Dissolved organic nitrogen removal during water treatment by aluminum sulfate and cationic polymer coagulation

Coagulation of three surface waters was conducted with aluminum salt and/or cationic polymer to assess dissolved organic nitrogen (DON) removal. Coagulation with aluminum sulfate removed equal or slightly lower amounts of DON as compared to dissolved organic carbon (DOC). At aluminum sulfate dosages up to 5 mg per mg DOC, the cationic polymer improved DON removal by an additional 15% to 20% over aluminum sulfate alone. At very high aluminum sulfate dosages (>8 mg aluminum sulfate per mg DOC), however, the cationic polymer addition negligibly increased DON removal. Molecular weight fractionation before and after coagulation experiments indicated that cationic polymer addition can increase the removal of all molecular weight fractions of DON with the highest molecular weight fraction (>10,000 Da) being preferentially removed. Results indicated that the DON added as part of the cationic polymer was almost completely removed at optimum aluminum sulfate and polymer doses.     

A study of titanium sulfate flocculation for water treatment

There are limited studies available on titanium salt flocculation. In this research, coagulation experiments of titanium sulfate were conducted using both distilled water and kaolin clay suspension. Results showed that titanium sulfate flocculation was most effective in the pH range 4-6, and negligible concentrations of titanium were found in the well-flocculated water. The floc isoelectric point (IEP) was found to be near pH 5. Measurements showed that the titanium flocs possessed greater density, diameter and settling velocity than the aluminum flocs. The titanium flocs were composed of TiO(OH)₂, which would change from the amorphous phase into anatase titanium dioxide under elevated temperatures. Floc images showed the structural similarity of titanium and aluminum flocs. Laboratory results and a pilot experiment showed that titanium sulfate could be an alternative coagulant for water and wastewater treatment.     

The impact of water consumption, point-of-use filtration and exposure categorization on exposure misclassification of ingested drinking water contaminants

The use of population-level indices to estimate individual exposures is an important limitation of previous epidemiologic studies of disinfection by-products (DBPs). We examined exposure misclassification resulting from the use of system average DBP concentrations to estimate individual-level exposures. Data were simulated (n=1000 iterations) for 100 subjects across 10 water systems based on the following assumptions: DBP concentrations ranged from 0-99 microg/L with limited intra-system variability; water intake ranged from 0.5-2.5 L/day; 20% of subjects used bottled water exclusively; 20% of subjects used filtered tap water exclusively; DBP concentrations were reduced by 50% or 90% following filtration. DBP exposure percentiles were used to classify subjects into different exposure levels (e.g., low, intermediate, high and very high) for four classification approaches. Compared to estimates of DBP ingestion that considered daily consumption, source type (i.e., unfiltered tap, filtered tap, and bottled water), and filter efficiency (with 90% DBP removal), 48-62% of subjects were misclassified across one category based on system average concentrations. Average misclassification across at least two exposure categories (e.g., from high to low) ranged from 4-14%. The median classification strategy resulted in the least misclassification, and volume of water intake was the most influential modifier of ingestion exposures. These data illustrate the importance of individual water use information in minimizing exposure misclassification in epidemiologic studies of drinking water contaminants.     

Formation and fate of haloacetic acids (HAAs) within the water treatment plant

Most research on the occurrence of chlorinated disinfection by-products (DBPs) in drinking water has focused on trihalomethane (THM) formation and evolution, in particular within distribution systems. In this research, we investigated the variability of the occurrence of haloacetic acids (HAAs) during the treatment process in two facilities where surface water is pre-chlorinated before being treated by conventional physico-chemical processes. The investigation focused on both seasonal and point-to-point fluctuations of HAAs. In both facilities, samples were collected weekly during 1 complete year at four points in order to generate robust data on HAAs and on complementary parameters. The results showed that the initial formation of HAAs was the highest and the most variable in the plant where levels of DBP precursor indicators and the pre-chlorination dose were both higher and more variable. Subsequent formation of HAAs from the pre-chlorination point until the settled water occurred due to remaining levels of residual chlorine and DBP precursors. However, HAA levels and in particular dichloroacetic acid (DCAA) (the preponderant HAA species in the waters under study) decreased dramatically during filtration, very probably because of biodegradation within the filter. The effect of filtration on DCAA fate was season-dependant, with the highest degradation in warm water periods and practically no variation during winter. Statistical modeling was applied to empirically identify the operational factors responsible for HAA formation and fate. Model performance to identify HAA variability in waters following pre-chlorination was much better than for water following filtration, which is due to the lack of information on mechanisms and conditions favoring DCAA degradation.     

UV/H2O2 treatment of drinking water increases post-chlorination DBP formation

Ultraviolet (UV) irradiation has become popular as a primary disinfectant because it is very effective against Cryptosporidium and does not directly form regulated disinfection by-products. Higher UV doses and UV advanced oxidation (UV/H₂O₂) processes are under consideration for the treatment of trace organic pollutants (e.g. pharmaceuticals, personal care products). Despite the disinfection effectiveness of UV light, a secondary disinfectant capable of maintaining a distribution system residual is required to meet current U.S. regulation. This study investigated changes in disinfection by-product (DBP) formation attributed to UV or UV/H₂O₂ followed by application of free chlorine to quench hydrogen peroxide and provide residual disinfectant. At a UV dose of 1000 mJ/cm², trihalomethane (THM) yield increased by up to 4 μg/mg-C and 13 μg/mg-C when treated with low and medium pressure UV, respectively. With the addition of hydrogen peroxide, THM yield increased by up to 25 μg/mg-C (5 mg-H₂O₂/L) and 37 μg/mg-C (10 mg-H₂O₂/L). Although no changes in DBPs are expected during UV disinfection, application of UV advanced oxidation followed by chlorine addition was assessed with regard to impacts on DBP formation.     

Treatability of chloro-s-triazines by conventional drinking water treatment technologies

Recent research shows that herbicide atrazine (ATZ), simazine (SIM), and propazine (PROP), as well as their three chlorinated degrades-desethylatrazine (DEA), deisopropylatrazine (DIA), and didealkylatrazine (DDA)-may cause a common toxic effect in terms of endocrine disruption. The US Environmental Protection Agency (EPA) is currently considering a regulatory trigger based on the sum of these concentrations of these six chloro-s-triazines. While limited removal data exists for the parent compounds, little information is available for the degrades formed biologically and/or chemically in the environment and in the treatment plants. It is therefore critical to assess the removal efficiency in a typical water plant of the parent herbicides, as well as the daughter products. In this work, conventional drinking water treatment technologies were evaluated under typical water treatment plant conditions to determine their effectiveness in removing six chloro-s-triazines: ATZ, SIM, PROP, DEA, DIA, and DDA. Experiments were conducted using synthetic solutions prepared by spiking both distilled water and Missouri River water with the study compounds. Two powder activated carbons (PAC)--Calgon WPH and Norit HDB-were shown to be partially effective in removing the studied chloro-s-triazines. Ozonation efficiency varied, depending on different water sources, with respect to the removal of atrazine and didealkylatrazine. Coagulation/flocculation/sedimentation with alum and iron salts, excess lime/soda ash softening, and disinfection by free chlorine were all ineffective methods for removing chloro-s-triazines. It appears that chloro-s-triazine compounds are not readily removed by most conventional drinking water treatment processes, with the exception of use of activated carbon.     

Submicron capsules extracted from rapeseed as novel flocculant agents for the treatment of turbid water

Flocculation is an important step in water treatment as it is responsible for the separation of suspended solids and colloids. The currently used flocculants have certain limitations with respect to environmental impact and disposal as well as potentially being harmful to human health, which has encouraged the study of natural flocculants originating from oleaginous plants. Oil-bodies are individual small organelles in which oleaginous seeds store triacylglycerols reserves. In this article, the flocculant properties of oil-bodies have been investigated. Oil-bodies flocculate at pH 5, 7 and 9 and high ionic strength (100 mM NaCl) and it was demonstrated that their intact structure is necessary for the flocculation activity as treatment with protease K and diethyl ether, that remove the protein coat and the oil-core, respectively, dramatically decreased the flocculation activity. This study shows that oil-bodies have the potential to be novel, natural, sustainable, environmentally friendly and biodegradable flocculant candidates for water treatment.     

Ozonation of drinking water: part II. Disinfection and by-product formation in presence of bromide,iodide or chlorine

Ozone is an excellent disinfectant and can even be used to inactivate microorganisms such as protozoa which are very resistant to conventional disinfectants. Proper rate constants for the inactivation of microorganisms are only available for six species (E. coli, Bacillus subtilis spores, Rotavirus, Giardia lamblia cysts, Giardia muris cysts, Cryptosporidium parvum oocysts). The apparent activation energy for the inactivation of bacteria is in the same order as most chemical reactions (35-50 kJ mol(-1)), whereas it is much higher for the inactivation of protozoa (80 kJ mol(-1)). This requires significantly higher ozone exposures at low temperatures to get a similar inactivation for protozoa. Even for the inactivation of resistant microorganisms, OH radicals only play a minor role. Numerous organic and inorganic ozonation disinfection/oxidation by-products have been identified. The by-product of main concern is bromate, which is formed in bromide-containing waters. A low drinking water standard of 10 microg l(-1) has been set for bromate. Therefore, disinfection and oxidation processes have to be evaluated to fulfil these criteria. In certain cases, when bromide concentrations are above about 50 microg l(-1), it may be necessary to use control measures to lower bromate formation (lowering of pH, ammonia addition). Iodate is the main by-product formed during ozonation of iodide-containing waters. The reactions involved are direct ozone oxidations. Iodate is considered non-problematic because it is transformed back to iodide endogenically. Chloride cannot be oxidized during ozonation processes under drinking water conditions. Chlorate is only formed if a preoxidation by chlorine and/or chlorine dioxide has occurred.     

Haloacetic acids in drinking water in the United Kingdom

We measured concentrations of haloacetic acids (HAAs) in the water supply in regions covered by three water companies in the UK Approximately 30 samples in each region were obtained for analysis of both THMs and HAAs to assess the levels of HAAs and the relationship between HAAs and THMs, temperature, pH, free and total chlorine. We have found that there is a range of HAA levels in drinking water with the means ranging from 35-95mug/l and a maximum concentration of 244mug/l. In two out of the three regions there was a high correlation between total THMs and total HAAs, but whereas the HAA and THM levels in one of these companies were approximately equal, in another company the HAA levels were 3-4 times higher than the THM levels. In the third region there was no correlation between total THMs and total HAAs even though the average levels were approximately equal. The ratio of total THM and total HAAs levels was significantly correlated with temperature, pH, free and total chlorine. Overall total THM levels are therefore not considered to be a good indicator of HAA levels. Epidemiological studies using total THM levels should be taking this into account in the interpretation of their results, and regulatory authorities when setting water guidelines.     

Controversies about the occurrence of chloral hydrate in drinking water

Besides trihalomethanes (THMs) and haloacetic acids (HAAs), chloral hydrate (CH) is the next most prevalent disinfection by-product (DBP) in drinking water, formed as a result of the reaction between chlorine and natural organic matter (NOM). Chloral hydrate (trichloroacetaldehyde) should be limited in drinking water because of its adverse health effect. The controversies concerning the appearance of CH in disinfected water found in literature are discussed in the present paper. According to some authors the CH yield during chlorination of water depends only on TOC. However, there are other data available that do not confirm this relationship. Another fact requiring clarification is the dependence of CH formation on pH. In the present study, CH formation is analysed in different types of water disinfected with different doses of chlorine. Formation of CH is correlated with the dose of Cl₂ and the contact time. The formation of chloral hydrate takes place as long as chlorine is available in the water. Total organic carbon (TOC) is not considered the main factor influencing the production of chloral hydrate in water treated with Cl₂ as the production depends also on the nature of NOM. Higher levels of CH are observed at alkaline conditions (pH > 7). A significant correlation (R² > 0.9) between the concentrations of chloral hydrate and chloroform has been observed. The preozonation increases significantly the chloral hydrate formation potential in the water treated. Biofiltration process does not remove all of CH precursors and its efficiency depends strongly on the contact time. Chloral hydrate was analyzed by gas chromatography with electron capture detector with the detection limit 0.1 μg L⁻¹.     

Measurement of dissolved organic nitrogen in a drinking water treatment plant: size fraction, fate, and relation to water quality parameters

This paper investigates the characteristics of dissolved organic nitrogen (DON) in raw water from the Huangpu River and also in water undergoing treatment in the full-scale Yangshupu drinking water treatment plant (YDWTP) in Shanghai, China. The average DON concentration of the raw water was 0.34 mg/L, which comprised a relatively small portion (~ 5%) of the mass of total dissolved nitrogen (TDN). The molecular weight (MW) distribution of dissolved organic matter (DOM) was divided into five groups: > 30, 10-30, 3-10, 1-3 and < 1 kDa using a series of ultrafiltration membranes. Dissolved organic carbon (DOC), UV absorbance at wavelength of 254 nm (UV254) and DON of each MW fraction were analyzed. DON showed a similar fraction distribution as DOC and UV254. The < 1 kDa fraction dominated the composition of DON, DOC and UV254 as well as the major N-nitrosodimethylamine formation potential (NDMAFP) in the raw water. However, this DON fraction cannot be effectively removed in the treatment line at the YDWTP including pre-ozonation, clarification and sand filtration processes. The results from linear regression analysis showed that DON is moderately correlated to DOC, UV254 and trihalomethane formation potential (FP), and strongly correlated to haloacetic acids FP and NDMAFP. Therefore, DON could serve as a surrogate parameter to evaluate the reactivity of DOM and disinfection by-products FP.     

贵州村镇供水工程净水技术的选择

分析了贵州村镇供水工程现状及特点,并结合我省供水工程运行经验,提出适用于贵州村镇的净水技术,有利于保障居民饮用水安全、提高供水水质、降低供水成本,保证供水工程能取得良好的社会、经济、环境效益。     

Comparison of seven kinds of drinking water treatment processes to enhance organic material removal: a pilot test

Organic matter in source water has presented many challenges in the field of water purification, especially for conventional treatment. A two-year-long pilot test comparing water treatment processes was conducted to enhance organic matter removal. The tested process combinations included the conventional process, conventional plus advanced treatment, pre-oxidation plus conventional process and pre-oxidation plus conventional plus advanced treatment. The efficiency of each kind of process was assayed with the comprehensive indices of COD(Mn), TOC, UV(254), AOC, BDOC, THMs, and HAAs and their formation potential. The results showed that the combination of the conventional process and O(3)-BAC provides integrated removal of organic matter and meets the required standards. It is the best performing treatment tested in this investigation for treating polluted source water in China. Moreover, much attention should be paid to organic removal before disinfection to control DBP formation and preserve biostability. This paper also reports the range of efficiency of each unit process to calculate the total efficiency of different process combinations in order to help choose the appropriate water treatment process.     

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.     

Recent developments in photocatalytic water treatment technology: A review

In recent years, semiconductor photocatalytic process has shown a great potential as a low-cost, environmental friendly and sustainable treatment technology to align with the “zero” waste scheme in the water/wastewater industry. The ability of this advanced oxidation technology has been widely demonstrated to remove persistent organic compounds and microorganisms in water. At present, the main technical barriers that impede its commercialisation remained on the post-recovery of the catalyst particles after water treatment.This paper reviews the recent R&D progresses of engineered-photocatalysts, photoreactor systems, and the process optimizations and modellings of the photooxidation processes for water treatment. A number of potential and commercial photocatalytic reactor configurations are discussed, in particular the photocatalytic membrane reactors. The effects of key photoreactor operation parameters and water quality on the photo-process performances in terms of the mineralization and disinfection are assessed. For the first time, we describe how to utilize a multi-variables optimization approach to determine the optimum operation parameters so as to enhance process performance and photooxidation efficiency. Both photomineralization and photo-disinfection kinetics and their modellings associated with the photocatalytic water treatment process are detailed. A brief discussion on the life cycle assessment for retrofitting the photocatalytic technology as an alternative waste treatment process is presented. This paper will deliver a scientific and technical overview and useful information to scientists and engineers who work in this field.     

Evaluation of an MBR-RO system to produce high quality reuse water: microbial control, DBP formation and nitrate

A membrane bioreactor and reverse osmosis (MBR-RO) system was developed to assess potential reuse applications of municipal wastewater. The objective of the study was to examine the water quality throughout the system with a focus on waterborne pathogens, disinfection by-products (DBPs) and nitrate. This paper will discuss the presence of these contaminants in MBR effluent and focus on their subsequent removal by RO. This study has shown that high quality reuse water can be produced from municipal wastewater through the use of an MBR-RO system. The water meets California Title 22 reuse regulations for non-potable applications and US EPA drinking water limits for trihalomethanes (THM) (80 microg/L), haloacetic acids (HAA) (60 microg/L), chlorite (1.0 mg/L), total coliform (not detectable), viruses (not detectable), and nitrate/nitrite (10 mg N/L). However, THM formation (182-689 microg/L) attributed to cleaning of the MBR with chlorine and incomplete removal by subsequent RO treatment resulted in reuse water with THM levels (40.2+/-19.9 microg/L) high enough to present a potential concern when considering drinking water applications. Nitrate levels of up to 3.6 mg N/L, which resulted from incomplete removal by the RO membrane, are also a potential concern. A denitrification step in the MBR should be considered in potable water applications.     

Measuring the concentrations of drinking water disinfection by-products using capillary membrane sampling-flow injection analysis

A capillary membrane sampling-flow injection analysis method is presented for selectively measuring the concentrations of total trihalomethanes (THMs) and total haloacetic acids (HAAs) in drinking water. The method is based on the reaction between nicotinamide and THM or HAA species to yield a fluorescent product. Two configurations are presented, one selective for total THMs and another selective for total HAAs. The construction of a capillary membrane sampler is described, and the results of method detection limit, accuracy and precision studies are reported for each method. Interference, selectivity and linearity studies are reported as well as the effect of temperature and ionic strength changes. Drinking water samples were analyzed by each proposed method and the results were compared to USEPA methods 502.2 and 552.3.     

Impact of water stagnation in residential cold and hot water plumbing on concentrations of trihalomethanes and haloacetic acids

This study demonstrates that levels of trihalomethanes (THMs) increase considerably when cold water stagnates in residential pipes and, more significantly, when water remains in the hot water tank. Levels of haloacetic acids (HAAs) increase as well in both cases, but less significantly in comparison to THMs. The study also demonstrates that in both the plumbing system and residential hot water tank, chlorinated and brominated DBP species do not behave in the same manner. Finally, the study shows that sustained use of water in households helps to maintain THM and HAA levels close to those found in water of the distribution system. The results are useful to identify methods of indoor water use that minimize population exposure to DBPs and improve DBP exposure assessment for epidemiological studies.     

Application of GaN-based ultraviolet-C light emitting diodes--UV LEDs--for water disinfection

GaN-based ultraviolet-C (UV-C) light emitting diodes (LEDs) are of great interest for water disinfection. They offer significant advantages compared to conventional mercury lamps due to their compact form factor, low power requirements, high efficiency, non-toxicity, and overall robustness. However, despite the significant progress in the performance of semiconductor based UV LEDs that has been achieved in recent years, these devices still suffer from low emission power and relatively short lifetimes. Even the best UV LEDs exhibit external quantum efficiencies of only 1-2%.The objective of this study was to investigate the suitability of GaN-based UV LEDs for water disinfection. The investigation included the evaluation of the performance characteristics of UV LEDs at different operating conditions as well as the design of a UV LED module in view of the requirements for water treatment applications. Bioanalytical testing was conducted using Bacillus subtilis spores as test organism and UV LED modules with emission wavelengths of 269 nm and 282 nm.The results demonstrate the functionality of the developed UV LED disinfection modules. GaN-based UV LEDs effectively inactivated B. subtilis spores during static and flow-through tests applying varying water qualities. The 269 nm LEDs reached a higher level of inactivation than the 282 nm LEDs for the same applied fluence. The lower inactivation achieved by the 282 nm LEDs was compensated by their higher photon flux. First flow-through tests indicate a linear correlation between inactivation and fluence, demonstrating a well designed flow-through reactor. With improved light output and reduced costs, GaN-based UV LEDs can provide a promising alternative for decentralised and mobile water disinfection systems.     

The degradation products of UV filters in aqueous and chlorinated aqueous solutions

Ultraviolet (UV) filters are vital constituents of sunscreens and other personal care products since they absorb, reflect and/or scatter UV radiation, therefore protecting us from the sun’s deleterious UV radiation and its effects. However, they suffer degradation, mainly through exposure towards sunlight and from reactions with disinfectant products such as chlorine. On the basis of their increasing production and use, UV filters and their degradation products have already been detected in the aquatic environment, especially in bathing waters. This paper presents a comprehensive review on the work done so far as to identify and determine the by-products of UV filter photodegradation in aqueous solutions and those subsequent to disinfection-induced degradation in chlorinated aqueous solutions, namely swimming pools.