Investigation of microbially available phosphorus (MAP) in flemish drinking water

Several researchers have reported phosphorus growth limitations of heterotrophic bacteria instead of main energy source--organic carbon. Usually this phenomenon was noticed in waters with high organic carbon content, where phosphorus concentration was deficient to maintain the growth on level suggested by high organic carbon amount. We analysed the microbially available phosphorus (MAP) and assimilable organic carbon (AOC) in several drinking waters in Flanders, Belgium. Our aim was the investigation whether organic carbon or phosphorus is the restricting nutrient in specific water and determination of the impact of some treatment processes on MAP content. We obtained a wide range of MAP concentrations being from 0.3 to 15.2 microg P-PO(4)/l in finished drinking water. In a treatment unit applying ozone, MAP was found to be the nutrient that limits bacterial growth instead of organic carbon. Moreover, ozone caused slight MAP decrease. Granular activated carbon (GAC) filtration was able to diminish further the MAP content significantly but not below a certain level. The biofilm monitor supplied with the MAP-limited water resulted in significantly lower biofilm formation rate (BFR) value than the same installation fed with AOC-limited water.     

Investigation of assimilable organic carbon (AOC) in flemish drinking water

The aim of the study was to investigate the drinking water supplied to majority of residents of Flanders in Belgium. Over 500 water samples were collected from different locations, after particular and complete treatment procedure to evaluate the efficiency of each treatment step in production of biologically stable drinking water. In this study assimilable organic carbon (AOC) was of our interest and was assumed as a parameter responsible for water biostability. The influence of seasons and temperature changes on AOC content was also taken into account. The AOC in most of the non-chlorinated product water of the studied treatment plants could not meet the biostability criteria of 10 mug/l, resulting in the mean AOC concentration of 50 microg/l. However, majority of the examined chlorinated water samples were consistent with proposed criteria of 50--100 microg/l for systems maintaining disinfectant residual. Here, mean AOC concentration of 72 microg/l was obtained. Granular activated carbon filtration was helpful in diminishing AOC content of drinking water; however, the nutrient removal was enhanced by biological process incorporated into water treatment (biological activated carbon filtration). Disinfection by means of chlorination and ozonation increased the water AOC concentration while the ultraviolet irradiation showed no impact on the AOC content. Examination of seasonal AOC variations showed similar fluctuations in six units with the highest values in summer and lowest in winter.     

Changes in content of microbially available phosphorus,assimilable organic carbon and microbial growth potential during drinking water treatment processes

There are regions where microbial growth in drinking water is limited by phosphorus instead of organic carbon. In phosphorus limited waters small changes in phosphorus concentration significantly affect microbial growth. We studied how water treatment processes in waterworks affect the availability of microbial nutrients and microbial growth potential in drinking water. The nutrients studied were assimilable organic carbon (AOCpotential) and microbially available phosphorus (MAP) which both were quantified by bioassays. Chemical coagulation, commonly used in surfacewater works, effectively removed AOCpotential and MAP. In contrast to activated carbon filtration, ozonation increased the concentrations of AOCpotential and MAP, and also microbial growth potential. In most of the drinking waters, microbial growth was limited by phosphorus, and microbial growth potential correlated with the MAP concentration. Microbial growth potential was lowest in drinking waters produced from surface waters with efficient treatment technique and highest in less treated ground waters.     

Microbially available organic carbon, phosphorus, and microbial growth in ozonated drinking water

Ozonation is a disinfection technique commonly used in the treatment of drinking water. It destroys harmful microbes, but it also degrades organic matter in water, increasing the bioavailability of organic matter. Recently, it was found that not only organic carbon but also phosphorus can limit the microbial growth in drinking water, which contains high amount of organic matter. We used a bioassay to analyze whether ozone could also increase the microbially available phosphorus (MAP) in drinking water, and whether MAP in ozone-treated water was associated with the growth of heterotrophic microbes. We found that both assimilable organic carbon and MAP concentrations were increased by ozone treatment. In ozonated water, microbial growth was mainly limited by phosphorus, and even minor changes in MAP concentration dramatically increased the growth potential of heterotrophic microbes. In this study, ozonation increased the MAP by 0.08-0.73 microgram P/l, resulting in an increase of 80,000-730,000 CFU/ml in water samples. In contrast to MAP, the content of assimilable organic carbon (AOCpotential) did not correlate with microbial growth. The results show that in water treatment not only AOCpotential but also MAP should be considered as an important factor that can limit microbial growth in drinking water.     

Mechanistic and kinetic evaluation of organic disinfection by-product and assimilable organic carbon (AOC) formation during the ozonation of drinking water

Ozonation of drinking water results in the formation of low molecular weight (LMW) organic by-products. These compounds are easily utilisable by microorganisms and can result in biological instability of the water. In this study, we have combined a novel bioassay for assessment of assimilable organic carbon (AOC) with the detection of selected organic acids, aldehydes and ketones to study organic by-product formation during ozonation. We have investigated the kinetic evolution of LMW compounds as a function of ozone exposure. A substantial fraction of the organic compounds formed immediately upon exposure to ozone and organic acids comprised 60-80% of the newly formed AOC. Based on experiments performed with and without hydroxyl radical scavengers, we concluded that direct ozone reactions were mainly responsible for the formation of small organic compounds. It was also demonstrated that the laboratory-scale experiments are adequate models to describe the formation of LMW organic compounds during ozonation in full-scale treatment of surface water. Thus, the kinetic and mechanistic information gained during the laboratory-scale experiments can be utilised for upscaling to full-scale water treatment plants.     

The effects of UV disinfection on drinking water quality in distribution systems

UV treatment is a cost-effective disinfection process for drinking water, but concerned to have negative effects on water quality in distribution system by changed DOM structure. In the study, the authors evaluated the effects of UV disinfection on the water quality in the distribution system by investigating structure of DOM, concentration of AOC, chlorine demand and DBP formation before and after UV disinfection process. Although UV treatment did not affect concentration of AOC and characteristics of DOM (e.g., DOC, UV_254, SUVA₂₅₄, the ratio of hydrophilic/hydrophobic fractions, and distribution of molecular weight) significantly, the increase of low molecular fraction was observed after UV treatment, in dry season. Chlorine demand and THMFP are also increased with chlorination of UV treated water. This implies that UV irradiation can cleave DOM, but molecular weights of broken DOM are not low enough to be used directly by microorganisms in distribution system. Nonetheless, modification of DOM structure can affect water quality of distribution system as it can increase chlorine demands and DBPs formation by post-chlorination.     

Impact of microparticles on UV disinfection of indigenous aerobic spores

Numerous studies have shown that the efficacy of ultraviolet (UV) disinfection can be hindered by the presence of particles that can shield microorganisms. The main objective of this study was to determine to what extent natural particulate matter can shield indigenous spores of aerobic spore-forming bacteria (ASFB) from UV rays. The extent of the protective shielding was assessed by comparing the inactivation rates in three water fractions (untreated, dispersed and filtered on an 8 microm membrane) using a collimated beam apparatus with a low-pressure lamp emitting at 254 nm. Levels of inactivation were then related to the distribution and abundance of particles as measured by microflow imaging. Disinfection assays were completed on two source waters of different quality and particle content. A protocol was developed to break down particles and disperse aggregates (addition of 100mg/L of Zwittergent 3-12 and blending at 8000 rpm for 4 min). Particle size distribution (PSD) analysis confirmed a statistically significant decrease in the number of particles for diameter ranges above 5 microm following the dispersion protocol and 8 microm filtration. The fluence required to reach 1-log inactivation of ASFB spores was independent of particle concentration, while that required to reach 2-log inactivation or more was correlated with the concentration of particles larger than 8 microm (R(2)>0.61). Results suggest that natural particulate matter can protect indigenous organisms from UV radiation in waters with elevated particle content, while source water with low particle counts may not be subject to this interference.     

Role of discontinuous chlorination on microbial production by drinking water biofilms

Microbial quality in water distribution systems is strongly affected by the development of microbial biofilms. Production and release of microbial cells by the biofilm affect microbial levels in the water column and in some cases this fact constitutes a public health concern. In this study, we attempt to analyze in which way the existence of different episodes of chlorine depletion affects both biofilm formation and microbial load of an artificial laboratory system. The work was carried out using two parallel packed bed reactors both supplied with running tap water. One of the reactors was used as a control and was permanently exposed to the action of chlorine. In the other reactor, chlorine was neutralized at selected times during the experiment and for periods of variable length. During the experiment the concentration of total and viable cells from the effluent was monitored at the exit of each of the reactors. The data obtained were used to estimate microbial production from the biofilms. As an average, release of microbial cells to the water phase increased tenfold in the absence of chlorine. The results also indicate that disinfectant efficiency against the biofilm was not recovered when chlorine returned to normal levels after each event of chlorine neutralization. Cell viability in the water phase in the presence of chlorine was low at the beginning of the experiment but increased 4 orders of magnitude after five neutralization periods. Therefore, subsequent episodes of chlorine depletion may accelerate the development of microbial communities with reduced susceptibility to disinfection in real drinking water systems.     

Rapid, cultivation-independent assessment of microbial viability in drinking water

Fast and accurate monitoring of chemical and microbiological parameters in drinking water is essential to safeguard the consumer and to improve the understanding of treatment and distribution systems. However, most water utilities and drinking water guidelines still rely solely on time-requiring heterotrophic plate counts (HPC) and plating for faecal indicator bacteria as regular microbiological control parameters. The recent development of relative simple bench-top flow cytometers has made rapid and quantitative analysis of cultivation-independent microbial parameters more feasible than ever before. Here we present a study using a combination of cultivation-independent methods including fluorescence staining (for membrane integrity, membrane potential and esterase activity) combined with flow cytometry and total adenosine tri-phosphate (ATP) measurements, to assess microbial viability in drinking water. We have applied the methods to different drinking water samples including non-chlorinated household tap water, untreated natural spring water, and commercially available bottled water. We conclude that the esterase-positive cell fraction, the total ATP values and the high nucleic acid (HNA) bacterial fraction (from SYBR((R)) Green I staining) were most representative of the active/viable population in all of the water samples. These rapid methods present an alternative way to assess the general microbial quality of drinking water as well as specific events that can occur during treatment and distribution, with equal application possibilities in research and routine analysis.     

Effect of medium-pressure UV irradiation on bromate concentrations in drinking water, a pilot-scale study

This study investigated the potential for bromate removal from drinking water on irradiation with medium-pressure UV lamps-a technique gaining considerable interest for drinking water disinfection. Waters from two different sources were spiked with 20microg/L of bromate and irradiated with UV fluences up to 718mJ/cm(2) utilizing a pilot-scale reactor (Calgon Carbon Corp.) at a flow of 76L/min (20 gallon/min). Essentially no removal was observed in one of the source waters. Limited bromate removal, up to 19%, was observed in the second source water at high UV fluences (696mJ/cm(2)) and a fluence-response relationship was clearly evident. All removals would be negligible at UV fluences anticipated for drinking water disinfection (< or =40mJ/cm(2)). Different water characteristics, in particular competitive absorption by nitrate and possibly DOC, were most likely responsible for the differences in bromate removal in the waters tested. The source water that did not show any removal had a higher nitrate concentration (4 vs. 0.1mg N/L) and also a higher DOC concentration (4.1 vs. 3.1mg C/L) than the other source water which showed 19% bromate removal.     

Implications of sequential use of UV and ozone for drinking water quality

The formation of bromate levels exceeding the drinking water standard of 10 microg L-1 may impose the reduction of ozone doses used in the treatment of drinking water. This paper illustrates the procedure of evaluating the use of reduced ozone doses while implementing an additional UV disinfection step for an actual drinking water treatment plant. Ozonation was performed at low ozone doses in bench-scale experiments with a pretreated river water from the Paris area (France). At the low ozone dose of 0.5 mg L-1, bromate formation could be kept below 0.4 microg L-1, while inactivation of vegetative bacteria and UV-resistant viruses was calculated to exceed 5 log units, and a substantial decoloration (31% of the absorption at lambda=254 nm) was achieved. Based on the measured transient ozone and OH radical concentrations, the oxidation of micropollutants was calculated. Fast reacting micropollutants containing phenol, amine or double bond moieties, such as sulfamethoxazole, diclofenac and 17-alpha-ethinylestradiol, were completely oxidized. Slow-reacting synthetic micropollutants, e.g., atrazine, iopromide and methyl tertiary butyl ether (MTBE), were oxidized by only 20%, 20% and 10%, respectively, and the taste and odor compounds 2-methylisoborneol (MIB) and geosmin by 40% and 50%, respectively. The addition of an UV treatment step to the existing treatment train, which should guarantee disinfection of ozone-resistant pathogenic microorganisms, including Cryptosporidium parvum oocysts, has negligible effects on water matrix components but may induce significant transformation of micropollutants. Overall, the combination of ozonation at reduced doses and UV treatment leads to an improved water quality with regard to disinfection, oxidation of micropollutants and minimization of bromate.     

Spatial and temporal evaluations of disinfection by-products in drinking water distribution systems in Beijing, China

Disinfection by-products were determined in 15 water treatment plants in Beijing City. The effects of different water sources (surface water source, mixture water source and ground water source), seasonal variation and spatial variation were examined. Trihalomethanes and haloacetic acids were the major disinfection by-products found in all treated water samples, which accounted for 42.6% and 38.1% of all disinfection by-products respectively. Other disinfection by-products including haloacetonitriles, chloral hydrate, haloketones and chloropicrin were usually detected in treated water samples but at lower concentrations. The levels of disinfection by-products in drinking water varied with different water sources and followed the order: surface water source > mixture water source > ground water source. High spatial and seasonal variation of disinfection by-products in the drinking water of Beijing was shown as a result.     

UV disinfection in a model distribution system:; biofilm growth and microbial community

Two model distribution systems were operated in parallel to investigate the impact of UV disinfection on water distribution system biofilms and microbial community composition. One system received an influent irradiated with UV light, whereas the control received the same influent with no treatment. The biofilm in the UV system, as compared to the control, was more responsive (i.e., had a greater increase in steady-state density of heterotrophic bacteria) to the increased nutrient availability afforded by a decrease in HRT from 12 to 2 h. However, the UV treatment did not have a consistent impact on the biofilm community, indicating the processes controlling HPC density were independent of the specific strains of bacteria forming the biofilm. There was evidence that particle shielding contributed to the survival of UV-susceptible bacteria. This hypothesis was consistent with the presence of UV-susceptible bacteria in the UV system, as well as the high similarity of the biofilm communities in the UV and control systems in one of the experiments. To simulate an intrusion event, opportunistic pathogens were added to each system after the biofilm community reached steady-state. Opportunistic pathogen attachment was not affected by the UV treatment, but was instead correlated to the biofilm density of heterotrophic bacteria.     

Occurrence and formation of chloro- and bromo-benzoquinones during drinking water disinfection

Consumption of chlorinated drinking water has shown somewhat consistent association with increased risk of bladder cancer in a series of epidemiological studies, but plausible causative agents have not been identified. Halobenzoquinones (HBQs) have been recently predicted as putative disinfection byproducts (DBPs) that might be of toxicological relevance. This study reports the occurrence frequencies and concentrations of HBQs in plant effluents from nine drinking water treatment plants in the USA and Canada, where four common disinfection methods, chlorination, chloramination, chlorination with chloramination, and ozonation with chloramination, are used. In total, 16 water samples were collected and analyzed for eight HBQs: 2,6-dichloro-1,4-benzoquinone (2,6-DCBQ), 2,6-dibromo-1,4-benzoquinone (2,6-DBBQ), 2,6-dichloro-3-methyl-1,4-benzoquinone (2,6-DC-3-MBQ), 2,3,6-trichloro-1,4-benzoquinone (2,3,6-TriCBQ), 2,5-dibromo-1,4-benzoquinone (2,5-DBBQ), 2,3-dibromo-5,6-dimethyl-1,4-benzoquinone (2,3-DB-5,6-DM-BQ), tetrabromo-1,4-benzoquinone (TetraB-1,4-BQ), and tetrabromo-1,2-benzoquinone (TetraB-1,2-BQ). Of these, 2,6-DCBQ, 2,6-DBBQ, 2,6-DC-3-MBQ and 2,3,6-TriCBQ were detected in 16, 11, 6, and 3 of the 16 samples with the method detection limit (DL) of 1.0, 0.5, 0.9 and 1.5 ng/L, respectively, using a solid phase extraction and high performance liquid chromatography-tandem mass spectrometry method. The concentrations were in the ranges of 4.5-274.5 ng/L for 2,6-DCBQ, below DL to 37.9 ng/L for 2,6-DBBQ, below DL to 6.5 ng/L for 2,6-DC-3-MBQ, and below DL to 9.1 ng/L for 2,3,6-TriCBQ. These authentic samples show DCBQ and DBBQ as the most abundant and frequently detectable HBQs. In addition, laboratory controlled experiments were performed to examine the formation of HBQs and their subsequent stability toward hydrolysis when the disinfectants, chlorine, chloramine, or ozone followed by chloramines, reacted with phenol (a known precursor) under various conditions. The controlled reactions demonstrate that chlorination produces the highest amounts of DCBQ, while pre-ozonation increases the formation of DBBQ in the presence of bromide. At pH < 6.8, 2,6-DCBQ was observed to be stable, but it was easily hydrolyzed to form mostly 3-hydroxyl-2,6-DCBQ at pH 7.6 in drinking water.     

Formation and removal of genotoxic activity during UV/H2O2-GAC treatment of drinking water

The objective of this study was to determine the genotoxic activity of water after UV/H₂O₂ oxidation and GAC filtration. Pre-treated surface water from three locations was treated with UV/H₂O₂ with medium pressure (MP) lamps and passed through granulated activated carbon (GAC). Samples taken before and after each treatment step were extracted and concentrated by solid phase extraction (SPE) and analyzed for genotoxicity using the Comet assay with HepG2 cells and the Ames II assay.The Comet assay showed no genotoxic response in any of the samples. In the Ames II, no genotoxic response was obtained with the TAMix (a mix of six strains), but the TA98 strain showed an increase in genotoxic activity after MP-UV/H₂O₂ for all three locations. GAC post treatment effectively reduced the activities to control levels at two of the three locations and to below the level of the pre-treated water at one site. The results indicate that UV/H₂O₂ treatment may lead to the formation of genotoxic by-products, which can be removed by subsequent GAC filtration.     

浅谈饮用水消毒中常用的几种方法

对饮用水消毒中常用的几种方法进行了介绍，对这几种方法进行了比较，认为在目前国内的饮用水消毒处理中次氯酸钠发生器消毒是比较好的一种，而紫外线消毒法是今后可能取代传统的化学消毒法并且具有广阔应用前景的一种绿色环保高效的消毒方法。     

Effect of water composition, distance and season on the adenosine triphosphate concentration in unchlorinated drinking water in the Netherlands

The objective of our study was to determine whether water composition, distance to the treatment plant and season significantly affect the adenosine triphosphate (ATP) concentration in distributed drinking water, in order to resolve the suitability of ATP as an indicator parameter for microbial regrowth. Results demonstrated that the ATP concentration in distributed water averaged between 0.8 and 12.1 ng ATP L⁻¹ in the Netherlands. Treatment plants with elevated biofilm formation rates in treated water, showed significantly higher ATP concentrations in distributed drinking water and ATP content was significantly higher in the summer/autumn compared to the winter period at these plants. Furthermore, transport of drinking water in a large-sized distribution system resulted in significantly lower ATP concentrations in water from the distal than the proximal part of the distribution system. Finally, modifications in the treatment significantly affected ATP concentrations in the distributed drinking water. Overall, the results from our study demonstrate that ATP is a suitable indicator parameter to easily, rapidly and quantitatively determine the total microbial activity in distributed drinking water.     

Comparison of methods for the measurement of biodegradable organic carbon and assimilable organic carbon in water

In the last few years different methods for determining assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC) in drinking water have been proposed. However, there is no agreement on the most suitable methods for the assessment of treatment processes. A comparison of six methods, one for AOC(P17) determination and five for BDOC determination, using water samples taken at different steps in a water-treatment process in Sant Joan Despí (Barcelona, Spain) is reported. Results show that the biodegradable matter values given by AOC measurements are substantially lower than those obtained using BDOC methods. The various BDOC methods do not differ significantly in their results.     

Impact of hydrogen peroxide on nitrite formation during UV disinfection

One concern with UV disinfection of water is the production of nitrite when polychromatic UV sources are utilized. Based on previous work, it was hypothesized that a small addition of hydrogen peroxide (H(2)O(2)) may be useful in controlling nitrite during UV disinfection. However, it was found that H(2)O(2) addition (5 or 10mg/L) during polychromatic UV irradiation of drinking water at doses used for disinfection significantly increases the levels of nitrite produced relative to solutions without H(2)O(2). Enhancement rates ranged from approximately 15% to 40% depending upon pH and H(2)O(2) concentration; the relative increase in the NO(2)(-) yield was greater at pH 6.5 than at pH 8.3. The observed effects are tentatively ascribed to a combination of enhanced superoxide production and increased hydroxyl radical scavenging when H(2)O(2) is added. These results indicate that H(2)O(2) cannot be used to control nitrite production during UV disinfection and that enhanced nitrite formation will occur if H(2)O(2) is added during UV water treatment to achieve advanced oxidation of contaminants.