Removal Of Microspheres Research Articles

Removal of Cryptosporidium and polystyrene microspheres from swimming pool water with sand, cartridge, and precoat filters

Cryptosporidium has caused the majority of waterborne disease outbreaks in treated recreational water venues in the USA for many years running. This research project evaluated some common US swimming pool filters for removing Cryptosporidium oocysts, 5-µm diameter polystyrene microspheres, and 1-µm diameter polystyrene microspheres. A 946 L hot tub with interchangeable sand, cartridge, and precoat filters was used at room temperature for this research. Simulated pool water for each experiment was created from Charlotte, NC (USA) tap water supplemented with alkalinity, hardness, chlorine, and a mixture of artificial sweat and urine. Precoat (i.e., diatomaceous earth and perlite) filters demonstrated pathogen removal efficiencies of 2.3 to 4.4 log (or 99.4-99.996%). However, sand and cartridge filters had average Cryptosporidium removals of 0.19 log (36%) or less. The combined low filter removal efficiencies of sand and cartridge filters along with the chlorine-resistant properties of Cryptosporidium oocysts could indicate a regulatory gap warranting further attention and having significant implications on the protection of public health in recreational water facilities. The 5-µm microspheres were a good surrogate for Cryptosporidium oocysts in this study and hold promise for use in future research projects, field trials, and/or product testing on swimming pool filters.

Ni Inverse Opals for Water Electrolysis in an Alkaline Electrolyte

A vertical electrophoretic deposition technique was employed to prepare polystyrene (PS) colloidal crystals with negligible crystallographic defects. The colloidal crystals were plated with Ni, followed by selective removal of PS microspheres to fabricate inverse opals. With adjustments in relevant processing parameters, we were able to obtain inverse opals in multiple layers with excellent surface uniformities. The inverse opals were used as the electrode material for water electrolysis. Results from current–potential polarizations in 1 M KOH aqueous solution indicated that the catalytic abilities for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) increased with the layers of inverse opals. Estimation of the effective current densities determined that the entire area of the inverse opals was available for electrochemical reactions. In galvanostatic measurements for both OER and HER, the inverse opals demonstrated stable voltage profiles without notable degradations for 120 h. Compared with a planar Ni plate, the inverse opals exhibited a significantly reduced overpotential for the water electrolysis.

Influence of organic carbon loading, sediment associated metal oxide content and sediment grain size distributions upon Cryptosporidium parvum removal during riverbank filtration operations, Sonoma County, CA

This study assessed the efficacy for removing Cryptosporidium parvum oocysts of poorly sorted, Fe- and Al-rich, subsurface sediments collected from 0.9 to 4.9 and 1.7–13.9 m below land surface at an operating riverbank filtration (RBF) site (Russian River, Sonoma County, CA). Both formaldehyde-killed oocysts and oocyst-sized (3 μm) microspheres were employed in sediment-packed flow-through and static columns. The degree of surface coverage of metal oxides on sediment grain surfaces correlated strongly with the degrees of oocyst and microsphere removals. In contrast, average grain size ( D 50) was not a good indicator of either microsphere or oocyst removal, suggesting that the primary mechanism of immobilization within these sediments is sorptive filtration rather than physical straining. A low specific UV absorbance (SUVA) for organic matter isolated from the Russian River, suggested that the modest concentration of the SUVA component (0.8 mg L −1) of the 2.2 mg L −1 dissolved organic carbon (DOC) is relatively unreactive. Nevertheless, an amendment of 2.2 mg L −1 of isolated river DOC to column sediments resulted in up to a 35.7% decrease in sorption of oocysts and (or) oocyst-sized microspheres. Amendments (3.2 μM) of the anionic surfactant, sodium dodecyl benzene sulfonate (SDBS) also caused substantive decreases (up to 31.9 times) in colloid filtration. Although the grain-surface metal oxides were found to have a high colloid-removal capacity, our study suggested that any major changes within the watershed that would result in long-term alterations in either the quantity and (or) the character of the river's DOC could alter the effectiveness of pathogen removal during RBF operations.

Chitosan and metal salt coagulant impacts on Cryptosporidium and microsphere removal by filtration

Maintenance of appropriate chemical pretreatment is a critical component of ensuring proper filtration performance. Pilot-scale in-line filtration studies were performed to investigate the relative impacts of chitosan, alum, and FeCl 3 coagulation on the removal of Cryptosporidium parvum oocysts and oocyst-sized polystyrene microspheres by granular media filtration. Similar removals of oocysts and microspheres were achieved when optimal coagulant doses were utilized. Sub-optimal alum and FeCl 3 coagulation resulted in a deterioration filter effluent turbidity (0.2–0.3 NTU) and total particle counts (30–100 total particles ≥2 μm/mL) that were accompanied by reduced (by ∼2–3-log) median oocyst and microsphere removals by filtration. At all doses investigated, chitosan coagulation resulted in excellent turbidity and particle reductions by filtration. Nonetheless, chitosan coagulation at doses of 0.1, 0.5, and 1.0 mg/L did not result in appreciable improvements in C. parvum oocyst removal relative to complete coagulation failure (median oocyst removals were <∼1-log). As well, oocyst-sized polystyrene microspheres appear to be reasonable indicators of C. parvum oocyst removal by in-line filtration preceded by alum and FeCl 3 coagulation, but not chitosan coagulation.

Laser-induced defect insertion in DNA-linked 2D colloidal crystal array

Insertion of vacancies at predetermined sites within the lattice of colloidal crystals is a prerequisite in order to realize high-quality, opaline-based photonic devices. In this contribution, we demonstrate a novel methodology to afford controlled insertion of vacancies within two-dimensional (2D) opaline arrays. These 2D opaline arrays have been substrate-anchored with the help of DNA hybridization. This provides a heat-sensitive ‘adhesive’ between substrate and microspheres within a surrounding aqueous medium that enables tuning the hybridization strength of DNA linker as well as a mechanism to facilitate the removal of unbound microspheres. Focusing a laser beam onto the substrate/microsphere interface induces a localized heating event that detaches the irradiated microspheres, leaving behind vacancies. By repeating this process, line vacancies were successfully obtained. The effects of salt concentration, laser power, light-absorbing dyes, DNA length and refractive-index mismatch were investigated and found to correlate with heat-induced microsphere release.

Superhydrophobic Films of Electrospun Fibers with Multiple-Scale Surface Morphology

Superhydrophobic nanofiber films were created from electrospun nanofibers with undulated surfaces at multiple scales in micrometers and nanometers. The electrospun nanofibers were produced out of aqueous solutions which contained water-soluble polymers and different colloids: monodisperse silica or polystyrene microspheres for larger particles and monodisperse silica nanoparticles for smaller particles. Various types of fibrous films were produced depending on the properties of the dispersing medium, the effects of additives, and the compositions of the bidisperse colloids. When polystyrene microspheres were used as sacrificial templates, macropores were left behind in the nanofibers during the removal of polystyrene microspheres by calcination. The nonwoven films of electrospun nanofibers, which were decorated with silica microspheres or macropores, could be continuously produced with considerable ease under a relatively wide range of operating conditions. The surface properties of the films were characterized by contact angle measurement and an X-ray photoelectron spectrometer. Through the surface modification of the electrospun nanofibers with fluorinated silane coupling agents, superhydrophobic surfaces with low sliding angles were successfully prepared.

Inside Front Cover: Curling Colloidal Photonic Crystals (Adv. Mater. 18/2006)

AbstractThe inside cover features a schematic illustration (right) and three representative electron microscopy images (left) of photonic‐crystal strips with controlled curvature. As reported by Kitaev and co‐workers on p. 2481, the curvature is induced by infiltration of polymer opal with alkoxide precursors to attain an overlayer that experiences controllable shrinkage upon hydrolysis. Both continuity and high structural order are perfectly preserved throughout precursor infiltration and polymer microsphere removal.

Comparison of Conventional and Biological Filter Performance for Cryptosporidium and microsphere removal

Previous studies involving filter runs seeded with oocysts have not shown significantly poorer removals during ripening. However, these studies typically did not seed oocysts throughout the preceding filter run, which is necessary for representative numbers of oocysts to be present in the backwash‐remnant water. In this study, four trials consisting of three to five consecutive filter runs were continuously seeded with oocysts and/or microsphere surrogates so that they would appear in the backwash‐remnant water of the successive run. Compared with concentrations in the postripening period, the concentrations of oocysts and microspheres found in the effluent under the influence of backwash‐remnant particles ranged from no higher to more than an order of magnitude higher, depending on filter type. Significant carryover of different‐colored microspheres was not observed in consecutive filter runs following the filter‐ripening period. During this study, conventional and biological filters showed similar average postripening oocyst and microsphere removals (roughly 1.7 and 2.1 log, respectively), but the biological filters exhibited significantly lower concentrations of oocysts and microspheres in the initial effluent samples containing backwash‐remnant particles left in the filter at the conclusion of the backwashing procedure.

Physicochemical aspects of Cryptosporidium surrogate removal in carbon block filtration

As the final barrier before consumption, properly designed and operated point‐of‐use water treatment systems like carbon block filters are useful in protecting public health. This article evaluates the relative importance of adsorptive filtration, straining filtration, and cake filtration in the removal of nominal test dust (NTD) and latex microspheres, the latter being a Cryptosporidium oocyst surrogate, by carbon block filtration. Three different carbon blocks were tested, and only one of these was able to pass a National Sanitation Foundation (NSF) certification test. Surface charge characteristics can explain why two carbon blocks failed the test; however, they cannot explain why one carbon block passed the test. Scanning electron microscopy and energy dispersive X‐ray spectroscopy results together with the use of particle size distributions confirmed a lack of NTD penetration into the successful carbon block and suggest that cake filtration was the dominant NTD removal mechanism in this carbon block. Particle size analysis revealed that D15appears to be one of the determining factors in the passing the NSF certification test.

Microspheres as Surrogates for Cryptosporidium Filtration

Pilot‐scale studies were conducted to determine if polystyrene microspheres are reasonable surrogates for Cryptosporidium parvum removal by filtration. Previously reported data from a conventional pilot plant using a high coagulant dose optimized for combined total organic carbon and particle removal were contrasted with data from a pilot‐scale, in‐line filtration plant using a low coagulant dose optimized for particle removal. The removal of oocysts and microspheres was investigated during optimal operation as well as periods of process challenge and ranged from 0.5 log to &gt;5 logs. When data over a wide range of operating conditions (and oocyst and microsphere removals) were available, approximately linear relationships were discerned (the coefficient of determination [R2] ranged from 0.74 to 0.96). Although the exact relationship between oocyst and microsphere removals by filtration was somewhat site‐specific, it was demonstrated that oocyst‐sized microspheres are a useful tool during filtration‐optimization studies and performance assessments.

Cryptosporidium and microsphere removal during late in‐cycle filtration

Pilot‐scale studies were performed to evaluate Cryptosporidium parvum oocyst removal by a dual‐media filter during optimized, end‐of‐run, and breakthrough operating conditions. Oocyst‐sized polystyrene microspheres were also evaluated as surrogates for C. parvum removal by filtration. At optimal conditions, the pilot‐scale filter consistently achieved ~5‐log removal of C. parvum and microspheres. During end‐of‐run operation when filter effluent turbidity levels were &lt;0.1 ntu, median oocyst removals deteriorated to ~3 log. During early (0.1–0.3 ntu) and late (&gt;0.3 ntu) breakthrough, filtration oocyst removals deteriorated to ~2.1 and ~1.4 log, respectively. Microsphere removals by filtration were similar to oocyst removals during both stable and challenged operating periods, suggesting that microspheres are useful surrogates for investigating C. parvum removal.

Double-labelling technique in the evaluation of nasal mucoadhesion of disodium cromoglycate microspheres

99mTc-labelled disodium cromoglycate particles and 111In-labelled microspheres of disodium cromoglycate and polyacrylic acid were administered simultaneously to the nasal cavities of four healthy volunteers. The initial deposition patterns of the inhaled powder mixture as well as the drug removal due to the mucociliary clearance were monitored by a gamma camera. The double-labelling technique enabled in vivo comparison of simultaneously administered plain drug particles and polyacrylic acid microspheres of disodium cromoglycate. After administration, both the plain drug particles and the microspheres distributed equally effectively. On average, 27% of the 99mTc-labelled plain drug particles and 50% of the 111In-labelled microspheres were retained at the initial site of deposition 30 min after inhalation. Thus, the removal of microspheres from the nasal cavities was clearly impeded by polyacrylic acid.