Municipal Drinking Water Treatment Plant Research Articles

Applying Microbial Source Tracking Techniques for Identification of Pathways of Faecal Pollution from Water Sources to Point of Use in Vhembe District, South Africa

A safe water supply is a necessity, but it remains one of the backlogs of services rendered in rural areas of developing countries. This leads to vulnerable communities using water from available sources that is unsafe as it is contaminated with faecal matter. Microbial source tracking (MST) methods are gold-standard techniques that detect the exact sources of faecal contamination. This study, therefore, tracked and identified the exact sources of faecal contamination from the catchment to the point of use in rural areas of Vhembe District Municipality. Collected water samples (n = 1048) were concentrated by membrane filtration for the enumeration and detection of E. coli, followed by DNA extraction. The extracted DNA was subjected to a quantitative polymerase chain reaction (qPCR) to track target host-specific Bacteroidales genetic markers from the water source to the point of use. Rivers and dams exhibited maximum E. coli counts of up to 90 CFU/100 mL during the wet season and up to 50 CFU/100 mL during the dry season. Due to the effective treatment of these water sources, no E. coli bacteria were detected in any of the sampled municipal drinking water treatment plants at the point of treatment, while this indicator bacterium was detected at the point of use (households), with a maximum of 4 CFU/100 mL recorded during both the wet and dry seasons. Overall, the most prevalent MST marker exhibited during the wet season was BacCan (dog-associated, 6.87%), followed by BacCow (cow-associated, 5.53%), while Pig-2-Bac (pig-associated, 2.48%) was the least prevalent. The most prevalent marker exhibited during the dry season was BacCan (5.34%), followed by BacCow, with Pig-2-Bac (1.72%) being the least prevalent. A positive correlation (r = 0.31, p = 0.001) was established between the presence of the MST markers and detected E. coli from water sources to the point of use. The knowledge of the faecal contamination attributes in both public and domestic domains will assist in developing prevention and control strategies.

Full‐scale application of an electrochemical disinfection solution in a municipal drinking water treatment plant

AbstractFew studies employ electrochemical technology for urban water disinfection. This paper presents the replacement of a Cl2 gas system by an on‐site chlorine generation system (electrochemical disinfectant solution, EDS) and application at a water treatment plant. The study compares the Cl2 gas and EDS systems over 36 months, with 18 months for Cl2 gas and, after the implementation, 18 months for the EDS system (12‐month dry season and 6‐month wet season). Turbidity, residual Cl2, pH, total and faecal coliforms and DBPs were monitored. Turbidity was within legal limits and DBPs below both legal limits and limits of detection. For Cl2 gas, residual Cl2 suffered a decrease in wet and dry periods. However, the EDS maintained residual Cl2 to the network tips without significant variations, with operational costs reduced by ~41%. The study demonstrates that on‐site Cl2 generation can be employed for water disinfection for large urban areas with considerable economic and technical advantages.

Operating parameters optimization of combined UF/NF dual-membrane process for brackish water treatment and its application performance in municipal drinking water treatment plant

As an important water resource, brackish water has been extensively utilized in the industry. However, there are few cases of municipal potable water treatment plants that use low chloride content brackish water as the source. In this paper, the brackish water treatment efficiency of ultrafiltration (UF)/nanofiltration (NF) dual-membrane process was evaluated in a municipal potable water treatment plant, combining with a pilot optimization experiment. Results showed that UF guaranteed the inlet water quality of NF and NF could efficiently reject organics and salts, with a chloride removal over 95 %. Pilot experiment showed that the UF membrane flux decreased only 12 % after continuously 30-days operation under the optimized UF operation conditions, effectively extending the chemical cleaning interval. Response surface method was adopted in the NF removal efficiency and energy consumption optimization. With the increase of feed water conductivity, the influences of pressure and recovery on the removal efficiency were strengthened, and the removal efficiency could be regulated over a wider range. When the conductivity was less than 3500 μS/cm, NF could perform high treatment efficiency under the operation pressure of 0.65−0.85 MPa and recovery of 55–70 % . Besides, as feed conductivity increased, it was necessary to increase the pressure and reduce the recovery within this range to maintain efficient operation. This paper will provide a guidance for the UF/NF dual-membrane process design and operational optimization.

Degradation of sulfadiazine in drinking water by a cathodic electrochemical membrane filtration process

In this study, a novel electrochemical membrane filtration (EMF) process was proposed to degrade sulfadiazine (SDZ) in drinking water, and the oxidation mechanisms, kinetics, byproducts and primary impact factors were investigated. In the EMF process, a novel membrane was used as the cathode and two graphite plates were used as anodes. Five oxidation byproducts including 4-OH-sulfadiazine or 5-OH-sulfadiazine, 2-aminopyrimidine, 4-amino-N-carbamimidoyl benzene sulfonamide and 2,5-dihydroxypyrimidine were identified. Possible degradation pathways for SDZ were proposed, and OH and ▪ were recognized to be the major reactive oxygen species contributed for SDZ degradation. The degradation of SDZ by EMF followed pseudo-first-order kinetics in batch experiment and the rate constant increased as the applied voltages increased. Compared with the batch experiment, the flow-through mode of EMF slowed SDZ degradation, and the degradation rate also decreased as the flux increased. However, on the base of mass balance calculations more SDZ was degraded in flow-through mode as compared with that in batch experiment. Finally, the degradation of SDZ in natural waters from a municipal drinking water treatment plant was investigated with flow-through mode, and the result shows that the degradation rate (79%) was slightly lower than that obtained for deionized water due to the low conductivity of real-world water systems.

Efficacy of Water Treatment Processes and Endemic Gastrointestinal Illness – A Multi-City Study in Sweden

Outbreaks of acute gastrointestinal illnesses (AGI) have been linked to insufficient drinking water treatment on numerous occasions in the industrialized world, but it is largely unknown to what extent public drinking water influences the endemic level of AGI. This paper aimed to examine endemic AGI and the relationship with pathogen elimination efficacy in public drinking water treatment processes. For this reason, time series data of all telephone calls to the Swedish National Healthcare Guide between November 2007 and February 2014 from twenty Swedish cities were obtained. Calls concerning vomiting, diarrhea or abdominal pain (AGI calls) were separated from other concerns (non-AGI calls). Information on which type of microbial barriers each drinking water treatment plant in these cities have been used were obtained, together with the barriers' theoretical pathogen log reduction efficacy. The total log reduction in the drinking water plants varied between 0.0 and 6.1 units for viruses, 0.0-14.6 units for bacteria and 0.0-7.3 units regarding protozoans. To achieve one general efficacy parameter for each plant, a weighted mean value of the log reductions (WLR) was calculated, with the weights based on how commonly these pathogen groups cause AGI. The WLR in the plants varied between 0.0 and 6.4 units. The effect of different pathogen elimination efficacy on levels of AGI calls relative non-AGI calls was evaluated in regression models, controlling for long term trends, population size, age distribution, and climatological area. Populations receiving drinking water produced with higher total log reduction was associated with a lower relative number of AGI calls. In overall, AGI calls decreased by 4% (OR = 0.96, CI: 0.96-0.97) for each unit increase in the WLR. The findings apply to both groundwater and surface water study sites, but are particularly evident among surface water sites during seasons when viruses are the main cause of AGI. This study proposes that the endemic level of gastroenteritis can indeed be reduced with more advanced treatment processes at many municipal drinking water treatment plants.

Efficacy of water treatment processes and endemic gastrointestinal illness – A multi-city study in Sweden

Outbreaks of acute gastrointestinal illnesses (AGI) have been linked to insufficient drinking water treatment on numerous occasions in the industrialized world, but it is largely unknown to what extent public drinking water influences the endemic level of AGI. This paper aimed to examine endemic AGI and the relationship with pathogen elimination efficacy in public drinking water treatment processes. For this reason, time series data of all telephone calls to the Swedish National Healthcare Guide between November 2007 and February 2014 from twenty Swedish cities were obtained. Calls concerning vomiting, diarrhea or abdominal pain (AGI calls) were separated from other concerns (non-AGI calls). Information on which type of microbial barriers each drinking water treatment plant in these cities have been used were obtained, together with the barriers’ theoretical pathogen log reduction efficacy. The total log reduction in the drinking water plants varied between 0.0 and 6.1 units for viruses, 0.0–14.6 units for bacteria and 0.0–7.3 units regarding protozoans. To achieve one general efficacy parameter for each plant, a weighted mean value of the log reductions (WLR) was calculated, with the weights based on how commonly these pathogen groups cause AGI. The WLR in the plants varied between 0.0 and 6.4 units. The effect of different pathogen elimination efficacy on levels of AGI calls relative non-AGI calls was evaluated in regression models, controlling for long term trends, population size, age distribution, and climatological area. Populations receiving drinking water produced with higher total log reduction was associated with a lower relative number of AGI calls. In overall, AGI calls decreased by 4% (OR = 0.96, CI: 0.96–0.97) for each unit increase in the WLR. The findings apply to both groundwater and surface water study sites, but are particularly evident among surface water sites during seasons when viruses are the main cause of AGI. This study proposes that the endemic level of gastroenteritis can indeed be reduced with more advanced treatment processes at many municipal drinking water treatment plants.

Variation of levels and distribution of N-nitrosamines in different seasons in drinking waters of East China.

We surveyed the occurrence of nine N-nitrosamine species in ten bottled drinking waters from supermarket and other water samples including raw waters, finished waters, and distribution system waters from nine municipal drinking water treatment plants in eight cities of Jiangsu Province, East China. N-nitrosodimethylamine (NDMA) was detected in one of ten bottled drinking water samples at concentration of 4.8 ng/L and N-nitrosomorpholine (NMor) was detected in four of the ten bottles with an average concentration and a standard deviation of 16 ± 15 ng/L. The levels of nitrosamines in the distribution system water samples collected during summer season ranged from below detection limit (BDL) to 5.4 ng/L for NDMA, BDL to 9.5 ng/L for N-nitrosomethylethylamine (NMEA), BDL to 2.7 ng/L for N-nitrosodiethylamine (NDEA) and BDL to 8.5 ng/L for N-nitrosopyrrolidine (NPyr). Samples of distribution system waters collected in winter season had levels of nitrosamines ranged from BDL to 45 ng/L for NDMA, BDL to 5.2 ng/L for NPyr, and BDL to 309 ng/L for N-nitrosopiperidine (NPip). A positive correlation of the concentration of NDMA as well as the total nine N-nitrosamines between finished waters and distribution system waters was observed. Both dissolved organic carbon and nitrite were found to correlate linearly with N-nitrosamine levels in raw waters.

Malaysia's largest river bank filtration and ultrafiltration systems for municipal drinking water production

This paper presents a case study of Wakaf Bunut water treatment plant (the ‘plant’) in Kelantan, Malaysia. The plant was successfully commissioned in February 2013 and started operating in March 2013. It is capable of supplying up to 14 million liters a day of potable water to Tok Bali. Feasibility studies were carried out on the combination of river bank filtration (RBF) and ultrafiltration (UF) to reduce operating costs while maintaining filtrate quality. The plant is the largest municipal drinking water treatment plant in Malaysia using combined RBF and UF technologies. Actual operating data from the plant were collected and are discussed in this paper.

Removal of geosmin and 2-methylisoboneol (2-MIB) by membrane system combined with powdered activated carbon (PAC) for drinking water treatment

Adsorption kinetic tests and step-feeding tests were performed to evaluate adsorption characteristics of geosmin and 2-methylisoborneol (2-MIB). Removal efficiencies of each unit process in powdered activated carbon (PAC) membrane hybrid system were evaluated as well. The hybrid system consists of two unit processes; a coarse powder activated carbon (C-PAC) contactor and a submerged membrane tank. A pilot plant having a capacity of 500m3day−1 was installed in W municipal drinking water treatment plant. C-PAC contactor has C-PAC (80–150 mesh) slurry blanket with a high concentration of 30,000mgL−1 and the blanket is maintained in the contactor without loss. After the adsorption capacity of the C-PAC was exhausted, C-PAC turned into a biological activated carbon. In step feeding tests, 2-MIB and geosmin were continuously injected to the raw water as a concentration of 50ngL−1 for 2-MIB and 200ngL−1 for geosmin. Addition of fresh PAC of 15mgL−1 and 5mgL−1 was required to reduce the concentration of 2-MIB or geosmin below odor threshold concentration, respectively. These values are less than half of required dose from kinetic tests. The removal of Geosmin and 2-MIB by the bio-film formed on the C-PAC in the contactor was accounted for approximately up to 25% of the overall removal. As the raw water temperature increased from 5 to 20°C, the biological removal efficiency was almost doubled. The operating pressure of membrane had been stable when the flux was maintained below 33Lm−2h−1 with recovery rate of 98% for three months. The recovery cleaning is expected every 6 months for the long term operation.

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 of the logistic model for GAC performance in water treatment

Full‐scale field measurement and rapid small‐scale column test data from the Greater Cincinnati (Ohio) Water Works (GCWW) were used to calibrate and investigate the application of the logistic model for simulating breakthrough of total organic carbon (TOC) in granular activated carbon (GAC) contactors. The logistic model parameters were estimated using a nonlinear regression algorithm. The calibrated logistic model was validated using data from multiple GAC contactors operating in parallel at the GCWW Richard Miller Treatment Plant. This facility has experienced large seasonal variations in flow rate and TOC influent concentration. Proper estimation of logistic model parameters depends on the run‐time length of the GAC breakthrough data set. A critical minimum runtime threshold must be achieved to produce reliable parameter estimates. A properly calibrated logistic model provides an effective tool for accurately simulating the blended TOC concentrations in the GAC contactor effluent at a municipal drinking water treatment plant.

Diversity and antibiotic resistance of Acinetobacter spp. in water from the source to the tap

Acinetobacter spp. are ubiquitous bacteria in the environment. Acinetobacter spp. isolated from a municipal drinking water treatment plant and from connected tap water were identified to the species level on the basis of rpoB gene partial sequence analysis. Intraspecies variation was assessed based on the analysis of partial sequences of housekeeping genes (rpoB, gyrB, and recA). Antibiotic resistance was characterized using the disk diffusion method and isolates were classified as wild or non-wild type (non-WT), according to the observed phenotype. The strains of Acinetobacter spp. were related to 11 different validly published species, although three groups of isolates, presenting low rpoB sequence similarities with previously described species, may represent new species. Most of the isolates were related to the species A. johnsonii and A. lwoffii. These two groups, as well as others related to the species A. parvus and A. tjernbergiae, were detected in the water treatment plant and in tap water. Other strains, related to the species A. pittii and A. beijerinckii, were isolated only from tap water. Most of the isolates (80%) demonstrated wild type (WT) to all of the 12 antibiotics tested. Non-WT for tetracycline, meropenem, and ceftazidime, among others, were observed in water treatment plant or in tap water samples. Although, in general, this study suggests a low prevalence of acquired antibiotic resistance in water Acinetobacter spp., the potential of some species to acquire and disseminate resistance via drinking water is suggested.

Identifying host sources, human health risk and indicators of Cryptosporidium and Giardia in a Canadian watershed influenced by urban and rural activities

Cryptosporidium and Giardia were characterized in a watershed in southern Ontario, Canada, over a 2½ year period. River samples were collected every two weeks, primarily near a municipal drinking water treatment plant intake. Cryptosporidium and Giardia were frequently detected with an overall occurrence rate of 88 and 97%, respectively. Giardia concentrations were higher than Cryptosporidium, with median values of 80 cysts 100 L(-1) and 12 oocysts 100 L(-1), respectively. Although pathogens rarely show a significant relationship with fecal or water quality indicators, this study determined that Cryptosporidium, but not Giardia, was significantly correlated with Escherichia coli, turbidity and river flow. There was no correlation between the two types of protozoa, and only Giardia showed a seasonal trend with higher concentrations at cold water temperatures. Cryptosporidium genotyping of all samples found that farm animals and wildlife were an important contributor of oocysts in the watershed, and that Cryptosporidium strains/genotypes of medium to high risk for human infection (C. hominis, C. parvum and C. ubiquitum) were detected in 16% of samples. This study was able to identify Cryptosporidium host sources and human health risk, and to identify differences between Cryptosporidium and Giardia occurrence in the watershed.

Photodegradation and toxicity changes of antibiotics in UV and UV/H 2O 2 process

The photodegradation of three antibiotics, oxytetracycline (OTC), doxycycline (DTC), and ciprofloxacin (CIP) in UV and UV/H 2O 2 process was investigated with a low-pressure UV lamp system. Experiments were performed in buffered ultrapure water (UW), local surface water (SW), and treated water from local municipal drinking water treatment plant (DW) and wastewater treatment plant (WW). The efficiency of UV/H 2O 2 process was affected by water quality. For all of the three selected antibiotics, the fastest degradation was observed in DW, and the slowest degradation occurred in WW. This phenomenon can be explained by R OH,UV, defined as the experimentally determined OH radical exposure per UV fluence. The R OH,UV values represent the background OH radical scavenging in water matrix, obtained by the degradation of para-chlorobenzoic acid (pCBA), a probe compound. In natural water, the indirect degradation of CIP did not significantly increase with the addition of H 2O 2 due to its effective degradation by UV direct photolysis. Moreover, the formation of several photoproducts and oxidation products of antibiotics in UV/H 2O 2 process was identified using GC–MS. Toxicity assessed by Vibrio fischer (V. fischer), was increased in UV photolysis, for the photoproducts still preserving the characteristic structure of the parent compounds. While in UV/H 2O 2 process, toxicity increased first, and then decreased; nontoxic products were formed by the oxidation of OH radical. In this process, detoxification was much easier than mineralization for the tested antibiotics, and the optimal time for the degradation of pollutants in UV/H 2O 2 process would be determined by parent compound degradation and toxicity changes.

Oxidation kinetics of cyclophosphamide and methotrexate by ozone in drinking water

This study investigates the aqueous degradation by ozone of two target cytostatic drugs, cyclophosphamide and methotrexate. A column switching technique for on-line solid phase extraction (SPE) coupled to electro-spray ionization-tandem mass spectrometry (LC–ESI-MS/MS) was used for the simultaneous detection of the trace contaminants. The second-order kinetic rate constants for the reaction of cyclophosphamide with molecular ozone and hydroxyl radicals were determined in bench-scale experiments at pH 8.10. The molecular ozone oxidation kinetics was studied in buffered ultrapure water and compared to the oxidation kinetics in natural water from a municipal drinking water treatment plant in the province of Quebec (Canada). For cyclophosphamide, the degradation rate constant with molecular ozone in ultrapure water was low ( k O 3 = 3.3 ± 0.2 M −1 s −1) and the extent of oxidation was linearly correlated to the ozone exposure. The impact of water quality matrix on oxidation efficacy was not significant during direct ozone reaction ( k O 3 = 2.9 ± 0.3 M −1 s −1). The rate constant with hydroxyl radicals was higher at 2.0 × 10 9 M −1 s −1. Methotrexate reacted quickly with molecular ozone at dosages typically applied in drinking water treatment ( k O 3 > 3.6 × 10 3 M −1 s −1). Overall, the results confirmed that organic compounds reactivity with ozone was dependent of their chemical structure. Ozone was very effective against methotrexate but high oxidant concentration × contact time (CT) values were required to completely remove cyclophosphamide from drinking water. Further studies should be conducted in order to identify the ozonation by-products and explore the impact of ozone on their degradation and toxicity.

Phosphorus retention mechanisms of a water treatment residual.

Water treatment residuals (WTRs) are a by-product of municipal drinking water treatment plants and can have the capacity to adsorb tremendous amounts of P. Understanding the WTR phosphorus adsorption process is important for discerning the mechanism and tenacity of P retention. We studied P adsorbing mechanism(s) of an aluminum-based [Al2(SO4)3 x 14H2O] WTR from Englewood, CO. In a laboratory study, we shook mixtures of P-loaded WTR for 1 to 211 d followed by solution pH analysis, and solution Ca, Al, and P analysis via inductively coupled plasma atomic emission spectroscopy. After shaking periods, we also examined the solids fraction by X-ray diffraction (XRD) and electron microprobe analysis using wavelength dispersive spectroscopy (EMPA-WDS). The shaking results indicated an increase in pH from 7.2 to 8.2, an increase in desorbed Ca and Al concentrations, and a decrease in desorbed P concentration. The pH and desorbed Ca concentration increases suggested that CaCO3 controlled Ca solubility. Increased desorbed Al concentration may have been due to Al(OH)4 formation. Decreased P content, in conjunction with the pH increase, was consistent with calcium phosphate formation or precipitation. The system appeared to be undersaturated with respect to dicalcium phosphate (DCP; CaHPO4) and supersaturated with respect to octacalcium phosphate [OCP; Ca4H(PO4)3 x 2.5H2O]. The Ca and Al increases, as well as OCP formation, were supported by MINTEQA2 modeling. The XRD and EMPA-WDS results for all shaking times, however, suggested surface P chemisorption as an amorphous Al-P mineral phase.

Drinking water off-flavour caused by the formation of short-chain fatty acids in slow sand filters

A case study carried out at a municipal drinking water treatment plant in southern Sweden showed that the formation of short-chain fatty acids in slow sand filters can result in severe off-flavour problems. When an extract of the headspace of the surface layer of a sand filter was subjected to gas chromatographic analysis with sensory detection (GC sniffing), several strong, rancid odours were detected. Mass spectrometric analysis of the same extract, before and after methylation, showed that substantial amounts of butyric acid, valeric acid and isovaleric acid were present in the analysed sample. The off-flavour caused by these compounds was removed by repeated shock chlorination of the malfunctioning slow sand filter. Analysis of fatty acid esters may provide an early warning of the described off-flavour problem.

Drinking water off-flavour caused by the formation of short-chain fatty acids in slow sand filters

A case study carried out at a municipal drinking water treatment plant in southern Sweden showed that the formation of short-chain fatty acids in slow sand filters can result in severe off-flavour problems. When an extract of the headspace of the surface layer of a sand filter was subjected to gas chromatographic analysis with sensory detection (GC sniffing), several strong, rancid odours were detected. Mass spectrometric analysis of the same extract, before and after methylation, showed that substantial amounts of butyric acid, valeric acid and isovaleric acid were present in the analysed sample. The off-flavour caused by these compounds was removed by repeated shock chlorination of the malfunctioning slow sand filter. Analysis of fatty acid esters may provide an early warning of the described off-flavour problem.