Conventional Drinking Water Treatment Research Articles

Use of microscopic and molecular techniques to assess removal of parasitic protozoa via conventional and compact drinking water treatment processes

Use of microscopic and molecular techniques to assess removal of parasitic protozoa via conventional and compact drinking water treatment processes

Formation and interdependence of disinfection byproducts during chlorination of natural organic matter in a conventional drinking water treatment plant.

It is crucial to explore the source, formation process and interdependence of disinfection byproducts (DBPs) to reduce their risk on public health. In this investigation, a source water was chlorinated to evaluate the initial formation rates and the maximum yields of trichloromethane (TCM), dichloroacetic acid (DCAA), and trichloroacetic acid (TCAA) based on a hyperbola model. The results showed that TCM achieved the highest initial formation rate and maximum theoretical concentration compared with DCAA and TCAA. The TCM yield can be used to forecast the yields of DCAA and TCAA throughout the whole reaction process, and the yields of chloral hydrate (CH), dichloroacetonitrile (DCAN) and 1,1,1-trichloropropanone (1,1,1-TCP) within the initial reaction stage. Besides, the raw water, settled water and filtered water collected from a drinking water treatment plant were divided into five fractions, respectively, by ultrafiltration membranes to evaluate their DBP formation after chlorination. Compared with the medium molecular weight species, high and low molecular weight organic matters exhibited relatively high specific regulated and unregulated DBP yields (expressed as μg/mg C), respectively. Humic acid-like compositions predominantly contributed to regulated DBP yields, while soluble microbial by-product-like compounds preferentially generated DCAN. The correlation study revealed that the TCM could also serve as an indicator for the measured DBPs from chlorination of sample fractions with different molecular weight. Finally, it was found that the theoretical cytotoxicity was enhanced during chlorination of filtered water compared with chlorination of settled water.

Effective removal of fluorescent microparticles as Cryptosporidium parvum surrogates in drinking water treatment by metallic membrane

The diarrhoea-causing parasitic protozoan Cryptosporidium parvum (C. parvum) cannot be efficiently removed by conventional drinking water treatment and poses a biological threat to public health. To ensure the biological safety, three kinds of metallic membranes, laminating metal mesh filter, non-woven metal filter and sintered metal fiber filter were employed to compare their properties. The results showed that the sintered membrane possessed the best filtration performance and lowest membrane resistance among three metallic membranes. Therefore, the sintered membrane was selected for subsequent experiments. Due to the low infectious dose of C. parvum and sophisticated detection methods, fluorescent particle tracers, Crypto-tracer-1, were chosen as a feasible surrogate was proposed to investigate the removal efficiency of sintered membrane for C. parvum. The results indicated that the tracer log removal value (LRV) ranged between 5.1 and 5.4 log10 under different filtration flux, which equivalently means that C. parvum could be completely removed and further tests are needed to confirm the results obtained using C. parvum. Furthermore, a pilot-scale study was performed for 10 weeks in full-scale drinking water treatment systems. The turbidity could be efficiently removed (outlet water of membrane was 0.08 ± 0.04 NTU) and the average transmembrane pressure recovery rate was 84.6% after physical backwash. Fouling mechanism analysis indicated that the interaction energy between foulants and membrane material became stronger over time. The practical operation results showed that sintered membrane performed well in continuous operation for a long time and also had a good anti-pollution ability. These findings could facilitate application of metallic membrane in drinking water treatment.

Contributions of volatilization, photolysis, and biodegradation to N‑nitrosodimethylamine removal in conventional drinking water treatment plants

N‑nitrosodimethylamine (NDMA) was detected in the source water of some Chinese drinking water treatment plants (DWTPs), which decreased in concentration along the treatment train. Volatilization, photolysis, and/or biodegradation were suspected of being capable of attenuating NDMA. In this study, the contribution of these mechanisms to NDMA removal was investigated by a field study in a conventional DWTP with aerated bio-pretreatment, as well as in laboratory-based experiments. The effluent of each unit process (i.e., aerated bio-pretreatment tank, horizontal sedimentation tank, sand filter) of this DWTP was sampled in the winter and summer, and the concentration of NDMA, its formation potential, and other water quality parameters were measured. NDMA removal by volatilization and biodegradation was simulated in batch experiments, and that by photolysis was calculated with parameters reported in the literature. The sampling results indicated that the aerated biofilm reactor of this DWTP removed 48% of the NDMA in August and 22% in December. According to modeling results, it could be well explained by photolysis (NDMA removal of 51% in summer and 25% in winter) and biotreatment (NDMA removal of 0.2–12% in summer and 0.1–6.1% in winter), with little contribution from aeration (NDMA removal of 0.8%). The sampling results indicated that the sedimentation tank removed 19% of NDMA in August and 9.2% in December. According to modeling results, it could be well explained by photolysis (NDMA removal of 16% in August and 9.4% in December), but little by volatilization. Thus, photolysis was shown to be the most important process for NDMA removal in this DWTP. Further investigation is needed to better understand NDMA removal during biotreatment.

An investigation of changes in water quality throughout the drinking water production/distribution chain using toxicological and fluorescence analyses

Changes in water quality from source water to finished water and tap water at two conventional drinking water treatment plants (DWTPs) were monitored. Beside the routine water quality testing, Caenorhabditis elegans-based toxicity assays and the fluorescence excitation–emission matrices technique were also applied. Both DWTPs supplied drinking water that met government standards. Under current test conditions, both the investigated finished water and tap water samples exhibited stronger lethal, genotoxic and reprotoxic potential than the relative source water sample, and the tap water sample was more lethal but tended to be less genotoxic than the corresponding finished water sample. Meanwhile, the nearly complete removal of tryptophan-like substances and newly generated tyrosine-like substances were observed after the treatment of drinking water, and humic-like substances were identified in the tap water. Based on these findings, toxic pollutants, including genotoxic/reproductive toxicants, are produced in the drinking water treatment and/or distribution processes. Moreover, further studies are needed to clarify the potentially important roles of tyrosine-like and humic-like substances in mediating drinking water toxicity and to identify the potential sources of these contaminants. Additionally, tryptophan-like fluorescence may be adopted as a useful parameter to monitor the treatment performance of DWTPs. Our observations provided insights into the importance of utilizing biotoxicity assays and fluorescence spectroscopy as tools to complement the routine evaluation of drinking water.

Prediction of 1,4-dioxane decomposition during VUV treatment by model simulation taking into account effects of coexisting inorganic ions

1,4-Dioxane is one of the most persistent organic micropollutants and is quite difficult to remove via conventional drinking water treatment consisting of coagulation, sedimentation, and sand filtration. Vacuum ultraviolet (VUV) treatment has recently been found to show promise as a treatment method for 1,4-dioxane removal, but the associated decomposition rate of 1,4-dioxane is known to be very sensitive to water quality characteristics. Some computational models have been proposed to predict the decomposition rate of micropollutants during VUV treatment, but the effects of only bicarbonate and natural organic matter have been considered in the models. In the present study, we attempted to develop a versatile computational model for predicting the behavior of 1,4-dioxane during VUV treatment that took into account the effects of other coexisting inorganic ions commonly found in natural waters. We first conducted 1,4-dioxane decomposition experiments with low-pressure mercury lamps and test waters that had been prepared by adding various inorganic ions to an aqueous phosphate buffer. The apparent decomposition rate of 1,4-dioxane was suppressed when bicarbonate, chloride, and nitrate were added to the test waters. Whereas bicarbonate and chloride directly suppressed the apparent decomposition rate by consuming HO•, nitrate became influential only after being transformed into nitrite by concomitant UV light (λ = 254 nm) irradiation. Cl-related radicals (Cl• and Cl2•−) did not react with 1,4-dioxane directly. A computational model consisting of 31 ordinary differential equations with respect to time that had been translated from 84 reactions (10 photochemical and 74 chemical reactions) among 31 chemical species was then developed for predicting the behavior of 1,4-dioxane during VUV treatment. Nine of the parameters in the ordinary differential equations were determined by least squares fitting to an experimental dataset that included different concentrations of bicarbonate, chloride, nitrate, and nitrite. Without further parameter adjustments, the model successfully predicted the behavior of 1,4-dioxane during VUV treatment of three groundwaters naturally contaminated with 1,4-dioxane as well as one dechlorinated tap water sample supplemented with 1,4-dioxane.

Evaluation of conventional drinking water treatment plant efficiency according to water quality index and health risk assessment

The objective of this research is to investigate the effluent water quality of a treatment plant in Turkey fed from surface and groundwater, according to water quality index (WOI) and health risk assessment (HRA). In order to achieve this goal, the quality of the influent and effluent water of the treatment plant was monitored monthly from January 2017 to January 2019. Water quality parameter results were compared with the Turkish drinking water standards and the World Health Organization (WHO), revealing that all parameters were within approved limits. Principal component analysis (PCA) was applied to determine the water quality parameter impacts in the overall quality of water and the most attractive parameters were trace elements, heavy metals, NH3-N, NO3, and TKN. To evaluate water quality and the impacts on human health, WQI and HRA, including hazard quotient (HQ) and hazard index (HI), were used. The WQI values were calculated by taking into account PCA results. WQI results demonstrated that the influent and effluent of water treatment plant values have a small number of WQI ranking that expressed the water category was "excellent" for drinking purpose. Finally, metal contamination in influent and effluent waters was assessed and the associated health risks to rural populations were estimated for different age groups, children and adults in the service area of the treatment plant. The health risk assessment with similar to WQI results, the acute, sub-chronic, and chronic risks of trace elements was "negligible" level, i.e., to a level affecting 1 person in 1,000,000 inhabitants.

Laboratory simulation of postfire effects on conventional drinking water treatment and disinfection byproduct formation

AbstractWildfires can abruptly transform forests, char vegetation and soils, and create an environment susceptible to postfire erosion and runoff to nearby surface waters serving as potable water supplies. The rising trend in wildfire activity increases the risk to source waters, while postwildfire implications on drinking water treatment are not well understood. A laboratory‐based approach was used to simulate the effects of forest floor heating during wildfire on water quality. Surface soil and litter samples were heated in a furnace and leached to evaluate changes to water‐soluble compounds. Leachates were diluted to a dissolved organic carbon (DOC) concentration of 5.0 ± 1.0 mgC/L. Heated and unheated (control) leachates were compared for dissolved organic matter (DOM) properties, treatability by alum coagulation, and disinfection byproduct formation. Size exclusion chromatography, optical property characterization, and organic nitrogen levels suggest that the DOM character shifted to lower‐molecular‐weight, nitrogen‐enriched aromatic compounds following heating. Raw water total trihalomethane and haloacetic acid precursor yields were not significantly different following heating; however, pairwise responses varied. Chloropicrin precursor yields increased by an average of 155% following heating, while haloacetonitrile precursor yields showed minimal changes. Even at high coagulant doses (>80 mg/L), the heated leachates consistently exhibited a poor coagulation response to turbidity and DOC removal. The DOC removal per mg alum was statistically lower for the heated leachates compared to the control samples (mean Δ = −0.06 mgC/mg‐alum). The adverse effect of heating on the DOC removal of the leachates might be explained by a lower‐molecular‐weight DOM composition. While findings suggest an altered DOM character, utilities may also experience an increase in influent DOC concentrations coupled with higher, or even extreme, sediment loads, resulting in compounding effects on water treatment.

Optimizing the performance of conventional water treatment system using quantitative microbial risk assessment, Tehran, Iran

The performance of conventional drinking water treatment plants (WTPs) can be improved using quantitative microbial risk assessment (QMRA). A QMRA study on Cryptosporidium using actual pathogen density was conducted to examine the performance of Jalaliyeh WTP in Tehran, Iran. The infection risk and the burden of disease attributed to the parasite presence in finished water were estimated incorporating physical and chemical log reduction values (LRVs), using stochastic modeling and disinfection profiling. The risk and burden of disease were compared with health-based targets, i.e. one case of infection per 10,000 people or 10−6 DALYs per person per year. The parasite's LRVs were 2.31 and 0.034 log provided by physico-chemical treatment and disinfection processes, respectively. The mean of estimated risk (111 cases per 104 people per year) and the burden of disease (11.7 DALYs per 106 people per year) both exceeded the targets. To control the excess risk, three QMRA-based disinfection scenarios were examined including: (1) employing chlorine dioxide (ClO2) instead of chlorine (2) ozonation with a concentration of 0.75 mg/L (Ct = 22.5 min mg/L) and (3) UV irradiation with a dose of 10 mJ/cm2. The LRV of parasite may be increased to 3.0, 5.1 and 4.9 log by employing ClO2, ozonation and UV irradiation, respectively. The use of ozone or UV as alternative disinfectants, could enhance the disinfection efficacy and provide sufficient additional treatment against the excess risk of parasite. QMRA could make it easier applying appropriate improvement to conventional WTPs in order to increase the system performance in terms of health-based measures.

Occurrence of swampy/septic odor and possible odorants in source and finished drinking water of major cities across China

Swampy/septic odors are one of the most important odor types in drinking water. However, few studies have specifically focused on it compared to the extensive reported musty/earthy odor problems, even though the former is much more offensive. In this study, an investigation covering the odor characteristics, algal distribution and possible odorants contributing to swampy/septic odor, including dimethyl disulfide (DMDS), dimethyl trisulfide (DMTS), diisopropyl sulfide (DIPS), dipropyl sulfide (DPS), dibutyl sulfide (DBS), 2-methylisoborneol (2-MIB) and geosmin (GSM), was performed in source and finished water of 56 drinking water treatment plants (DWTPs) in 31 cities across China. While the musty/earthy and swampy/septic odors were dominant odor descriptors, the river source water exhibited a higher proportion of swampy/septic odor (38.5%) compared to much higher detection rate of musty/earthy odor (50.0%) in the lake/reservoir source water. The occurrence of swampy/septic odor, which was much easier to remove by conventional drinking water treatment processes compared to musty/earthy odors, was decreased by 62.9% and 46.3% in river and lake/reservoir source water respectively. Statistical analysis showed that thioethers might be responsible for the swampy/septic odor in source water (R2 = 0.75, p < 0.05). Specifically, two thioethers, DMDS and DMTS were detected, and other thioethers were not found in all water samples. DMDS was predominant with a maximum odor activity value (OAV) of 2.0 in source water and 1.3 in finished water. The distribution of the thioethers exhibited a marked regional characteristics with higher concentrations being detected in the east and south parts of China. The high concentrations of thioethers in lake/reservoir source water samples could be partly interpreted as the bloom of the cyanobacteria. This study provides basic information for swampy/septic odor occurrence in drinking water and will be helpful for further water quality management in water industry in China.

Occurrence and reduction of antibiotic resistance genes in conventional and advanced drinking water treatment processes

Antibiotic resistance is extensively detected in drinking water sources, threatening its safety and human health, which deserves further attention to the removal of antibiotic resistance genes (ARGs) in the drinking water system. In this study, the occurrence and reduction of integrase gene intI1 and forty-one ARG subtypes, which confers resistance to six antibiotic classes (β-lactam, aminoglycoside, macrolide, tetracycline, sulfonamide, and quinolone), were investigated in a drinking water treatment plant (DWTP). Seventeen ARG subtypes with absolute concentrations ranging from 1.4 × 100 to 7.3 × 105 and 3.9 × 104 genes/mL (intI1) were detected in the raw water; and sul1 and sul2 were the two dominant ARG subtypes. Overall, the whole DWTPs achieved 0.03–2.4 log reduction of ARGs compared with those presented in raw water. The reduction efficiencies of sul1, strA, and intI1 were the highest (1.0–2.4 log) in both conventional and advanced processes. However, the levels of sul1, sul2, and ermC still remained high (1.3 × 100–1.9 × 104 genes/mL) in finished water. The treatment units, including pre-flocculation/sedimentation/sand filtration, and ozonation units, were beneficial for the reduction of ARGs, which was mostly ascribed to the decline in biomass and the strong oxidizing properties of ozone. However, the reduction effect was subsequently counteracted by the granular activated carbon and chlorination units. This study provides basic data for ARG pollution in the drinking water system, and suggests that ARGs persist in drinking water, even after conventional chlorination or advanced treatment processes, highlighting the need for new and efficient water purification technologies.

Removal of pesticide residues after conventional drinking water treatment: byproducts and acetylcholinesterase inhibition

Water is of extreme importance to living creatures. However, due to human’s action, that resource has been contaminated by different compounds, among them, the pesticides. Whenever in water, pesticides can cause some damage to aquatic environments or to those who consume it. In this way, it becomes a concern if the water treatment systems can remove these pollutants from water. In this perspective, the objective of this work is to investigate whether conventional water treatment has the ability to remove the pesticides atrazine, ametryn, malathion and chlorpyrifos. According to the results, it was observed that the conventional treatment after filtration was not capable of removing those pesticides with efficiency, being the organophosphorus (malathion and chlorpyrifos) removed in a higher percentage than the triazines (atrazine and ametryn). Postchlorination reduced the pesticides levels, however were generated the byproducts malaoxon and ametryn sulphoxide, which caused a greater acetilcolinesterase inhibition. Thus, advanced steps are required to the conventional treatment to remove these persistent contaminants.

Occurrence and removal of sulfonamide antibiotics and antibiotic resistance genes in conventional and advanced drinking water treatment processes.

Sulfonamides (SAs) and sul antibiotic resistance genes (ARGs) have been extensively detected in drinking water sources and warrant further studies on the removal of them in different drinking water treatment processes (DWTPs). The prevalence of 13 SAs, sul1, sul2 and class I integrase gene intI1 in conventional and advanced processes was investigated using HPLC-MS/MS and real-time quantitative PCR (qPCR), respectively. The most abundant SA was sulfamethoxazole, with the maximum concentration of 67.27 ng/L. High concentration of sulfamethoxazole was also measured in finished water in both conventional (22.05 ng/L) and advanced (11.24 ng/L) processes. Overall, the removal efficiency of advanced process for each SA was higher than that of conventional process, except for sulfameter. The absolute concentrations of sul1, sul2 and intI1 in raw water ranged from 1.8 × 103 to 2.4 × 105 gene abundance/mL. After treatment, the residual sul ARGs and intI1 in finished water still remained at 102 - 104 gene abundance/mL. Conventional treatment units, including flocculation/sedimentation/sand filtration, played a more important role in removing sul1, sul2 and intI1 than oxidation (chlorination or ozonation) and granular activated carbon filtration treatments. Based on this work, more investigations are needed to help improve the removal of both antibiotics and ARGs in DWTPs.

Special issue: Plasma and Liquids

Special issue: Plasma and Liquids

Application of double filtration with activated carbon for the removal of phenols in drinking water treatment processes

Abstract The primary source of the discharge of phenols into the environment is industrial activity, such as the production of pharmaceuticals, plastics, and pesticides, being the majority discharged into surface water sources, reaching concentrations around 0.001 to 0.400 mg/L. These compounds are considered a priority contaminant due to their toxicity to aquatic life and effects on human health. The presence of phenols even at low concentrations generates flavour and odour in drinking water. Due to the molecular stability and solubility of phenols in water, their removal by conventional water treatment methods is inefficient. However, adsorption with granular activated carbon (GAC), after conventional filtration with sand and anthracite, is an efficient technique for the reduction of organic compounds such as phenols. This paper studied the effect of applying double filtration to the reduction of phenols present in the filtered water of a conventional drinking water treatment plant, using two types of GAC (vegetable and mineral) and three GAC:Sand configurations (100:00; 00:100; 50:50). The configurations with GAC showed an efficient reduction of turbidity, organic matter indicator variables (UV254 absorbance and total organic carbon) and phenols, the mineral GAC being the most efficient GAC.

Protozoan Parasites in Drinking Water: A System Approach for Improved Water, Sanitation and Hygiene in Developing Countries.

Improved water, sanitation and hygiene (WASH) are significant in preventing diarrhea morbidity and mortality caused by protozoa in low- and middle-income countries. Due to the intimate and complex relationships between the different WASH components, it is often necessary to improve not just one but all of these components to have sustainable results. The objective of this paper was to review the current state of WASH-related health problems caused by parasitic protozoa by: giving an overview and classification of protozoa and their effect on people’s health, discussing different ways to improve accessibility to safe drinking water, sanitation services and personal hygiene behavior; and suggesting an institutional approach to ensure improved WASH. The findings indicate that Giardia and Cryptosporidium are more often identified during waterborne or water-washed outbreaks and they are less sensitive than most of the bacteria and viruses to conventional drinking water and wastewater treatment methods. There are various institutions of control and prevention of water-related diseases caused by protozoa in developed countries. Unfortunately, the developing regions do not have comparable systems. Consequently, the institutional and systems approach to WASH is necessary in these countries.

Influence of spent filter backwash water recycling on pesticide removal in a conventional drinking water treatment process

The effects of recycling spent filter backwash water (SFBW) on the removal of 14 organic pesticides were examined in a simulated conventional drinking water treatment process.

Photocatalysis with easily recoverable linear engineered TiO2 nanomaterials to prevent the formation of disinfection byproducts in drinking water

Two photocatalytic linear engineered TiO2 nanomaterials (LENs) were synthesized and evaluated against commercial standard P25 TiO2 nanoparticles in terms of their effects on common parameters used to measure and characterize natural organic matter (NOM) and disinfection byproduct (DBP) precursors in drinking water. DBPs, some of which have been linked to cancer and other negative human health outcomes, are regulated in most jurisdictions in North America and Europe as well as parts of Asia, Africa, and South America, and the removal of DBP precursors is a central goal of conventional drinking water treatment plants. All three of the nanomaterials evaluated in this study were capable of degrading NOM, including DBP precursors, when irradiated with UVA LED light. The materials differed in terms of crystal phase, surface morphology, and available surface area. These differences impacted the predominant NOM removal processes occurring in each case and consequently the overall treatment efficacy of the two materials in two different water sources. One of the LENs evaluated in this study, designated NB 700, reduced the DBP formation potential of one of the water sources by 90% and was readily removed from the water via filtration. Irrespective of the nanomaterial employed, DBP precursor degradation was faster in the water source with higher NOM and lower alkalinity and hardness. The electrical energy per order (EEO) required to degrade DOC and THM precursors in one of the water sources was comparable to reported values for the degradation of these compounds with UV/H2O2, another advanced oxidation process.

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.