Simulated Drinking Water Research Articles

Synthesis of hybrid silica materials with tunable pore structures and morphology and their application for heavy metal removal from drinking water

Porous silica materials S8, S12, S16, and SBA with controllable pore structures and morphology were synthesized by varying the type or alkyl chain length of the surfactant. Diverse amino-functionalized organic–inorganic hybrid porous materials were then prepared by post-grafting. Depending on the relation between the pore diameter of the porous silica materials and the size and content of the moiety to be grafted, the functionalized materials exhibited varying degrees of decline of structure properties, i.e. regular arrangement of pores, specific surface area, pore size, and pore volume. The hybrid silica materials have been employed as heavy metal ions adsorbents from simulated drinking water at room temperature. The results indicated that the diverse pore structures and different amino group densities influence the heavy metal ions adsorption of functionalized silicas significantly. The best adsorbent was found to be monoamino-functionalized silica S16-1N, which could effectively remove heavy metal Cd(II), Pb(II), Fe(III), as well as Mn(II). The good performance can be attributed to the accessibility of effective amino groups in the pores, as well as the suitable pore structure with high specific surface area of 728 m 2/g and total pore volume of 0.34 cm 3/g.

Experimental and model comparisons of H2O2 assisted UV photodegradation of Microcystin-LR in simulated drinking water

The degradation of Microcystin-LR (MC-LR) in water by hydrogen peroxide assisted ultraviolet (UV/H2O2) process was investigated in this paper. The UV/H2O2 process appeared to be effective in removal of the MC-LR. MC-LR decomposition was primarily ascribed to production of strong and nonselective oxidant-hydroxyl radicals within the system. The intensity of UV radiation, initial concentration of MC-LR, MC-LR purity, dosages of H2O2, the initial solution pH, and anions present in water, to some extent, influenced the degradation rate of MC-LR. A modified pseudo-first-order kinetic model was developed to predict the removal efficiency under different experimental conditions.

Arsenic (V) removal from groundwater by GE-HL nanofiltration membrane: effects of arsenic concentration, pH, and co-existing ions

A laboratory-scale investigation was performed to study arsenic (As (V)) removal by negatively charged GE-HL nanofiltration (NF) membrane in simulated drinking water. Effects of As (V) concentration (0–200 μg·L−1), pH, and co-ions and counter-ions were investigated. The NF membrane presented good stability, and the rejection rates exceeded 90%. The rejection rates of As (V) decreased with the increase of As (V) concentration, while it increased with the increase of pH (reached 96% at pH 6.75). Moreover, a negative relationship was observed between the co-existing ions of Cl−, Na+, SO42−, and Ca2+ and the removal of As (V), in which bivalent ions presented more significant effects than monovalent ions.

Transformation of Organophosphorus Pesticides in the Presence of Aqueous Chlorine: Kinetics, Pathways, and Structure−Activity Relationships

The fate of organophosphorus (OP) pesticides in the presence of aqueous chlorine was investigated under simulated drinking water treatment conditions. Intrinsic rate coefficients were found for the reaction of hypochlorous acid (k(HOCl,OP)) and hypochlorite ion (k(OCl,OP) for several OP pesticides. The reaction of hypochlorous acid (HOCl) with each OP pesticide was relatively rapid near neutral pH, k(HOCl,OP) = 0.86 - 3.56 x 10(6) M(-1)h(-1). HOCI reacts at the thiophosphate (P = S) moiety of the OP pesticide resulting in the formation of the corresponding oxon (P=0), which is more toxic than the parent pesticide. Hypochlorite ion (OCl-) was found not to oxidize OP pesticides but act like a nucleophile accelerating hydrolysis, k(OCl,OP) = 37.3-15910 M(-1)h(-1). Both the k(HOCl,OP) and the k(OCl,OP) were found to correlate well with molecular descriptors within each subgroup of the OP pesticide class. A model was developed to predict the transformation of OP pesticides in the presence of aqueous chlorine. With hydrolysis rate coefficients, the transformation of OP pesticides under drinking water treatment conditions was found to be adequately predicted. The structure-activity relationships and model developed here could be used by risk assessors to determine exposure to OP pesticides and their transformation products in potable water.

Impact of biofilms in simulated drinking water and urban heat supply systems

Biofouling and biocorrosion were studied in drinking water and heating water systems by forming biofilms on steel and on polymethylmetacrylate. In the drinking water system, biofilm development was more significant on corroded surfaces, suggesting that in these conditions they were largely protected from disinfection, probably because of sheltering and chlorine demand by corrosion products. In the urban heat supply system, results suggest a higher biofilm activity at lower pH. Sulphate-reducing bacteria were detected in the urban heating biofilms, but little corrosion was observed on steel coupons. Results indicate that surface and bulk medium properties, as well as bacterial diversity are determinant parameters when studying biofouling and biocorrosion.

Solar radiation disinfection of drinking water at temperate latitudes: Inactivation rates for an optimised reactor configuration

Solar radiation-driven inactivation of bacteria, virus and protozoan pathogen models was quantified in simulated drinking water at a temperate latitude (34°S). The water was seeded with Enterococcus faecalis, Clostridium sporogenes spores, and P22 bacteriophage, each at ca 1 × 10 5 m L −1, and exposed to natural sunlight in 30-L reaction vessels. Water temperature ranged from 17 to 39 °C during the experiments lasting up to 6 h. Dark controls showed little inactivation and so it was concluded that the inactivation observed was primarily driven by non-thermal processes. The optimised reactor design achieved S 90 values (cumulative exposure required for 90% reduction) for the test microorganisms in the range 0.63–1.82 MJ m −2 of Global Solar Exposure (GSX) without the need for TiO 2 as a catalyst. High turbidity (840–920 NTU) only reduced the S 90 value by <40%. Further, when all S 90 means were compared this decrease was not statistically significant (prob. > 0.05). However, inactivation was significantly reduced for E. faecalis and P22 when the transmittance of UV wavelengths was attenuated by water with high colour (140 PtCo units) or a suboptimally transparent reactor lid (prob. < 0.05). S 90 values were consistent with those measured by other researchers ( ca 1–10 MJ m −2) for a range of waters and microorganisms. Although temperatures required for SODIS type pasteurization were not produced, non-thermal inactivation alone appeared to offer a viable means for reliably disinfecting low colour source waters by greater than 4 orders of magnitude on sunny days at 34°S latitude.

Oxidation of selected organophosphate pesticides during chlorination of simulated drinking water

Ten organophosphate (OP) pesticides: phorate, disulfoton, terbufos, methidathion, bensulide, chlorethoxyfos, phosmet, methyl parathion, phostebupirim, and temephos were evaluated for their potential to undergo oxidation to their respective oxons and/or other oxidation analogues in laboratory water. Samples were collected at time intervals up to 72 h of chlorination and analyzed by both gas chromatography–mass selective detection (GC–MSD) and liquid chromatography–tandem mass spectrometry (LC–MS/MS). The results show that methidathion and methyl parathion were stable in unchlorinated water, while all other OP pesticides were not stable over the 72 h exposure period. In chlorinated water, phorate and disulfoton formed stable sulfone oxons. Temephos formed stable dioxon sulfoxide and dioxon sulfone. Methidathion, bensulide, chlorethyoxyfos, methyl parathion, and phostebupirim formed stable oxons over the 72 h exposure period. Terbufos, phorate, disulfoton and temephos oxon sulfoxides; temephos sulfoxide; and phosmet oxon were initially formed but were not detected after 24 h. The data illustrate that organothiophosphate pesticides may form oxons and/or other oxidation analogues during chlorination in water treatment plants, which are persistent for at least 72 h.

Book reviewDr Space: The Life of Wernher von Braun, B. Ward, Naval Institute Press (2005), (328pp., $29.95), ISBN: 1-59114-926-6

This study characterized the fate of nano-TiO2 in both powder (TiO2(P)) and suspension (TiO2(S)) forms in simulated drinking water treatments. Nano-TiO2 solutions of 0.1, 1.0, and 10 mg/L were prepared with deionized water and raw waters from the Changxing and Fengshan Water Treatment Plants in Taiwan to assess the effects of water matrices on nano-TiO2 behavior during water treatment. After the laboratory simulated water treatment, including pre-chlorination, coagulation, sedimentation, filtration and post-chlorination, the residual Ti concentration ranged from 2.7 to 47.4% in different treatment units and overall removal efficiency was between 52.6% and 97.3% in all cases except for nano-TiO2 at concentration of 0.1 mg/L. Overall removal efficiency for the TiO2 at 10 mg/L concentration ranged from 9.3 to 53.5%. Sedimentation (after coagulation) and filtration were the most important processes for removing nano-TiO2 due in part to particle agglomeration, which was confirmed by size distribution and zeta potential measurements. The size of nano-TiO2 increased from 21–36 nm to 4490 nm in the supernatant after sedimentation, and subsequent filtration treatment further removed all agglomerates at size > 1 μm. Zeta potential revealed interactions between nano-TiO2 particles and anionic functional groups or negatively-charged natural organic matters, leading to a decrease in surface charge. After sedimentation and filtration, the zeta potential of supernatants and filtrates were close to zero, meaning the absence of nanoparticles. The highest Ti removal after sedimentation occurred in Fengshan raw water due to higher ionic strength and coagulant dosage applied. On the other hand, the surfactant additives in TiO2(S) promoted dispersion of nano-TiO2 particles, which in turn led to lower particle removal. SEM images of nanoparticles after chlorination or coagulation revealed the coverage of nano-TiO2 particles by viscous substances and formation of colloidal structures.

Perchlorate in water via US Environmental Protection Agency Method 331: Determination of method uncertainties, lowest concentration minimum reporting levels, and Hubaux-Vos detection limits in reagent water and simulated drinking water

US Environmental Protection Agency (EPA) Method 331 determines perchlorate in drinking water using non-suppressed ion chromatography with tandem mass spectrometry. This study reports the results of calibration and recovery studies in reagent water, as well as of a recovery study in simulated drinking water (i.e., total dissolved solids are 500 mg/mL each of chloride, sulfate, and bicarbonate). The perchlorate concentrations in the study ranged from 0.05 to 64 ng/mL. At 95% confidence, the Hubaux-Vos detection limit (H-V DL) was 0.04 ng/mL for the calibration study and the simulated-drinking-water recovery study, and 0.03 ng/mL for the reagent-water recovery study. The lowest concentration minimum reporting level was 0.03 ng/mL for reagent water and 0.07 ng/mL for simulated drinking water, again at 95% confidence.

Removal of neutral chloroacetamide herbicide degradates during simulated unit processes for drinking water treatment

Four chloroacetamide herbicides and 20 neutral chloroacetamide derivatives (known to occur as their environmental degradates) were subjected to simulated drinking water treatment (coagulation, oxidation and adsorption). Coagulation with alum and ferric chloride, at doses for optimum turbidity removal, provided little to no (<10%) removal of parent herbicides or neutral degradates. Chlorination with 6 mg/L applied free chlorine for 6 h was able to achieve 100% removal of those degradates lacking an acetanilide substituent; compounds possessing this functional group exhibited low (0–16%) removal efficiencies. Products were generally not identified, except in the case of dimethenamid and its deschloro degradate, both of which formed a single ring-chlorination product on their ready reaction (84% and 96% removal, respectively) with aqueous chlorine species. Treatment with ozone at an applied dose of 3 mg/L for 30 min proved effective (60–100%) at transforming all of the compounds under investigation to unidentified products. The parent herbicides and neutral degradates underwent adsorption by powdered activated carbon (PAC). Adsorption capacities (Freundlich K constants) correlated with K ow values.

Removal of suspended clay from water using transmembrane pressure pulsed microfiltration

Transmembrane pressure pulsing (TPP) uses the frequent and periodic reversal of the transmembrane pressure to reduce flux resistances due to membrane fouling. This study examined the effect of TPP on the microfiltration of simulated drinking water (hydrated aluminum silicate solution). Solutions of kaolin clay (0.1–4.0 μm particles, at an approximate concentration of 500 mg l −1 and a turbidity of 402±17 NTU, 0.5 mM CaCl, 2.0 mM NaHCO 3, pH 7.5–7.8) were microfiltered with polyethersulfone (PES) 0.16 μm microfiltration membranes at an operating pressure of 30 kPa. Crossflow shear rates were varied between 165 and 1490 s −1. Pulse frequency was varied between 0.3×10 −2 and 2 Hz, and pulse amplitude was varied between −3 and −16.5 kPa. It was found that the crossflow shear rates did not significantly effect the non-pulsed permeate flux. An optimum pulse amplitude of about 10 kPa was necessary to maximize the permeate flux for pulse frequencies between 0.3×10 −2 and 2.0 Hz. To insure a reduced solute flux, pulse frequencies less than 0.1 Hz were required. These results indicate that TPP can significantly reduce membrane fouling by inorganic particulate materials that are potentially important constituents of natural waters without negatively impacting the rejection of sub-micron particles due to interactions with material accumulated on the membrane.

Attachment and fate of carbon fines in simulated drinking water distribution system biofilms

Concern over the release of colonized carbon fines from filters has increased with the interest in operating granular activated carbon filters optimized for biological activity. These fines may transport bacteria to the distribution system and become entrained in biofilms. The capture and release of carbon fines of two size ranges (1.2–50 μm and 1.2–8 μm) in biofilms and their impact on the biomass was studied using a bench-scale simulated drinking water system. Size of the particles was important, with large carbon fines (1.2–50 μm) remaining in the biofilms while the small ones (1.2–8 μm) were entrained and then detached. The presence of carbon fines did not influence the number or activity of bacteria present in the biofilms. Disinfection assays on biofilms containing particles were performed with chlorine (0.5 mg/L) and monochloramine (1 mg/L). Even in the presence of substantial numbers of carbon fines, the effect of the disinfectants on the biofilms as determined by destructive analysis and direct microscopic observation was limited. Carbon fines were released from the biofilms during disinfection.