Conventional Drinking Water Treatment Plants Research Articles

Improvement on algae and turbidity removal in an integrated flotation and sedimentation unit using side flow-inclined plate settlers: evidence from a full-scale field experiment

Operation of conventional drinking water treatment plants (DWTPs) is limited by seasonal variations in the characteristics of raw water, such as algae levels and turbidity. In this study, an integrated flotation and sedimentation unit (IFSU) with side flow-inclined plate settlers (SFIPS) was applied to enhance the removal ratio of algae and turbidity in a full-scale field experiment. To accomplish this, the performance of two IFSU reactors (with and without SFIPS) treating algal-rich water, low-turbidity water and high-turbidity water was compared. Extensive experiments were conducted based on a central composite face-centered design, and the results were analyzed using response surface methodology. Polyaluminium chloride dose, NaOH dose, influent turbidity level and influent chlorophyll level were selected as the operating variables to analyze, optimize and model the process. The results showed that SFIPS functioned as a counterflow inducer to enhance the effects of stratified flow patterns and decrease the clarification loading rate in the separation zone during the dissolved air flotation process, leading to considerable increases in algae and turbidity removal in the IFSU reactor. The results of this study will facilitate upgrades of conventional DWTPs to improve their potential.

Characterization of water and sludge produced from different designed clarifiers, case study.

The conventional drinking water treatment plant is depending on coagulation as the main step. In semiarid countries, Quality of produced sludge is major challenges in terms of assessing its optimal operation and performance due to temperature and inappropriate technologies. We study the removal efficiencies of the different designed clarifiers fed with same water comparing to WHO environmental guidelines. According to the analysis of water produced from different clarifiers in El-Asher Water Treatment Plant, the water quality of one clarifier was better than other one. While, nitrate and total phosphate were recorded higher values according to low formation rate of sludge. Improper coagulant dosage is another probable cause production of high aluminum content sludge especially if the coagulant is not dosed optimally. This is depending on the clarifier design and operation and maintenance problems.

Assessment of Conventional Drinking Water Treatment Plants as Removal Systems of Virulent Microsporidia

Assessment of Conventional Drinking Water Treatment Plants as Removal Systems of Virulent Microsporidia

Distribution and relevance of iodinated X-ray contrast media and iodinated trihalomethanes in an aquatic environment

Distribution and relevance of iodinated X-ray contrast media (ICM) and iodinated disinfection byproducts (I-DBPs) in a real aquatic environment have been rarely documented. In this paper, some ICM were proven to be strongly correlated with I-DBPs through investigation of five ICM and five iodinated trihalomethanes (I-THMs) in surface water and two drinking water treatment plants (DWTPs) of the Yangtze River Delta, China. The total ICM concentrations in Taihu Lake and the Huangpu River ranged from 88.7 to 131 ng L−1 and 102–252 ng L−1, respectively. While the total I-THM concentrations ranged from 128 to 967 ng L−1 in Taihu Lake and 267–680 ng L−1 in the Huangpu River. Iohexol, the dominant ICM, showed significant positive correlation (p < 0.01) with CHClI2 in Taihu Lake. Iopamidol and iomeprol correlated positively (p < 0.01) with some I-THMs in the Huangpu River. The observed pronounced correlations between ICM and I-THMs indicated that ICM play an important role in the formation of I-THMs in a real aquatic environment. Characteristics of the I-THM species distributions indicated that I-THMs may be transformed by natural conditions. Both DWTPs showed negligible removal efficiencies for total ICM (<20%). Strikingly high concentrations of total I-THMs were observed in the finished water (2848 ng L−1 in conventional DWTP and 356 ng L−1 in advanced DWTP). Obvious transformation of ICM to I-THMs was observed during the chlorination and ozonization processes in DWTPs. We suggest that ICM is an important source for I-DBP formation in the real aquatic environment.

Energy intensity of treating drinking water: Understanding the influence of factors

To provide safe drinking water to urban populations, raw water must be treated in drinking water treatment plants, which are energy-intensive facilities. Previous studies have assessed energy intensity (EI: unit of energy required per unit of treated water) of conventional drinking water treatment plants, but they ignored variations related to water treatment trains. By modeling 179 facilities of four water treatment trains, we explored factors potentially affecting energy intensity, such as removal efficiencies of pollutants and treatment capacities of drinking water treatment plants. We also investigated the economies of scale in energy intensity of drinking water treatment plants. Our results illustrated that the energy intensity of water facilities using pressure filter systems is affected by several pollutant removal efficiencies, but not by plant capacity. In contrast, the volume of water treated is the main factor responsible for the energy intensity in plants using rapid gravity filter systems and, therefore, their energy intensities are significantly affected by economies of scale. The results of this study should be useful to policy makers planning new facilities and developing policies to reduce the carbon footprints of urban water treatment plants.

The removal process of 2,2-dichloroacetamide (DCAcAm), a new disinfection by-product, in drinking water treatment process and its toxicity on zebrafish

The removal process of 2,2-dichloroacetamide (DCAcAm), a new disinfection by-product (DBP) in conventional drinking water treatment plant (C-DWTP) and advanced DWTP (ADWTP) was studied with newly maximum formation potential (MFP) process. It was demonstrated that the advanced treatment displayed greater removal efficiency towards DCAcAm formation potential (MFP) than the conventional treatment. The hydrophilic natural organic matter and natural organic matter with molecular weight <1 kDa or >10 kDa leaded to more DCAcAm formation, and the aromatic protein was inferred as one part of DCAcAm precursor. DCAcAm was found to cause delayed development and malformation to zebrafish embryos at embryonic growth stage. Compared with heart toxicity, it caused a significant neuron toxicity. It also could cause the acute DNA damage to adult zebrafish, which should be extremely cautioned.

Análisis experimental de la distribución de caudal en los sedimentadores de una planta de tratamiento de agua potable

En estructuras hidráulicas con sistemas múltiples de distribución lateral a flujo libre, se asume que la repartición equitativa del caudal se da usando áreas iguales en cada lateral, pero no sucede así. Esta situación es recurrente en plantas de tratamiento convencional de agua para consumo humano, donde se usan sistemas múltiples laterales, especialmente a la entrada de floculadores y sedimentadores. El análisis de la distribución de caudal se efectuó mediante un trabajo de investigación desarrollado a partir de 2008 en el sistema de múltiples de cuatro laterales de igual área, consistente en compuertas circulares a la entrada de los dos sedimentadores de la planta de tratamiento de agua del perímetro urbano de Cajamarca (Tolima), mediante análisis experimental, usando un modelo a escala donde se evidenció diferencias de caudal al ingreso de cada sedimentador, con potencial afectación del proceso de clarificación que se lleva a cabo, al dejar remanentes que inciden en el tratamiento del agua para consumo, con incidencia en la salud humana.

A Preliminary Study on the Occurrence of Pharmaceutically Active Compounds in the River Basins and Their Removal in Two Conventional Drinking Water Treatment Plants in Chongqing, China

The occurrence of 21 selected pharmaceutically active compounds (PhACs) in river water was examined; meanwhile the presence and removal of these PhACs at different water treatment steps in two conventional drinking water treatment plants (DWTPs) were evaluated. Monitoring results showed that of all 21 target PhACs, twelve PhACs were ubiquitously detected in water samples from the Yangtze river and its two tributaries (Jialing River and Huaxi stream), whereas alodipine was not found in any river water sample. The concentrations of PhACs detected in Huaxi stream were statistically significantly higher than those found in the Jialing River and the Yangzi River because of the direct discharges of uncontrolled domestic sewage and poultry wastewater and the abuse of PhACs in the rural areas served by the Huaxi stream. An environmental risk assessment of PhACs based on the risk quotient value approach indicated that sulfamethoxazole, ofloxacin and dehydrated erythromycin and clofibric acid had a medium risk, and the mixture of the studied PhACs showed high risk for the aquatic ecosystems. Fourteen out of 21 target PhACs were found in the raw water of the two studied DWTPs with azithromycin having the highest concentration (about 20 ng/L). Following the conventional water treatment processes, the studied PhACs were found to be removed by an average of 54 and 48% in DWTP A and DWTP B, respectively. Among the target PhACs, six and three PhACs were detected in finished water of DWTP B and DWTP A, respectively. This is the first study in southwestern China reporting the presence of PhACs in surface water and drinking water.

Using coagulation to restrict microbial re-growth in tap water by phosphate limitation in water treatment

Extensive microbial re-growth in a drinking water distribution system can deteriorate water quality. The limiting factor for microbial re-growth in a tap water produced by a conventional drinking water treatment plant in China was identified by determining the microbial re-growth potential (MRP) by adding different nutrients to stimulate growth of a natural microbial consortium as inoculum and flow-cytometric enumeration. No obvious change of MRP was found in tap water after addition of carbon, whereas, a 1- to 2-fold increase of MRP was observed after addition of phosphate (P). This clearly demonstrated that microbial re-growth in this tap water was limited by P. Most of the re-grown microbial flora (>85%) consisted of high nucleic acid content cells.A subsequent investigation of the MRP in the actual water treatment plant demonstrated that coagulation was the crucial step for decreasing MRP and producing P-limited water. Therefore, a comparison concerning the control of MRP by three different coagulants was conducted. It showed that all the three coagulants efficiently reduced the MRP and shifted the limitation regime from C to P, but the required dose was different. The study shows that it is feasible to restrict microbial re-growth by P limitation using coagulation in water treatment.

Tratamiento de lodos generados en el proceso convencional de potabilización de agua

Waterworks sludge from sedimentation process in conventional drinking water treatment plant, recovery tests under aluminum adding H2SO4, thickening and settling properties were investigated. Using H2SO4, was recovered 60-70% of the initial concentration of aluminum in the sludge, and pH=1.5 Und mixture 5-30 minutes. For testing the settleability and thickening Nalclear 8173 and Trafloc 496 polymers were used. With a significance level of 0.05, the settling properties significant for SST and turbidity removal was obtained; there were no significant differences between the polymers; dose efficiencies presented significant removal was 10 mg/L. In thickening, adding Trafloc and the time factor influenced significantly on removal efficiencies of COD, BOD, TSS and turbidity; there were no significant differences between the doses of polymer used. The settleability provided best technical conditions for the treatment of sludge tested.

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 (&gt; 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 (&gt; 95%), while Ceratium cells were removed by sand filtration (&gt; 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

Occurrence and Removal of Earthy-Musty Odorants in Two Waterworks in Kinmen Island, Taiwan

AbstractIn this study, the occurrence and treatment of two earthy-musty odorants, geosmin and 2-MIB, produced by cyanobacteria is investigated at two conventional drinking-water treatment plants (WTPs) at Kinmen Island, Taiwan. Samples of the source, processed, and finished waters and tap water at the two WTPs were collected and analyzed. Both geosmin and 2-MIB were commonly detected in most water samples, with the 2-MIB concentration much higher than the geosmin concentration. About 78% of the source water samples and 35% of the finished and tap water samples showed detected 2-MIB levels higher than the odor threshold concentration (OTC, ∼10 ng/L). Sampling and analysis of the reservoir water indicated that 2-MIB is uniformly distributed in the reservoir, with ∼70% of which existing in the dissolved phase. The chlorination study of the raw water indicates that both geosmin and 2-MIB are resistant to chlorine. However, the cyanobacterial cells in raw water were effectively ruptured within15 min of the co...

Pre-treatment of Llobregat River raw water through pressurised inside/out hollow fibre ultrafiltration membranes

ABSTRACT The feasibility of raw river direct ultrafiltration, as an alternative to conventional drinking water treatment plant pre-treatment, was investigated at prototype scale (May–October 2011). A highly variable and challenging water resource was selected, in order to assess different scenarios, covering a broad range of conditions. The prototype was able to deal with conditions ranging from 20 to >800 NTU successfully, without any chemical pre-treatment and consuming low amount of chemical reagents for cleaning purposes. The membranes’ performance proved to work better in terms of water production yield and resistance build up stability at medium and high turbidity episodes than at lower ones, probably due to a cake layer formation which prevented small binding organic species and particles reaching the membrane. Permeate quality, both in physico-chemical and microbiological terms, was independent of the feed water characteristics.

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.

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.

Disinfection characteristics of the dissolved organic fractions at several stages of a conventional drinking water treatment plant in Southern China

Dissolved organic matter (DOM) influences many aspects of drinking water treatment, including the formation of harmful disinfection by-products (DBPs) when disinfectants are applied. DOM was isolated and fractionated using membrane ultra-filtration (UF) and reverse osmosis (RO) to eight individual fractions based on molecular weight cut-offs from a conventional surface water treatment plant (WTP) in Guangzhou of PR China. Molecular weights of these eight fractions were further calibrated using high performance size exclusion chromatography (HPSEC) and they ranged from 0.36 to 182.6 kDa. Fractions with molecular weight <0.80 kDa obtained by YC-05 UF membrane and RO were the major ones in all four stages of the water treatment processes; both ZM-500 and YM-100 membranes showed the highest removal efficiency when coupling with conventional coagulation and sedimentation processes. The elemental analysis showed that YC-05 fraction had greater polarity and aromaticity than any of the others. Furthermore, disinfection characteristics and trihalomethane formation potential (THMFP) were determined for all DOM fractions obtained in this study. YC-05 fraction was the major precursor for trihalomethane (THMs) formation among the samples tested and could be removed effectively by particulate activated carbon (PAC) adsorption. RO fraction could not be removed by PAC adsorption and, as a result, consumed more chlorine in the disinfection process. The results suggested that advanced drinking water treatment should focus on the removal of low molecular weight DOM in the source water.

Synthetic Musk Fragrances in a Conventional Drinking Water Treatment Plant with Lime Softening.

Synthetic musk fragrances are common personal care product additives and wastewater contaminants that are routinely detected in the environment. This study examines the presence eight synthetic musk fragrances (AHTN, HHCB, ATII, ADBI, AHMI, musk xylene, and musk ketone) in source water and the removal of these compounds as they flow through a Midwestern conventional drinking water plant with lime softening. The compounds were measured in water, waste sludge, and air throughout the plant. HHCB and AHTN were detected in 100% of the samples and at the highest concentrations. A mass balance on HHCB and AHTN was performed under warm and cold weather conditions. The total removal efficiency for HHCB and AHTN, which averaged between 67% to 89%, is dominated by adsorption to water softener sludge and its consequent removal by sludge wasting and media filtration. Volatilization, chlorine disinfection, and the disposal of backwash water play a minor role in the removal of both compounds. As a result of inefficient overall removal, HHCB and AHTN are a constant presence at low levels in finished drinking water.

Stimulatory Drugs of Abuse in Surface Waters and Their Removal in a Conventional Drinking Water Treatment Plant

The presence of psychoactive stimulatory drugs in raw waters used for drinking water production and in finished drinking water was evaluated in a Spanish drinking water treatment plant (DWTP). Contamination of the river basin which provides raw water to this DWTP was also studied. In surface waters, illicit drugs such as cocaine, benzoylecgonine (cocaine metabolite), amphetamine, methamphetamine, MDMA (ecstasy), and MDA were detected at mean concentrations ranging from 4 to 350 ng/L. Nicotine, caffeine, and their metabolites were also found at the microg/L level. The elimination of these compounds during drinking water treatment was investigated in a real waterworks. Amphetamine-type stimulants (except MDMA) were completely removed during prechlorination, flocculation, and sand filtration steps, yielding concentrations lowerthan their limits of detection (LODs). Further, ozone treatment was shown to be effective in partially eliminating caffeine (76%), while subsequent granulated activated carbon (GAC) filtration removed cocaine (100%), MDMA(88%), benzoylecgonine (72%), and cotinine (63%). Postchlorination achieved the complete elimination of cocaine and nicotine and only one parent compound (caffeine) and two metabolites (cotinine and benzoylecgonine) persisted throughout treatment although reductions of 90% for caffeine and benzoylecgonine and 74% for cotinine were obtained.

Inactivation of Bacillus subtilis spores during ozonation in water treatment plant: Influence of pre-treatment and consequences for positioning of the ozonation step

This study reports on quantitative methodology for rational selection of the ozone injection point within unit processes of conventional drinking water treatment plants to improve disinfection efficiencies. The method is based on the fact that a specific inactivation level of microorganisms is achieved at a unique value of ozone exposures, independent of ozone dose and type of water, and quantitatively described by a Delayed Chick–Watson model ( C ¯ T lag : 1.03 mg l −1, k: 1.44 mg −1 l min −1). This study demonstrated this phenomenon by performing the inactivation of Bacillus subtilis ( B. subtilis) spores with ozone in various types of water collected from a series of unit processes in a water treatment plant. Simple measurements of the ozone decomposition behavior in waters from each unit process of a water treatment plant can allow the quantitative evaluation of the ozone needed to achieve a required level of inactivation. This methodology will be useful for drinking water treatment plants which intend to improve the disinfection efficiencies of their ozonation process.

Organic THMs precursors removal from surface water with low TOC and high alkalinity by enhanced coagulation

NOM removal from surface waters is needed because of potentially carcinogen compound (trihalomethane, THM) formation due to reaction between NOM and free residual chlorine used for disinfection. The stringent limits for THMs (e.g., 30 μg/l in Italy) force conventional drinking water treatment plants to increase TOC removal efficiency by enhanced coagulation. This study was performed on 17 samples taken from a surface water resource with low TOC content (&amp;lt;3 mg/l) and high alkalinity (190 mg as CaCO3/l) to remove TOC and other parameters (DOC, UV254, SUVA, turbidity), typically used to characterize NOM content. Four different coagulants (Al2(SO4)3·18H2O, FeCl3·6H2O, FeSO4·7H2O and PACl) were used in jar test without adding polymer as flocculant. There was no correlation between DOC and SUVA in raw and treated water. TOC removal efficiencies (15–30%) required by the USEPA D/DBPs rule were obtained using 30–50 mg/l alum, 30–50 mg/l of FeCl3, and less than 20 mg/l of PACl (as Al2O3, 10%). The use of PACl is suggested for both lesser TTHMFP and residual Al levels (&amp;lt;100 μg/l) occurrences without any pH adjustment.