Conventional Water Treatment Plants Research Articles

Research on correlation between nitrogen compounds, iron and manganese concentrations in drinking water supply systems

A wide range of material sources potentially contribute to contaminant loads in potable water. The ability of water supply systems to act as emission control barriers to tap water micro pollutants, thereby providing environmental benefits in addition to potable water savings, have not been fully explored. This paper investigates the sources, presence and potential fate of a selection of nitrogen micro pollutants in water supply systems. All of the investigated compounds are listed under the requirements to the quality of water intended for human consumption. Significant water quality changes are identified. A wide range of potential treatment trains are available for water treatment and reuse but treatment efficiency data for nitrogen substances is very limited. Nitrogen substances removal through water treatment is following to be predominantly due to ammonium ions, nitrate and nitrite limited concentrations requirement, with only minor contributions to the water supply network. The majority of conventional water treatment plants periodically supply water with nitrogen compounds residual to the potable water distribution system. Hence, it is important to ensure that other nitrogen sources control options (e.g. pipelines materials, and groundwater sources controls) for potable water supply continue to be pursued, in order that nitrogen compounds emissions from these sources are effectively reduced and/or phased out as required under the demands of the requirements to the quality of water intended for human consumption. The aim of this research was to estimate the correlation between nitrogen compounds, iron and manganese concentrations in drinking water supply pipelines in Vilnius (Lithuania) and Warsaw (Poland). First published online: 11 Oct 2012

Removal of DOM and THM formation potential of tropical surface water by ceramic microfiltration

Dissolved organic matter (DOM) and trihalomethane formation potential (THMFP) removal by ceramic microfiltration (CMF) under different operating conditions was investigated and compared with the performance of a conventional water treatment plant at Bangkhen, Thailand. The tropical surface raw water for all the experiments was taken from Chaophraya River, Bangkok, Thailand. CMF studies were conducted with both pilot scale (Pilot-CMF) and laboratory scale (Lab-CMF) units. Observations indicate that the properties of raw water such as dissolved organic carbon (DOC) concentration and specific ultraviolet absorbance (SUVA) vary with time. Under these varying raw water conditions, the conventional water treatment process demonstrates varying THMFP removals. The Pilot-CMF provides better and steady THMFP removals compared to conventional process. Bangkhen water treatment plant (BWTP) filtrate SUVA (2.01 ± 1.07) and Pilot-CMF filtrate SUVA (3.22 ± 0.98) were significantly lower compared to raw water SUVA (4.79 ± 1.39). This SUVA reduction indicated a higher removal of aromatic DOMs through both treatment processes. Pilot-CMF manifest a grater removal of hydrophilic DOM compared to filtrate from BWTP. This corresponds to a higher reduction of THMFP by Pilot-CMF over BWTP. It was found that higher removal of DOC by Pilot-CMF is associated with coagulation process, effects of suspended solids and membrane properties.

The effect of fluctuation in flow rate on the performance of conventional and membrane water treatment for a smart water grid

A smart water grid can save water and energy by delivering the water to consumers according to the time-dependent demands. One of the key water treatment technologies for a smart water grid is to control the water supply rate as per the consumers' demand. However, a conventional water treatment plant is designed for a constant production rate operation, which is not appropriate for a smart water grid. The present study focuses on the effect of fluctuation on the production rate of three water treatment technologies: i.e. (1) sedimentation followed by ozonation and coagulation/flocculation, (2) sand filtration followed by coagulation/flocculation and sedimentation, and (3) membrane process (microfiltration [MF]). For sedimentation and sand filtration processes, the pilot- and real-scale plant data were analyzed to investigate the fluctuation patterns of the flow rate and water quality. For the membrane process, an MF operation was simulated to investigate the effect of fluctuation flux on the membrane fouling rate. Two key findings emerged from the pilot and field data analyses and simulation results in the present study. First, there exists a time delay between the input and output flow fluctuations for sedimentation and sand filtration processes, and the water quality is changed during and after the time delay for the flow rate fluctuation. Second, in the MF process, the flow rate fluctuation does not have any significant effect either on the permeate water quality or on the fouling behavior.

Characterization of low molecular weight dissolved natural organic matter along the treatment trait of a waterworks using Fourier transform ion cyclotron resonance mass spectrometry

Dissolved natural organic matter (DOM), particularly the low molecular weight DOM, can affect the performance of water treatment processes and serve as a main precursor of disinfection by-products (DBPs) during chlorination. In this study, electrospray ionization coupled to Fourier transform ion cyclotron resonance mass spectrometry (ESI FT-ICR MS) was used to characterize the low molecular weight DOM along the treatment trait of a conventional drinking water treatment plant. The ESI FT-ICR MS data showed that various C, H, O-only class species were the major components in the source water. According to the van Krevelen diagram analysis, lignin- and tannin-like compounds were the most abundant components. Within an isobaric group, the DOM molecules with a high degree of oxidation (high O/C value) were preferentially removed during coagulation, while those with low degree of oxidation were found to be more reactive toward chlorine. In addition, 357 one-chlorine containing products and 199 two-chlorine containing products formed during chlorination were detected in the chlorination effluent sample at a high confidence level. The chlorinated products can be arranged into series, suggesting that they were originated from C, H, O-only precursor compounds, which were in series related by the replacement of CH4 against oxygen. For the first time, this study explored the behavior of low molecular weight DOM along a drinking water treatment trait on the molecular level, and revealed the presence of abundant unknown chlorinated products, which are probably rich in carboxylic and phenolic groups, in drinking water.

Assessing and maintaining membrane performance in a post-sedimentation ultrafiltration process

A pilot test program was conducted to evaluate methods for maintaining the productivity of a hollow fiber ultrafiltration membrane operating at constant flux values of 49.2 and 62.3 gallons/ft2-day. The ultrafiltration pilot filtered settled water from a conventional surface water treatment plant in Florida. The testing assessed the impact of different chemical maintenance protocols on UF membrane performance. Seasonal variations in water quality necessitated changes in the type and combination of cleaning agents used to maintain membrane performance. Sodium hypochlorite, citric acid and sodium hydroxide were used during pilot testing as the fouling characteristics of the water changed with time. Pilot results were used to develop alternative chemically enhanced backwash strategies that varied with seasonally-impacted changes in feed water quality. Citric acid, with a target pH of <3, was found to be effective in August and September; whereas, a combination of citric acid and high pH sodium hydroxide chemically enhanced backwashes successfully maintained performance between November, 2010 and May, 2011.

Water Hardness Removal for Industrial Use: Application of the Electrolysis Process

Lime–soda softening for treating very hard waters is generally applied as a conventional water treatment process for municipal use. However, for industrial use, this treatment is not applied because: (a) it requires a long detention time for magnesium and calcium precipitation (about 4, 5 hours); (b) a supersaturation associated with an hexahydrate CaCO 3 formation can be accomplished leading to severe incrustation of conduits and (c) a post stabilization of final water is needed. This paper addresses a study on the performance of the electrolysis process applied “per se” and with alkaline chemical dosing for removal of noncarbonated hardness for industrial use. The water used in experiments was the tap water of the reticulation system of Campina Grande in Paraiba state, Brazil. Results showed that the production of primary coagulant during electrolysis improved flotation of both calcite (calcium carbonate, CaCO 3 ) and magnesium hydroxide, Mg (OH) 2. The overall removal rate obtained with this process was 80% with a detention time of 40 minutes which is about 17% of the time needed in conventional Water Treatment Plants.

A review of the potential of surface flow constructed wetlands to enhance macroinvertebrate diversity in agricultural landscapes with particular reference to Integrated Constructed Wetlands (ICWs)

Integrated Constructed Wetlands (ICWs) constitute an alternative way of cleansing water in agricultural areas to conventional water treatment plants. These pond systems integrate their water treatment capabilities with other functions such as biodiversity enhancement, carbon sequestration and landscape fit, by virtue of mimicking natural wetlands. ICWs have shown to have potential to enhance macroinvertebrate diversity in agricultural areas due to their unique design flexibility. We suggest that ICWs characterised by adequate shore sloping and presence of complex habitat mosaics, as well as other design considerations, would maximise the potential of these systems to enhance macroinvertebrate diversity. In addition, it would be highly beneficial to increase the total ICW area and to increase the total number of ponds in a system accordingly from a minimum of four to at least five. This article also highlights the need not only to develop policies that focus on the creation of ICWs but also to foster a number of management practices that rely on the active involvement of farmers. The inclusion of additional ponds in selected ICW systems could be the means to inform local communities as to the importance, attractiveness and conservation value of ponds.

Study of Adsorbability of the Colloidal Particles from Different Stages of a Conventional Water Treatment Plant

The adsorbability of colloidal particles from different stages of a conventional water treatment plant was studied with the assistance of micro-membrane filtration experiment. The microfiltration (MF) performance and the scanning electron microscope (SEM) images of the foulants on membrane surface were investigated. The results showed that the particles in the ozonated water (OW) had the strongest adsorbability, and stronger than that in the clarified water (CW); and the particles in the sand filtrated water (SFW) had relatively weaker adsorbability than that in the raw water (RW). The particles in the sand filter backwash water (SFBW) were mainly consisted of detached aggregates and had weak attachment with the membrane surface.

A Ten-year Survey ofGiardia Cystsin Drinking Water Supplies of Seoul, the Republic of Korea

To understand the distribution of Giardia cysts in drinking water supplies in Seoul, Korea, we collected water samples quarterly at 6 intakes in the Han River, its largest stream and 6 conventional water treatment plants (WTPs) serving drinking water, from 2000 to 2009. Giardia cysts in each of 10 L water were confirmed in 35.0% of intake water samples and the arithmetic mean was 1.65 cysts/10 L (range 0-35 cysts/10 L). The lowest cyst density was observed at Paldang and Kangbuk intakes, and the pollution level was higher at 4 intakes downstream. It seemed that these 4 intakes were under influence of Wangsuk stream at the end of which cysts were found in all samples with the mean of 140 cysts/10 L. The annual mean number of cysts was 0.21-4.21 cysts/10 L, and the cyst level at the second half of the 10 years was about 1/5 of that at first half on average. The cysts were more frequently found in winter, and their mean density was 3.74 cysts/10 L in winter and 0.80-1.08 cysts/10 L in other seasons. All finished water samples collected at 6 WTPs were negative for Giardia in each of 100 L sample for 10 years and cyst removal by physical process was average 2.9-log. It was concluded that conventional water treatment at 6 WTPs of Seoul appears to remove the cysts effectively under the present level of their source water. Domestic wastewater from the urban region could be an important source of Giardia pollution in the river.

Heavy Metal Pollution in Xiangjiang River Basin and Its Emergency Response

Xiangjiang River is a major tributary of the Yangtze River, with a population of 40 million covering the whole river basin. As the important non-ferrous metal mining and smelting industrial area of China, As a result of extensive development of non-ferrous metal mining, smelting and processing industry, the basin suffered severe heavy metal pollution, especially mercury, cadmium, lead, arsenic, etc both in water body and sediment. In response to this severe situation, the central and local governments have developed the corresponding heavy metal pollution emergency mechanisms, and control of heavy metal pollution in Xiangjiang River has been included in the agenda of national governance plan. In recent years, our group has also conducted researches in heavy metal removal technologies, including adsorption and enhanced coagulation processes for conventional water treatment plants to response emergent contamination.

Modeling formation and control of disinfection byproducts in chlorinated drinking waters

While disinfection of drinking water reduces the risks of pathogenic infection, threats to human health due to the formation of disinfection byproducts (DBPs) may arise due to natural organic precursors. Regression-based models characterizing the formation of DBPs are derived from data for 28 conventional water treatment plants in Ontario. DBPs are shown to be correlated statistically with dissolved organic carbon, pre-and post-chlorination dosages, pH and temperature. Using backward elimination nonlinear regression, a set of mathematical functions are obtained (R2=0.62 to 0.79) for an array of DBPs. The models are used to guide decision-markers in the selection and operation of drinking water treatment processes to decrease DBP formation, indicating that a shift from emphasis on pre-chlorination to post-chlorination has the most effect on DBP formation.

Modeling the formation and assessing the risk of disinfection by-products in water distribution systems

The effect of water quality parameters and operation conditions of water treatment on the formation of trihalomethanes (THM) and haloacetic acids (HAA) in pilot-scale reactor and water distribution system were investigated. Results indicated that dissolved organic carbon and THM formation increased while the concentration of free chlorine decreased along the length of pipeline from the water treatment plant; but HAA formation showed no relationship with the pipeline length. THM concentration was predicted with hydraulic analytic software, namely WaterCAD. The predicted THM data were within ±10% of measurements; HAA had a relatively high error of ±16% due to complex bio-decomposition reactions occurred in the distribution system. Both the hazardous quotient and cancer risk of THM in the water distribution system of an advanced water treatment plant were much lower than those of a conventional water treatment plant; there was no significant difference in hazard quotient and cancer risk of HAA in the above two water distribution systems.

Disinfection by-products in filter backwash water: Implications to water quality in recycle designs

The overall purpose of this research was to investigate disinfection by-product (DBP) concentrations and formation potential in filter backwash water (FBWW) and evaluate at bench-scale the potential impact of untreated FBWW recycle on water quality in conventional drinking water treatment. Two chlorinated organic compound groups of DBPs currently regulated in North America were evaluated, specifically trihalomethanes (THMs) and haloacetic acids (HAAs). FBWW samples were collected from four conventional filtration water treatment plants (WTP) in Nova Scotia, Canada, in three separate sampling and plant audit campaigns. THM and HAA formation potential tests demonstrated that the particulate organic material contained within FBWW is available for reaction with chlorine to form DBPs. The results of the study found higher concentrations of TTHMs and HAA9s in FBWW samples from two of the plants that target a higher free chlorine residual in the wash water used to clean the filters (e.g., clearwell) compared to the other two plants that target a lower clear well free chlorine residual concentration. Bench-scale experiments showed that FBWW storage time and conditions can impact TTHM concentrations in these waste streams, suggesting that optimization opportunities exist to reduce TTHM concentrations in FBWW recycle streams prior to blending with raw water. However, mass balance calculations demonstrated that FBWW recycle practice by blending 10% untreated FBWW with raw water prior to coagulation did not impact DBP concentrations introduced to the rapid mix stage of a plant’s treatment train.

Manganese-oxidizing and -reducing microorganisms isolated from biofilms in chlorinated drinking water systems

The interaction of chemical, physical and biological factors that affect the fate, transport and redox cycling of manganese in engineered drinking water systems is not clearly understood. This research investigated the presence of Mn-oxidizing and -reducing bacteria in conventional water treatment plants exposed to different levels of chlorine. Mn(II)-oxidizing and Mn(IV)-reducing bacteria, principally Bacillus spp., were isolated from biofilm samples recovered from four separate drinking water systems. Rates of Mn-oxidation and -reduction for selected individual isolates were represented by pseudo-first-order kinetics. Pseudo-first-order rate constants were obtained for Mn-oxidation (range: 0.106–0.659 days −1), aerobic Mn-reduction (range: 0.036–0.152 days −1), and anaerobic Mn-reduction (range: 0.024–0.052 days −1). The results indicate that microbial-catalyzed Mn-oxidation and -reduction (aerobic and anaerobic) can take place simultaneously in aqueous environments exposed to considerable oxygen and chlorine levels and thus affect Mn-release and -deposition in drinking water systems. This has important implications for Mn-management strategies, which typically assume Mn-reduction is not possible in the presence of chlorine and oxidizing conditions.

Performance of conventional multi-barrier drinking water treatment plants for the removal of four artificial sweeteners

Due to incomplete removal of artificial sweeteners in wastewater treatment plants some of these compounds end up in receiving surface waters, which are used for drinking water production. The sum of removal efficiency of single treatment steps in multi-barrier treatment systems affects the concentrations of these compounds in the provided drinking water. This is the first systematic study revealing the effectiveness of single treatment steps in laboratory experiments and in waterworks. Six full-scale waterworks using surface water influenced raw water were sampled up to ten times to study the fate of acesulfame, saccharin, cyclamate and sucralose. For the most important treatment technologies the results were confirmed by laboratory batch experiments. Saccharin and cyclamate proved to play a minor role for drinking water treatment plants as they were eliminated by nearly 100% in all waterworks with biologically active treatment units like river bank filtration (RBF) or artificial groundwater recharge. Acesulfame and sucralose were not biodegraded during RBF and their suitability as wastewater tracers under aerobic conditions was confirmed. Sucralose proved to be persistent against ozone and its transformation was <20% in lab and field investigations. Remaining traces were completely removed by subsequent granular activated carbon (GAC) filters. Acesulfame readily reacts with ozone (pseudo first-order rate constant k = 1.3 × 10 −3 s −1 at 1 mg L −1 ozone concentration). However, the applied ozone concentrations and contact times under typical waterworks conditions only led to an incomplete removal (18–60%) in the ozonation step. Acesulfame was efficiently removed by subsequent GAC filters with a low throughput of less than 30 m 3 kg −1, but removal strongly depended on the GAC preload. Thus, acesulfame was detected up to 0.76 μg L −1 in finished water.

A Sustainable Approach to Low Pressure Reverse Osmosis Concentrate Management

Population increases within the city of Ormond Beach, Fla., increased demands on the city's existing 8-mgd conventional lime-softening water treatment plant. Because of deteriorating raw water quality, the city's consultant conducted a pilot study and completed preliminary and final designs for a 4-mgd low pressure reverse osmosis (LPRO) expansion. A critical aspect of the project focused on managing the concentrate stream. Although concentrate characteristics are functions of raw water quality, membrane selectivity, and system operating conditions, LPRO concentrate is generally characterized by elevated values of total dissolved solids, chloride, total hardness, organic carbon, and/or color. The concentrate management strategy implemented for the project consisted of blending LPRO concentrate with reclaimed water at the city's wastewater treatment plant (WWTP), which augmented reclaimed water supplies with an unused resource without consuming the WWTP's treatment capacity.

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.

A survey of Cryptosporidium oocysts in water supplies during a 10-year period (2000-2009) in Seoul.

This study has been conducted to estimate the occurrence of Cryptosporidium oocysts in water supplies in the Metropolitan area of Seoul, South Korea, for 10 years from 2000 to 2009. Water samples were collected quarterly at 6 intakes in the Han River and its largest stream and 6 conventional Water Treatment Plants (WTPs) serving drinking water for 10 million people of Seoul. Cryptosporidium oocysts were found in 22.5% of intake water samples and arithmetic mean was 0.65 oocysts/10 L (range 0-22 oocysts/10 L). Although the annual mean of oocyst number was as low as 0.04-1.90 oocysts/10 L, 3 peaks in 2004 and 2007 were observed and the pollution level was a little higher in winter. The lowest density was observed at Paldang intake and the pollution level increased at Kuui and Jayang intakes. At the end of the largest stream, oocysts were found in 70% of collected samples (mean 5.71 oocysts/10 L) and it seemed that its joining the Han River resulted in the increase at Kuui intake and downstream. Oocyst removal by physical process exceeded 2.0-2.3 log and then all finished water samples collected at 6 WTPs were negative for Cryptosporidium in each 100 L sample for 10 years. These results suggested that domestic wastewater from the urban region could be a source of Cryptosporidium pollution and separating sewage systems adjacent to the intakes could be meaningful for some intakes having weakness related to parasitological water quality.

Proposta de Índice de Qualidade para Água Bruta afluente a estações convencionais de tratamento

O presente trabalho tem por objetivo propor um Índice de Qualidade da Água Bruta (IQAB) afluente para estações convencionais de tratamento que permita comparar a tratabilidade dos mananciais superficiais. A metodologia Delphi para a elaboração do IQAB fundamentou-se basicamente na mesma utilizada para o desenvolvimento do Índice de Qualidade de Água, no início da década de 1970, contando com um painel composto inicialmente por 24 especialistas. De acordo com a opinião do painel, o IQAB foi composto por oito parâmetros comumente monitorados em parcela significativa das estações brasileiras. Sua aplicação a cinco mananciais superficiais permite recomendar seu emprego como ferramenta adicional de avaliação da performance das estações de tratamento pelas concessionárias de abastecimento de água do país.

Development of a rapid and sensitive battery of bioassays for risk assessment of cyanobacterial microcystin-LR in drinking water of rural water treatment plants, South Africa

Due to the lack of toxin standards and resource limitations for wide scale use of analytical methods for e.g. high-performance liquid chromatography (HPLC) and enzyme-linked immunosorbent assay (ELISA) in cyanobacterial toxin monitoring, it has become necessary to assess and develop additional methods that are rapid, yet realistic and cheap for the detection of cyanobacterial toxins in drinking water of rural conventional water treatment plants in South Africa. A well-known cyanobacterial secondary metabolite (microcystin-LR) which is the dominant cyanotoxin variant in South African surface waters was tested for its adverse effect on the macrophyte plant Spirodela punctata (duckweed) and the insects Periplanetaamericana (American cockroach), Tenebrio molitar (yellow mealworm), Gryllus bimaculatus (common cricket) as well as the crustacean zooplankton (Artemia salina). In this study Gryllus bimaculatus and Artemia salina LD50 body weight values were calculated as 0.45 µg/animal and 0.1 µg/animal, respectively, within the first 48 h after exposure to microcystin-LR. These values obtained indicate that sensitivities of G. bimaculatus and A. salina to low concentrations of microcystin-LR were comparable to the mouse bioassay. No mortalities of P. americana and T. molitar were observed after 48 h of exposure to different concentrations of synthetic microcystin-LR (0.5, 1.0, 5.0 µg/L). Moreover, on sub-organism or cellular level, DNA fragmentation occured in P. americana, T. molitar, A. salina and G. bimaculatus within the first 48 h after exposure to synthetic microcystin-LR. Although the ease of culturing of the American cockroach and yellow mealworm make them ideal organisms to be included in a battery of bioassays, their 48 h LD50non-response on organism level to low concentrations of microcystin exclude these species from a rapid sensitive battery of bioassays. From the data generated in this study the 5 day Spirodela punctata bioassay was the most sensitive bioassay by showing reduction of root growth and fronds weight as well as changes in the chlorophyll a and b ratio content within the first 12 h after exposure to a low concentration (0.1 µg/L) of synthetic microcystin-LR. Key words: Battery of bioassays, microcystin-LR, apoptosis, chlorosis, Spirodela punctata.