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Assimilable Organic Carbon as an Indicator of Bacterial Regrowth
Abstract
The relationship between the level of regrowth of heterotrophic bacteria and the level of easily assimilable organic carbon (AOC) was determined by collecting and examining a series of distribution water samples from 20 supplies during two summer and autumn periods. The AOC concentration of distribution system water decreased with increasing distance from the treatment plant, but AOC uptake was limited at concentrations < 10 μg C/L. A significant correlation was found between the concentration of AOC in water leaving the treatment plant and the geometric mean of the counts of heterotrophic bacteria in distribution water as determined on diluted broth agar medium. At AOC concentrations < 10 μg C/L, the geometric mean of the colony counts on plate count agar medium (incubated at 22°C) remained below the guideline value of 100 cfu/mL. La relación que existe entre el nivel de recrecimiento de bacterias heterofóbicas y el del carbón orgánico fácilmente asimilable (AOC) fue determinado recogiendo y examinando una serie de aguas de distribución de 20 fuentes diferentes durante dos períodos de verano y otoño. La concentración de AOC en el agua del sistema de distribución disminuyó al aumentar la distancia de la planta de tratamiento, pero la toma de AOC estaba limitada a concentraciones de < 10 μg C/L Se encontró una correlación significativa entre la concentración del AOC en el agua que salía de la planta de tratamiento y la media geométrica del conteo de bacteria heterofóbica en el agua distribuida tal como se determina por el medio agar diluido. A concentraciones de AOC < 10 μg C/L, la media geométrica del conteo de colonias de bacterias en la placa de conteo del medio agar permaneció por debajo de los valores dados por las normas de 100 cfu/mL.
... BOM is commonly measured as assimilable organic carbon (AOC) or biodegradable dissolved organic carbon (BDOC). AOC is determined using a bioassay (van der Kooij, 1990Kooij, , 1992 and measures the microbial response to biodegradable materials in water. AOC levels ( Figure 5) in 94 North American drinking water systems ranged from 20 to 214 µg/L, median 100 µg/L (LeChevallier et al., 1996; Volk and LeChevallier, 2000). ...
... Similar models developed for specific systems have yielded higher predictive probabilities (Volk et al., 1992). In systems that do not maintain a disinfectant residual, very low AOC levels (<10 µg/L ) are required to minimize bacterial growth (van der Kooij, 1990Kooij, , 1992. LeChevallier et al. (1996) found that unfiltered water utilities experienced coliform bacterial growth at levels much higher than filtered systems. ...
In contrast to “frank” pathogens, like Salmonella entrocolitica, Shigella dysenteriae, and Vibrio cholerae, that always have a probability of disease, “opportunistic” pathogens are organisms that cause an infectious disease in a host with a weakened immune system and rarely in a healthy host. Historically, drinking water treatment has focused on control of frank pathogens, particularly those from human or animal sources (like Giardia lamblia, Cryptosporidium parvum, or Hepatitis A virus), but in recent years outbreaks from drinking water have increasingly been due to opportunistic pathogens. Characteristics of opportunistic pathogens that make them problematic for water treatment include: 1) they are normally present in aquatic environments, 2) they grow in biofilms that protect the bacteria from disinfectants, and 3) under appropriate conditions in drinking water systems (e.g., warm water, stagnation, low disinfectant levels, etc.) these bacteria can amplify to levels that can pose a public health risk. The three most common opportunistic pathogens in drinking water systems include Legionella pneumophila, Mycobacterium avium, and Pseudomonas aeruginosa. This report focuses on these organisms to provide information on their public health risk, occurrence in drinking water systems, susceptibility to various disinfectants and other operational practices (like flushing and cleaning of pipes and storage tanks). In addition, information is provided on a group of nine other opportunistic pathogens that are less commonly found in drinking water systems, including Aeromonas hydrophila, Klebsiella pneumoniae, Serratia marcescens, Burkholderia pseudomallei, Acinetobacter baumannii, Stenotrophomonas maltophilia, Arcobacter butzleri, and several free-living amoebae including Naegleria fowleri and species of Acanthamoeba. The public health risk for these microbes in drinking water is still unclear, but in most cases, efforts to manage Legionella, mycobacteria, and Pseudomonas risks will also be effective for these other opportunistic pathogens. The approach to managing opportunistic pathogens in drinking water supplies focuses on controlling the growth of these organisms. Many of these microbes are normal inhabitants in biofilms in water, so the attention is less on eliminating these organisms from entering the system and more on managing their occurrence and concentrations in the pipe network. With anticipated warming trends associated with climate change, the factors that drive the growth of opportunistic pathogens in drinking water systems will likely increase. It is important, therefore, to evaluate treatment barriers and management activities for control of opportunistic pathogen risks. Controls for primary treatment, particularly for turbidity management and disinfection, should be reviewed to ensure adequacy for opportunistic pathogen control. However, the major focus for the utility’s opportunistic pathogen risk reduction plan is the management of biological activity and biofilms in the distribution system. Factors that influence the growth of microbes (primarily in biofilms) in the distribution system include, temperature, disinfectant type and concentration, nutrient levels (measured as AOC or BDOC), stagnation, flushing of pipes and cleaning of storage tank sediments, and corrosion control. Pressure management and distribution system integrity are also important to the microbial quality of water but are related more to the intrusion of contaminants into the distribution system – rather than directly related to microbial growth. Summarizing the identified risk from drinking water, the availability and quality of disinfection data for treatment, and guidelines or standards for control showed that adequate information is best available for management of L. pneumophila. For L. pneumophila the risk for this organism has been clearly established from drinking water, cases have increased worldwide, and it is one of the most identified causes of drinking water outbreaks. Water management best practices (e.g., maintenance of a disinfectant residual throughout the distribution system, flushing and cleaning of sediments in pipelines and storage tanks, among others) that have been shown to be effective for control of L. pneumophila in water supplies. In addition, there are well documented management guidelines available for the control of the organism in drinking water distribution systems. By comparison, management of risks for Mycobacteria from water are less clear than for L. pneumophila. Treatment of M. avium is difficult due to its resistance to disinfection, the tendency to form clumps and attachment to surfaces in biofilms. Additionally, there are no guidelines for management of M. avium in drinking water and one risk assessment study suggested a low risk of infection. The role of tap water in the transmission of the other opportunistic pathogens is less clear and in many cases actions to manage L. pneumophila (e.g., maintenance of a disinfectant residual, flushing, cleaning of storage tanks, etc.) will also be beneficial in helping to manage these organisms as well.
... However, the differences between the proposed AOC levels in water as a criterion suggest that other factors also affect the biostability of water in the distribution network. Water biostability depends on several factors, which include the content of readily biodegradable organic carbon compounds, temperature, and water residence time [12][13][14][15][16]. Other biological stability concepts have been described in the literature, that enable the highly effective analysis and in-depth characterisation of bacterial communities in drinking water; e.g., cell numbers by plate count (colony forming units/mL or CFUs) and/or confocal laser scanning microscopy (CLSM) measurements of the water before and after treatment can be performed [1,15,17]. ...
Studies were carried out to assess changes in biodegradable dissolved organic carbon (BDOC) and assimilable organic carbon (AOC) in groundwater and surface waters after two processes: ozonation and ozonation/UV. The tested water was in contact with O3 firstly for 4 and secondly for 15 min. Three doses of disinfectant were used: 1.6 mg/L, 5.0 mg/L, and 10.0 mg/L. The UV radiation time was 10 and 30 min. The greatest change in AOC and BDOC for groundwater was observed at an O3 dose of 10.0 mg/L and a contact time of 15 min, by 400 and 197%, respectively. On the other hand, for surface water, it was shown that after the ozonation/UV process, the AOC and BDOC content decreased after both 10 and 30 min of radiation in comparison to the water after ozonation. The AOC content decreased by 33% and 22%, respectively, and the BDOC content by 27% and 31%, respectively. The results obtained in this study provide new information on the effect of different ozonation conditions and the combined method on the level of biodegradable organic fraction of water. It is recommended that BDOC and AOC should be monitored in Poland as routine indicators during the preparation of drinking water.
Drinking water biosafety has become an increasing concern for public health. Chlorination is widely used as the main disinfection strategy worldwide but has clear and well-known byproduct issues. The Netherlands has successfully demonstrated an unchlorinated approach for almost 20 years but has not been widely adopted by other countries. To chlorine or not chlorine is becoming a critical question for all water utilities. This review aims to provide a good overview of current biosafety management strategies, their disadvantages, as well as the latest developments and future trends. Firstly, the advantages and deficiencies of conventional disinfection and non-disinfection were discussed. Secondly, the commonly used and promising methods for biostability assessment are described. Finally, critical views on the strategy selection for ensuring drinking water biosafety are discussed. It is recommended to achieve both biological and chemical balance by removing pathogens while minimizing the organic matter and dosing a minimum level of disinfectants, which would represent the compromise choice between the current chlorine-based disinfection and chlorine-free strategy. It's worth noting that the complexity of ensuring biosafety lies in the variations among different regions, the selection of suitable methods should be tailored to specific situations on a case-by-case basis.
In contrast to “frank” pathogens, like Salmonella entrocolitica, Shigella dysenteriae, and Vibrio cholerae, that always have a probability of disease, “opportunistic” pathogens are organisms that cause an infectious disease in a host with a weakened immune system and rarely in a healthy host. Historically, drinking water treatment has focused on control of frank pathogens, particularly those from human or animal sources (like Giardia lamblia, Cryptosporidium parvum, or Hepatitis A virus), but in recent years outbreaks from drinking water have increasingly been due to opportunistic pathogens. Characteristics of opportunistic pathogens that make them problematic for water treatment include: (1) they are normally present in aquatic environments, (2) they grow in biofilms that protect the bacteria from disinfectants, and (3) under appropriate conditions in drinking water systems (e.g., warm water, stagnation, low disinfectant levels, etc.), these bacteria can amplify to levels that can pose a public health risk. The three most common opportunistic pathogens in drinking water systems are Legionella pneumophila, Mycobacterium avium, and Pseudomonas aeruginosa. This report focuses on these organisms to provide information on their public health risk, occurrence in drinking water systems, susceptibility to various disinfectants, and other operational practices (like flushing and cleaning of pipes and storage tanks). In addition, information is provided on a group of nine other opportunistic pathogens that are less commonly found in drinking water systems, including Aeromonas hydrophila, Klebsiella pneumoniae, Serratia marcescens, Burkholderia pseudomallei, Acinetobacter baumannii, Stenotrophomonas maltophilia, Arcobacter butzleri, and several free-living amoebae including Naegleria fowleri and species of Acanthamoeba. The public health risk for these microbes in drinking water is still unclear, but in most cases, efforts to manage Legionella, mycobacteria, and Pseudomonas risks will also be effective for these other opportunistic pathogens. The approach to managing opportunistic pathogens in drinking water supplies focuses on controlling the growth of these organisms. Many of these microbes are normal inhabitants in biofilms in water, so the attention is less on eliminating these organisms from entering the system and more on managing their occurrence and concentrations in the pipe network. With anticipated warming trends associated with climate change, the factors that drive the growth of opportunistic pathogens in drinking water systems will likely increase. It is important, therefore, to evaluate treatment barriers and management activities for control of opportunistic pathogen risks. Controls for primary treatment, particularly for turbidity management and disinfection, should be reviewed to ensure adequacy for opportunistic pathogen control. However, the major focus for the utility’s opportunistic pathogen risk reduction plan is the management of biological activity and biofilms in the distribution system. Factors that influence the growth of microbes (primarily in biofilms) in the distribution system include, temperature, disinfectant type and concentration, nutrient levels (measured as AOC or BDOC), stagnation, flushing of pipes and cleaning of storage tank sediments, and corrosion control. Pressure management and distribution system integrity are also important to the microbial quality of water but are related more to the intrusion of contaminants into the distribution system rather than directly related to microbial growth. Summarizing the identified risk from drinking water, the availability and quality of disinfection data for treatment, and guidelines or standards for control showed that adequate information is best available for management of L. pneumophila. For L. pneumophila, the risk for this organism has been clearly established from drinking water, cases have increased worldwide, and it is one of the most identified causes of drinking water outbreaks. Water management best practices (e.g., maintenance of a disinfectant residual throughout the distribution system, flushing and cleaning of sediments in pipelines and storage tanks, among others) have been shown to be effective for control of L. pneumophila in water supplies. In addition, there are well documented management guidelines available for the control of the organism in drinking water distribution systems. By comparison, management of risks for Mycobacteria from water are less clear than for L. pneumophila. Treatment of M. avium is difficult due to its resistance to disinfection, the tendency to form clumps, and attachment to surfaces in biofilms. Additionally, there are no guidelines for management of M. avium in drinking water, and one risk assessment study suggested a low risk of infection. The role of tap water in the transmission of the other opportunistic pathogens is less clear and, in many cases, actions to manage L. pneumophila (e.g., maintenance of a disinfectant residual, flushing, cleaning of storage tanks, etc.) will also be beneficial in helping to manage these organisms as well.
Water is essential to life, but many people do not have access to clean and safe drinking water, and many die due to water-borne bacterial infections. The contaminants in drinking water cause serious health hazards which include nausea, lung irritation, skin rash, vomiting, dizziness, and even death. In this review, we have discussed diseases transmitted through water. Microbiological analysis of water is mainly based on the concept of faecal indicator bacteria, so we have covered different bacteria lying in this category. We have discussed conventional and current microbiological techniques used for maintaining potable water quality. In addition to this, different methods used for water treatment, namely, removal of microbes, filtration and disinfection have also been covered. One of the serious issues which is regrowth of bacteria after water treatment has also been taken into account.
Water is essential to life, but many people do not have access to clean and safe drinking
water, and many die due to water-borne bacterial infections. The contaminants in drinking
water cause serious health hazards which include nausea, lung irritation, skin rash, vomiting,
dizziness, and even death. In this review, we have discussed diseases transmitted through water.
Microbiological analysis of water is mainly based on the concept of faecal indicator bacteria, so
we have covered different bacteria lying in this category. We have discussed conventional and
current microbiological techniques used for maintaining potable water quality. In addition to
this, different methods used for water treatment, namely, removal of microbes, filtration and
disinfection have also been covered. One of the serious issues which is regrowth of bacteria after
water treatment has also been taken into account.
Water is essential to life, but many people do not have access to clean and safe drinking
water, and many die due to water-borne bacterial infections. The contaminants in drinking
water cause serious health hazards which include nausea, lung irritation, skin rash, vomiting,
dizziness, and even death. In this review, we have discussed diseases transmitted through water.
Microbiological analysis of water is mainly based on the concept of faecal indicator bacteria, so
we have covered different bacteria lying in this category. We have discussed conventional and
current microbiological techniques used for maintaining potable water quality. In addition to
this, different methods used for water treatment, namely, removal of microbes, filtration and
disinfection have also been covered. One of the serious issues which is regrowth of bacteria after
water treatment has also been taken into account.
Keywords: Water, Faecal indicator, Microbiological techniques, Disinfection
Water quality is a critical issue for the water industry today, and membrane fi ltration a highly effective treatment used to provide clean water for the global population. Experimental processes and methods are being developed for assessing fouling, scaling, performance and modelling of membrane systems, and research is needed to further improve the sustainability and feasibility of these technologies, and to mitigate the challenges of water scarcity for billions of people, particularly in developing countries.
This book aims to address this vital issue by bringing together experts in the fi eld to share their learning, including: Membrane processes: microfi ltration (MF), ultrafi ltration (UF), reverse osmosis (RO), forward osmosis (FO) and membrane distillation (MD)Particulate fouling: silt density index (SDI), modifi ed fouling index (MFI-0.45 and MFI-UF)Inorganic fouling and scaling: assessment, characterization tools and mitigationOrganic fouling: size exclusion chromatography (LC-OCD), fl uorescence spectroscopy (FEEM) and transparent exopolymer particles (TEP)Biological fouling: genomic tools, bacterial growth potential (BGP) of seawater and low-nutrient water and optical coherence tomography (OCT)General applications: membrane autopsy and computational fl uid dynamics (CFD) modelling
In recent years, metal alloys used for drinking water distribution are gradually being replaced by PVC and HDPE pipes. In areas of distribution networks made of plastic, consumer complaints related to a significant deterioration of organoleptic parameters of water are frequently recorded. The decline in water quality is most likely the result of chemical and biological processes occurring on the inner walls of the transmission pipes coexisting with the disappearance of disinfectant residues. Plastic pipes are also characterized by high failure rates associated with aging of polymeric materials under operating conditions. Published reports indicate disturbing phenomena occurring in plastic pipes: oxidative aging of polymers, degradation of antioxidant coatings, release of organic compounds to water as well as surface damage and scaling, generating microplastic particles. PE and PVC networks are also susceptible to biofilm formation, characterized by a high phylogenetic diversity of microorganisms. Studies presented in the literature, indicating the risks resulting from the exploitation of PE and PVC pipes, are mainly based on model tests. There is a lack of works, which would complementarily explain all the phenomena occurring in working water pipes made of plastics. The aim of this review is to present the current state of knowledge regarding the phenomena and processes that can occur in PE and PVC pipes in service and their relevance to the safety and quality of drinking water in distribution networks, as well as to identify areas that require further analysis to enable water producers to deliver an appropriately high‐quality product to consumers.
This article is categorized under: Engineering Water > Water, Health, and Sanitation
Science of Water > Water Quality
Water and Life > Conservation, Management, and Awareness
Description
The International Symposium on Bacterial Indicators of Potential Health Hazards Associated With Water was held 28-29 June 1976 at Chicago, Ill. The American Society for Testing and Material's Committee D19 on Water sponsored the symposium, and A. W. Hoadley, Georgia Institute of Technology, served as symposium chairman. B. J. Dutka, Canada Centre for Inland Waters, and A. W. Hoadley served as editors of this publication.
Description
The International Symposium on Bacterial Indicators of Potential Health Hazards Associated With Water was held 28-29 June 1976 at Chicago, Ill. The American Society for Testing and Material's Committee D19 on Water sponsored the symposium, and A. W. Hoadley, Georgia Institute of Technology, served as symposium chairman. B. J. Dutka, Canada Centre for Inland Waters, and A. W. Hoadley served as editors of this publication.
Microbial and physical–chemical data were statistically analyzed to determine whether variations in microbial dynamics were related to variations in physicochemical variables. These data included endotoxin, standard plate count, membrane standard plate count, acid-fast organism, temperature, total organic carbon, free and total chlorine, turbidity, and pH measurements of samples collected from two water distribution systems. The results of the statistical analyses did not support the hypothesis that the physicochemical measurements would suffice to produce reliable predictions of microbial water quality.
Experiences have been described before and after the Amsterdam Water Works had stopped safety chlorination. The results of the experiment provide a sound basis for a more balanced judgement on the advantages and disadvantages of the safety chlorination with respect to hygienic parameters and bacterial regrowth. It is preferable to prevent regrowth of micro-organisms by reduction of organic matter - particularly assimilable organic carbon - rather than by oxidative disinfectants - such as ozone and chlorine - since they promote regrowth, at least when applied at the end of the purification process. Slow sand filtration in roof covered filter buildings is suggested as an attractive possibility to replace final chemical disinfection before distribution of drinking water.
This paper presents the many changes taking place in the numbers of microorganisms found in water between the works and the consumer premises. Tests are outlined to identify these organisms and growths at different temperatures are recorded.
Widespread occurrences of Klebsiella in water distribution networks have resulted in much discussion about this organism's effect on public health and about action that should be taken when Klebsiella is detected in public water supplies. Results obtained during development and testing of an improved medium for detecting Klebsiella showed that the medium (M-Kleb) has excellent differentiating characteristics and an average recovery rate of 94 percent for Klebsiella. This medium can also be used as a supplemental streak plate to demonstrate the presence of Klebsiella during membrane filter coliform verification or during the multiple tube confirmation process. La existencia más frequente de Klebsiella en redes de distribución de agua ha resultado en much discusión sobre el efecto de este organismo en la salud del público y sobre la acción que debería ser tomada cuando Klebsiella es detectada en provisiones de agua pública. Resultados obtenidos durante el desarrollo y pruebas de un medio mejorado para detectar Klebsiella mostraron que el medio (M-Kleb) tiene excelentes características diferenciales y una velocidad promedio de recuperación de 94 por ciento para Klebsiella. Este medio también puede ser usado como una placa de raya suplemental para demonstrar la presencia de Klebsiella durante verificación de colibacilos de filtro de membrana o durante el proceso de confirmación de tubos multiplos.
In this study, the diversity of organisms identified by using standard plate count (SPC) and membrane filtration strohgiy suggests an established microbiai ecosystem in two distribution systems. The SPC exhibited no relationship with coliform count when the SPC was less than 50 organisms/mL. The SPC was not dependent on low-level turbidity and varied with respect to free chlorine residuals. The frequency of coliform isolation was independent of turbidity and free chlorine. Specifically, encapsulated coliforms (Klebslella pneumonias, Enterobacter cloacae, E. aerogenes, and E. agglomerane), which gave typical coliforrn results, exhibited the ability to survive a free chlorine residual of 0.2 mg/L or more. Encapsulation was a major factor in all of these results.