not easily implemented. An underlying issue with these indicators is that, because of their small size, they will also diffuse through the membrane and understate the pathogen removal that is occurring. An article presented in Journal AWWA proposes that the results of a conductivity profile can be used to increase the sensitivity and calculate a higher LRV. Using the dilution model as the underlying approach, the technique differentiates conductivity that would be associated with diffusion from conductivity that would be associated with a defect. Literature review of prior work with MS‐2 challenge studies has been limited to small‐scale pilot evaluations. Information regarding the removal of MS‐2 coliphage in a typical production system was not present in literature. Conceptually, there should be no difference in MS‐2 removal between a pilot‐ and a full‐scale system; however, loss of rejection due to membrane aging may be a consideration. This article provides the challenge test results of MS‐2 bacteriophage (virus) through a full‐scale RO train operating in a water recycling facility. Challenge testing was performed at various operating conditions and includes the conductivity profiling results to characterize removal under integral, as well as intentionally compromised, conditions.

An Overview of the Design Principles of Drinking Water Chlorination

The goal of drinking water chlorination is the inactivation of pathogenic organisms in water. It offers the advantage of producing residuals useful for the preservation of water quality in a distribution system. Basic key chlorination concepts include chlorine demand/decay, chlorine residuals, and CT disinfection. The application of these concepts required a good understanding of the hydraulic condition of the system. Important consideration is the determination of initial required chlorine dose. A demonstration model using a public school water supply scheme with an overhead tank is done. This incorporates the kinematic of Contact Time (CT) disinfection, and the application of a demand model for the determination of initial chlorine concentration/dose required. Optimal application of chlorine will prevent incidences of either an over-dose or under-doze which highlight the importance of this study. Keywords— chlorine demand, CT Disinfection, initial chlorine concentration, log removal value, residual concentration.

Effective removal of fluorescent microparticles as Cryptosporidium parvum surrogates in drinking water treatment by metallic membrane

The diarrhoea-causing parasitic protozoan Cryptosporidium parvum (C. parvum) cannot be efficiently removed by conventional drinking water treatment and poses a biological threat to public health. To ensure the biological safety, three kinds of metallic membranes, laminating metal mesh filter, non-woven metal filter and sintered metal fiber filter were employed to compare their properties. The results showed that the sintered membrane possessed the best filtration performance and lowest membrane resistance among three metallic membranes. Therefore, the sintered membrane was selected for subsequent experiments. Due to the low infectious dose of C. parvum and sophisticated detection methods, fluorescent particle tracers, Crypto-tracer-1, were chosen as a feasible surrogate was proposed to investigate the removal efficiency of sintered membrane for C. parvum. The results indicated that the tracer log removal value (LRV) ranged between 5.1 and 5.4 log10 under different filtration flux, which equivalently means that C. parvum could be completely removed and further tests are needed to confirm the results obtained using C. parvum. Furthermore, a pilot-scale study was performed for 10 weeks in full-scale drinking water treatment systems. The turbidity could be efficiently removed (outlet water of membrane was 0.08 ± 0.04 NTU) and the average transmembrane pressure recovery rate was 84.6% after physical backwash. Fouling mechanism analysis indicated that the interaction energy between foulants and membrane material became stronger over time. The practical operation results showed that sintered membrane performed well in continuous operation for a long time and also had a good anti-pollution ability. These findings could facilitate application of metallic membrane in drinking water treatment.

Fate of antibiotic resistance genes in reclaimed water reuse system with integrated membrane process

The fate of antibiotic resistance genes (ARGs) in reclaimed water reuse system with integrated membrane process (IMR) was firstly investigated. Results indicated that ARGs, class 1 integrons (intI1) and 16S rRNA gene could be reduced efficiently in the IMR system. The absolute abundance of all detected ARGs in the reuse water after reverse osmosis (RO) filtration of the IMR system was 4.03 × 104 copies/mL, which was about 2–3 orders of magnitude lower than that in the raw influent of the wastewater treatment plants (WWTPs). Maximum removal efficiency of the detected genes was up to 3.8 log removal values. Daily flux of the summation of all selected ARGs in the IMR system decreased sharply to (1.02 ± 1.37) ×1014 copies/day, which was 1–3 orders of magnitude lower than that in the activated sludge system (CAS) system. The strong clustering based on ordination analysis separated the reuse water from other water samples in the WWTPs. Network analysis revealed the existence of potential multi-antibiotic resistant bacteria. The potential multi-antibiotic resistant bacteria, including Clostridium and Defluviicoccus, could be removed effectively by microfiltration and RO filtration. These findings suggested that the IMR system was efficient to remove ARGs and potential multi-antibiotic resistant bacteria in the wastewater reclamation system.

Does Activated Silver Reduce Recontamination Risks in the Reservoirs of Ceramic Water Filters?

Efforts to provide safe water are challenged by recontamination and regrowth of pathogens in treated water during storage. This study evaluated the potential of metallic silver with a chemically etched surface to reduce recontamination risks during water storage in ceramic water filters. Batch experiments were conducted in the laboratory with water storage buckets containing three configurations of varying amounts of silver. Field trials in a rural area in Kenya assessed the effect of the same configurations in the storage buckets of locally produced ceramic pot filters without colloidal silver coating. The tests revealed that the etched silver slightly reduced microbiological recontamination risks during water storage despite the low diffusion of silver ions (<5 µg Ag/L). The effect was strongly influenced by water chemistry parameters. A statistically significant difference in the removal of E. coli (Δ Log Removal Value (LRV) = 0.6) and total coliforms (Δ LRV = 1.7) was found between households using a filter with silver in the water reservoir and those using a filter without silver. Multivariate regression of water handling factors and hygiene practices on filter performance revealed that the presence of silver in the reservoir and cleaning the filter element with a brush were associated with a better filter performance.

Integration of Membrane Bioreactor and Nanofiltration for the Treatment Process of Real Hospital Wastewater in Ho Chi Minh City, Vietnam

Hospital wastewater contains pharmaceutical residues, chemicals, and pathogens that cause coloration and nourish pathogenic microorganisms. The objective of the study was to evaluate the effectiveness of a medical wastewater treatment system at Military Hospital 175 (Ho Chi Minh City, Vietnam) that combined a membrane bioreactor (MBR) system with nanofiltration (NF). The influent of the system was the wastewater discharged from the operating rooms of the hospital. The system has a capacity of 50 L/day and operates at three organic load rates (OLR) of 0.5, 1.5 and 2.5 kgCOD/m3day (COD: Chemical oxygen demand), in which each load rate operates for 40 days. The results showed that most nutritional criteria generally achieved positive results. Specifically, the average COD removal was shown to be consistently high throughout the three phases at 94%, 93.3%, and 92.7%, respectively. For removal of nitrogen, the system demonstrated efficiencies of 75%, 79%, and 83%, respectively, to three phases. The log removal value (LRV) for Escherichia coli and coliform bacteria were higher than four throughout the study period. The average removal efficiency for color and total iron was approximately 98% and 99%, respectively. The water quality after treatment, especially after NF, meets the Vietnamese standard of grade A. The arrangement in which the MBR preceded NF was also found to limit the amount of soil and solids entering subsequent treatment, which therefore improved the efficiency of NF, as demonstrated by the stability of post-NF transmembrane pressures throughout three cycles renewed by two backwashes.

Metagenomic and Resistome Analysis of a Full-Scale Municipal Wastewater Treatment Plant in Singapore Containing Membrane Bioreactors.

Reclaimed water provides a water supply alternative to address problems of scarcity in urbanized cities with high living densities and limited natural water resources. In this study, wastewater metagenomes from 6 stages of a wastewater treatment plant (WWTP) integrating conventional and membrane bioreactor (MBR) treatment were evaluated for diversity of antibiotic resistance genes (ARGs) and bacteria, and relative abundance of class 1 integron integrases (intl1). ARGs confering resistance to 12 classes of antibiotics (ARG types) persisted through the treatment stages, which included genes that confer resistance to aminoglycoside [aadA, aph(6)-I, aph(3′)-I, aac(6′)-I, aac(6′)-II, ant(2″)-I], beta-lactams [class A, class C, class D beta-lactamases (blaOXA)], chloramphenicol (acetyltransferase, exporters, floR, cmIA), fosmidomycin (rosAB), macrolide-lincosamide-streptogramin (macAB, ereA, ermFB), multidrug resistance (subunits of transporters), polymyxin (arnA), quinolone (qnrS), rifamycin (arr), sulfonamide (sul1, sul2), and tetracycline (tetM, tetG, tetE, tet36, tet39, tetR, tet43, tetQ, tetX). Although the ARG subtypes in sludge and MBR effluents reduced in diversity relative to the influent, clinically relevant beta lactamases (i.e., blaKPC, blaOXA) were detected, casting light on other potential point sources of ARG dissemination within the wastewater treatment process. To gain a deeper insight into the types of bacteria that may survive the MBR removal process, genome bins were recovered from metagenomic data of MBR effluents. A total of 101 close to complete draft genomes were assembled and annotated to reveal a variety of bacteria bearing metal resistance genes and ARGs in the MBR effluent. Three bins in particular were affiliated to Mycobacterium smegmatis, Acinetobacter Iwoffii, and Flavobacterium psychrophila, and carried aquired ARGs aac(2′)-Ib, blaOXA−278, and tet36 respectively. In terms of indicator organisms, cumulative log removal values (LRV) of Escherichia coli, Enterococci, and P. aeruginosa from influent to conventional treated effluent was lower (0–2.4), compared to MBR effluent (5.3–7.4). We conclude that MBR is an effective treatment method for reducing fecal indicators and ARGs; however, incomplete removal of P. aeruginosa in MBR treated effluents (<8 MPN/100 mL) and the presence of ARGs and intl1 underscores the need to establish if further treatment should be applied prior to reuse.

Rejection of micron-sized particles using beech wood xylem

Investigating the removal efficiency of wood tissue in a dead-end filtration of micron-sized surrogates by determining the log removal values as well as the permeability of the material to water.

Advancing performance evaluation standards for household water treatment technologies.

Diarrheal illnesses and fatalities continue to be major issues in many regions throughout the world. Household water treatment (HWT) technologies (including both point-of-use (POU) and point-of-entry (POE) treatment solutions) have been shown as able to deliver safe water in many low-income communities. However, as shown herein, there are important inconsistencies in protocols employed for validating performance of HWTs. The WHO does not stipulate influent concentration as a parameter that could influence removal efficacy, nor does it indicate an influent concentration range that should be used during technology evaluations. A correlation between influent concentration and removal is evidenced herein (R2 = 0.88) with higher influent concentrations resulting in higher log-removal values (LRVs). The absence of a recommended standard influent concentration of bacteria (as well as for viruses and protozoa) could have negative consequences in intervention efforts. Recommendations are provided that regulatory bodies should specify an influent concentration range for testing and verification of HWT technologies.

Low cost drinking water treatment using nonwoven engineered and woven cloth fabrics.

The study investigated two engineered fabrics and five cloth fabrics for low cost drinking water treatment. An optimized fabric filtration method has been developed and tested. Numerical models for predicting particulate removal efficiency have been developed for each fabric as support tools for selecting optimal process configuration. Both engineered fabrics showed better performance and achieved the most effective particulate removal for the highest number of layers used. Sequential filtration was done on eight layers for representative fabrics of each type and recorded higher contaminant removal than one filtration run. Geotextile 1 was better than geotextile 2 in particulate removal and recorded Escherichia coli removals of up to 1.4 log removal value (LRV) for eight-layer normal filtration and 3.0 LRV for four-pot sequential filtration. Brushed cotton was best among the cloth fabrics in particulate removal but performed below expectation in bacterial removal. It recorded E. coli removals of only 0.04 LRV and 0.2 LRV for eight-layer normal filtration and four-pot sequential filtration, respectively. Effluent turbidity decreased exponentially with number of fabric layers, in line with porous media filtration theory. The optimized filtration method produced very clear drinking water of relatively safe quality using geotextile 1. Appropriate disinfection is still recommended to ensure continued water safety.

Proposed Methodology for Determining Reverse Osmosis Unit Integrity for Pathogen Removal Credit

It is intuitive to suggest that reverse osmosis (RO), which is used for the removal of dissolved solutes (salts), can also be used to achieve the removal of virus, Giardia, and Cryptosporidium. The challenge is that the use of conductivity for water quality monitoring of the RO process lacks sufficient sensitivity, and a direct integrity test that translates water quality performance to regulatory compliance for pathogen removal has not been established or accepted as a practice. The basis of this article is as follows: It is proposed for a production‐level (e.g., 1 mgd or larger) RO system that the sensitivity can be increased by using the results of a conductivity profile, which is an existing diagnostic tool used to identify integrity defects within an RO unit. The proposed direct integrity test methodology uses the results of a conductivity profile to (1) determine that RO unit integrity exists within statistical limits, (2) isolate and differentiate between the conductivity associated with diffusion and with a defect, and (3) calculate the log removal value (LRV) that would be associated with an RO membrane defect. The resulting calculation approach significantly increases the sensitivity of the LRV calculation and is supported by full‐scale testing data using MS2 coliphage as the challenge organism.