Characterization of a support-free carbon nanotube-microporous membrane for water and wastewater filtration

© 2018 Elsevier B.V. Nonwoven carbon nanotube (CNT) laminates were characterized as support-free membranes for water filtration in terms of structural morphology, water permeability, selectivity and chemical resistance. Nominal pore rating (12–23 nm) estimated by rejection of globular proteins and fluorescence beads fall within the selectivity range of tight ultrafiltration (UF) membranes applied for wastewater treatment. The membranes displayed high permeability (120–400 LMH/bar). High selectivity regardless of high permeability seems to be due to tortuosity and pore structure of the membranes (25–50 μm thickness). The chemical stability of the membranes was tested towards common chemicals used for membrane cleaning (HCl, NaOH, NaClO) but at much severe conditions (24 h exposure at 4–10 fold higher concentrations). High resolution-X-ray photoelectron spectroscopy (XPS) was applied to evaluate chemical resistance. The relative C/O-carbon to oxygen ratio and typical deconvolution curves of C1s lines of the membranes after 24 h exposure depicted no significant changes compared to the reference samples, confirming resistance to chemical oxidation. This combination of features, added to simplicity of fabrication and post-synthesis modification and support-free configuration that enhances chemical stability, offer a worthwhile opportunity of application of these dense-array outer-walled CNT membranes in the UF range, especially at harsh conditions such as wastewater treatment

Low voltage electric potential as a driving force to hinder biofouling in self-supporting carbon nanotube membranes

© 2017 Elsevier Ltd This study aimed at evaluating the contribution of low voltage electric field, both alternating (AC) and direct (DC) currents, on the prevention of bacterial attachment and cell inactivation to highly electrically conductive self-supporting carbon nanotubes (CNT) membranes at conditions which encourage biofilm formation. A mutant strain of Pseudomonas putida S12 was used a model bacterium and either capacitive or resistive electrical circuits and two flow regimes, flow-through and cross-flow filtration, were studied. Major emphasis was placed on AC due to its ability of repulsing and inactivating bacteria. AC voltage at 1.5 V, 1 kHz frequency and wave pulse above offset (+0.45) with 100Ω external resistance on the ground side prevented almost completely attachment of bacteria (>98.5%) with concomitant high inactivation (95.3 ± 2.5%) in flow-through regime. AC resulted more effective than DC, both in terms of biofouling reduction compared to cathodic DC and in terms of cell inactivation compared to anodic DC. Although similar trends were observed, a net reduced extent of prevention of bacterial attachment and inactivation was observed in filtration as compared to flow-through regime, which is mainly attributed to the permeate drag force, also supported by theoretical calculations in DC in capacitive mode. Electrochemical impedance spectroscopy analysis suggests a pure resistor behavior in resistance mode compared to involvement of redox reactions in capacitance mode, as source for bacteria detachment and inactivation. Although further optimization is required, electrically polarized CNT membranes offer a viable antibiofouling strategy to hinder biofouling and simplify membrane care during filtration

Successful treatment of osseous lesion associated with palatoradicular groove using local drug delivery and guided tissue regeneration: A report of two cases

Developmental grooves are not rare and often appear on maxillary lateral and central incisors and are an important predisposing factor to localized periodontal disease. Various techniques have been adopted to eliminate the groove and regenerate lost periodontium. This report of two cases describes the technique of using the local drug delivery system with chlorehexidine and the guided tissue regeneration (GTR) to control the disease progression and regeneration

Optimized Electrocoagulation Pre-Treatment for Fouling Reduction During Nanofiltration of Lake Water Containing Microcystin-LR

Microcystin-LR (MCLR) is a toxin produced by harmful algal blooms that is emerging as a threat to drinking and recreational water systems worldwide. Nanofiltration (NF) is an effective technique for purifying contaminated water sources; however, membrane fouling caused by coexisting organic matter limits the practicality of the process. This research studies the use of an electrocoagulation (EC) pretreatment to limit fouling during the NF process. Water for this study was taken from Lake Fayetteville, a local body of water where MCLR concentrations have been recorded to be >15 µg/L. EC was performed using polyaluminum chloride as a background electrolyte at various operating conditions. EC-treated water was then further treated with NF to assess the impact of the EC pretreatment on NF fouling. It was found that the larger particle size of the sludge produced using aluminum electrodes at pH 7 had the best combination of settling ability and organic carbon removal (92%). This also led to the smallest flux decline during six-hour NF experiments of just 9%. These results highlight the potential of an EC pretreatment as an antifouling technique for the NF treatment of water contaminated with algal toxins