Conventional Drinking Water Treatment Processes Research Articles

Efficacy of conventional drinking water treatment processes in removing problem-causing phytoplankton and associated organic compounds

Seven phytoplankton groups were recorded in the source water supplied to South Africa’s largest conventional drinking water treatment plant (DWTP). Two phytoplankton genera, Anabaena and Ceratium were identified as the problem-causing phytoplankton due to their ability to interfere with the water treatment process and negatively impact on water quality. The objectives of this study were to identify problem-causing phytoplankton genera and investigate the efficacy of unit processes in removing phytoplankton genera and associated organic compounds. Phytoplankton and organic compound data were obtained from four different sampling localities throughout the treatment plant and statistically analysed to evaluate the removal efficiencies of unit processes. The highest percentage removal for the Cyanophyceae average seasonal concentration (> 1 000 cells/mℓ) was recorded at 98%, while the highest percentage removal for the Dinophyceae average seasonal concentration (± 9 cells/mℓ) was recorded at 100%. Microcystis and Anabaena were removed by the processes of coagulation, flocculation and sedimentation (> 95%), while Ceratium cells were removed by sand filtration (> 80%). Ineffective removal of Ceratium by coagulation, flocculation and sedimentation (and subsequent penetration to the sand filtration step) will negatively impact on filter run times when these phytoplankton genera are present in high concentrations in the source water. Total photosynthetic pigments (TPP) were removed effectively by all the different water treatment processes. Not enough statistical evidence could be displayed to suggest effective removal of geosmin in this conventional water treatment plant. With good removal of intact cyanobacteria cells during coagulation, flocculation and sedimentation, geosmin concentrations in the final water could be kept to accepted organoleptic levels of 5–10 ng/ℓ in the final water. Optimising conventional drinking water treatment processes can effectively remove problem-causing phytoplankton as well as their associated organic compounds and thereby reduce the potential risk to drinking water consumers.Keywords: coagulation, sand filtration, drinking water, Ceratium, Anabaena, Microcystis, geosmin

Efficiency of conventional drinking water treatment process in the removal of endosulfan, ethylenethiourea, and 1,2,4-triazole

The aim of this work was to study the removal of three pesticides using conventional drinking water treatment (DWT) processes. These methods are the most used in Brazil, and include coagulation–flocculation of water. The pesticides/metabolites evaluated were: endosulfan, ethylenethiourea (ETU), and 1,2,4-triazole. The laboratory tests were carried out in triplicate using the jar test. Synthetic water samples prepared with kaolin, simulating the dry and rainy periods, were contaminated with different concentrations of pesticides. Results showed that conventional DWT methods are not suitable for the removal of the pesticides/metabolites evaluated. No significant difference ( p K oc , log K ow and molar mass, in relation to the other two pesticides.

The Distribution Characteristics of the Typical Antibiotics in the Aquatic Environment of a City in China

The distribution characteristics of six typical antibiotics in the aquatic environment (wastewater treatment plant effluent, Shiao-ching River, Yellow River, Yellow river Reservoir, drinking water treatment plant effluent) of a city in china were analyzed by using high performance liquid chromatography-tandem mass spectrometry. The results show that except for erythromycin, other five antibiotics include sulfamethoxazole, sulfamethazine, amoxicillin, tetracycline and oxytetracycline were detected in the aquatic environment, the concentrations of tetracycline and oxytetracycline were relatively higher, the tetracycline and oxytetracycline concentrations of wastewater treatment plant effluent were 32.39 ng/L and 59.36 ng/L respectively. The wasterwater treatment plant process can not completely remove the antibiotic,and the five antibiotics concentrations in the wastewater treatment plant effluent were higher than their concentrations in the other water bodies. A certain content antibiotics was discharged into the receiving water and wastewater treatment plant drainage is the main way of antibiotics to release into the water environment. Traces of antibiotics were detected in the water samples which were taken from the Yellow River and the Shiao-ching River in the city, but they were less polluted by antibiotics levels. The antibiotics removal effect of conventional drinking water treatment process is not obvious.

Removal of diclofenac by conventional drinking water treatment processes and granular activated carbon filtration

This study was carried out to evaluate the efficiency of conventional drinking water treatment processes with and without pre-oxidation with chlorine and chlorine dioxide and the use of granular activated carbon (GAC) filtration for the removal of diclofenac (DCF). Water treatment was performed using the Jar test with filters on a lab scale, employing nonchlorinated artesian well water prepared with aquatic humic substances to yield 20HU true color, kaolin turbidity of 70 NTU and 1mgL−1 DCF. For the quantification of DCF in water samples, solid phase extraction and HPLC–DAD methods were developed and validated. There was no removal of DCF in coagulation with aluminum sulfate (3.47mgAlL−1 and pH=6.5), flocculation, sedimentation and sand filtration. In the treatment with pre-oxidation and disinfection, DCF was partially removed, but the concentration of dissolved organic carbon (DOC) was unchanged and byproducts of DCF were observed. Chlorine dioxide was more effective than chorine in oxidizing DCF. In conclusion, the identification of DCF and DOC in finished water indicated the incomplete elimination of DCF through conventional treatments. Nevertheless, conventional drinking water treatment followed by GAC filtration was effective in removing DCF (⩾99.7%). In the oxidation with chlorine, three byproducts were tentatively identified, corresponding to a hydroxylation, aromatic substitution of one hydrogen by chlorine and a decarboxylation/hydroxylation. Oxidation with chlorine dioxide resulted in only one byproduct (hydroxylation).

MIEX® and PAC for removal of hydrophilic DBP precursors

The objective of this research was to investigate promising materials for potential reduction of disinfection by‐product (DBP) formation resulting from reactions with hydrophilic natural organic matter (NOM), a source of precursors that is difficult to remove with conventional drinking water treatment process units. DBP reduction in other reported research was attributable to greater removal of hydrophobic fractions of NOM. Two nonionic resins were used to fractionate NOM before and after treatment with magnetic ion exchange (MIEX®) and a powdered activated carbon. At the chosen doses of treatment materials, bulk NOM removal remained the same (< 10% difference in dissolved organic carbon after treatment with activated carbon versus MIEX); compared with the powdered activated carbon, however, MIEX provided greater reduction of trihalomethane and haloacetic acid formation potential resulting from reactions with hydrophilic NOM. Therefore, MIEX preferentially removed hydrophilic DBP precursors. Similar results were observed for the transphilic fraction, whereas differences in the hydrophobic fraction were minimal. This research has implications for treatment facilities with elevated levels of highly reactive hydrophilic NOM in their influents and highlights the importance of source water chemistry in the selection of DBP mitigation strategies.

Effects of organic fractions on the formation and control of N-nitrosamine precursors during conventional drinking water treatment processes

Knowledge of N-nitrosamine precursors from dissolved organic matter (DOM) is important for water professionals to better control N-nitrosamine formation. The characterization of DOM from the Luan River in Northern China was conducted using Amberlite XAD resins and ultra-filtration methods. N-nitrosamine formation potentials were investigated for various DOM fractions. The removal of the DOM during water treatment were evaluated using dissolved organic carbon (DOC) and ultraviolet absorbance at 254nm (UV254) bulk parameters as well as size exclusion chromatography and fluorescence spectroscopy. The results indicated that the XAD-4 hydrophilic fraction, with normalized yields of N-nitrosodimethylamine (NDMA), N-nitrosopyrrolidine (NPYR), N-nitrosomorpholine (NMOR), and N-nitrosopiperidine (NPIP) of 27.2, 5.2, 5.9, and 6.1ng/mg-DOC, respectively, tended to form more N-nitrosamines than the hydrophobic and the transphilic fractions. The DOM fraction with a molecular weight (MW) below 1kDa, with normalized yields of NDMA, NPYR, NMOR, and NPIP of 39.6, 8.1, 14.7, and 3.3ng/mg-DOC, respectively, tended to form more N-nitrosamines than those with a higher MW. The limited removal of the hydrophilic fraction and the lower MW DOM faction during conventional water treatment processes suggests that the process may not effectively remove the nitrosamine precursors.

Formation of N-nitrosamines from chlorination and chloramination of molecular weight fractions of natural organic matter

N-Nitrosamines are a class of disinfection by-products (DBPs) that have been reported to be more toxic than the most commonly detected and regulated DBPs. Only a few studies investigating the formation of N-nitrosamines from disinfection of natural waters have been reported, and little is known about the role of natural organic matter (NOM) and the effects of its nature and reactivity on the formation of N-nitrosamines. This study investigated the influence of the molecular weight (MW) characteristics of NOM on the formation of eight species of N-nitrosamines from chlorination and chloramination, and is the first to report on the formation of eight N-nitrosamines from chlorination and chloramination of MW fractions of NOM. Isolated NOM from three different source waters in Western Australia was fractionated into several apparent MW (AMW) fractions using preparative-scale high performance size exclusion chromatography. These AMW fractions of NOM were then treated with chlorine or chloramine, and analysed for eight species of N-nitrosamines. Among these N-nitrosamines, N-nitrosodimethylamine (NDMA) was the most frequently detected. All AMW fractions of NOM produced N-nitrosamines upon chlorination and chloramination. Regardless of AMW characteristics, chloramination demonstrated a higher potential to form N-nitrosamines than chlorination, and a higher frequency of detection of the N-nitrosamines species was also observed in chloramination. The results showed that inorganic nitrogen may play an important role in the formation of N-nitrosamines, while organic nitrogen is not necessarily a good indicator for their formation. Since chlorination has less potential to form N-nitrosamines, chloramination in pre-chlorination mode was recommended to minimise the formation of N-nitrosamines. There was no clear trend in the formation of N-nitrosamines from chlorination of AMW fractions of NOM. However, during chloramination, NOM fractions with AMW <2.5 kDa were found to produce higher concentrations of NDMA and total N-nitrosamines. The precursor materials of N-nitrosamines appeared to be more abundant in the low to medium MW fractions of NOM, which correspond to the fractions that are most difficult to remove using conventional drinking water treatment processes. Alternative or advanced treatment processes that target the removal of low to medium MW NOM including activated carbon adsorption, biofiltration, reverse osmosis, and nanofiltration, can be employed to minimise the formation of N-nitrosamines.

Assessment of waterborne protozoan passage through conventional drinking water treatment process in Venezuela

Three drinking water treatment plants (DWTPs) differing in source water and treatment capacity were investigated for the potential passage of waterborne protozoan (oo)cysts through conventional processing. DWTP I (15,000 L/s), DWTP II (7,500 L/s) and DWTP III (4,300 L/s) provide drinking water for approximately 2.7 million inhabitants of the Metropolitan District of Caracas (Venezuela). The US Environmental Protection Agency Method 1623 for detection of Cryptosporidium and Giardia was used to analyze raw water and finished drinking water samples collected from the three plants. (Oo)cyst recovery efficiencies varied between 23 and 84%. The concentration of confirmed (oo)cysts detected in raw water samples ranged between 1 and 100 per 100 L. (Oo)cyst levels in finished water samples ranged from 2 to 25 per 100 L. These data indicated that the conventional treatment process to produce finished water at two filtration plants was not effective in preventing the passage of protozoan (oo)cysts. Monitoring strategies that include multiple microbial indicators and waterborne pathogens are strongly recommended for accurate source water characterization and for verification of the effectiveness of treatment process barriers to microbial breakthrough in the finished water.

Molecular quantification of virulence gene-containing Aeromonas in water samples collected from different drinking water treatment processes

Pathogenic species of Aeromonas produce a range of virulence factors, including aerolysin, cytotonic enterotoxins, and serine protease, to cause acute gastroenteritis and wound infections in humans and animals. Recognizing that not all Aeromonas strains are pathogenic, in this study, we proposed to evaluate Aeromonas removal effectiveness based on the presence of virulence gene-containing Aeromonas as a proper means to assess microbial risk of Aeromonas. We developed and applied real-time PCR assays to quantify serine protease (ser) gene- and heat-labile cytotonic enterotoxin (alt) gene-containing Aeromonas in water samples. Among 18 Aeromonas isolates from the source water, only three isolates possessed all three genes (aer, ser, and alt). A higher percent of isolates has either ser gene (89%) or alt gene (72%) compared to the percent of isolates containing aer gene (44%). Results of this study suggested that several different conventional and unconventional drinking water treatment processes could effectively remove Aeromonas from source water. As the comprehensive knowledge of the distribution of virulence factors in different Aeromonas species is currently not available, using real-time PCR to quantify various virulence factor genes in water samples and/or isolates can be a practical means for better assessment of microbial risks in water.

The Removal Effect on Chironomus kiiensis larvae and Mutagenicity in Urban Water Source with Chlorine Dioxie

Chironomus kiiensis larvae which cannot be exterminated by conventional disinfection process propagates prolifically in eutrophic water body, and it therefore turns to be a potential problem encountered in drinking water quality. In order to tackle this problem, a pilot-scale study of removal effect on Chironomus kiiensis larvae with chlorine dioxide in a waterworks is performed. The experiment results showed that Chironomus kiiensis larvae can be effectively removed from water by 0.55 mg/L chlorine dioxide pre-oxidation combined with the conventional drinking water treatment process. Higher oxidizability and molecular state of chlorine dioxide in water is the key to the inactivation of Chironomus kiiensis larvae. The chlorite, disinfection by-products (DBPs) of chlorine dioxide, is stable at 0.217 mg/L, which is lower than that critical value of the WHO. Ames test revealed that the mutagenicity was reduced by chlorine dioxide with respect to prechlorine. The propagation of Chironomus kiiensis larvae can be inactivated effectively and safely by chlorine dioxide pre-oxidation.

Changes of NOM fractions during conventional drinking water treatment process in Riga, Latvia

In Latvia, as in other countries of the Boreal region, raw water sources contain elevated concentration of natural organic matter (NOM). Originally the conventional water treatment plants (WTP) were mainly designed for removal of turbidity hence the optimization of water treatment processes for more effective removal of NOM is often needed nowadays. In this paper a rapid fractionation (RF) technique of NOM developed by Chow et al. was applied to better understand the removal mechanisms of NOM during chemical precipitation and ozonation-biofiltration processes at WTP in Riga, Latvia. Results showed that NOM removal, determined as dissolved organic carbon (DOC) constituted from 15.34±3.84 mg/L in raw water to 5.33±1.45 mg/L in drinking water and was mainly due to decrease of very hydrophobic acids (VHA) during coagulation and precipitation processes. Other NOM fractions viz. slightly hydrophobic acids (SHA) and hydrophilic charged acids (CHA) were only slightly removed. During ozonation the fraction of CHA were transformed into hydrophilic neutral (NEU) fractions and removed by biologically activated carbon (BAC) filters. However, this trend was not observed during the cold season. In conclusion, coagulation and precipitation mainly removed humic substances, as indicated by VHA removal, whereas ozonation-BAC filtration was not effective since biologically degradable fractions of NOM were either transformed into other substances (from NEU to VHA) or were not removed (in cold season) due to insufficient biological activity or contact time in BAC filters.

Dispersion of C 60 in natural water and removal by conventional drinking water treatment processes

The first objective of this study is to examine the fate of C 60 under two disposal scenarios through which pristine C 60 is introduced to water containing natural organic matter (NOM). A method based on liquid–liquid extraction and HPLC to quantify nC 60 in water containing NOM was also developed. When pristine C 60 was added to water either in the form of dry C 60 or in organic solvent, it formed water stable aggregates with characteristics similar to nC 60 prepared by other methods reported in the literature. The second objective of this study is to examine the fate of the nC 60 in water treatment processes, which are the first line of defense against ingestion from potable water – a potential route for direct human consumption. Results obtained from jar tests suggested that these colloidal aggregates of C 60 were efficiently removed by a series of alum coagulation, flocculation, sedimentation and filtration processes, while the efficiency of removal dependent on various parameters such as pH, alkalinity, NOM contents and coagulant dosage. Colloidal aggregates of functionalized C 60 could be well removed by the conventional water treatment processes but with lesser efficiency compared to those made of pristine C 60.

Disinfection by-products and their precursors in a water treatment plant in North China: Seasonal changes and fraction analysis

A one-year-long monitoring project was conducted to assay the concentrations of THMs, HAAs and their formation potential along the conventional process in a water treatment plant in North China. Subsequent investigations of organic matter fractionation and the contribution of the algae to the precursor were also conducted to trace the source of the DBPs. The results showed that the concentration of DBPs and their formation potential varied with the seasons. The highest concentrations of THMs and the highest HAAs formation potential, each almost 500 µg/L, were detected in autumn and the lowest were in spring, no more than 100 µg/L. Both organic matter and algae were found to be important DBP precursors. The hydrophobic acid fraction in dissolved organic matter has the highest formation potential for both THM and HAA. Algae contribute about 20% to 50% of the total formation potential during an algal bloom. The efficiency of each unit process for DBPs and precursors was also assayed. Unfortunately, the conventional drinking water treatment process is limited in its efficiency for precursor removal. The pre-chlorination and filtration process had a negative effect on DBP or precursor removal.

Pilot Study on Pre-Ozonation Enhanced Drinking Water Treatment Process

The enhancement of TOC, CODMn, and UV254 reduction in the conventional drinking water treatment process by pre-ozonation was investigated in South China on treating dam source water with a pilot plant consisting of pre-ozonation, coagulation-sedimentation, and filtration units. Pre-ozonation enhanced the reduction of NOM in the conventional coagulation-sedimentation and filtration process, and the total removals of UV254, CODMn and TOC were improved for 34.6%, 18.1% and 15.3%, respectively by the adoption of pre-ozonation under an ozone dose (in ozone consumption base) of 0.85 mg/L. The enhancement of UV254 and CODMn removals was mainly achieved through direct ozonation on humic substances, and that for TOC removal was achieved through biodegradation in sand filtration. In comparison with the TOC removal of 38%, a removal of 49% was acquired for SDS-THM under a pre-ozonation dose of 0.80 mg/L, indicating the selective removal of THMFP. The reduction of SDS-THM paralleled the reduction of CODMn to a significant degree, suggesting that the CODMn might be an effective surrogate parameter for SDS-THM if the raw water does not contain the reductive inorganic matters. Although the source water contains 13.2–27.0μg/L bromide, the formation of bromate was negligible when the ozone dose was below 1.0 mg/L.

Determining estrogenic steroids in Taipei waters and removal in drinking water treatment using high-flow solid-phase extraction and liquid chromatography/tandem mass spectrometry

River water and wastewater treatment plant (WWTP) effluents from metropolitan Taipei, Taiwan were tested for the presence of the pollutants estrone (E1), estriol (E3), 17beta-estradiol (E2), and 17alpha-ethinylestradiol (EE2) using a new methodology that involves high-flow solid-phase extraction and liquid chromatography/tandem mass spectrometry. The method was also used to investigate the removal of the analytes by conventional drinking water treatment processes. Without adjusting the pH, we extracted 1-L samples with PolarPlus C18 Speedisks under a flow rate exceeding 100 mL/min, in which six samples could be done simultaneously using an extraction station. The adsorbent was washed with 40% methanol/60% water and then eluted by 50% methanol/50% dichloromethane. The eluate was concentrated until almost dry and was reconstituted by 20 microL of methanol. Quantitation was done by LC-MS/MS-negative electrospray ionization in the selected reaction monitoring mode with isotope-dilution techniques. The mobile phase was 10 mM N-methylmorpholine aqueous solution/acetonitrile with gradient elution. Mean recoveries of spiked Milli-Q water were 65-79% and precisions were within 2-20% of the tested concentrations (5.0-200 ng/L). The method was validated with spiked upstream river water; precisions were most within 10% of the tested concentrations (10-100 ng/L) with most RSDs<10%. LODs of the environmental matrixes were 0.78-7.65 ng/L. A pre-filtration step before solid-phase extraction may significantly influence the measurement of E1 and EE2 concentrations; disk overloading by water matrix may also impact analyte recoveries along with ion suppression. In the Taipei water study, the four steroid estrogens were detected in river samples (ca. 15 ng/L for E2 and EE2 and 35-45 ng/L for E1 and E3). Average levels of 19-26 ng/L for E1, E2, and EE2 were detected in most wastewater effluents, while only a single effluent sample contained E3. The higher level in the river was likely caused by the discharge of untreated human and farming waste into the water. In the drinking water treatment simulations, coagulation removed 20-50% of the estrogens. An increased dose of aluminum sulfate did not improve the performance. Despite the reactive phenolic moiety in the analytes, the steroids were decreased only 20-44% of the initial concentrations in pre- or post-chlorination. Rapid filtration, with crushed anthracite playing a major role, took out more than 84% of the estrogens. Except for E3, the whole procedure successfully removed most of the estrogens even if the initial concentration reached levels as high as 500 ng/L.

Efficiency of conventional drinking-water-treatment processes in removal of pharmaceuticals and other organic compounds

Samples of water and sediment from a conventional drinking-water-treatment (DWT) plant were analyzed for 113 organic compounds (OCs) that included pharmaceuticals, detergent degradates, flame retardants and plasticizers, polycyclic aromatic hydrocarbons (PAHs), fragrances and flavorants, pesticides and an insect repellent, and plant and animal steroids. 45 of these compounds were detected in samples of source water and 34 were detected in samples of settled sludge and (or) filter-backwash sediments. The average percent removal of these compounds was calculated from their average concentration in time-composited water samples collected after clarification, disinfection (chlorination), and granular-activated-carbon (GAC) filtration. In general, GAC filtration accounted for 53% of the removal of these compounds from the aqueous phase; disinfection accounted for 32%, and clarification accounted for 15%. The effectiveness of these treatments varied widely within and among classes of compounds; some hydrophobic compounds were strongly oxidized by free chlorine, and some hydrophilic compounds were partly removed through adsorption processes. The detection of 21 of the compounds in 1 or more samples of finished water, and of 3 to 13 compounds in every finished-water sample, indicates substantial but incomplete degradation or removal of OCs through the conventional DWT process used at this plant.

Removal effect on Mesocyclops leukarti and mutagenicity with chlorine dioxide

Mesocyclops leukarti of zooplankton propagates excessively in eutrophic water body and it cannot be effectively inactivated by the conventional drinking water treatment process. In order to tackle this problem, a study of removal effect on Mesocyclops leukarti with chlorine dioxide in a waterworks was performed. The results showed that Mesocyclops leukarti could be effectively removed from water by 1.0 mg/L chlorine dioxide preoxidation combined with the conventional drinking water treatment process. Higher oxidizability and molecular state of chlorine dioxide in water is the key to the inactivation of Mesocyclops leukarti. The chlorite, disinfection by-products (DBPs) of chlorine dioxide, was stable at 0.45 mg/L, which is lower than that critical value of the USEPA. GC-MS examination showed that the quantity of organic substance in the water treated by chlorine dioxide obviously decreased. Ames test further revealed that the mutagenicity was reduced by chlorine dioxide with respect to prechlorine. The propagation of Mesocyclops leukarti can be inactivated effectively and safely by chlorine dioxide pre-oxidation.

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.

Persistence of pharmaceutical compounds and other organic wastewater contaminants in a conventional drinking-water-treatment plant

In a study conducted by the US Geological Survey and the Centers for Disease Control and Prevention, 24 water samples were collected at selected locations within a drinking-water-treatment (DWT) facility and from the two streams that serve the facility to evaluate the potential for wastewater-related organic contaminants to survive a conventional treatment process and persist in potable-water supplies. Stream-water samples as well as samples of raw, settled, filtered, and finished water were collected during low-flow conditions, when the discharge of effluent from upstream municipal sewage-treatment plants accounted for 37–67% of flow in stream 1 and 10–20% of flow in stream 2. Each sample was analyzed for 106 organic wastewater-related contaminants (OWCs) that represent a diverse group of extensively used chemicals. Forty OWCs were detected in one or more samples of stream water or raw-water supplies in the treatment plant; 34 were detected in more than 10% of these samples. Several of these compounds also were frequently detected in samples of finished water; these compounds include selected prescription and non-prescription drugs and their metabolites, fragrance compounds, flame retardants and plasticizers, cosmetic compounds, and a solvent. The detection of these compounds suggests that they resist removal through conventional water-treatment processes. Other compounds that also were frequently detected in samples of stream water and raw-water supplies were not detected in samples of finished water; these include selected prescription and non-prescription drugs and their metabolites, disinfectants, detergent metabolites, and plant and animal steroids. The non-detection of these compounds indicates that their concentrations are reduced to levels less than analytical detection limits or that they are transformed to degradates through conventional DWT processes. Concentrations of OWCs detected in finished water generally were low and did not exceed Federal drinking-water standards or lifetime health advisories, although such standards or advisories have not been established for most of these compounds. Also, at least 11 and as many as 17 OWCs were detected in samples of finished water. Drinking-water criteria currently are based on the toxicity of individual compounds and not combinations of compounds. Little is known about potential human-health effects associated with chronic exposure to trace levels of multiple OWCs through routes such as drinking water. The occurrence in drinking-water supplies of many of the OWCs analyzed for during this study is unregulated and most of these compounds have not been routinely monitored for in the Nation's source- or potable-water supplies. This study provides the first documentation that many of these compounds can survive conventional water-treatment processes and occur in potable-water supplies. It thereby provides information that can be used in setting research and regulatory priorities and in designing future monitoring programs. The results of this study also indicate that improvements in water-treatment processes may benefit from consideration of the response of OWCs and other trace organic contaminants to specific physical and chemical treatments.

Investigation of NOM size, structure and functionality (SSF): impact on water treatment process with respect to disinfection by-products formation

This study was undertaken to evaluate existing conventional treatment processes, as opposed to specific membrane processes, to minimize haloacetic acid (HAA) formation, by examining in detail the characteristics of natural organic matter (NOM) size, structure and functionality. Through these evaluations, both size exclusion and charge interaction mechanisms, based on NOM size and functionality analyses, were also used to evaluate the performance of each process in conjunction with NOM structural effects. Such integrated evaluations (beyond a simple combination of the characterizations of NOM size, structure and functionality) were shown to be useful for the selection of advanced alternative membrane processes in order to maximize the removal of hydrophilic NOM fractions, which have a relatively high HAA producing potential, as conventional drinking water treatment processes examined in this study are unable to remove the hydrophilic NOM fraction effectively.