Regrowth In Water Distribution Systems Research Articles

Biofilm formation and antioxidation were responsible for the increased resistance of N. eutropha to chloramination for drinking water treatment

Chloramination is an effective strategy for eliminating pathogens from drinking water and repressing their regrowth in water distribution systems. However, the inevitable release of NH4+ potentially promotes nitrification and associated ammonia-oxidizing bacteria (AOB) contamination. In this study, AOB (Nitrosomona eutropha) were isolated from environmental water and treated with two disinfection stages (chloramine disinfection and chloramine residues) to investigate the occurrence mechanisms of AOB in chloramination. The results showed that N. eutropha had considerable resistance to monochloramine compared to Escherichia coli, whose inactivation rate constant was 19.4-fold lower. The higher resistance was attributed to high levels of extracellular polymer substances (EPS) in AOB, which contribute to AOB surviving disinfection and entering the distribution system. In AOB response to the chloramine residues stage, the respiratory activity of N. eutropha remained at a high level after three days of continuous exposure to high chloramine residue concentrations (0.5–1.5 mg/L). Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) suggested that the mechanism of N. eutropha tolerance involved a significantly high expression of the intracellular oxidative stress-regulating (sodB, txrA) and protein-related (NE1545, NE1546) genes. Additionally, this process enhanced EPS secretion and promoted biofilm formation. Adhesion predictions based on the XDLVO theory corroborated the trend of biofilm formation. Overall, the naturally higher resistance contributed to the survival of AOB in primary disinfection; the enhanced antioxidant response of surviving N. eutropha accompanied by biofilm formation was responsible for their increased resistance to the residual chloramines.

Ammonia-oxidizing microbes and biological ammonia removal in drinking water treatment

Ammonia in drinking water can lead to formation of disinfection byproducts in disinfection and bacteria regrowth in water distribution systems. Biological ammonia removal is an economical and environment-friendly way in controlling ammonia.

A review: organic matter and ammonia removal by biological activated carbon filtration for water and wastewater treatment

Biological activated carbon filters provide solutions to remove organic matter from drinking water and municipal wastewater, mainly biodegradable organic compounds not easily removed in conventional treatments based on physical–chemical processes. These biodegradable organic compounds may be responsible for bacterial regrowth in water distribution systems and also for increasing the formation of by-products during disinfection processes due to their capacity to react with disinfectants such as chlorine. Simultaneously to organic matter removal, biological activated carbon filtration can potentially remove the nutrient nitrogen commonly present in contaminated water resources and municipal wastewater, especially under the form of ammonia which is very harmful when discharged into the environment and toxic to living organisms. Thus, the potential of biological activated carbon filters in removing organic matter and ammonia for the treatment of drinking water and wastewater was reviewed. Operating parameters, such as contact time, backwashing regime and filtration rate, adopted for the filter operation and the biofilm growth in the activated carbon media were also discussed, as they may influence the treatment performance. Various scientific studies point out the remarkable ability of activated carbons to adsorb organic matter when compared to their performance for organic matter biodegradation. However, strategies to enhance the biological activity, and consequently biodegradation efficiency should be considered. These strategies, for instance, can include operational changes in contact times or in backwashing regimes. Investigations related to organic matter removal in biological activated carbon filters are more explored when compared to ammonia removal; however, high efficiencies of ammonia removal have been reported.

Bacterial regrowth in water reclamation and distribution systems revealed by viable bacterial detection assays.

Microbial regrowth needs to be managed during water reclamation and distribution. The aim of present study was to investigate the removal and regrowth of Escherichia coli (E. coli) and Salmonella in water reclamation and distribution system by using membrane integrity assay (PMA-qPCR), reverse transcriptional activity assay (Q-RT-PCR) and culture-based assay, and also to evaluate the relationships among bacterial regrowth, and environmental factors in the distribution system. The results showed that most of the water reclamation processes potentially induced bacteria into VBNC state. The culturable E. coli and Salmonella regrew 1.8 and 0.7 log10 in distribution system, which included reactivation of bacteria in the viable but non-culturable (VBNC) state and reproduction of culturable bacteria. The regrowth of culturable E. coli and Salmonella in the distribution system mainly depended on the residual chlorine levels, with correlations (R(2)) of -0.598 and -0.660. The abundances of membrane integrity and reverse transcriptional activity bacteria in reclamation effluents had significant correlations with the culturable bacteria at the end point of the distribution system, demonstrating that PMA-qPCR and Q-RT-PCR are sensitive and accurate tools to determine and predict bacterial regrowth in water distribution systems. This study has improved our understanding of microbial removal and regrowth in reclaimed water treatment and distribution systems. And the results also recommended that more processes should be equipped to remove viable bacteria in water reclamation plants for the sake of inhibition microbial regrowth during water distribution and usages.

Fate of free chlorine in drinking water during distribution in premise plumbing.

Free chlorine is a potent oxidizing agent and has been used extensively as a disinfectant in processes including water treatment. The presence of free chlorine residual is essential for the prevention of microbial regrowth in water distribution systems. However, excessive levels of free chlorine can cause adverse health effects. It is a major challenge to maintain appropriate levels of free chlorine residual in premise plumbing. As the first effort to assessing the fate of chlorine in premise plumbing using actual premise plumbing pipe sections, three piping materials frequently used in premise plumbing, i.e. copper, galvanized iron, and polyvinyl chloride (PVC), were investigated for their performance in maintaining free chlorine residual. Free chlorine decay was shown to follow first-order kinetics for all three pipe materials tested. The most rapid chlorine decay was observed in copper pipes, suggesting the need for higher chlorine dosage to maintain appropriate levels of free chlorine residual if copper piping is used. PVC pipes exhibited the least reactivity with free chlorine, indicative of the advantage of PVC as a premise plumbing material for maintaining free chlorine residual. The reactivity of copper piping with free chlorine was significantly hindered by the accumulation of pipe deposits. In contrast, the impact on chlorine decay by pipe deposits was not significant in galvanized iron and PVC pipes. Findings in this study are of great importance for the development of effective strategies for the control of free chlorine residual and prevention of microbiological contamination in premise plumbing.

Modeling and process evaluation of membrane bioreactor for removing biodegradable organic matter from water

A membrane bioreactor (MBR) process was employed for removing biodegradable organic matter (BOM) and ozonation disinfection byproducts (DBPs) exemplified by total aldehydes from ozonated potable water. The BOM removal was to prevent or reduce microbial regrowth in water distribution systems and to reduce DBP forming potential after ozonation. A mathematical modeling approach was used as a tool for performance prediction and process design with implication to process upscaling. The modeling protocol integrated adsorption and biodegradation in liquid and adsorbent phases with model parameters obtained from independent experiments. The BOM was expressed as biodegradable dissolved organic carbon (BDOC), assimilable organic carbon (AOC), and total aldehydes. The MBR studies demonstrated the process effectiveness in removing AOC, BDOC and total aldehydes, and validated the model's predictive capability. Sensitivity studies qualitatively evaluated parameters influencing process dynamics. The simulation studies were unique in examining shutdown and startup effects on process dynamics and process recovery.

Heterotrophic bacteria in drinking water distribution system: a review

The microbiological quality of drinking water in municipal water distribution systems (WDS) depends on several factors. Free residual chlorine and/or chloramines are typically used to minimize bacterial recontamination and/or regrowth in WDS. Despite such preventive measures, regrowth of heterotrophic (HPC) and opportunistic bacteria in bulk water and biofilms has yet to be controlled completely. No approach has shown complete success in eliminating biofilms or HPC bacteria from bulk water and pipe surfaces. Biofilms can provide shelter for pathogenic bacteria and protect these bacteria from disinfectants. Some HPC bacteria may be associated with aesthetic and non-life threatening diseases. Research to date has achieved important success in understanding occurrence and regrowth of bacteria in bulk water and biofilms in WDS. To achieve comprehensive understanding and to provide efficient control against bacteria regrowth, future research on bacteria regrowth dynamics and their implications is warranted. In this study, a review was performed on the literature published in this area. The findings and limitations of these papers are summarized. Occurrences of bacteria in WDS, factors affecting bacteria regrowth in bulk water and biofilms, bacteria control strategies, sources of nutrients, human health risks from bacterial exposure, modelling of bacteria regrowth and methods of bacteria sampling and detection and quantification are investigated. Advances to date are noted, and future research needs are identified. Finally, research directions are proposed to effectively control HPC and opportunistic bacteria in bulk water and biofilms in WDS.

Logistic regression for prediction and diagnosis of bacterial regrowth in water distribution system

This paper focuses on the quantitative expression of bacterial regrowth in water distribution system. Considering public health risks of bacterial regrowth, the experiment was performed on a distribution system of selected area. Physical, chemical, and microbiological parameters such as turbidity, temperature, residual chlorine and pH were measured over a three-month period and correlation analysis was carried out. Combined with principal components analysis (PCA), a logistic regression model is developed to predict and diagnose bacterial regrowth and locate the zones with high risks of microbiology in the distribution system. The model gives the probability of bacterial regrowth with the number of heterotrophic plate counts as the binary response variable and three new principal components variables as the explanatory variables. The veracity of the logistic regression model was 90%, which meets the precision requirement of the model.

Implications of nutrient release from iron metal for microbial regrowth in water distribution systems

Control of microbial regrowth in iron pipes is a major challenge for water utilities. This work examines the inter-relationship between iron corrosion and bacterial regrowth, with a special focus on the potential of iron pipe to serve as a source of phosphorus. Under some circumstances, corroding iron and steel may serve as a source for all macronutrients necessary for bacterial regrowth including fixed carbon, fixed nitrogen and phosphorus. Conceptual models and experimental data illustrate that levels of phosphorus released from corroding iron are significant relative to that necessary to sustain high levels of biofilm bacteria. Consequently, it may not be possible to control regrowth on iron surfaces by limiting phosphorus in the bulk water.

The Pseudomonas group as an indicator of potential regrowth in water distribution systems.

The regrowth of micro-organisms in the water distribution system is assisted by the presence of biodegradable organic matter (BDOC). The low concentration of available organic carbon in this type of water favours the growth of bacteria belonging to the Pseudomonadaceae family, as this group can grow better at low concentrations of substrate than other bacteria also present in the distribution system. Although the genus Aeromonas has already been adopted as an indicator of this potential regrowth, members of the Pseudomonadaceae have not yet been proposed as indicators of potential bacterial regrowth in the water distribution system. The results are presented of a year-long study of the Barcelona distribution system in which the presence of Pseudomonas and Aeromonas was analysed and the validity of these micro-organisms as indicators of potential regrowth in the distribution system was assessed. It seems that, at least in the drinking waters of the Barcelona area, Pseudomonas is a better indicator of potential bacterial regrowth than Aeromonas.

Role of inorganic phosphorus in controlling regrowth in water distribution system

Conventionally organic carbon is assumed to be the limiting nutrient of regrowth. Inorganic phosphorus in comparison to carbon should be a good candidate for regrowth control because it can be measured and controlled. It may be able to limit regrowth in drinking water distribution systems. In order to clarify whether inorganic phosphorus can really control or limit regrowth, three kinds of bioassays were performed: 1. for different combinations of acetate, phosphorus, and other inorganic nutrients added to different test tubes containing pure water, 2. for different tap water dilutions with pure water, and 3. for different phosphorus addition to test tubes containing all nutrients but phosphorus. The inoculum used was taken from a drinking water distribution system carrying chlorinated groundwater. Results indicated the following: 1. tap water bacteria cannot grow on simple organic carbon source (acetate) alone, 2. not organic carbon but inorganic nutrients limited the growth in tap water, and 3. tap water bacterial growth was suppressed when phosphorus was not present and it was not affected by over-presence of phosphorus when carbon or other nutrients became limiting. This gave a clue that phosphorus might play a major role in controlling regrowth in drinking water distribution system.

Role of inorganic phosphorus in controlling regrowth in water distribution system

Conventionally organic carbon is assumed to be the limiting nutrient of regrowth. Inorganic phosphorus in comparison to carbon should be a good candidate for regrowth control because it can be measured and controlled. It may be able to limit regrowth in drinking water distribution systems. In order to clarify whether inorganic phosphorus can really control or limit regrowth, three kinds of bioassays were performed: I. for different combinations of acetate, phosphorus, and other inorganic nutrients added to different test tubes containing pure water, 2. for different tap water dilutions with pure water, and 3. for different phosphorus addition to test tubes containing all nutrients but phosphorus. The inoculum used was taken from a drinking water distribution system carrying chlorinated groundwater. Results indicated the following: t. tap water bacteria cannot grow on simple organic carbon source (acetate) alone, 2. not organic carbon but inorganic nutrients limited the growth in tap water, and 3. tap water bacterial growth was suppressed when phosphorus was not present and it was not affected by over-presence of phosphorus when carbon or other nutrients became limiting. This gave a clue that phosphorus might play a major role in controlling regrowth in drinking water distribution system. © 1997 IAWQ. Published by Elsevier Science Ltd

A survey of BOM in US drinking waters

The data collected in this survey represent the first comparison of three methods for measuring biodegradable organic matter in a wide range of US drinking waters.Bacteria that pose a public health threat through their potential regrowth in water distribution systems derive energy and carbon for their growth from biodegradable organic matter. Three methods for determining biodegradable organic matter—which is necessary if the process of bacterial regrowth is to be fully understood—were compared in this study of a broad range of US drinking waters and treatment processes: the assimilable organic carbon (AOC) assay, the biodegradable dissolved organic carbon (BDOC) assay, and the coliform growth response (CGR). The source of water—surface water versus groundwater—had a strong influence on AOC and BDOC. The correlations between AOC and BDOC, between AOC and dissolved organic carbon (DOC), and between BDOC and DOC were statistically significant. CGR did not correlate well with either AOC or BDOC. The authors caution that these data are limited and urge increased focus on individual systems.