Reducing the dimension of water quality parameters in source water: An assessment through multivariate analysis on the data from 441 supply systems.

In this research, multivariate statistical analysis was performed on twenty water quality parameters (WQP) collected on tri-monthly basis (four times/year) from 441 drinking water sources in Newfoundland and Labrador (NL), Canada for 18 years (1999-2016). The WQP included alkalinity (Alk), color (Col), conductivity (Cond), hardness (Hard), pH, total dissolved solids (TDS), turbidity (Turb), bromide (Br), calcium (Ca), chloride (Cl), fluoride (F), potassium (K), sodium (Na), sulfate (SO4), dissolved organic carbon (DOC), ammonia (NH3), nitrate (NO3), Kjeldahl nitrogen (N), total phosphorus (P) and magnesium (Mg). The assessment was conducted on surface water (SWS) and groundwater (GWS) sources separately. In SWS and GWS, number of samples analyzed for each WQP were in the ranges of 3434-6057 and 1915-1919 respectively. Averages of DOC and pH showed increasing trends (SWS: DOC = 0.0722 mg/L/year; pH = 0.0375 units/year; GWS: DOC = 0.0491 mg/L/year; pH = 0.0441 units/year) while the other WQP showed variable characteristics, which could increase treatment cost and deteriorate tap water quality. Strong correlations were observed for Ca-Hard (r = 0.97-0.98), TDS-Cond (r = 0.91-0.99) and Na-Cl (r = 0.87-0.96). In SWS, Alk had stronger correlations with Cond, Hard, pH, TDS, Ca and Mg (r = 0.62-0.94) than GWS (r = 0.56-0.63). Principal Component Analysis revealed separate clusters for DOC-Col, Na-Cl, TDS-Cond, Ca-Alk and Mg-Hard, indicating that these WQP moved together. In SWS and GWS, six principal components were significant (eigenvalue ≥ 1.0), and explained 74.8% and 72.9% of overall variances respectively. In Factor Analysis, six varifactors explained 73.4% and 70.5% of total variances in SWS and GWS respectively. For SWS and GWS, eleven and ten WQP, respectively explained these variances, indicating 45% and 50% data reduction respectively. The findings can assist in controlling water quality through monitoring reduced number of WQP, which is likely to minimize the monitoring cost.

Disinfection by-products in desalinated and blend water: formation and control strategy.

Desalinated seawater is the major source of drinking water in many countries. During desalination, several activities including pretreatment, desalination, stabilization, mixing, storage and distribution are performed. Few disinfectants are used during these activities to control the biofouling agents and microbiological regrowth. The reactions between the disinfectants and natural organic matter (NOM), bromide and iodide form disinfection by-products (DBPs) in product water. The product water is stabilized and mixed with treated freshwater (e.g., groundwater) to meet the domestic water demands. The DBPs in desalinated and blend water are an issue due to their possible cancer and non-cancer risks to humans. In this paper, formation and distribution of DBPs in different steps of desalination and water distribution systems prior to reaching the consumer tap were reviewed. The variability of DBPs among different sources and desalination processes was explained. The toxicities of DBPs were compared and the strategies to control DBPs in desalinated water were proposed. Several research directions were identified to achieve comprehensive control on DBPs in desalinated water, which are likely to protect humans from the adverse consequences of DBPs.

Water quality degradation in the sources of drinking water: an assessment based on 18 years of data from 441 water supply systems.

Degradation of source water quality complicates water treatment processes, resulting in additional treatment cost and tap water quality deterioration. In this study, source water quality was investigated for 441 water supply systems (WSSs) during the period of 18 years (1999-2016). The investigation was performed on 21 water quality parameters (WQPs) for groundwater (GWS) and surface water (SWS) sources. The averages of dissolved organic carbon (DOC), color, and Kjeldahl nitrogen (N) were much higher in SWS than GWS while other 18 WQPs (e.g., alkalinity, conductivity, and pH) were higher in GWS. In SWS, averages of DOC during 2000-2005, 2006-2010, and 2011-2015 were 6.08, 6.74, and 6.78 mg/L, respectively. In these periods, pH were 6.39, 6.62, and 6.77, respectively. In GWS, averages of DOC in these periods were 1.43, 1.36, and 1.81 mg/L, respectively, while pH were 7.50, 7.69, and 7.89, respectively. The DOC in SWS and GWS were increasing at the rates of 0.0722 and 0.0491 mg/L/year, respectively, while pH were increasing at the rates of 0.0375 and 0.0441 units/year, respectively. Trihalomethanes showed increasing trends in drinking water from SWS and GWS while haloacetic acids showed no trend. In SWS, DOC and its rate of increase were higher while in GWS, pH and its rate of increase were higher. The higher DOC and pH, and their increasing rates could increase disinfection byproducts (DBPs) in drinking water. Many DBPs are known as possible or probable human carcinogens and some DBPs are regulated. The other WQP and their increasing patterns can also impart new challenges, which are likely to increase the treatment cost and/or deteriorate drinking water quality.

Occurrences and changes of disinfection by-products in small water supply systems.

The small water supply systems (WSSs) often report high concentrations of disinfection by-products (DBPs) in drinking water. In this study, occurrences of trihalomethanes (THMs) and haloacetic acids (HAAs) in Newfoundland and Labrador (NL), Canada, were investigated from 441 WSSs for a period of 18 years (1999-2016). The WSSs were divided into groundwater (GWP) and surface water (SWP) systems, which were further classified into eight sub-groups (P1-P8) based on the population served (≤ 100; 101-250; 251-500; 501-1000; 1001-3000; 3001-5000; 5001-10,000; and 10,000+, respectively). The DBPs with probable and possible carcinogenic forms were estimated. Overall, 31.1% of WSSs were GWP, in which averages of THMs and HAAs were 32.2 and 27.7 µg/L, respectively, while the SWP had averages of THMs and HAAs of 97.6 and 129.2 µg/L, respectively. The very small WSSs (P1-P3) of GWP had averages of THMs and HAAs in the ranges of 29.1-43.5 and 15.8-64.3 µg/L, respectively. The P1-P3 of SWP had averages of THMs and HAAs in the ranges of 92.6-112.8 and 108.0-154.0 µg/L, respectively, which often exceeded the Canadian guideline limits. If the samples represented the populations homogenously, the total populations exposed to THMs or HAA5 above the guideline values would be in the range of 132.08-181.38 in thousands (30.3-41.6% of total populations). The probable and possible carcinogenic forms of THMs in GWP and SWP were in the ranges of 4.8-48.8 and 4.4-7.0% of THMs, respectively. In HAAs, carcinogenic forms were in the ranges of 82.6-98.4 and 97.6-98.7%, respectively. The findings indicated that the SWP might need further attention to better protect human health.

Effects of plumbing systems on human exposure to disinfection byproducts in water: a case study.

Disinfection byproducts (DBPs) in water distribution systems (WDS) are monitored for regulatory compliance, while populations are exposed to DBPs in tap water that may be different due to stagnation of water in plumbing pipes (PP) and heating in hot water tanks (HWT). This study investigated the effects of water stagnation in PP and HWT on exposure and risk of DBPs to humans. Trihalomethanes (THMs) in PP and HWT were observed to be 1.1-2.4 and 1.6-3.0 times, respectively, to THMs in the WDS, while haloacetic acids (HAAs) were 0.9-1.8 and 1.2-1.9 times, respectively, to HAAs in the WDS. The chronic daily intakes of DBPs from PP and HWT were 0.6-1.8 and 0.5-2.3 times the intakes from WDS. The cancer risks from PP and HWT were 1.46 (0.40-4.3) and 1.68 (0.35-5.1) times the cancer risks from WDS. The findings may assist in regulating DBPs exposure concentrations.

Predicting human exposure and risk from chlorinated indoor swimming pool: a case study.

This study predicted human exposure to disinfection by-products (DBPs) in a chlorinated indoor swimming pool. Human exposure was predicted through ingestion, inhalation, and dermal routes while ingestion exposure was accidental with water intake of 18-34 mL/h. The number of pool attendants and duration and frequency of swimming were in the ranges of 14-62 persons/day, 40-85 min/event, and 26-48 times/year, respectively. Trihalomethanes (THMs) in pool water and air were 28.7-95.5 µg/L and 44.1-133.6 µg/m(3), respectively, while haloacetic acids (HAAs) in pool water were 68.9-158.9 µg/L. The brominated THMs in water and air were 95.4 and 94.3% of total THMs, respectively, while brominated HAAs were 94.4 % of total HAAs. Chronic daily intakes of THMs and HAAs were 2.16 × 10(-5)-3.14 × 10(-3) and 8.4 × 10(-8)-4.6 × 10(-6) mg/kg-day, respectively. The cancer risk from three THMs and two HAAs was 2.46 × 10(-5) with a range of 8.1 × 10(-6)-5.7 × 10(-5), in which THMs contributed 99.6% of total risks. Approximately 99.3% of risks were through inhalation and dermal routes, indicating that the ingestion route may be insignificant. The cancer risks from THMs in swimming pool were 4.06-6.64 times to the cancer risks from THMs in drinking water.

Modeling heterotrophic bacteria in plumbing system of drinking water.

This study investigated occurrences of heterotrophic (HPC) bacteria and developed predictive models for HPC bacteria in plumbing pipes (PP) and hot water tanks (HWT) of two houses in Dhahran (Saudi Arabia). Heterotrophic bacteria in PP and HWT were observed to be 2.4 to 5.3 and 0.4 to 5.9 times the HPC bacteria in water distribution system (WDS), respectively. Three linear, one nonlinear, and one neural network models were investigated to predict HPC bacteria in PP and HWT. Significant factors for bacteria regrowth in PP and HWT were identified through numerical and graphical techniques. The R2 values of the models varied between 0.57 and 0.96, indicating moderate to excellent predictive ability for HPC bacteria in PP and HWT. The models were found to be statistically significant, which were also validated using additional data. These models can be used to predict HPC bacteria regrowth from WDS to PP and HWT, and could help to predict exposure and risks.

Water quality change in dam reservoir and shallow aquifer: analysis on trend, seasonal variability and data reduction.

Change of water quality in dam reservoir and aquifer complicates safe drinking water supply. Few parameters are monitored to control water quality in these sources. Adequate knowledge on the correlation structure, interaction effect, trends and seasonal variability of these parameters is essential to control water quality. This study applied time series and multivariate analyses on 15 water quality parameters, collected from the King Fahd dam reservoir (L1) and aquifer (L2) in Saudi Arabia during April 2010 to February 2012. Moderate to strong correlations were observed between sulfate, hardness, fluoride, chloride, magnesium, conductivity, turbidity and total dissolved solids (TDS), while separate clusters were visible for TDS-chloride-magnesium-conductivity; fluoride-turbidity; chloride-hardness; ammonia-nitrate; and calcium-magnesium-hardness. Four major principal components explained 81.1% and 83.2% of the overall variances in L1 and L2, respectively. The factor analysis showed that 53% and 67% of the data were necessary to explain 81.3% and 83.2% of total variances for L1 and L2, respectively, indicating the possibility of data reduction. Possible degradation of water quality in these sources was highlighted, while such degradation may require enhanced treatment for producing drinking water in future.

Applications of artificial intelligence (AI) in drinking water treatment processes: Possibilities.

In water treatment processes (WTPs), artificial intelligence (AI) based techniques, particularly machine learning (ML) models have been increasingly applied in decision-making activities, process control and optimization, and cost management. At least 91 peer-reviewed articles published since 1997 reported the application of AI techniques to coagulation/flocculation (41), membrane filtration (21), disinfection byproducts (DBPs) formation (13), adsorption (16) and other operational management in WTPs. In this paper, these publications were reviewed with the goal of assessing the development and applications of AI techniques in WTPs and determining their limitations and areas for improvement. The applications of the AI techniques have improved the predictive capabilities of coagulant dosages, membrane flux, rejection and fouling, disinfection byproducts (DBPs) formation and pollutants' removal for the WTPs. The deep learning (DL) technology showed excellent extraction capabilities for features and data mining ability, which can develop an image recognition-based DL framework to establish the relationship among the shapes of flocs and dosages of coagulant. Further, the hybrid techniques (e.g., combination of regression and AI; physical/kinetics and AI) have shown better predictive performances. The future research directions to achieve better control for WTPs through improving these techniques were also emphasized.

Fusing probability density function into Dempster-Shafer theory of evidence for the evaluation of water treatment plant.

The evaluation of the status of a municipal drinking water treatment plant (WTP) is important. The evaluation depends on several factors, including, human health risks from disinfection by-products (R), disinfection performance (D), and cost (C) of water production and distribution. The Dempster-Shafer theory (DST) of evidence can combine the individual status with respect to R, D, and C to generate a new indicator, from which the overall status of a WTP can be evaluated. In the DST, the ranges of different factors affecting the overall status are divided into several segments. The basic probability assignments (BPA) for each segment of these factors are provided by multiple experts, which are then combined to obtain the overall status. In assigning the BPA, the experts use their individual judgments, which can impart subjective biases in the overall evaluation. In this research, an approach has been introduced to avoid the assignment of subjective BPA. The factors contributing to the overall status were characterized using the probability density functions (PDF). The cumulative probabilities for different segments of these factors were determined from the cumulative density function, which were then assigned as the BPA for these factors. A case study is presented to demonstrate the application of PDF in DST to evaluate a WTP, leading to the selection of the required level of upgradation for the WTP.

Evaluation and strategy for improving the quality of desalinated water.

Seawater desalination is practiced in many coastal countries, which is accepted as clean water by the general populations. The untreated seawater reported high concentrations of bromide (50,000 - 80,000 µg/L) and iodide (21 - 60 µg/L) ions, which are reduced to non-detectable levels during thermal desalination while the concentrations of bromide and iodide ions were reduced to 250-600 µg/L and < 4-16 µg/L, respectively during reverse osmosis processes. During the treatment and/or disinfection, many brominated and iodinated disinfection byproducts (Br-DBPs and I-DBPs) are formed in desalinated water, some of which are genotoxic and cytotoxic to the mammalian cells and possible/probable human carcinogens. In this paper, DBPs' formation in desalinated and blended water from source to tap, toxicity to the mammalian cells, their risks to humans and the strategies to control DBPs were investigated. The lifetime excess cancer risks from groundwater, and desalinated and blended water sourced DBPs were 4.15 × 10-6 (4.72 × 10-7 - 1.30 × 10-5), 1.75 × 10-5 (2.58 × 10-6 - 5.25 × 10-5) and 2.59 × 10-5 (4.02 × 10-6 - 8.35 × 10-5) respectively, indicating higher risks from desalinated and blended water (2.56 and 4.51 times respectively) than groundwater systems. Few emerging DBPs in desalinated/blended water showed higher cyto- and genotoxicity in the mammalian cells. The findings were compared with safe drinking water standards and strategies to produce cleaner desalinated water were demonstrated.

Comparing risk of disinfection byproducts in drinking water under variable scenarios of seawater intrusion.

The higher levels of halides in seawater increase bromide and iodide in the coastal aquifers, leading to higher concentrations of halogenated disinfection byproducts (DBPs). The populations in the coastal areas are susceptible to increased concentrations of DBPs while many DBPs are cyto- and genotoxic to mammalian cells, and are possible/probable human carcinogens. The implications of seawater intrusion on the concentrations of trihalomethanes (THMs) and haloacetic acids (HAAs), and the risks were analyzed by adding 0.0-2.0 % seawater (SW) (by volume) and chlorine to groundwater. Bromide and iodide concentrations in groundwater (0.0 %SW) were observed as 42.5 and non-detected (ND) µg/L respectively. With 2.0 %SW, these were spiked up to 1100 and 2.1 µg/L respectively. The most common THMs (THM4), iodinated THMs (I-THMs) and HAAs were 30.4, 0.13 and 27.9 µg/L for 0.0 % SW respectively. With 2.0 %SW, these values were 106.3, 1.6 and 72.9 µg/L, respectively. At 0.0 %SW, averages of chronic daily intakes (CDI) for THM4, HAAs and I-THMs were 2.61 × 10-4, 2.26 × 10-4 and 7.69 × 10-7 mg/kg/day respectively, which were increased to 9.97 × 10-4, 4.70 × 10-4 and 9.47 × 10-6 mg/kg/day, respectively for 2.0 %SW. For 0.0 %SW, overall cancer risks from few DBPs was 3.09 × 10-5 (6.46 × 10-6 - 7.23 × 10-5) while at 1.0 % and 2.0 %SW, risks were 4.88 × 10-5 (1.26 × 10-5-1.08 × 10-4) and 4.11 × 10-5 (1.21 × 10-5-9.28 × 10-5) respectively. The reduction of risks for 2.0 %SW was due to the increase of bromoform (TBM), and decrease in bromodichloromethane (BDCM) and dibromochloromethane (DBCM) at 2.0 %SW. The disability-adjusted life years (DALY) loss showed an increasing trend from 0.0 %SW (DALY: 77.30) to 1.0 %SW (DALY: 122.0) while an increase to 2.0 %SW showed a decrease in DALY (DALY: 102.8). Future study on toxicity of other regulated and emerging DBPs is warranted to better predict cancer risks.

Associated health risk assessment due to exposure to BTEX compounds in fuel station workers.

OBJECTIVES: The purpose of this review study was to assess the risk of exposure to BTEX compounds in gas station workers and operators. CONTENT: The main components of BTEX compounds are Benzene, Toluene, Ethyl benzene and Xylene. Petroleum, coal large quantities in crude oil and its products are the most important sources of BTEX compounds. These compounds have both high solubility (found in surface and underground waters) and evaporate quickly. Gas stations are one of the most important sources of emission of these compounds in communities. Workers who work in these places have a lot of exposure to these compounds. Exposure to these dangerous compounds can cause many problems for workers. This study was a narrative review article. According to different databases: PubMed, Web of Science, Springer, Cochran and Science Direct, 451 articles were retrieved. 55 full-text articles entered into the analysis process. Finally, 32 articles were selected in this study. The search was restricted to English-language papers published between 1 February 1995 and 13 August 2022. The results of our study showed that the carcinogenic risk (ILCR) for gas station workers in Bangkok (1.82 ∗ 10-4 - 2.50 ∗ 10-4), Shiraz (6.49∗10-7 - 1.27 ∗ 10-5), Brazil (1.82 ∗ 10-4), Ardabil (390∗10-6 ± 1884 ∗ 10-6) and Johannesburg (3.78 ∗ 10-4) was high. The non-cancer risk for oil industry workers of Dilijan (Iran) who were exposed to toluene was also reported in the range of 10-6∗176. The health of gas station workers is affected by exposure to BTEX and gasoline vapor emissions. According to the result this study, BTEX compounds cause genotoxic changes, chromosomal and genetic abnormalities. SUMMARY AND OUTLOOK: Genotoxicity at high levels in gas station workers can cause cancerous and non-cancerous risks. Improving the production process of diesel fuel and gasoline in refineries, using periodical examinations of workers and operators at gas and fuel stations, using Euro 4 and 5 fuels, and replacing worn out cars can play an important role in reducing the emission of BTEX compounds and thus reducing health risks and carcinogenic.

Heterotrophic bacteria in drinking water distribution system: a review.

The microbiological quality of drinking water in municipal water distribution systems (WDS) depends on several factors. Free residual chlorine and/or chloramines are typically used to minimize bacterial recontamination and/or regrowth in WDS. Despite such preventive measures, regrowth of heterotrophic (HPC) and opportunistic bacteria in bulk water and biofilms has yet to be controlled completely. No approach has shown complete success in eliminating biofilms or HPC bacteria from bulk water and pipe surfaces. Biofilms can provide shelter for pathogenic bacteria and protect these bacteria from disinfectants. Some HPC bacteria may be associated with aesthetic and non-life threatening diseases. Research to date has achieved important success in understanding occurrence and regrowth of bacteria in bulk water and biofilms in WDS. To achieve comprehensive understanding and to provide efficient control against bacteria regrowth, future research on bacteria regrowth dynamics and their implications is warranted. In this study, a review was performed on the literature published in this area. The findings and limitations of these papers are summarized. Occurrences of bacteria in WDS, factors affecting bacteria regrowth in bulk water and biofilms, bacteria control strategies, sources of nutrients, human health risks from bacterial exposure, modelling of bacteria regrowth and methods of bacteria sampling and detection and quantification are investigated. Advances to date are noted, and future research needs are identified. Finally, research directions are proposed to effectively control HPC and opportunistic bacteria in bulk water and biofilms in WDS.

Effects of seawater intrusion on the formation of disinfection byproducts in drinking water.

Seawater contains high levels of halides, which can increase the concentrations of bromide and iodide ions in coastal groundwater and surface water sources. Intrusion of seawater alters the chemistry of fresh water leading to the formation of additional brominated and iodinated disinfection byproducts (DBPs), many of which are cyto- and genotoxic to the mammalian cells, and have cancer risks to humans. In this study, effects of seawater intrusion on the formation of trihalomethanes (THMs), and haloacetic acids (HAAs) were investigated by spiking groundwater using 0.0-2.0% seawater (by volume) and liquid chlorine as disinfectant. The concentrations of bromide and iodide ions in groundwater (0.0% seawater) were 42.5 and non-detected (ND) µg/L respectively, which were increased up to 1100 and 2.1 µg/L respectively, following mixing with 2.0% seawater. The regulated THMs (THM4) were increased from 30.4 to 106.3 µg/L while iodinated THMs (I-THMs) were increased from 0.13 to 1.6 µg/L respectively due possibly to molecular substitution and additional pathways of THMs formation. Bromoform was increased from 0.5 to 94.3 µg/L while iodoform was increased from ND to 1.02 µg/L. HAAs were increased from 27.9 to 72.9 µg/L where tribromoacetic acid was increased from 2.0 to 43.7 µg/L. In 0.0% seawater, bromine incorporation factor (BIF) for THM4 and HAAs were 0.077 and 0.050 respectively, which were increased to 0.942 and 0.38 at 2% seawater respectively. For dihalogenated HAAs (X2AA) and trihalogenated HAAs (X3AA), BIF in 0.0% seawater were 0.098 and 0.14 respectively, which were increased to 0.863 and 0.924 for 2.0% seawater respectively. Mixing of 2.0 seawater increased the toxicity of THM4, HAAs and I-THMs by 4.2, 5.9 and 201.8 folds, respectively indicating the importance of reducing seawater intrusion into the freshwater sources. Further, alteration of water sources and/or adaptation of advanced treatment can assist in lowering the risks.

Removal of halides from drinking water: technological achievements in the past ten years and research needs.

Disinfection is an essential process for drinking water supplies resulting in the formation of unintended disinfection by-products (DBPs), many of which are potentially toxic and are known as the possible or probable human carcinogens. As of now, 100+ DBPs were characterized while about 600+ others can be formed in the supply water. To protect the human health, many regulatory agencies have set the guideline values for several DBPs. Removal of halide ions and natural organic matter prior to disinfection is an important step to reduce DBPs, and the associated exposure and risks. To date, many publications have reported various methods for halide removal from drinking water. The most review about halide removal technologies, associated challenges, and future research needs was published in 2012. Since then, a number of studies have been published on different methods of halide removal techniques. This paper aims to review the state of research on halide removal techniques focusing on the development during the past 10 years (2012-2021). The techniques were clustered into six major groups: adsorption, ion exchange, coagulation, advanced oxidation, membrane separation, and combined techniques. The progress on these groups of technologies, their advantages, and limitations were examined, and the future research directions to produce the safe drinking water were identified.

Removal of Pb2+ from water using the carbon nanotube-g-poly[(sodium methacrylate)-co- 2-(methacryloyloxy)ethyl acetoacetate]: experimental investigation and modeling.

A solid polymer, poly[(sodium methacrylate)-co-2-(methacryloyloxy)ethyl acetoacetate], p(MAA-co-MEAA) was synthesized and then grafted onto carbon nanotubes to prepare poly(MAA-co-MEAA)-grafted carbon nanotubes [CNT-g-p(MAA-co-MEAA)]. NMR, TGA, and FT-IR characterized the synthesized polymers and adsorbents. SEM-EDX was used to investigate the surface characteristics of the adsorbents. Pb2+ was removed from the aqueous solution using the CNT-g-p(MAA-co-MEAA). A batch adsorption experiment was performed at different Pb2+ concentrations (1, 10, 25, 50 mg/L), pH (4 and 6.75), temperature (25 and 35 °C), and contact periods (1, 5, 20, 60, and 1440 min) to study the adsorption kinetics and isotherm. The adsorbent dose of 2.5 g/L could effectively lower the initial Pb2+ concentration of 1000 to 2 ppb. The maximum adsorption capacity of the adsorbent was found to be 1178 mg/g. In addition, the adsorbents have been shown to effectively reduce the coexisting metal ion concentrations from industrial wastewater, which indicated the potential of the proposed adsorbent in removing metal ions from coexisting metals containing wastewater. To predict the adsorption efficiency of Pb2+, various linear, non-linear, and neural network models were established. An additional data set, not incorporated in model training, was used to validate the models. A number of models showed excellent performance with R2 in the range of 0.89-0.98. In model validation studies, the correlation coefficients (r) ranged from 0.94 to 0.99. The novel adsorbent and models will most likely aid in the development of a robust treatment technique for removing Pb2+ ions from water and wastewater.

Removal of lead ions (Pb2+) from water and wastewater: a review on the low-cost adsorbents.

The presence of lead compounds in the environment is an issue. In particular, supply water consumption has been reported to be a significant source of human exposure to lead compounds, which can pose an elevated risk to humans. Due to its toxicity, the International Agency for Research on Cancer and the US Environmental Protection Agency (USEPA) have classified lead (Pb) and its compounds as probable human carcinogens. The European Community Directive and World Health Organization have set the maximum acceptable lead limits in tap water as 10 µg/L. The USEPA has a guideline value of 15 µg/L in drinking water. Removal of lead ions from water and wastewater is of great importance from regulatory and health perspectives. To date, several hundred publications have been reported on the removal of lead ions from an aqueous solution. This study reviewed the research findings on the low-cost removal of lead ions using different types of adsorbents. The research achievements to date and the limitations were investigated. Different types of adsorbents were compared with respect to adsorption capacity, removal performances, sorbent dose, optimum pH, temperature, initial concentration, and contact time. The best adsorbents and the scopes of improvements were identified. The adsorption capacity of natural materials, industrial byproducts, agricultural waste, forest waste, and biotechnology-based adsorbents were in the ranges of 0.8-333.3 mg/g, 2.5-524.0 mg/g, 0.7-2079 mg/g, 0.4-769.2 mg/g, and 7.6-526.0 mg/g, respectively. The removal efficiency for these adsorbents was in the range of 13.6-100%. Future research to improve these adsorbents might assist in developing low-cost adsorbents for mass-scale applications.

Factorial analysis of trihalomethanes formation in drinking water.

Disinfection of drinking water reduces pathogenic infection, but may pose risks to human health through the formation of disinfection byproducts. The effects of different factors on the formation of trihalomethanes were investigated using a statistically designed experimental program, and a predictive model for trihalomethanes formation was developed. Synthetic water samples with different factor levels were produced, and trihalomethanes concentrations were measured. A replicated fractional factorial design with center points was performed, and significant factors were identified through statistical analysis. A second-order trihalomethanes formation model was developed from 92 experiments, and the statistical adequacy was assessed through appropriate diagnostics. This model was validated using additional data from the Drinking Water Surveillance Program database and was applied to the Smiths Falls water supply system in Ontario, Canada. The model predictions were correlated strongly to the measured trihalomethanes, with correlations of 0.95 and 0.91, respectively. The resulting model can assist in analyzing risk-cost tradeoffs in the design and operation of water supply systems.

Human exposure and risk of trihalomethanes during continuous showering events.

Exposure to disinfection byproducts (DBPs) in municipal water mainly occurs through ingestion, inhalation during showering, house cleaning and dermal permeation. While showering, the air-phase DBPs [e.g., trihalomethanes (THMs)] can pose risk to humans through inhalation pathway. In assessing inhalation risk during showering, current approaches assume negligible initial concentrations of air-phase THMs in shower stalls, which may not be realistic in places with common shower stalls (e.g., gymnasiums). The time difference between successive showering events in these places is likely to be minimal, resulting in significant initial concentrations of THMs due to prior showering events. In this study, exposure to air-phase THMs during the successive showering events were predicted. In the 2nd showering event, averages of chronic daily intake (CDI), cancer risk (CR) and hazard index (HI) were 1.82, 1.83 and 1.85 times the CDI, CR and HI in the first event, respectively. In the 3rd event, these were 2.50, 2.54 and 2.58 times, respectively. The increasing trends of CDI, CR and HI were observed for up to the 9th event (5.06, 4.98 and 5.60 times, respectively). By widening the time-gap between the successive showering events, reducing showering duration and enhancing ventilation, human exposure and risk can be controlled.