Synthesis, characterization and performance of polystyrene/PMMA blend membranes for potential water treatment

© 2017 Elsevier B.V. PS membranes were prepared from polymeric blends of PS and PMMA via a phase inversion induced by an immersion precipitation in water coagulation baths. The effects of the casting parameters (e.g., solvent selection, the composition of the coagulation bath) and the type of polystyrene (substituents at the aromatic ring, tacticity) on the morphology and water permeation flux were studied. The findings reveal that modified PS promoting instantaneous demixing with NMP/water systems result in membranes wit- h macrovoids while the addition of 2% of PS-r-PMMA results in membranes with high water fluxes. The membranes morphologies were governed by a trade-off between thermodynamic and kinetic aspects. The antibacterial effect of (aPS)70-co-aPS(I)30/PMMA-based membrane was examined using static and cross-flow systems. These results illustrate the diversity in the design of these PS/PMMA based membranes and highlight the possibility to control the polymer chemistry for tailoring specific morphology, permeation, and antibacterial properties for the desired function

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

Integrated treatment of reverse osmosis brines coupling electrocoagulation with advanced oxidation processes

© 2018 Elsevier B.V. The potential of integrating electrocoagulation (EleC) with two-stage reverse osmosis (RO) to enhance desalination of secondary/tertiary effluents through removal of dissolved organic matter (DOM) and scaling salts from brines was studied. EleC appears advantageous due to the high electrical conductivity of RO brines and low residual ions concentration. EleC was performed in batch mode in a flow-through cell with recirculation through a stirred reservoir at 9.4 mA/cm2 current density. Anode was made of Fe or Al as indicated, and cathode of stainless steel. Chemical coagulation (CC) with FeCl3 was tested as reference. EleC resulted in effective removal of phosphate (>99%), carbonate (88–98%) and DOM (40–50%) at a high Faradaic efficiency (>90%). Fe-EleC resulted less suitable than Al-EleC due to partial Fe(II) oxidation at pH 5.5 required for optimal DOM removal, leaving high Fe content and consequently turbidity in the supernatant, whereas residual Al was negligible. At optimal conditions Al release was 75 mg/L for 1st-stage brines-RO1 (2-fold concentrated) and 300 mg/L for 2nd-stage brines-RO2 (∼8.3-fold concentrated), corresponding to a specific energy consumption of 0.30 and 0.23 [Formula presented], respectively. Similar results were obtained with CC, however, its main disadvantage was the considerable increase of chlorides in the supernatant. Since coagulation removes quenching components from brines, coupling EleC with advanced oxidation processes (AOP), either UVA/TiO2 or UVC/H2O2, was also evaluated for oxidation of model micropollutants from brines prior to discharge. Either EleC or CC in tandem with AOP increased micropollutants oxidation by 3–4 fold compared to raw brines, achieving practically complete transformation

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

Controlling nitritation in a continuous split-feed/aeration biofilm nitrifying bioreactor

© 2019 Elsevier Ltd This study explored the stability of partial ammonium oxidation at low feed concentration (50 g N/m3), suitable for anammox process, in continuous fixed bed up-flow biofilm reactors with external recirculation-aeration. The reactors, filled with crushed basalt, were fed with synthetic medium at 20–25 °C at constant flow-rate with limiting dissolved oxygen concentration controlled by the recirculation ratio (R). Successful nitritation was achieved at R ≅ 4–6 with approx. 50% of NH4+ oxidized to NO2- with <5% NO3-accumulation. q-PCR analysis along the reactor showed ammonia oxidizing bacteria being the prevalent nitrifiers over the three-fourths of the bed in the flow direction, negligible denitrifiers and absent ammonium oxidizing archaea. A numerical model for predicting the concentration of the nitrogen species and DO was formulated. The model successfully predicted the experimental results and displayed good sensitivity to intrinsic oxygen uptake parameters. The proposed numerical model can serve both as an operational and design tool

Modification of a polypropylene feed spacer with metal oxide-thin film by chemical bath deposition for biofouling control in membrane filtration

© 2018 Elsevier B.V. Surface modification of polypropylene feed spacers typical of spiral wound membrane modules was studied by generation of crystalline ZnO nanorods. A seeding layer made by deposition of ZnO nanoparticles (20–40–60 nm diameter) from aqueous dispersions served as nucleation centers for crystallization. A uniform layer of ZnO nanorods was grown on the seeding layer by chemical bath deposition from a zinc acetate solution. Biocidal activity was estimated by antibacterial tests in static liquid culture against Escherichia coli and antibiofouling tests in flow-through/cross-flow mode against a mixture of Pseudomonas fluorescens and Bacillus subtilis. Best biocidal activity was displayed by 20 nm ZnO particles, suggesting a tradeoff between surface coverage, roughness and particle size. Although the seed layer itself displayed acceptable antibacterial activity, a marked improvement was achieved by the nanorods, proving that the morphology of the deposition layer was involved in the antibacterial mechanism. Antibiofouling activity was further improved by superhydrophobic over-coating of the nanorods with octadecyl-phosphonic acid. Modified spacers reduced permeate flux decay by at least 40% compared to controls. The enhanced antibiofouling activity of crystalline ZnO nanorods, compared with amorphous ZnO nanoparticles, can be explained by a combination of the abrasive surface of the crystalline nanorods, hydrophobic repulsion and cumulative oxidation