Exploring impacts of water-extractable organic matter on pre-ozonation followed by nanofiltration process: Insights from pH variations on DBPs formation

This study investigated the influence of pH (4-10) on the treatment of water-extractable organic matter (WEOM), and the associated disinfection by-products (DBPs) formation potential (FP), during the pre-ozonation/nanofiltration treatment process. At alkaline pH (9-10), a rapid decline in water flux (> 50 %) and higher membrane rejection was observed, as a consequence of the increased electrostatic repulsion forces between the membrane surface and organic species. Parallel factor analysis (PARAFAC) modeling and size exclusion chromatography (SEC) provides detailed insights into the WEOM compositional behavior at different pH levels. Ozonation at higher pH significantly reduced the apparent molecular weight (MW) of WEOM in the 4000-7000 Da range by transforming the large MW (humic-like) substances into small hydrophilic fractions. Fluorescence components C1 (humic-like) and C2 (fulvic-like) exhibited a predominant increase/decrease in concentration for all pH conditions during pre-ozonation and nanofiltration treatment process, however, the C3 (protein-like) component was found highly associated with the reversible and irreversible membrane foulants. The ratio C1/C2 provided a strong correlation with the formation of total trihalomethanes (THMs) (R² = 0.9277) and total haloacetic acids (HAAs) (R² = 0.5796). The formation potential of THMs increased, and HAAs decreased, with the increase of feed water pH. Ozonation markedly reduced the formation of THMs by up to 40 % at higher pH levels, but increased the formation of brominated-HAAs by shifting the formation potential of DBPs towards brominated precursors.

Sulfonated graphene oxide-based pervaporation membranes inspired by a tortuous brick and mortar structure for enhanced resilience against silica scaling and organic fouling

A novel tortuous brick-and-mortar structure utilizing intercalation of polyvinyl alcohol (PVA) on sulfonated graphene oxide (SGO) membranes was specifically tailored for brine treatment by pervaporation to ensure excessive resistance to silica scaling and organic fouling, as well as ultrafast water transport without compromising salt rejection. The synthesized SGO membrane showed a smoother surface morphology, improved zeta potential, and a higher hydration capacity than the graphene oxide (GO) membrane. Further intercalation of PVA through glutaraldehyde (GA) crosslinking, confirmed by Fourier transform infrared spectroscopy and X-ray diffraction analysis, conferred increased cohesiveness, and the SGO-PVA-GA membrane was therefore able to withstand ultrasonication tests without any erosion of the coating layer. According to a pervaporative desalination test, the SGO-PVA-GA membrane exhibited 62 kg m^-2 h^-1 of permeate flux, with an extraordinary salt rejection of 99.99% for a 10 wt% NaCl feed solution at 65 °C. The 72 h organic fouling, silica scaling, and combined fouling and scaling tests proved that the SGO-PVA-GA membrane sustains a stable flux with less scaling and fouling than the GO-PVA-GA membrane, attributable to dense surface negative charges and great hydration capacities caused by sulfonic acid. Thus, the SGO-PVA-GA membrane offers superlative advantages for long-term brine treatment by pervaporation, related to its ability to withstand silica scaling and organic fouling.

Aqueous monomethylmercury degradation using nanoscale zero-valent iron through oxidative demethylation and reductive isolation

This paper proposes a Fenton-like reaction activated by nanoscale zero-valent iron (nZVI) for aqueous monomethylmercury (MMHg) decomposition. Reacting 10 μg L^-1 MMHg with 280 mg L^-1 nZVI removed 70% of the aqueous MMHg within 1 min, and its main product was aqueous Hg(II). Within 1 - 5 min, the aqueous Hg(II) decreased while the aqueous, solid, and gas-phase Hg(0) increased with 92% MMHg removal. Then, a secondary Hg(II) reduction to solid Hg(0) was prevalent within 30 - 60 min, with 98% MMHg removal. Diverse-shaped magnetite crystals were observed on the surface of nZVI in 2 h, suggesting that Fe(II) oxidation on magnetite can be a source of electrons for secondary Hg(II) reduction. When FeCl₂ and H₂O₂ were added to the MMHg solution without nZVI, 99% of the MMHg changed to Hg(II) within 1 min. The reactive oxygen species (ROS) produced by the Fenton-like reaction accounted for the rapid demethylation but not for the further reduction of Hg(II) to Hg(0). The results suggest a three-step pathway of MMHg decomposition by nZVI: (1) rapid MMHg demethylation by ROS; (2) rapid Hg(II) reduction by Fe(0); and (3) slow Hg(II) reduction by magnetite on the nZVI surface.

Applying the diffusive gradient in thin films method to assess soil mercury bioavailability to the earthworm Eisenia fetida

This study assessed the critical soil characteristics affecting mercury (Hg) bioavailability to the earthworm Eisenia fetida using the diffusive gradient in thin films (DGT) method. The soil samples were collected from a tributary of the Hyeongsan River contaminated with industrial waste and landfill leachates called Gumu Creek. The Hg concentration in the soil had a range of 0.33-170 μg g^-1 (average 33 ± 56 μg g^-1), and the Hg concentration of earthworms incubated in the soils was 0.83-11 μg g^-1 (average 2.9 ± 3.2 μg g^-1). When correlation analysis was used to detect the key variables among the soil properties related to Hg accumulation in the soils, earthworms, and resins, the water-holding capacity, which is covaried with the organic matter content, was determined to be a primary factor in increasing Hg accumulation in the soils, earthworms, and resins. However, the experimentally determined earthworm bioaccumulation factor and the DGT accumulation factor were negatively affected by the water-holding capacity. Therefore, the water-holding capacity played a dual role in the Gumu Creek deposits: increasing the soil Hg concentration and decreasing Hg bioavailability and leachability. Further, the DGT-Hg flux was positively correlated with the Hg concentration in earthworms (r = 0.93). Although the earthworm accumulation of Hg is not processed by passive diffusion, this study proves that the DGT method is promising for predicting soil Hg bioavailability to the earthworm E. fetida, and the water-holding capacity simultaneously regulates Hg availability to the DGT and the earthworms.

Ultrasound in the selective screening of developmental dysplasia of the hip

INTRODUCTION

Developmental dysplasia of the hip (DDH) can result in chronic pain, gait abnormalities and degenerative arthritis. Infants with a family history, Breech delivery or unstable/"clicking" of the hip on examination are at higher risk. The goal is to detect cases early enough for normal hip development and function by the end of adolescence, but clinical examination alone is ineffective.

MATERIALS AND METHODS

All infants born at the West Middlesex University Hospital, Isle-worth, U.K., between 3/3/2005 and 21/10/2006 underwent prospective clinical screening to reveal risk factors of unstable hip on examination, family history of DDH and Breech delivery. Infants with risk factors underwent static and dynamic ultrasound of the hips (Harke's method with Terjesen measurements), performed by a consultant radiologist or sonographer. The infant was then examined by an Orthopaedic Surgeon who was blinded to the ultrasound findings until after creating a management plan.

RESULTS

5772 infants were born during the study period. 200 (3.5%) at-risk infants were identified, resulting in 400 hip ultrasounds. Following review of ultrasound findings, the majority of cases (163/200, 81.5%) lead to no change in management. Change in timing or type of clinical follow up occurred in 31 cases with normal ultrasounds and 20 cases with abnormal (immature hip) ultrasounds. Dysplasia was demonstrated in 6 infants (3%) on ultrasound, who were treated with Parvlik Harness. Of these, only 5 were detected on examination. Therefore, the ultrasound findings lead to 1 intervention with Parvlik Harness which would have otherwise gone undiagnosed from clinical examination.

CONCLUSION

Whereas type and timing of follow up was adjusted in 18.5% of the at-risk infants, targeted screening of at-risk with ultrasound lead to only one intervention. This encourages discussion on the resource implication and viability of ultrasound screening, as only one from two hundred lead to an intervention.