Cyanobacteria are ubiquitous microorganisms considered as important contributors to the formation of Earth's atmosphere and nitrogen fixation. However, they are also frequently associated with toxic ...blooms. Indeed, the wide range of hepatotoxins, neurotoxins and dermatotoxins synthesized by these bacteria is a growing environmental and public health concern. This paper provides a state of the art on the occurrence and management of harmful cyanobacterial blooms in surface and drinking water, including economic impacts and research needs. Cyanobacterial blooms usually occur according to a combination of environmental factors e.g., nutrient concentration, water temperature, light intensity, salinity, water movement, stagnation and residence time, as well as several other variables. These environmental variables, in turn, have promoted the evolution and biosynthesis of strain-specific, gene-controlled metabolites (cyanotoxins) that are often harmful to aquatic and terrestrial life, including humans. Cyanotoxins are primarily produced intracellularly during the exponential growth phase. Release of toxins into water can occur during cell death or senescence but can also be due to evolutionary-derived or environmentally-mediated circumstances such as allelopathy or relatively sudden nutrient limitation. Consequently, when cyanobacterial blooms occur in drinking water resources, treatment has to remove both cyanobacteria (avoiding cell lysis and subsequent toxin release) and aqueous cyanotoxins previously released. Cells are usually removed with limited lysis by physical processes such as clarification or membrane filtration. However, aqueous toxins are usually removed by both physical retention, through adsorption on activated carbon or reverse osmosis, and chemical oxidation, through ozonation or chlorination. While the efficient oxidation of the more common cyanotoxins (microcystin, cylindrospermopsin, anatoxin and saxitoxin) has been extensively reported, the chemical and toxicological characterization of their by-products requires further investigation. In addition, future research should also investigate the removal of poorly considered cyanotoxins (β-methylamino-alanine, lyngbyatoxin or aplysiatoxin) as well as the economic impact of blooms.
•Blooms of cyanobacteria occur mostly in eutrophic water and can be toxic.•Toxin biosynthesis is determined by the genes pool and environmental factors.•Human can be exposed to toxins through food, drinking water and swimming.•Toxin removal in drinking water treatment should rely on a multibarrier approach.•50% of publications focus on microcystin, 25% on saxitoxin and 25% on other toxins.
Due to alarming increase in population and rapid industrialization, drinking water quality is being deteriorated day by day in Pakistan. This review sums up the outcomes of various research studies ...conducted for drinking water quality status of different areas of Pakistan by taking into account the physicochemical properties of drinking water as well as the presence of various pathogenic microorganisms. About 20% of the whole population of Pakistan has access to safe drinking water. The remaining 80% of population is forced to use unsafe drinking water due to the scarcity of safe and healthy drinking water sources. The primary source of contamination is sewerage (fecal) which is extensively discharged into drinking water system supplies. Secondary source of pollution is the disposal of toxic chemicals from industrial effluents, pesticides, and fertilizers from agriculture sources into the water bodies. Anthropogenic activities cause waterborne diseases that constitute about 80% of all diseases and are responsible for 33% of deaths. This review highlights the drinking water quality, contamination sources, sanitation situation, and effects of unsafe drinking water on humans. There is immediate need to take protective measures and treatment technologies to overcome unhygienic condition of drinking water supplies in different areas of Pakistan.
The bacterial growth potential is important to understand and manage bacterial regrowth-related water quality concerns. Bacterial growth potential depends on growth promoting/limiting compounds, ...therefore, nutrient availability is the key factor governing bacterial growth potential. Selecting proper tools for bacterial growth measurement is essential for routine implementation of the growth potential measurement.
This study proposes a growth potential assay that is universal and can be used for different water types and soil extract without restrictions of pure culture or cultivability of the bacterial strain. The proposed assay measures the sample bacterial growth potential by using the indigenous community as inocula. Flow cytometry (FCM) and adenosine tri-phosphate (ATP) were used to evaluate the growth potential of six different microbial communities indigenous to the sample being analyzed, with increasing carbon concentrations. Bottled mineral water, non-chlorinated tap water, seawater, river water, wastewater effluent and a soil organic carbon extract were analyzed.
Results showed that indigenous bacterial communities followed normal batch growth kinetics when grown on naturally present organic carbon. Indigenous bacterial growth could detect spiked organic carbon concentrations as low as 10 μg/L. The indigenous community in all samples responded proportionally to the increase in acetate-carbon and proportional growth could be measured with both FCM and ATP. Bacterial growth was proportional to the carbon concentration but not the same proportion factor for the different water samples tested. The effect of inoculating the same water with different indigenous microbial communities on the growth potential was also examined. The FCM results showed that the highest increase in total bacterial cell concentration was obtained with bacteria indigenous to the water sample.
The growth potential assay using indigenous bacterial community revealed consistent results of bacterial growth in all the different samples tested and therefore providing a fast, more stable, and accurate approach for monitoring the biological stability of waters compared to the previously developed assays. The growth potential assay can be used to aid in detecting growth limitations by compounds other than organic carbon.
•Bacterial community growth potential assay tested using six different sample types.•Indigenous communities from the sample were used as inocula.•Two suitable methods for assessing growth: FCM cell count and ATP analysis.•Reproducible results in triplicate growth tests.•Proportionality in growth with increase in carbon concentration for all sample types.
In recent years, there has been a growing interest on the occurrence of antibiotic-resistant bacteria (ARB) and antibiotic resistant genes (ARGs) in treated and untreated drinking water. ARB and ARGs ...pose a public health concern when they transfer antibiotic resistance (AR) to human pathogens. However, it is still unclear whether the presence of environmental ARB and ARGs in source water, drinking water treatment plants, and drinking water distribution systems has any significant impact on human exposure to pathogenic ARB. In this review, we critically examine the occurrence of AR in groundwater, surface water, and treated distributed water. This offered a new perspective on the human health threat posed by AR in drinking water and helped in crafting a strategy for monitoring AR effectively. Using existing data on removal of ARB and ARGs in drinking water treatment plants, presence and proliferation of AR in drinking water distribution systems, and mechanisms and pathways of AR transfer in drinking water treatment plants, we conclude that combining UV-irradiation with advanced oxidative processes (such as UV/chlorine, UV/H2O2, and H2O2/UV/TiO2) may enhance the removal of ARB and ARGs, while disinfection may promote horizontal gene transfer from environmental ARB to pathogens. The potential human health risks of AR were determined by examining human exposure to antibiotic resistant human pathogens and re-evaluating waterborne disease outbreaks and their links to environmental AR. We concluded that integrating disease outbreak analysis, human exposure modelling, and clinical data could provide critical information that can be used to estimate the dose-response relationships of pathogenic ARB in drinking water, which is required for accurate risk assessments.
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•Pathogenic antibiotic-resistant bacteria (ARB) have been detected in drinking water.•Disinfection may increase the transfer of antibiotic resistant genes (ARGs) to pathogens.•Combining UV-irradiation and advanced oxidation may enhance ARG and ARB removal.•Antibiotic resistance removal strategies in drinking water are critically examined.•Monitoring priority ARB in drinking water is vital for human health risk assessment.
Knowing the survival rates of water-borne Escherichia coli is important in evaluating microbial contamination and making appropriate management decisions. E. coli survival rates are dependent on ...temperature, a dependency that is routinely expressed using an analogue of the Q10 model. This suggestion was made 34 years ago based on 20 survival curves taken from published literature, but has not been revisited since then. The objective of this study was to re-evaluate the accuracy of the Q10 equation, utilizing data accumulated since 1978. We assembled a database of 450 E. coli survival datasets from 70 peer-reviewed papers. We then focused on the 170 curves taken from experiments that were performed in the laboratory under dark conditions to exclude the effects of sunlight and other field factors that could cause additional variability in results. All datasets were tabulated dependencies “log concentration vs. time.” There were three major patterns of inactivation: about half of the datasets had a section of fast log-linear inactivation followed by a section of slow log-linear inactivation; about a quarter of the datasets had a lag period followed by log-linear inactivation; and the remaining quarter were approximately linear throughout. First-order inactivation rate constants were calculated from the linear sections of all survival curves and the data grouped by water sources, including waters of agricultural origin, pristine water sources, groundwater and wells, lakes and reservoirs, rivers and streams, estuaries and seawater, and wastewater. Dependency of E. coli inactivation rates on temperature varied among the water sources. There was a significant difference in inactivation rate values at the reference temperature between rivers and agricultural waters, wastewaters and agricultural waters, rivers and lakes, and wastewater and lakes. At specific sites, the Q10 equation was more accurate in rivers and coastal waters than in lakes making the value of the Q10 coefficient appear to be site-specific. Results of this work indicate possible sources of uncertainty to be accounted for in watershed-scale microbial water quality modeling.
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► We apply the Q10 temperature-dependence model to Escherichia coli survival in natural waters. ► We use a database consisting of 170 E. coli survival datasets. ► Average inactivation rates at the reference temperature depend on the water type. ► The value of the Q10 temperature coefficient is site-specific. ► The uncertainty in Q10 value has to be factored in microbial water quality modeling.
In this study, simultaneous nitrification and denitrification (SND) process was successfully established in a hybrid sequencing batch biofilm reactor (HSBBR). High removal efficiency of NH4+-N ...(98.0±2.4% to 99.8±0.4%) and COD (86.6±4.0% to 91.6±1.8%) was observed in the salinity range of 0.0 to 2.4%. SND via nitrite, replacing SND via nitrate, became the main nitrogen removal pathway at 1.6% and 2.4% salinity. Suspended sludge and biofilm shared similar microbial composition. Dominant genera were substituted by salt-adaptable microbes as salinity increasing. Abundance of autotrophic ammonia-oxidizing bacteria (Nitrosomonas) increased with elevated salinity, while autotrophic nitrite-oxidizing bacteria (Nitrospira) exhibited extreme sensitivity to salinity. The presence of Gemmata demonstrated that heterotrophic nitrification co-existed with autotrophic nitrification in the SND process. Aerobic denitrifiers (Denitratisoma and Thauera) were also identified. Thiothrix, Sedimenticola, Sulfuritalea, Arcobacter (sulfide-based autotrophic denitrifier) and Hydrogenophaga (hydrogen-based autotrophic denitrifier) were detected in both S-sludge and biofilm. The occurrence of ANAMMOX bacteria Pirellula and Planctomyces indicated that ANAMMOX process was another pathway for nitrogen removal. Nitrogen removal in the HSBBR was accomplished via diverse pathways, including traditional autotrophic nitrification/heterotrophic denitrification, heterotrophic nitrification, aerobic and autotrophic denitrification, and ANAMMOX.
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•The SND process was mainly via nitrite not nitrate at salinity of 1.6% and 2.4%.•Elevated salinity led to shift of functional groups and nitrogen removal pathways.•S-sludge and biofilm shared similar microbial community composition in the HSBBR.•Enrichment of salt-adaptable microbes stabilized SND performance under salt stress.•Diverse pathways of nitrogen removal occurred in the HSBBR with and without salt.
Driven by the development of water purification technologies and water quality regulations, the use of better source water and/or upgraded water treatment processes to improve drinking water quality ...have become common practices worldwide. However, even though these elements lead to improved water quality, the water quality may be impacted during its distribution through piped networks due to the processes such as pipe material release, biofilm formation and detachment, accumulation and resuspension of loose deposits. Irregular changes in supply-water quality may cause physiochemical and microbiological de-stabilization of pipe material, biofilms and loose deposits in the distribution system that have been established over decades and may harbor components that cause health or esthetical issues (brown water). Even though it is clearly relevant to customers' health (e.g., recent Flint water crisis), until now, switching of supply-water quality is done without any systematic evaluation. This article reviews the contaminants that develop in the water distribution system and their characteristics, as well as the possible transition effects during the switching of treated water quality by destabilization and the release of pipe material and contaminants into the water and the subsequent risks. At the end of this article, a framework is proposed for the evaluation of potential transition effects.
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•Loose deposits, biofilm matrix and pipe scales developed and stabilized over decades in DNs.•Irregular changes of water quality may cause destabilization of pipe material and contaminants.•The potential transition effects can lead to health or esthetic issues (e.g., Flint water crisis).•A framework for systematic transition effects evaluation is proposed.
Antibiotic resistance is a major public health concern. Triclosan is an antimicrobial compound with direct links to antibiotic resistance that was widely used in soaps in the U.S. until its ban by ...the U.S. Food and Drug Administration. Benzalkonium chloride (BAC), a quaternary ammonium compound, has widely replaced triclosan in soaps marketed as an antibacterial. BAC has been detected in surface waters and its presence will likely increase following increased use in soap products. The objective of this study was to determine the effect of BAC on relative abundance of antibiotic resistance in a bacterial community from a surface water used as a source for drinking water treatment. Bench-scale microcosm experiments were conducted with microbial communities amended with BAC at concentrations ranging from 0.1 μg L−1 to 500 μg L−1. Phenotypic antibiotic resistance was quantified by culturing bacteria in the presence of different antibiotics, and genotypic resistance was determined using qPCR to quantify antibiotic resistance genes (ARGs). BAC at concentrations ranging from 0.1 μg L−1 to 500 μg L−1 was found to positively select for bacteria resistant to ciprofloxacin and sulfamethoxazole, and negatively select against bacteria with resistance to six other antibiotics. Exposure to BAC for 14 days increased the relative abundance of sul1 and blaTEM. This study re-highlights the importance of employing both culture and non-culture-based techniques to identify selection for antibiotic resistance. The widespread use of BAC will likely impact antibiotic resistance profiles of bacteria in the environment, including in source waters used for drinking water, wastewater treatment plants, and natural waterways.
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•Benzalkonium chloride (BAC) altered the antibiotic resistance profiles of bacteria in surface water.•BAC positively selected for bacteria resistant to ciprofloxacin and sulfamethoxazole.•BAC selected against bacteria resistant to cephalexin, chloramphenicol, and streptomycin.•Exposure to BAC over time showed increased relative abundance of the resistance genes sul1 and blaTEM.
Benzalkonium chloride (BAC) positively selected for bacteria resistant to ciprofloxacin and sulfamethoxazole and selected against bacteria resistant to cephalexin, chloramphenicol, and streptomycin in a surface water. Exposure to BAC over time increased relative abundance of the resistance genes sul1 and blaTEM.
In this study, a novel strategy based on the combination of 3D SERS and LIBS was developed for qualitative and quantitative detection of bacteria. SERS-active Ag nanoparticles (AgNPs) were prepared ...by an improved in situ synthesis method, and reproducible SERS spectra of bacteria were obtained by natural evaporation of a droplet of the in situ synthesized sample. Four types of bacteria were classified via principal component analysis (PCA) and hierarchy cluster analysis (HCA). LIBS acted as a quantitative technique for bacterial detection based on the intracellular mineral cations, and bacteria could be detected in a linear range of 5 × 103–5 × 107 CFU mL−1, with recovery values ranging from 81.0% to 101.7%. The whole detection process including sample preparation and detection could be completed in approximately 30 min. With short assay time and simple operation, the proposed strategy has showed great potential for bacterial analysis.
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•A novel strategy was developed for bacterial detection based on the combination of 3D SERS and LIBS.•Reproducible SERS spectra were obtained by natural evaporation of in situ synthesized AgNPs.•LIBS was for the first time used for quantitative detection of bacteria in natural waters.
Drinking water utilities and researchers continue to rely on the century-old heterotrophic plate counts (HPC) method for routine assessment of general microbiological water quality. Bacterial cell ...counting with flow cytometry (FCM) is one of a number of alternative methods that challenge this status quo and provide an opportunity for improved water quality monitoring. After more than a decade of application in drinking water research, FCM methodology is optimised and established for routine application, supported by a considerable amount of data from multiple full-scale studies. Bacterial cell concentrations obtained by FCM enable quantification of the entire bacterial community instead of the minute fraction of cultivable bacteria detected with HPC (typically < 1% of all bacteria). FCM measurements are reproducible with relative standard deviations below 3% and can be available within 15 min of samples arriving in the laboratory. High throughput sample processing and complete automation are feasible and FCM analysis is arguably less expensive than HPC when measuring more than 15 water samples per day, depending on the laboratory and selected staining procedure(s). Moreover, many studies have shown FCM total (TCC) and intact (ICC) cell concentrations to be reliable and robust process variables, responsive to changes in the bacterial abundance and relevant for characterising and monitoring drinking water treatment and distribution systems. The purpose of this critical review is to initiate a constructive discussion on whether FCM could replace HPC in routine water quality monitoring. We argue that FCM provides a faster, more descriptive and more representative quantification of bacterial abundance in drinking water.
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•Routine drinking water monitoring still relies on heterotrophic plate counts (HPC).•Flow cytometry (FCM) is proposed as a better method for process monitoring.•No good correlation was found between FCM and HPC data (n = 3,675).•Good correlations were found between FCM and ATP data (n = 1,441).•FCM advantages are: relevance, speed, accuracy, costs and automation potential.
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