Effect of dissolved organic matter on bacterial regrowth and response after ultraviolet disinfection.

The effect of dissolved organic matter (DOM) on bacterial regrowth in water after disinfection using ultraviolet (UV) light emitting diodes (UVLEDs) is still unclear. Herein, the regrowth and responses of Vibrio parahaemolyticus and Bacillus cereus were investigated after being exposed to UVLEDs at combined wavelengths (265 and 280 nm) in a phosphate-buffered saline consisting of Suwannee River natural organic matter (SRNOM) and Suwannee River fulvic acid (SRFA). Low-molecular-weight (MW) organic compounds, which may form into intermediary photoproducts, and indicate bacterial repair metabolism, were characterized through non-target screening using orbitrap mass spectrometry. This study demonstrates the ability of the UVLEDs-inactivated cells to regrow. After UV exposure, a considerable upregulation of RecA was observed in two strains. With increasing the incubation time, the expression levels of RecA in V. parahaemolyticus increased, which may be attributed to the dark repair mechanism. Coexisting anionic DOM affects both the disinfection and bacterial regrowth processes. The time required for bacterial regrowth after UV exposure reflects the time needed for the individual cells to reactivate, and it differs in the presence or absence of DOM. In the presence of DOM, the cells were less damaged and required less time to grow. The UVLEDs exposure results in the occurrence of low-MW organic compounds, including carnitine or acryl-carnitine with N-acetylmuramic acid, which are associated with bacterial repair metabolism. Overall, the results of this study expand the understanding of the effects of water matrices on bacterial health risks. This can aid in the development of more effective strategies for water disinfection.

Performance of electrokinetic remediation system for mercury contaminated marine sediment: Roles of electrode spacing and electrode configuration.

Understanding mercury (Hg) species existing after electrokinetic remediation (EK) for marine-sediment remediation is limited. Herein, the Hg fraction removal of EK from contaminated marine sediment was investigated appertaining to bipolar electrode settings along with the effects of electrode spacing and configuration considered. Based on the selective sequential Hg extractions (Hg SSE), much of the Hg in the sediment originated from F5 (i.e., HgS) and F4 (i.e., HgO). The F5 fraction removed by EK was about 30 %, while the F4 fraction had a slight increase of about 34 %. When it comes to electrode configuration, a hexagonal pattern has a higher Hg removal performance than that of a rectangular shape. The addition of anodes increases the remediation surface area, thus allowing superior Hg removal. This study indicates that the electrode spacing significantly affects the mercury removal and the remediation time. Determining suitable spacing enhances the electrical potentials in the migration flux.

Gaining new insights into macroplastic transport 'hotlines' and fine-scale retention-remobilisation using small floating high-resolution satellite drifters in the Chao Phraya River estuary of Bangkok.

In river plastic pollution research little is known about the detailed pathways and interruptions that occur during the journey of macroplastic debris (>5 cm) from land to sea. Data on fine-scale and high-accuracy transport trajectories and cycles of retention (when macroplastics are trapped, e.g. at a pier) and remobilisation is needed to inform global river plastic transport models as well as mechanical cleanup efforts. Though well established in the marine environment, the use of floating satellite drifters to understand macroplastic debris transport in tidal rivers and estuaries is in its infancy. Exploring the capacity to investigate fine-scale macroplastic debris-estuary interactions, this study brings together, on the one hand, a small, sensitive, floating satellite drifter with, on the other hand, the major riverine-marine habitat of the Chao Phraya River estuary at Bangkok, Thailand. The used grapefruit-sized drifters (n = 5) with minimal drogue (ρ ≈ 0.67 g/cm3) sent their positions at up to 4 m and 5 min spatiotemporal resolution via cellular GSM network for up to 48 days. This study indicates that river macroplastic debris transport 'hotlines' (positions where floating debris will likely pass by in a river) as well as retention-remobilisation cycles can be studied at fine scale. On their way through the river and gulf, covering between 9 and 696 km, drifters got stuck up to 23 times, spending 80% of their river lifetime in retention. Furthermore, it is outlined that the trajectories can be linked with environmental factors such as bathymetry and tides to more accurately model macroplastic debris behaviour in rivers. Finally, it is shown that trajectories crossing the riverine-marine continuum at the estuary can be accurately traced to support future investigations on the so far scarcely evidenced river mouth emissions of macroplastic debris.

Effects of Chemical Cleaning on the Ageing of Polyvinylidene Fluoride Microfiltration and Ultrafiltration Membranes Fouled with Organic and Inorganic Matter.

Herein, the effects of cleaning with sodium hydroxide and citric acid solutions as cleaning reagents on the changes in the properties of two hollow-fiber PVDF microfiltration (MF) and ultrafiltration (UF) membranes fouled with organic and inorganic matter were investigated. Accelerated membrane ageing was induced by use of high concentrations of tannic acid and iron oxide (Fe2O3) particles in the feed water; these conditions were kept with different membrane soaking times to observe temporal effects. It was found that tannic acid molecules adsorb onto the membrane surface that results in changes in surface characteristics, particularly surface functional groups that are responsible for enhancing membrane's hydrophilicity. Experimental results demonstrate that NaOH had a stronger effect on the tensile strength and surface chemistry of the fouled MF and UF membranes than citric acid. Prediction of lifetime by an exponential (decay) model confirmed that the UF membrane cleaned with NaOH would be aged within about 1.8 years and the MF membrane after about 5 years, at cleaning every 15 days, downtime 2 h per cleaning, when a 10% tensile strength decrease against the original membrane is allowed.

Unravelling capability of municipal wastewater treatment plant in Thailand for microplastics: Effects of seasonality on detection, fate and transport.

Many factors can affect microplastics (MPs) behaviors in aquatic environments. The effects of seasonal and meteorological conditions on MPs are not well understood. This study demonstrates the impacts of seasonality on the fate and transport, and the efficacy of MPs removal by a wastewater treatment plant. The fate and transport of MPs at a WWTP in Nonthaburi, Thailand were tracked during the dry and wet seasons of 2019-2020. Polypropylene (PP), polyethylene (PE), and toothpaste formulations were the most abundant MP types observed. Total detected MP quantities ranged between 76 and 192 particles L-1 during the dry season, and only 36-68 particles L-1 during the wet season, indicating runoff dilution effects. T-test analysis found a statistically significant difference between MP concentrations between the dry and wet seasons of 2019-2020. Spearman's correlation showed statistically strong negative relationships between MP concentrations versus wastewater flow, and MP concentrations versus precipitation; a positive correlation between MP abundance versus temperature in the treatment system was observed. During the dry seasons, MPs were mostly found in the aeration process, and were mostly rayon or polyester particles in the shape of fibers. Contrarily, in the wet seasons, MPs were detected in both the raw influent and aeration process, with PE, polyacrylate, and polyethylene terephthalate fragments dominating the make-up. MPs were also detected in the return activated sludge, thus calling for proper sludge age and drainage management. No MPs were detected in the plant's effluent during the wet season, suggesting that the plant had sufficient MPs removal capability during normal wet-season conditions. Overall, this study suggests that municipalities should focus on increasing MPs removal efficiency of wastewater treatment plants for dry seasons, while properly managing the water flows of combined sewage systems to prevent overflows that may inevitably become point-sources of MPs release into water bodies during wet seasons.

Fouling mitigation in an anaerobic membrane bioreactor via membrane surface modification with tannic acid and copper.

Anaerobic membrane bioreactors (AnMBRs) have recently received a great amount of attention as an alternative anaerobic treatment process due to their superior capability for sludge retention with high effluent quality. Nevertheless, membrane fouling in AnMBRs has been a major concern. In this study, the surfaces of polyvinylidene fluoride (PVDF) ultrafiltration membranes were modified with tannic acid (TA) and Cu(II) at various molar ratios of TA to Cu(II), including 3:1, 2:1, 1:1, 1:2, and 1:3. The hydrophilicity, morphology, chemical structure, elemental composition, and antibacterial properties of the unmodified and modified membranes were analyzed using water contact angle measurements, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR), SEM-energy dispersive X-ray spectrometry (SEM-EDX), and the clear zone method, respectively. The modified membrane with a TA-to-Cu(II) molar ratio of 1:3 had high hydrophilicity with certain antibacterial properties; therefore, it was selected to be further tested in an AnMBR along with an unmodified membrane. The chemical oxygen demand (COD) removal efficiencies of the unmodified membrane and modified membrane were 92.2 ± 3.6% and 91.8 ± 4.0%, respectively. The modified membrane had higher permeability after backwashing with less chemical cleaning (CC) than the unmodified membrane. Surface modification with TA and Cu(II) appeared to reduce irreversible fouling on the membranes.

Antibiotic resistant bacteria and genes in shrimp aquaculture water: Identification and removal by ferrate(VI).

Enclosed shrimp culturing ponds are breeding environments for the spread of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in the aquatic environment. This paper surveyed the presence of antibiotics, ARB, and ARGs in aquaculture waters and demonstrated their removal by ferrate (Fe(VI), FeO42-). Tetracyclines were the most prevalent antibiotics, followed by quinolones and ß-lactam. The bacterial resistance rates to three antibiotics were ordered as follows: amoxicillin (AMX) > oxytetracycline (OTC) > enrofloxacin (ENR). Proteobacteria, Verrucomicrobia, and Bacteroidetes were the predominant phyla, while sul1 and sul2 were the predominant ARGs. sul2 was positively correlated with Proteobacteria. Water quality parameters significantly influenced the dissemination of tetracycline resistance genes in aquacultures due to high organic waste accumulation. The removal efficiency of antibiotics by Fe(VI) depended on the structural moieties of antibiotics, with phenol-containing antibiotics more thoroughly oxidized (i.e., OTC) than amine-containing (ENR and AMX) antibiotics. Greater removal of antibiotics in aquaculture waters suggested that the constituents of farming water enhances the efficacy of antibiotics removal by Fe(VI). An acidic pH environment enhanced Fe(VI) inactivation of ARB over the circumneutral pH. The presented results are intended to improve aquaculture managing practices to minimize the antibiotic proliferation in aquaculture waters and the environment.

Effects of cathode coating materials and operational time on the mercury removal performance of electrokinetic remediation system for marine sediment.

Electrokinetic remediation (EK) is a promising in-situ technique for removing mercury (Hg) from contaminated sites; yet it demands long operational periods when conventional electrodes are used. Herein, we investigate the effectiveness of lab-prepared cathodes (Cu foam coated with reduced graphene oxide (rGO) or manganese oxide (MnO2)) to enhance Hg removal rates from sediment by EK. Although short term (2 h) Hg removal rates were insignificantly different (p-value > 0.05) when using the uncoated and coated Cu foam cathodes, long term (60 h) operations saw greater Hg removal by coated Cu foam cathodes over pure Cu foam, probably owing to the time required for Hg to migrate towards the electrodes from sediment. The highest Hg removal at the cathode was achieved when an αMnO2-coated Cu foam cathode was used with a strong-base anion exchange membrane (AEM) in the system. Using H3PO4, as a cathodic electrolyte resulted in a higher Hg removal efficiency than using NaCl and HCl electrolytes. Electromigration was found to be the dominant Hg-ions (e.g. HHgO2-, Hg2+) transport mechanism in the marine sediment during remediation. Overall, this research demonstrates that employing enhanced electrodes and AEMs can enhance Hg removal by EK processes in relatively shorter operating times than conventional EK processes.

Effects of microplastic accumulation on floc characteristics and fouling behavior in a membrane bioreactor.

Issues associated with accumulating microplastic (MP) in sewage sludge during wastewater treatment in a membrane bioreactor (MBR) system have not been studied in detail. Here, we investigated the microplastic's effects on floc characteristics, microbial community compositions, and fouling behavior inside sequencing-batch MBRs. MBRs were operated with 0, 7, 15, and 75 MPs/L of feed for 124-days. Results indicated that MP presence decreased sludge floc size, floc hydrophobicity, and extracellular polymeric substance (EPS) molecular size, and increased EPS concentration and the floc's negative zeta potential. These results were attributed to the facilitation of divalent cation (Ca2+ and Mg2+) uptake by MPs that weakened ion-bridging interactions within the sludge flocs. MPs accumulation slightly affected microbial structure and diversity. Relative abundances of dominant phyla, Actinobacteria, also decreased substantially. MPs also acted like a scouring material on membrane surfaces, inducing transformation of matured biofilm structures where protein content was substantially lower than nucleic acid content, in contrast to the control. Overall, MPs' negative effects on sludge flocs were counteracted by their scouring effect; consequently, SB-MBRs operated up to 4 months did not suffer from severe cake fouling, compared to control.

Large-scale pattern of resistance genes and bacterial community in the tap water along the middle and low reaches of the Yangtze River.

Antibiotic and metal resistance genes (ARGs and MRGs) in tap water are of great public health concern. However, very fewer studies focused on the relationship between resistance genes and opportunistic pathogens in tap water. In this study, the diversity and abundance of resistance genes and bacterial community from tap water at a large-scale along the middle and lower reaches of the Yangtze River were investigated. The total relative abundances of ARGs and MRGs were 2.95 × 10-3-1.22 × 10-1 and 1.93 × 10-3-1.20 × 10-1 copies/16S rRNA, respectively. The blaTEM and merP detected were major ARG and MRG subtypes, respectively. Mobile genetic elements (Intl1 and tnpA) showed significant correlations with the abundance of ARGs. Heavy metals also played a vital role in the co-selection of ARGs. Surprisingly, there were still eight opportunistic pathogens in tap water, among which Escherichia coli, Helicobacter pylori, Mycoplasma pneumoniae, and Porphyromonas gingivalis were the potential host of ARGs and MRGs. Escherichia coli had the highest abundance, while Bacillus anthracis had the highest detected frequency (100%), a widespread opportunistic pathogen in tap water.

Adsorptive performance of activated carbon reused from household drinking water filter for hexavalent chromium-contaminated water.

Powdered activated carbon blocks (PACBs) are waste products obtained from household drinking water purification systems. In this study, we demonstrate that they can be used as adsorbents for the cost-effective and environmentally benign removal of hexavalent chromium (Cr(VI)) from contaminated-water and rinse electroplating wastewater. To evaluate Cr(VI) sorption onto the PACB, studies on equilibrium, kinetics, and thermodynamics were performed using batch mode experiments. The experimental results indicated that Cr(VI) ions were efficiently adsorbed under acidic conditions (i.e., at initial pH below 3) and low initial Cr(VI) concentrations. The adsorptive behaviors of the PACB for Cr(VI) were well explained by the Langmuir isotherm, as well as pseudo-second-order kinetic models, suggesting that a Cr(VI) monolayer was adsorbed onto the PACB surface via chemisorption. The maximum adsorption capacity of Cr(VI) onto the PACB was determined to be 6.207 mg/g. The results of thermodynamic studies revealed that the adsorption process of Cr(VI) onto PACB was endothermic and non-spontaneous. Additionally, analysis of the PACB after Cr(VI) adsorption at an initial pH of 2 using scanning electron microscopy, energy dispersive spectrometry, Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) revealed that the interaction between the surface oxygenic functional groups on the PACB and Cr(VI) was primarily responsible for Cr(VI) sorption via surface complexation and electrostatic interactions. Based on the result of XPS analysis, the presence of trivalent chromium on the PACB surfaces indicated that some synergistic redox reactions involving Cr(VI) could have occurred during the sorption process. Although a commercially available powdered activated carbon outperformed the PACB adsorbent with respect to Cr(VI) removal from wastewater, complete Cr(VI) adsorption could be achieved using relatively large quantities of the PACB. These findings indicate that the PACB adsorbent could be used as a cheap and efficient material for the removal of Cr(VI) from wastewater.

IR microspectroscopic identification of microplastics in municipal wastewater treatment plants.

Municipal wastewater treatment plants (WWTPs) have been identified as a key source of microplastics (MPs) release into rivers and oceans. Varied extents of MPs pollution have been observed at different WWTPs with limited information in Thailand. This research aimed to study the occurrence of MPs in municipal WWTPs in Thailand by measuring MPs of three WWTPs which employ different treatment process. The WWTPs were selected to represent MP pollution from urbanized and suburbanized areas with different treatment set-ups, i.e., sequence batch reactor (WWTP-A), oxidation ditch (WWTP-B), and conventional activated sludge (WWTP-C). Water and sludge sampling was performed at the inlet and outlet of primary and secondary treatment units. The results indicate that the average MPs removal efficiency of the WWTPs was ca. 84%, with the aeration tank as the main removal unit by transferring MPs from the water phase to sludge. Primary treatment comprising of screening and grit chambers could not remove MPs effectively. Most of the MPs observed in the WWTPs were fibers (32-57%), mostly made of polyester, polyethylene, polyacrylate, and polypropylene. From these results, it is suggested to implement tertiary treatment options to improve MPs removal efficiency in WWTPs, and to apply post-treatment to the WWTPs' raw sludge to prevent the MPs' release into the environment when the sludge is applied to agricultural land.

Development of modified airlift reactor (MALR) for improving oxygen transfer: optimize design and operation condition using 'design of experiment' methodology.

Oxygen scarcity may significantly affect the process performance since it has low aqueous solubility and high demand by chemical and biological processes. The oxygen mass transfer is therefore necessary to enhance. This work aimed to develop the gas-liquid reactor, named Modified Airlift Reactor (MALR) for improving the oxygen transfer efficiency in terms of internal configurations and aeration parameters by equipping a vertical baffle for creating liquid circulation phenomena, and installing slanted baffles in the reactor riser to extend air-bubbles retention time and to improve their distributions. Since extremum conditions of the investigated factors may inefficient, optimum levels are required to identify. 2 k factorial and response surface design of Design of Experiment (DOE) methodology were applied to optimize these complex variables in terms of overall liquid mass transfer coefficient (K L a) of clean water. As a result, the main effective factors of MALR with their optimum value are amount of baffles (N b ∼ 3 baffles), baffle angle (α ∼ 50°), position of base area (Y r ∼ 10 cm), open space on baffle (A s ∼ 90 cm2), and gas flow (Qg). Increasing Qg resulted better K L a for the studied ranges (2-18 LPM). At the optimum condition, the improvement of MALR in terms of K L a coefficient was increased up to 97% and 28% compared to the regular bubble column and airlift reactor, respectively, at a certain gas flow without any extra energy. The correlation models of K L a coefficient with significant variables and power consumption were constructed for future estimation purposes.

Comparison between ferrihydrite adsorption and full-scale advanced drinking water treatment processes for controlling bacterial regrowth potential.

Bacterial regrowth in drinking water systems is a threat to public health. In this study, ferrihydrite (Fh) adsorption was compared with advanced drinking water treatment processes (ADWTP) during one and a half years of sampling to test the reduction in assimilable organic carbon (AOC) and bacterial regrowth potential (BRP). Dissolved organic matter (DOM) was removed by Fh through ligand exchange and electrostatic interaction. The DOM removal was higher below pH 6 due to protonation of Fh surfaces. The ADWTP exhibited higher removal rates of DOM than Fh and lower phosphate removal rates than Fh. Excitation-emission matrix (EEM) and size exclusion chromatography (SEC) revealed that Fh removed aromatic DOM larger than 1000 Da, while the biological activated carbon (BAC) of ADWTP could remove DOM smaller than 1000 Da. These differences of organic compositions resulted in the lowest AOC of BAC treated water, and the lowest BRP of Fh-treated water, indicating that it was the most biostable water. Phosphate addition experiments illustrated that phosphorus was the primary rate limiting nutrient, indicating that the higher phosphate removal of Fh made it possible to produce waters with lower BRP than ADWTP. Therefore, BRP is considered to be a better indicator of bacterial regrowth than AOC when phosphorus is a rate-limiting nutrient, as is the case with the Fh treatment.

Performance of integrated ferrate-polyaluminum chloride coagulation as a treatment technology for removing freshwater humic substances.

Ferrate-based technologies can play versatile roles in water treatment because of their potential for in situ production and because they do not form any harmful by-products. We compared the oxidative performance of Fe(VI) generated by an electrochemical process, with H2O2-UV irradiation (a standard oxidation process) for removing Suwannee River natural organic matter. It took only 5 min for Fe(VI) (Fe: 1.67 × 10-4 M) to reduce the fluorescence intensity of a humic-like fluorophore by 36% of the original value; in contrast, it took 120 min of irradiation using H2O2-UV ([OH] ∼ 1.8 × 10-13 M) to remove 68% of the original value. In addition to the short reaction time, ferrate can also form aggregates that can remove turbidity and adsorb organics and other contaminants present in water. Simultaneous addition of ferrate and polyaluminum chloride (PACl) to unfiltered natural water displayed the most efficient reduction of UVA254, primarily under acidic conditions. Ferrate pre-oxidation followed by PACl coagulation was the most effective process for reducing turbidity and chromaticity, because of the effects arising from the coagulation of ferrate that resulted in Fe(III)(s) species. Ferrate pre-oxidation generated low-molecular-weight UVA254-absorbing organics, whose dissolved organic matter (DOM) peak at 1250 Da was removed by PACl coagulation. Neither the initial pH nor the process order significantly affected the removal of organic carbon by the integrated ferrate-PACl process.

Properties of residual titanium dioxide nanoparticles after extended periods of mixing and settling in synthetic and natural waters.

Titanium dioxide nanoparticle (TiO2 NP) discharged into water bodies can affect ecosystems and human health adversely. We studied the properties of residual TiO2 NPs with and without gentle mixing (to simulate a natural environment more closely) and after settling for 12-h periods. Surface complexation, dynamic particle size changes, and TiO2 NP destabilization in synthetic and lake waters were investigated. The accumulation of inert ions (Na+ and Cl-) in the diffuse layer which was not discussed in other studies was supposed to be the main reason that aggregation occurred slowly and continuously. PO43- stabilized and destabilized TiO2 NPs at 10 mM and 100 mM, respectively. Destabilization occurred because high ionic strength overwhelmed increased negative charges of TiO2 NPs by complexation with PO43-. TiO2 NP destabilization was achieved in approximately 12 h in synthetic and lake waters, and is attributed to the slow diffusion of ions into aggregates. Despite the presence of moderately high concentrations of natural organic matter, which tends to stabilize TiO2 NPs, the addition of 20 mM PO43- destabilized the TiO2 NPs in lake water. Smaller aggregate sizes formed compared with those before destabilization, which indicates that stable residual TiO2 NPs could exist in aquatic environments after extended periods.

Analysis of adsorption processes of dissolved organic matter (DOM) on ferrihydrite using surrogate organic compounds.

Ferrihydrite (Fh) has been recently used in water treatment for removing dissolved organic matter (DOM), but its governing interactions with low-molecular weight DOM are largely unknown. This study aimed to elucidate the influence of chemical structure of DOM on the interactions between functional groups of DOM and Fh using various surrogates representing DOM in natural waters. We tested four surrogate compounds: L-glutamic acid, resorcinol, L-serine, and tannic acid, which represent the main chemical groups of carboxylic and hydroxyl groups; and the Suwannee River NOM (SRNOM) that represents the composition of DOM in natural aquatic systems. Batch adsorption experiments revealed that the DOM adsorption onto Fh was significantly influenced by the steric arrangements of -COOH and -OH functional groups. Both L-serine with α-carboxyl group and resorcinol with hydroxyl groups in meta-position were marginally removed by Fh, indicating that the adsorption of DOM on Fh was determined by their chemical structures and the relative positions of carboxylate and hydroxyl groups. The adsorption of L-glutamic acid was controlled by the pH-dependent ligand exchange of γ-carboxyl groups, which was similar to the SRNOM adsorption. In contrast, adsorption of tannic acid was not affected by pH, which can be explained by a two-step adsorption, namely, ligand exchange followed by multi-layer adsorption to the partitioning phase. The results of kinetic experiments demonstrated that adsorption of DOM by Fh was significant and rapid. The kinetic adsorption data can be expressed by the pseudo-second-order equation, indicating that the adsorption step might be the rate-limiting step.

Release of silver nanoparticles from fabrics during the course of sequential washing.

Increasing use of silver nanoparticles (AgNPs) in consumer products has raised concerns about the potential impacts of AgNPs on the environment. This study aimed to assess the potential release of AgNPs from textiles due to sequential washing. Different types of fabrics including cotton, polyester (PES), and cotton blended with PES (called TC) were coated with 4-5 nm AgNPs and used in the sequential washing experiments with Milli-Q water at neutral pH and with commercial detergent at alkaline pH. Similar experiments were also run-on consumer textile products washed with Milli-Q water. The percent Ag remaining on the products after washing was also investigated. The initial Ag contents ranged from 254 to 350 µg Ag/g of the product in lab-prepared fabrics and from 1.2 to 44 µg Ag/g of the product in consumer products. After 20 wash cycles, 48 to 72 % of Ag was lost from the prepared fabrics washed with Milli-Q water, while a greater loss of 84-94 % of Ag occurred after washing the prepared fabrics with commercial detergent. The Ag released during the washing process is present dominantly in particulate form. In the consumer products after 20 washes with Milli-Q water, the percent Ag remaining was found to be around 46 to 70 %. Statistical analysis of the Ag release rate between consumer products and lab-prepared fabrics in Milli-Q washing water by independent t test showed no significant difference after 20 washing cycles (p > 0.05).

Analysis of trihalomethane precursor removal from sub-tropical reservoir waters by a magnetic ion exchange resin using a combined method of chloride concentration variation and surrogate organic molecules.

In small reservoirs in tropical islands in Japan, the disinfection by-product formation potential is high due to elevated concentrations of dissolved organic matter (DOM) and bromide. We employed a combined method of variation of chloride concentrations and the use of DOM surrogates to investigate removal mechanisms of bromide and different fractions of DOM by chloride-based magnetic ion exchange (MIEX®) resin. The DOM in reservoir waters was fractionated by resins based on their hydrophobicity, and characterized by size-exclusion chromatography and fluorescence excitation-emission matrix spectrophotometry. The hydrophobic acid (HPO acid) fraction was found to be the largest contributor of the trihalomethane (THM) precursors, while hydrophilic acid (HPI acid) was the most reactive precursors of all the four THM species. Bromide and DOM with a molecular weight (MW) greater than 1kDa, representing HPO acid (MW 1-3kDa) and HPI acid (MW 1-2kDa), were effectively removed by MIEX® resin; however, DOM with a MW lower than 1kDa, representing HPI non-acid, was only moderately removed. The removal of THM precursors by MIEX® resin was interfered by high chloride concentrations, which was similar to the removal of glutamic acid (HPI acid surrogate) and bromide. However, elevated chloride concentrations had only a minor effect on tannic acid (HPO acid surrogate) removal, indicating that HPO acid fraction was removed by a combination of ion exchange and physical adsorption on MIEX® resin. Our study demonstrated that the combined use of DOM surrogates and elevated chloride concentrations is an effective method to estimate the removal mechanisms of various DOM fractions by MIEX® resin.

Simultaneous removal of dissolved organic matter and bromide from drinking water source by anion exchange resins for controlling disinfection by-products.

Anion exchange resins (AERs) with different properties were evaluated for their ability to remove dissolved organic matter (DOM) and bromide, and to reduce disinfection by-product (DBP) formation potentials of water collected from a eutrophic surface water source in Japan. DOM and bromide were simultaneously removed by all selected AERs in batch adsorption experiments. A polyacrylic magnetic ion exchange resin (MIEX®) showed faster dissolved organic carbon (DOC) removal than other AERs because it had the smallest resin bead size. Aromatic DOM fractions with molecular weight larger than 1600 Da and fluorescent organic fractions of fulvic acid- and humic acid-like compounds were efficiently removed by all AERs. Polystyrene AERs were more effective in bromide removal than polyacrylic AERs. This result implied that the properties of AERs, i.e. material and resin size, influenced not only DOM removal but also bromide removal efficiency. MIEX® showed significant chlorinated DBP removal because it had the highest DOC removal within 30 min, whereas polystyrene AERs efficiently removed brominated DBPs, especially brominated trihalomethane species. The results suggested that, depending on source water DOM and bromide concentration, selecting a suitable AER is a key factor in effective control of chlorinated and brominated DBPs in drinking water.