The effect of inorganic precursors on disinfection byproduct formation during UV-chlorine/chloramine drinking water treatment

Ultraviolet (UV) disinfection is being increasingly used in drinking water treatment. It is important to understand how its application to different types of water may influence finished water quality, particularly as anthropogenic activity continues to impact the quality of source waters. The objective of this study was to evaluate the effect of inorganic precursors on the formation of regulated and unregulated disinfection byproducts (DBPs) during UV irradiation of surface waters when combined with chlorination or chloramination. Samples were collected from three drinking water utilities supplied by source waters with varying organic and inorganic precursor content. The filtered samples were treated in the laboratory with a range of UV doses delivered from low pressure (LP, UV output at 253.7 nm) and medium pressure (MP, polychromatic UV output 200-400 nm) mercury lamps followed by chlorination or chloramination, in the presence and absence of additional bromide and nitrate. The regulated trihalomethanes and haloacetic acids were not affected by UV pretreatment at disinfection doses (40-186 mJ/cm²). With higher doses (1000 mJ/cm²), trihalomethane formation was increased 30-40%. While most effects on DBPs were only observed with doses much higher than typically used for UV disinfection, there were some effects on unregulated DBPs at lower doses. In nitrate-spiked samples (1-10 mg N/L), chloropicrin formation doubled and increased three- to six-fold with 40 mJ/cm² MP UV followed by chloramination and chlorination, respectively. Bromopicrin formation was increased in samples containing bromide (0.5-1 mg/L) and nitrate (1-10 mg N/L) when pretreated with LP or MP UV (30-60% with 40 mJ/cm² LP UV and four- to ten-fold increase with 40 mJ/cm² MP UV, after subsequent chlorination). The formation of cyanogen chloride doubled and increased three-fold with MP UV doses of 186 and 1000 mJ/cm², respectively, when followed by chloramination in nitrate-spiked samples but remained below the World Health Organization guideline value of 70 μg/L in all cases. MP UV and high LP UV doses (1000 mJ/cm²) increased chloral hydrate formation after subsequent chlorination (20-40% increase for 40 mJ/cm² MP UV). These results indicate the importance of bench-testing DBP implications of UV applications in combination with post-disinfectants as part of the engineering assessment of a UV-chlorine/chloramine multi-barrier disinfection design for drinking water treatment.     

Effect of particles and bioflocculation on ultraviolet disinfection of Escherichia coli

Presence of particles is known to decrease the effectiveness of ultraviolet (UV) disinfection by shielding the targeted microorganisms from UV light. This study aims to provide an in-depth understanding on the effect of particles and flocs on UV disinfection by using a stable, well-defined and well-controlled synthetic system that can simulate the bioflocculation of particles and microorganisms in water and wastewater samples. The synthetic system was created by using Escherichia coli, latex particles (1, 3.2, 11, 25, and 45 μm), alginate, and divalent cations; and the bioflocculation of particles was achieved naturally, as it would occur in the environment, without using chemical coagulants. E. coli was quantified before and after UV disinfection using membrane filtration. Even in the absence of particles, some of the self-aggregated E. coli could survive a UV dose of 90 mJ/cm². E. coli inactivation levels measured in the presence of particles were lower than the inactivation levels measured in the absence of particles. At low UV doses (<9 mJ/cm²), neither particle size nor degree of flocculation had a significant effect on the inactivation of E. coli. Particle size had a significant effect on the inactivation of E. coli only at high UV doses (80 mJ/cm²), and larger particles (e.g., 25 μm) protected bacteria more compared to smaller particles (e.g., 3.2 and 11 μm). What size of particles flocs were made of (3.2, 11, and 25 μm) did not make a significant difference on the inactivation levels of E. coli. For 3.2 μm particles, there was no significant difference in E. coli inactivation between non-flocculated and flocculated samples at any UV dose. For 11 and 25 μm particles, there was a significant difference in E. coli inactivation between non-flocculated and flocculated samples at 80 mJ/cm². Degree of flocculation became a significant factor in determining the number of surviving bacteria only at high UV doses and only for larger particles.     

Impact of lamp shadowing and reflection on the fluence rate distribution in a multiple low-pressure UV lamp array

Use of mathematical modeling for determination of ultraviolet (UV) fluence in disinfection reactors requires accurate knowledge of the fluence rate distribution in a multiple lamp array. A method for measuring the fluence rate among a multiple lamp array was demonstrated using spherical actinometry. A matrix of four low-pressure UV lamps in air were investigated to evaluate the potential for shadowing and reflection to impact the fluence rate within and surrounding the lamp array. Two fluence rate distribution models were tested to determine the ability to predict the fluence rate distribution measured by the actinometers. Shadowing proved to attenuate UV light. Reflection from the lamp surface added 3-9% to the fluence rate, depending upon position in the reactor. These effects, as well as the fluence rate at various points in the lamp matrix were effectively modeled using RAD-LSI and UVCalc3D fluence rate distribution models. At fluence rates above 8mWcm(-2), the actinometry measured fluence rate was lower than the modeled rate, presumably from saturation of the actinometer solution at high fluence rates (close to the lamp). With multiple lamp reactors, the impact of shadowing can significantly affect fluence rate distribution and thus the level of microbial inactivation. If shadowing is not included in fluence rate distribution models, the fluence rate will be over predicted in the shadow zone of a neighboring lamp, falsely skewing model inactivation predictions.     

Drinking water treatment of priority pesticides using low pressure UV photolysis and advanced oxidation processes

This study reports the efficiency of low pressure UV photolysis for the degradation of pesticides identified as priority pollutants by the European Water Framework Directive 2000/60/EC. Direct low pressure UV photolysis and advanced oxidation processes (using hydrogen peroxide and titanium dioxide) experiments were conducted in laboratory grade water, surface water, and groundwater.LP direct photolysis using a high UV fluence (1500 mJ/cm²) was found to be extremely efficient to accomplish the degradation of all pesticides except isoproturon, whereas photolysis using hydrogen peroxide and titanium dioxide did not significantly enhance their removal. In all matrices tested the experimental photolysis of the pesticides followed the same trend: isoproturon degradation was negligible, alachlor, pentachlorophenol, and atrazine showed similar degradation rate constants, whereas diuron and chlorfenvinphos were highly removed. The degradation trend observed for the selected compounds followed the decadic molar absorption coefficients order with exception of isoproturon probably due to its extremely low quantum yield.Similar direct photolysis rate constants were obtained for each pesticide in the different matrices tested, showing that the water components did not significantly impact degradation. Extremely similar photolysis rate constants were also obtained in surface water for individual compounds when compared to mixtures. The model fluence and time-based rate constants reported were very similar to the direct photolysis experimental results obtained, while overestimating the advanced oxidation results. This model was used to predict how degradation of isoproturon, the most resilient compound, could be improved.     

Comparison of low- and medium-pressure ultraviolet lamps: Photoreactivation of Escherichia coli and total coliforms in secondary effluents of municipal wastewater treatment plants

It has been reported that Medium-Pressure (MP) ultraviolet (UV) lamps have an advantage over low-pressure (LP) lamps for water disinfection in terms of the photoreactivation of pure cultured bacteria. However, few studies have investigated the behavior of microorganisms in wastewater. Hence, in this study, the degree of photoreactivation, after UV exposure using both LP and MP lamps, in municipal wastewater samples was examined under a variety of conditions. Pure cultured Escherichia coli was also used to provide a comparison with previous studies.E. coli was found to undergo photoreactivation after both LP and MP exposure. The Colony Forming Ability (CFA) ratios were 0.60 and 0.32, and the percentage of photoreactivation was 50% and 20%, respectively, for LP and MP lamps with a germicidal UV dose of 5 mJ/cm². However, the advantage of the MP lamp was diminished for larger UV doses, since no photoreactivation was detected when the UV dose was 15 mJ/cm² for either LP or MP lamps. The microorganisms present in wastewater showed similar results to those of E. coli, however, no significant difference was found between the use of either a LP or a MP lamp. Also, when a UV dose of 40 mJ/cm² was applied, the percentage photoreactivation was less than 1%, no matter which type of lamp was used. From this work, it is concluded that the selection of the type of UV lamp for wastewater treatment plants, as regards photoreactivation of total coliforms, is not critical as long as the applied germicidal UV dose is greater than 40 mJ/cm².     

Survival of Escherichia coli in two sewage treatment plants using UV irradiation and chlorination for disinfection

We investigated the survival of Escherichia coli in two STPs utilising UV irradiation (STP-A) or chlorination (STP-B) for disinfection. In all, 370 E. coli strains isolated from raw influent sewage (IS), secondary treated effluent (STE) and effluent after the disinfection processes of both STPs were typed using a high resolution biochemical fingerprinting method and were grouped into common (C-) and single (S-) biochemical phenotypes (BPTs). In STP-A, 83 BPTs comprising 123 isolates were found in IS and STE, of which 7 BPTs survived UV irradiation. Isolates tested from the same sites of STP-B (n = 220) comprised 122 BPTs, however, only two BPTs were found post-chlorination. A representative isolate from each BPT from both STPs was tested for the presence of 11 virulence genes (VGs) associated with uropathogenic (UPEC) or intestinal pathogenic (IPEC) E. coli strains. Strains surviving UV irradiation were distributed among seven phylogenetic groups with five BPTs carrying VGs associated with either UPEC (4 BPTs) or IPEC (1 BPT). In contrast, E. coli strains found in STP-B carried no VGs. Strains from both STPs were resistant to up to 12 out of the 21 antibiotics tested but there was no significant difference between the numbers of antibiotics to which surviving strains were resistant to in these STPs. Our data suggests that some E. coli strains have a better ability to survive STPs utilising chlorination and UV irradiation for disinfection. However, strains that survive UV irradiation are more diverse and may carry more VGs than those surviving SPTs using chlorination.     

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.     

The influence of water treatment processes on the presence of organic surrogates and mutagenic compounds in water

The effects of granular activated carbon filtration and of the combination of ozonation and GAC filtration on the quality of Rhine water were studied in a pilot plant. The scope of the study was to compare both systems in relation to the removal of organic contaminants in water, and to the reduction of the side effects of chlorination. The water quality was measured with organic surrogate parameters (organohalogen, -nitrogen, -phosphorus and -sulphur) and in bacterial mutagenicity assays.In this particular setting, the combination of ozonation and GAC filtration was superior in all points to GAC filtration alone. The effects of ozonation are sometimes quite different, depending on the type of water treated. Its positive influence should be confirmed in a local situation.As GAC treatment causes a shift towards formation of more brominated THM after chlorination, special attention was given to this item. A higher inorganic bromide/DOC ratio resulted in higher brominated THM concentrations after chlorination. However, the mutagens formed during chlorination in presence of more inorganic bromide could be inactivated more easily by rat liver homogenate than in the normal setting. The results of this study confirmed earlier findings stating a negative influence of chlorination on water quality.     

Effects of UV/H2O2 advanced oxidation on chemical characteristics and chlorine reactivity of surface water natural organic matter

The advanced oxidation process utilizing ultraviolet and hydrogen peroxide (UV/H₂O₂) is currently applied in commercial drinking water applications for the removal of various organic pollutants. Natural organic matter (NOM) present in the source water can also be oxidized and undergo changes at the fluence and H₂O₂ concentrations applied in commercial drinking water UV/H₂O₂ applications (fluences less than 2000 mJ cm⁻², initial H₂O₂ concentrations less than 15 mg L⁻¹). In this study, the impact of UV/H₂O₂ on NOM’s aromaticity, hydrophobicity, and potential to form trihalomethanes (THMs) and haloacetic acids (HAAs) was investigated for raw surface water and the same water with the very hydrophobic acid (VHA) fraction of NOM removed. During UV/H₂O₂ treatments, NOM in the raw surface water was partially oxidized to less aromatic and hydrophobic characteristics, but was not mineralized, confirming findings from past research. Below fluences of 1500 mJ cm⁻² UV/H₂O₂ treatment of the raw water did not lead to reduction in the formation potential of THMs. The formation potential of HAAs was reduced at a fluence of 500 mJ cm⁻² with only small additional reductions as fluence further increased. For the water from which the VHA fraction was removed, UV/H₂O₂ treatment led to mineralization of NOM suggesting that, when coupled with a pre-treatment capable of removing the VHA fraction, UV/H₂O₂ could achieve further reductions in NOM. These subsequent reductions in NOM led to continuous reductions in the formation potentials of THMs and HAAs as fluence increased.     

The effect of humic acids on nitrobenzene oxidation by ozonation and O3/UV processes

Three types of commercially available humic acids from different sources were used to simulate natural organic matter in water for the investigation of nitrobenzene oxidation by ozonation and O(3)/UV. Despite the structural differences among the Fluka, Aldrich and Suwanee River humic acids as reflected by the UV absorptivity, their effects on nitrobenzene removal rate was observed to be similar for the two processes. Removal rate of nitrobenzene was hindered by the addition of humic acids in ozonation as well as in O(3)/UV processes. However, the hindrance by the humic acids was more pronounced in O(3)/UV as compared to the ozonation process. The effect of humic acid in O(3)/UV was primarily a UV light screening. Addition of humic acids above a certain concentration did not cause any further retardation on nitrobenzene removal rate by ozonation and O(3)/UV.Accumulation of hydrogen peroxide as well as probable formation of peroxy radicals in the solutions might induce chain promoting reactions to produce hydroxyl radical during the nitrobenzene oxidation. For waters containing high levels of humic acid, ozonation alone might be as effective as O(3)/UV process for the removal of nitrobenzene.     

Measurement of the initial phase of ozone decomposition in water and wastewater by means of a continuous quench-flow system: application to disinfection and pharmaceutical oxidation

Due to a lack of adequate experimental techniques, the kinetics of the first 20s of ozone decomposition in natural water and wastewater is still poorly understood. Introducing a continuous quench-flow system (CQFS), measurements starting 350 ms after ozone addition are presented for the first time. Very high HO. to O3 exposures ratios (Rct=integralHO.dt/integralO3dt) reveal that the first 20s of ozonation present oxidation conditions that are similar to ozone-based advanced oxidation processes (AOP). The oxidation of carbamazepine could be accurately modeled using O3 and HO. exposures measured with CQFS during wastewater ozonation. These results demonstrate the applicability of bench scale determined second-order rate constants for wastewater ozonation. Important degrees of pharmaceutical oxidation and microbial inactivation are predicted, indicating that a significant oxidation potential is available during wastewater ozonation, even when ozone is entirely decomposed in the first 20s.     

Impact of UV disinfection on microbially available phosphorus,organic carbon,and microbial growth in drinking water

UV irradiation at a wavelength of 253.7 nm (UV(254)) is commonly used for drinking water disinfection. UV radiation is known to convert organically combined phosphorus to orthophosphate and to degrade natural organic matter. We studied if UV disinfection increases the amount of microbially available forms of organic carbon and phosphorus in drinking waters with different characteristics, and if these changes in water chemical quality could enhance the microbial growth in drinking water. The UV(254) dose (15-50 mWs/cm(2)) used in waterworks reduced the concentration of assimilable organic carbon and the sum of the molecular size fractions. The release of microbially available phosphorus needed higher doses (204 mWs/cm(2)) of UV(254) radiation. Of bacteria in drinking water, 90% were inactivated with UV(254)-irradiation doses below 50 mWs/cm(2). A high dose (501 mWs/cm(2)) of UV(254) radiation inhibited the microbial growth in water.     

Impact of feed water acidification with weak and strong acids on colloidal silica fouling in ultrafiltration membrane processes

Although acidification of feed water is a common practice to prevent scaling of the sparingly soluble minerals in nanofiltration and reverse osmosis processes, the change of acidity may have a potentially adverse impact on colloidal fouling, which is another important type of fouling on the membranes. In this paper, commonly used strong and weak acids are quantitatively investigated for their effect on colloidal silica fouling with a lab-scale ultrafiltration (UF) membrane system. Experiments showed that addition of either strong or weak acids in feed water would intensify colloidal fouling. However, the strength of colloidal fouling with strong acid addition was consistently higher (12-37%) than that with weak acid addition at pH 3. The smaller increase in colloidal fouling potential observed with weak acids was attributed to the adsorption of weak acid anions on the colloidal silica surface, which kept the absolute value of zeta potential of the colloids relatively high. Consequently, the difference in colloidal fouling potential with the additions of strong and weak acids diminished at high salt concentration. The findings implied that the type of acid used in feed water acidification could have a significant impact on colloidal fouling for low-salinity waters.     

Comparison of the action spectra and relative DNA absorbance spectra of microorganisms: Information important for the determination of germicidal fluence (UV dose) in an ultraviolet disinfection of water

The action spectra of Bacillus subtilis spores (ATCC6633) and Salmonella typhimurium LT2 were characterized using physical radiometry for irradiance measurements and a multiple target model to interpret the inactivation kinetics. The observed action spectrum of B. subtilis spores deviated significantly from the relative absorbance spectrum of the DNA purified from the spores, but matched quite well with the relative absorbance spectrum of decoated spores. The action spectrum of B. subtilis spores determined in this study was statistically different from those reported in previous studies. On the other hand, the action spectrum of S. typhimurium bacteria matched quite well with the relative absorbance spectrum of DNA extracted from vegetative cells, except in the region below 240 nm. It is concluded that the common use of the relative DNA absorbance spectrum as a surrogate for the germicidal action spectrum can result in systematic errors when evaluating the performance of a polychromatic UV light reactors using bioassays. For example, if the weighted germicidal fluence (UV dose) calculated using the relative DNA absorbance spectrum as the germicidal weighting factor is found to be 40 mJ cm⁻² for a medium pressure lamp UV reactor, that calculated using the relative action spectrum of B. subtilis spores, as determined in this study, would be 66 mJ cm⁻².     

The effect of electrode material on the generation of oxidants and microbial inactivation in the electrochemical disinfection processes

Electrochemical disinfection has gained increasing attention as an alternative for conventional drinking water treatment due to its high effectiveness and environmental compatibility. The most common method of electrochemical disinfection is the use of electro-generated oxidants, such as active chlorine and reactive oxygen species, as disinfectants. This study examined the role of electrode material on the generation of oxidants, and elucidated the different reaction pathways for generating individual oxidants by employing boron-doped diamond (BDD), Ti/RuO₂, Ti/IrO₂, Ti/Pt-IrO₂, and Pt as anode materials. The efficiency of OH production, as determined by para-chlorobenzoic acid (pCBA) degradation, was in the order of BDD ? Ti/RuO₂ ≈ Pt. No significant production of OH was observed at Ti/IrO₂ and Ti/Pt-IrO₂. The OH was found to play a key role in O₃ generation at BDD, but not at the other electrodes. The production of active chlorine was in the order of Ti/IrO₂ > Ti/RuO₂ > Ti/Pt-IrO₂ > BDD > Pt. The large difference in this order from that of ROS was attributed to the difference in the electrocatalytic activity of each electrode material toward the production of active chlorine, as evidenced by linear sweep voltammetry (LSV) measurements. In addition, the characteristics of microbial inactivation as a function of electrode material were examined under the presence of an inert electrolyte, using Escherichia coli as an indicator microorganism.     

铁锰超标对天然河床潜流水水质影响及处理

研究了铁锰离子超标对天然河床潜流水水质的影响及相应的处理技术,分析了潜流水中铁锰的危害及迁移富集规律,通过对除铁锰技术进行比选,得出接触氧化法是去除潜流水中铁锰的最佳方法,并对其工艺流程作了具体介绍,以期指导实践。     

Impact of UV/H(2)O(2) advanced oxidation treatment on molecular weight distribution of NOM and biostability of water

The presence of natural organic matter (NOM) poses several challenges to the commercial practice of UV/H₂O₂ process for micropollutant removal. During the commercial application of UV/H₂O₂ advanced oxidation treatment, NOM is broken down into smaller species potentially affecting biostability by increasing Assimilable Organic Carbon (AOC) and Biodegradable Organic Carbon (BDOC) of water. This work investigated the potential impact of UV/H₂O₂ treatment on the molecular weight distribution of NOM and biostability of different water sources. A recently developed flow cytometric method for enumeration of bacteria was utilized to assess biological stability of the treated water at various stages through measurement of AOC. BDOC was also assessed for comparison and to better study the biostability of water. Both AOC and BDOC increased by about 3-4 times over the course of treatment, indicating the reduction of biological stability. Initial TOC and the source of NOM were found to be influencing the biostability profile of the treated water. Using high performance size exclusion chromatography, a wide range of organic molecule weights were found responsible for AOC increase; however, low molecular weight organics seemed to contribute more. Positive and meaningful correlations were observed between BDOC and AOC of different waters that underwent different treatments.     

水上运动主题对日照城市发展的影响评价

通过实地考察,对水上运动主题对日照城市发展的影响进行了分析,从水上运动主题的发展丰富了城市文化内涵、改善了城市环境、提升了城市形象并推动了日照相关产业的发展等方面进行了论述,以期促进城市经济和社会事业的快速发展。     

The effect of different drinking water treatment processes on the rate of chloroform formation in the reactions of natural organic matter with hypochlorite

This study is concerned with the changes in the rate of chloroform formation during the reactions of groundwater natural organic matter (NOM) and sodium hypochlorite caused by different drinking water treatments schemes: coagulation with FeCl₃, Al₂(SO₄)₃ and polyaluminum chloride (PACl), filtration of the raw water through granular activated carbon (GAC) and filtration through the columns filled with strong base macroporous ion-exchange resins (Purolite A501P and A500P) with and without pretreatment by coagulation process. It was found that the change of the concentration of chloroform, within 2 h and c(Cl₂)=100 mg l⁻¹, can be described by a kinetic equation of the form [CHCl₃]=a+bt^c. On the basis of this equation rates of the reaction were calculated. All processes applied decreased the rate of chloroform formation (process of coagulation moderately decreased the rate of reactions, while GAC adsorption caused dramatically drop of the rate). Also, it was found that the resins have had a higher affinity towards slow-reacting chloroform precursors.

The value of the chloroform formation potential was conventionally determined after a 7-day reaction at pH 7. In addition, the same parameter was estimated with a satisfactory deviation for raw water and for treated water on the basis of the kinetic constant (k) or by determining the chloroform concentration after 2 h (ChFP₂) under rigourous chlorination conditions at pH 8.4.     

原水铁锰含量对细菌除铁除锰效能的影响

将从水厂成熟锰砂中分离出来的细菌进行驯化和增殖培养,通过改变原水中铁锰含量来改变细菌生长环境,考察了不同条件下混合细菌对铁锰的去除效果.结果表明:在有Fe2+存在的情况下,铁锰氧化细菌维持着正常的活性,对铁锰始终具有高效而稳定的去除能力;Fe2+的存在与否也影响着Mn2+的氧化速率;原水中锰的存在对细菌除铁影响较小.