Control of planktonic and sessile bacterial cells by essential oils

The antibacterial potential of essential oils (EOs) from Cinnamomum cassia bark and Melaleuca alternifolia and Cymbopogon flexuosus leaves was evaluated against planktonic and sessile cells of enteropathogenic Escherichia coli (EPEC) and Listeria monocytogenes. The EOs were tested singly and in different combinations of equal percentages: mixtures of two (1:1 in v/v) and three EOs (1:1:1 in v/v/v). The minimal inhibitory concentrations (MICs) were determined against planktonic cells and the anti-biofilm activity was verified against bacterial cells adhered in the wells of polystyrene microplates. These initial tests indicated the EO of C. cassia as a potential anti-biofilm agent, and their effect was studied against sessile cells of biofilms formed on stainless steel surface under agitation and static conditions. For both bacterial species, a solution containing 2% (v/v) of C. cassia EO was effective against the biofilm formed under static conditions, because the counts obtained were below the detection level of the plate count method employed. Although the biofilm of L. monocytogenes showed a decreased number of adhered cells after formation under agitating conditions (p < 0.05), it was surprisingly more resistant to the EO of C. cassia than the biofilm formed under static conditions (p < 0.05). All of the EOs and combinations tested presented antibacterial activity, almost against planktonic cells; however, the EO of C. cassia showed to be the most effective as a potential agent for the production of sanitizers for biofilm control in the food industries.     

Effluent organic matter removal from reverse osmosis feed by granular activated carbon and purolite A502PS fluidized beds

Applying pre-treatments to remove dissolved organic matter from reverse osmosis (RO) feed can help to reduce organic fouling of the RO membrane. In this study the performance of granular activated carbon (GAC), a popular adsorbent, and purolite A502PS, an anion exchange resin, in removing effluent organic matter (EfOM) from RO feed collected from a water reclamation plant located at Sydney Olympic Park, Australia were evaluated and compared through adsorption equilibrium, kinetics and fluidized bed experiments. The maximum adsorption capacity (Q_max) of GAC calculated from the Langmuir model with RO feed was 13.4 mg/g GAC. The operational conditions of fluidized bed columns packed with GAC and purolite A502PS strongly affected the removal of EfOM. GAC fluidized bed with a bed height of 10 cm and fluidization velocity of 5.7 m/h removed more than 80% of dissolved organic carbon (DOC) during a 7 h experiment. The average DOC removal was 60% when the bed height was reduced to 7 cm. When comparing GAC with purolite A502PS, more of the later was required to remove the same amount of DOC. The poorer performance of purolite A502PS can be explained by the competition provided by other inorganic anions present in RO feed. A plug flow model can be used to predict the impact of the amount of adsorbent and of the flow rate on removal of organic matter from the fluidized bed column.     

Optimized and functionalized paper sludge activated with potassium fluoride for single and binary adsorption of reactive dyes

The yield and adsorption uptake of optimized paper sludge activated carbon (PSAC) prepared using potassium fluoride as alternative chemical activation agent was investigated. The PSAC was functionalized with ethylenediamine (FPSAC) and both adsorbents were used for single and binary adsorption of Reactive orange 16 (RO16) and Reactive blue 19 (RB19). Effect of pH on the adsorption process, equilibrium, kinetics, isotherm and thermodynamic studies were carried out. Optimum PSAC preparation parameters were: activation temperature, X₁ = 810 °C; activation time, X₂ = 105 min; and impregnation ratio, X₃ = 0.95 which gave adsorption uptake of 178 and 158 mg/g for RO16 and RB19, respectively.     

In vitro Streptococcus mutans biofilm formation on surfaces of chlorhexidine-containing dentin bonding systems

This in vitro study evaluated the influence of chlorhexidine diacetate (CDA) when blended within dentin bonding systems (DBSs) on Streptococcus mutans (S. mutans) biofilm formation.One commercially available 0.2% wt CDA-containing DBS (Peak Universal Bond) and five experimental 0.2% wt CDA-containing DBS formulations (experimental Adper Scotchbond 1XT plus experimental resins, R₂, R₃, R₄, R₅) were assessed vs their no-CDA containing counterparts. Twenty-eight DBSs disks were prepared for each group (6.4 mm×1.0 mm) and cured for 80 s at 800 mW/cm² in a nitrogen atmosphere. A modified Drip-Flow Reactor was used to grow S. mutans biofilms on specimen surfaces for 24 h and adherent, viable biomass was evaluated using a tetrazolium salt assay (MTT). Two specimens from each of the tested materials were processed with LIVE/DEAD stain and observed using laser confocal microscopy (CLSM) while two disks from each group were examined by using scanning electron microscopy (SEM).MTT assay, CLSM and SEM observations showed that CDA addition decreased, increased or did not change S. mutans biofilm formation. The lowest biofilm formation was obtained with Peak Universal Bond and R₅ (with and without CDA).It may be concluded that the chemical composition of DBSs determines their ability to promote or hamper biofilm formation. Therefore, CDA addition may be helpful in modulating biofilm formation provided that DBS formulation is tuned and optimized.     

A novel set-up and a CFD approach to study the biofilm dynamics as a function of local flow conditions encountered in fresh-cut food processing equipments

The hydrodynamic conditions as well as design and surface properties within fresh-cut food processing equipment create a complex environment for biofilms. A new experimental approach was thus proposed to identify those physical parameters impacting biofilm development in such conditions. A set-up comprising original mock-ups mimicking generic features of washing tanks (e.g. welds, folds, flat surfaces, air/liquid/wall interface) was designed. The flow pattern therein was characterized using two computational fluid dynamic calculation approaches. Full trials were run for 48 h at 10 °C with a Pseudomonas fluorescens strain to identify the preferential biofilm formation areas. As in current industrial systems, the pilot rig had recirculation areas and low wall shear stress rates (τ_w < 0.1 Pa) in corners and angles. These were identified as critical areas with Surface Microbial Loads (SML) over 5 Log₁₀/cm². However, τ_w alone failed to explain why SML in areas under unidirectional flow was higher than in the mock-ups. Lastly, air/liquid/wall interface conditions were more critical than immersed surfaces. This study validated the possibility of using CFD methods to understand the way in which flow pattern influences biofilm formation. The methodology proposed would be helpful in quantifying equipment components criticality based on biofilm growth parameters.     

Magnetic resonance imaging and 3D simulation studies of biofilm accumulation and cleaning on reverse osmosis membranes

Reverse osmosis (RO) is one of the multiple pressure-driven membrane separation processes used primarily for the production of high purity water for various industries, including food processing. Biofilm growth in the spiral-wound membrane module, commonly referred to as biofouling, reduces the efficiency to produce water. Biofilm accumulation and removal using chemical cleaning on RO membranes were studied using magnetic resonance imaging (MRI) techniques. Additionally, a previously validated biofilm simulation model, which is based on a lattice Boltzmann platform, was modified to account for cleaning operations. The spatial and velocity MRI experimental results captured biofilm distribution and water flow within the fouled membrane modules and subsequent changes in the biofilm distribution and water flow due to cleaning. Cleaning was simulated by accounting for reductions in the biofilm cohesive strength in the numerical model. Qualitative and quantitative comparisons between the experimental and simulated images showed good agreement.     

Introduction of copper nanoparticles in chitosan matrix as strategy to enhance chromate adsorption

In this study, copper nanoparticles (CuNPs) were incorporated to chitosan (CHI) matrix as strategy to enhance the chromate adsorption by CHI membrane. The CuNPs were synthesized using NaBH₄ as the reducing agent. Dispersive X-ray Absorption Spectroscopy (DXAS) was used to monitor the in situ reduction of Cu(II). The influence of the presence of CuNPs on the hygroscopic behavior was also evaluated. DXAS technique showed that the adsorbed Cu(II) was reduced to Cu(I) (63%) and Cu(0) (37%) species, at the end of the reduction reaction (using NaBH₄, after ∼30 min). The hygroscopic behavior of the proposed sorbent was more influenced by CuNPs when the water vapor adsorption was conducted under synthetic air atmosphere. A decrease in the energy of interaction among the water molecules adsorbed on the monolayer was observed. The chromate adsorption study has shown a higher equilibrium concentration of adsorbed chromium species when the CHI membrane containing CuNPs was used as sorbent. The CuNPs offered a second active adsorption site, which was characterized by a higher coefficient of affinity (12 L mmol⁻¹, against 0.18 L mmol⁻¹ reported for CHI). The enhanced adsorption of chromium in the presence of CuNPs was associated to the redox reaction between the CuNPs and chromate anions.     

Threshold performance of a spiral-wound reverse osmosis membrane in the treatment of olive mill effluents from two-phase and three-phase extraction processes

A reverse osmosis (RO) treatment stage was examined for the complete depuration of the different effluents exiting the olive mill factories (OMW) working with diverse extraction procedures, that is, the two-phase and the three-phase extraction processes, respectively. In the present work, the modelization of batch RO purification of OMW by means of the relevant equations of the threshold flux theory for fouling control and plant dimension is addressed. Results show that higher threshold flux values (20.2–22.1% increase) and major feed recovery rates (80.2–85.0%) as well as very significant reduction of the long-term fouling index (27.3–52.7%) were achieved by using as pretreatment steps the following series of processes: pH-T flocculation, UV/TiO₂ photocatalysis, UF and NF in series. This leads to both lower energy and capital costs, in particular a reduction of the required membrane area in case of batch membrane processes equal to 22.3–44.8%. Accurate prediction of the rejection behavior was attained by the used leaky solution-diffusion model in all cases, with reflection coefficients (σ_COD) ranging from 0.86 to 1.0. The purified effluent streams are finally compatible with irrigation water quality standards (COD values below 1000 mg L⁻¹).     

Removal of biofilms using carbon dioxide aerosols

The formation of biofilm (bacterial film) has been serious concerns in a wide variety of applications, because it is involved in many human and device-associated infections. We present a novel method of effectively and rapidly removing Escherichia coli (XL1-blue) biofilm from a silicon chip, using carbon dioxide aerosols. The aerosols were generated by adiabatic expansion of a high-pressure CO₂ gas through a nozzle and they were applied to biofilms that had been grown for 24 h on silicon chips. We measured the percentage area cover of the bacteria from the scanning electron micrographs taken before and after applying the aerosols. The decrease in the percentage area cover, caused by the aerosols, was measured as several parameters such as the distance between the nozzle and the chip, the angle of the nozzle axis relative to the horizontal, CO₂ stagnation pressure, rinsing solution, the aerosol exposure time, and drying time were varied. Nearly 100% of the biofilms were removed within 90 s whether the chip surfaces were very humid (no-drying) or dry (7 h-drying) immediately before applying the aerosols. This method has potential application to cleaning of a wide variety of bio-contaminated surfaces.     

Thermal conductivity of PVDF/PANI-nanofiber composite membrane aligned in an electric field

Poly(vinylidene fluoride)(PVDF) is a semi-crystalline thermoplastic polymer with excellent thermal stability,electrochemical stability and corrosion resistance, which has been widely studied and applied in industrial nonmetallic heat exchanger and piezoelectric-film sensor. In this study, polyaniline(PANI) nanofibers were synthesized using dodecylbenzene sulfonic acid as the surfactant. The obtained PANI nanofibers were blended in PVDF matrix to enhance thermal conductivity and tensile strength of composite materials. Electric field was applied for the orientation of membrane structure during membrane formation. Scanning electron microscope(SEM) images exhibited that the PANI nanofibers were well-dispersed in the composite membranes. The structure of composite membranes was more orderly after alignment. X-ray diffraction(XRD) and differential scanning calorimetry(DSC) indicated that the content of PANI nanofibers contributed to the transformation of PVDF from α-phase to β-phase. Both the tensile strength and thermal conductivity of composite membranes were significantly improved. This tendency was further enhanced by the application of electric field. The maximum tensile strength was obtained when the content of PANI nanofibers was 3 wt%, which was 46.44% higher than that of pure PVDF membrane. The maximum thermal conductivity of composite membranes after alignment was 84.5% greater than that of pure PVDF membrane when the content of PANI nanofibers was 50 wt%. The composite membrane is a promising new potential material in heat transfer field and the mechanism explored in this study would be informative for further development of similar thermal conductive polymeric materials.     

Polyphosphates used for membrane scaling inhibition during water desalination by membrane distillation

The desalination of surface water (lake) was performed using direct contact membrane distillation. The membrane distillation process was carried out at 358 K. As a consequence of water heating the CaCO₃ deposit formed on the membrane surfaces, which resulted in a decrease in module efficiency. The polyphosphate antiscalant was used for restriction of carbonate deposition. In order to increase the scaling potential during the desalination process, the water was additionally enriched with bicarbonates (feed alkalinity 3.1 mmol HCO₃^–/dm³ and 4.5 mmol HCO₃^–/dm³). The membrane distillation with and without antiscalant was carried out to evaluate the scale inhibition effect. Various solution compositions (2–20 ppm) of the commercial polyphosphate based antiscalant (destined for reverse osmosis) and laboratory-grade sodium polyphosphate was used. SEM–EDS was used to investigate the chemical composition and morphology of the precipitate formed on the membrane surface. It was found that the formation of CaCO₃ crystallites was almost eliminated as a result of using antiscalant. However, a thin layer of amorphous deposits on the membrane surface was observed. As a results, a decline of the permeate flux was still observed. The initial module efficiency was restored by periodical rinsing of the membranes with diluted HCl solutions. The application of antiscalant minimized the penetration of deposit into the pores, and a high permeate flux was maintained over a period of 260 h of performed investigations when periodical rinsing with HCl solution was used.     

Fabrication of polyetherimide microporous membrane using supercritical CO2 technology and its application for affinity membrane matrix

Polyetherimide (PEI) microporous membranes with uniform cellular structure, high porosity, and narrow pore size distribution were formed by supercritical CO₂ (ScCO₂) phase inversion method, and the membrane was modified to be a matrix for the preparation of affinity membrane due to its low solvent residue and appropriate porous structure. The effects of ScCO₂ temperature and pressure on the morphology and pure water flux of the membrane were investigated. The membrane prepared at 24 MPa and 45 °C with a large mean cell diameter of 6.0 μm, high porosity of 73%, narrow pore size distribution and a pure water flux of 56 L/(m² h bar) was coated with chitosan to improve its hydrophilicity and coupled with Cibacron Blue F3GA (CB) as a special ligand to form an affinity membrane (PEI-coated chitosan-CB membrane). The PEI-coated chitosan-CB membrane showed a high adsorption capacity of 33.9 mg/g membrane to bovine serum albumin and was higher than most of affinity membranes. Moreover, the tensile strength of PEI-coated chitosan-CB membrane was 11.58 MPa and was much higher than those of affinity membranes. This work demonstrates that ScCO₂ phase inversion method is a potential method to prepare an affinity matrix.     

Pilot-scale hybrid bio-diatomite/dynamic membrane reactor for slightly polluted raw water purification

This study investigated the performance and mechanisms of a novel pilot-scale bio-diatomite dynamic membrane reactor (BDDMR) for slightly polluted surface water treatment in continuous-flow mode. The results revealed that the pilot-scale BDDMR was very effective at reducing particle number and removing turbidity, chemical oxygen demand (COD_Mn), UV absorbance at 254 nm (UV₂₅₄), NH₃-N and trihalomethane formation potential (THMFP) with a hydraulic retention time of 8 h. The transmembrane pressure (TMP) of the dynamic membrane was invariant for each selected flux, i.e., 30 L/m² h, 50 L/m² h and 80 L/m² h, in the early filtration stage and rose quickly to 4.5 kPa in the final stage of the operation period. Based on the results of the three-dimensional excitation and emission matrix fluorescence spectroscopy (3D-EEM) observation, the aromatic protein-like substance in the influent was removed effectively. In addition to suspended solid separation, the BDDMR could partially remove a MW 1000–3200 Da of dissolved organic matter (DOM). Three individual effects responsible for removing pollutants were investigated. The polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) was also used to verify the shift of microbial communities in the mixed liquor.     

Characterization of molecular mechanism of neuroglobin binding to cytochrome c: A surface plasmon resonance and isothermal titration calorimetry study

Neuroglobin (Ngb) is a six-coordinate heme protein predominantly expressed in the brain tissue with a protective role against hypoxic/ischemic and oxidative stress-related insults. Several intracellular proteins including cytochrome c have been identified as potential neuroglobin binding partners. To understand the factors that control Ngb association to cytochrome c (Cyt c) the thermodynamic parameters for Cyt c association to Ngb variants were probed using surface plasmon resonance and isothermal titration calorimetry techniques. The dissociation constant for human Ngb binding to Cyt c was determined to be ~ 10 μM using SPR and a similar value was obtained by ITC confirming that the covalent attachment of Cyt c to the gold surface modified with mixed alkanethiols does not impair Cyt c interactions with Ngb. Modification of the heme iron coordination sphere by replacement of histidine 64 in the position of sixth axial ligand with cyanide effectively inhibits the inter-protein complex formation. On the other hand, the presence of the Cys 46/Cys 55 disulfide bridge that restrains the CD loop flexibility and increases the distal histidine affinity for heme iron has no impact on complex stability. ITC data also show that the inter-protein complex formation is entropy driven (ΔH = 3.3 ± 0.2 kcal mol^− 1 and ΔS = 32.3 cal mol^− 1 K^− 1) likely due to a reorganization of solvent molecules surrounding charged amino-acid residues. The experimental data are consistent with the results of a docking study in which the residues in the E- and F-helix of Ngb were identified to form a binding site for Cyt c. We propose that association of the exogenous ligand to the heme iron triggers a repositioning of the E-helix that prevents Ngb-Cyt c complex formation.     

Effect of dechlorination point location and residual chlorine on biofouling in a seawater reverse osmosis plant

Experiments were carried out to test the effect of dechlorination dosing point location and the concentration of residual chlorine on bacterial growth and biofouling in a seawater reverse osmosis (SWRO) plant. The plant is located in Al-Birk on the Red Sea coast, southern Saudi Arabia. The plant was routinely operated with injection of chlorine as a biocide in the intake chamber in the open sea and with the injection of sodium metabisulfite (SBS) to remove chlorine after the dual media filter (DMF). During the experiments, the SBS dosing point was shifted to two locations after the micron cartridge filter (MCF): first, to a point 13 m ahead of the high pressure pump (HPP) and second, to a point just ahead (<1 m) of the HPP. Due to fluctuations in residual chlorine resulting from certain operational and physical circumstances, it was possible to assess biofouling potential when free chlorine is regarded as high (≥0.5 mg/l) or low (<0.5 mg/l) within a maximum of 1 mg/l. Bacterial generation (doubling) time was used to evaluate biofouling. Generation time was higher (lower multiplication capacity) when the SBS dosing point was before the MCF (after DMF). It decreased significantly, reflecting higher multiplication capacity and higher biofouling potential, when the SBS dosing point was moved to after the MCF. Generation times in high-pressure RO feed water were similar when the SBS dosing point was moved to two locations after the MCF. This indicated minimal contribution of the low-pressure pipe between the MCF and the HPP to biofouling. In general, biofouling increased as the SBS dosing point was moved forward along the pretreatment line, closer to the RO membranes. Generation times were similar when residual chlorine was less or more than 0.5 mg/l. Bacteria were capable of biofilm formation in the chlorinated section of the plant.     

Electrogeneration of hydrogen peroxide in gas diffusion electrodes modified with tert-butyl-anthraquinone on carbon black support

Hydrogen peroxide (H₂O₂) is a versatile oxidizing agent that is synthesized commercially by the reduction of oxygen in organic medium. Electrochemical technology employing a modified gas diffusion electrode (MGDE) offers a viable alternative for the industrial-scale synthesis of the oxidant. Addition of 1% (w/w) of tert-butyl-anthraquinone (TBAQ) to carbon black deposited in the form of a microporous layer onto the disk of a rotating ring-disk electrode produced an increase in the ring current, which is directly related to H₂O₂ formation, and presented an efficiency of H₂O₂ generation of 89.6% compared with 76.6% for carbon black alone. No significant changes were detected in the number of electrons transferred in the presence of the catalyst suggesting an electrochemical/chemical mechanism for H₂O₂ formation. Analogous improvements in the generation of H₂O₂ were obtained with MGDEs comprising TBAQ on carbon black. The highest concentrations of H₂O₂ (301 mg L⁻¹) were produced at the fastest rate (5.9 mg L⁻¹ min⁻¹) with the lowest energy consumption (6.0 kWh kg⁻¹) when a potential of −1.0 V vs SCE was applied to a MGDE containing 1.0% of TBAQ on carbon black. It is concluded that the application of MGDEs comprising TBAQ on carbon black support offers considerable advantages in the electrogeneration of H₂O₂.     

The effect of RO oxides on microstructure and chemical durability of borosilicate glasses opacified by P2O5

The microstructure, devitrification and chemical durability of borosilicate glass specimens opacified by P₂O₅, with the general composition SiO₂ 70, B₂O₃ 12, Al₂O₃ 2, P₂O₅ 2, Na₂O (13 − X), RO X (wt.%) (R = Ca, Mg, Ba, Zn) were investigated after being subjected to various heat treatment conditions, using DTA, XRD and SEM. It was shown that while heat treatments at 1073 K and >1123 K were generally detrimental for the hydrolytic resistance of glasses, due to the enhanced phase separation or formation of excessive amounts of cristobalite, heating at 1123 K for 1 h usually improved the resistance due to the partial crystallization or microstructural changes of specimens. It was also found that a progressive decrease in hydrolytic and alkaline resistance occurred during prolonged heat treatment at 1123 K due to the formation of exessive amounts of cristobalite. It was also revealed that ZnO and MgO had the worst effect on chemical durabilities of specimens containing 7 and 5.5 wt.% Na₂O, respectively.     

Rod-like micelle templated synthesis of porous hydroxyapatite

Use of macromolecular templates for controlling nanostructures of inorganic materials is an active area of research. In particular, oriented growth of hydroxyapatite in organic matrix is of great relevance to understand biomineralisation of bone and its potential biomedical applications. Natural bone being a composite of hydroxyapatite and collagen fibers, crystallization of hydroxyapatite in fibrous assemblies could mimic such biomineralisation. This motivated us to investigate the role of long rod-like micelles in modulating the structure of hydroxyapatite particles. In this article, we report the preparation of porous hydroxyapatite nanorods using rod-like micelles made up of a cationic surfactant cetyltrimethylammonium bromide (CTAB) and anionic hydrotrope sodium salicylate (SS) as a templating agent. The successful formation of hydroxyapatite crystals is evident from XRD, FTIR, TGA, SEM and TEM analyses. It has been observed that large hydroxyapatite nanorods of diameter ～50 nm are formed in surfactant mediated synthesis, whereas irregular shaped nanoaggregates of hydroxyapatite are obtained in the absence of surfactant. A comparative study on the porosity of hydroxyapatite clearly shows that monomodal distribution of mesopores with a peak at ～30 nm in the absence of surfactant while bimodal distribution of mesopores having maxima at ～4 nm and ～45 nm appear in hydroxyapatite prepared in the presence of surfactant template.     

Influences of quartz and muscovite on the formation of mullite from kaolinite

A kaolin containing muscovite and quartz (K-SZ) and a pure kaolin (K-SX) with the addition of potassium feldspar, K₂SO₄ and quartz, respectively, were used to investigate the influences of muscovite and quartz on the formation of mullite from kaolinite in the temperature range 1000–1500 °C. In K-SZ formation of mullite began at 1100 °C, and in K-SX at 1000 °C. In K-SZ quartz accelerated the formation of cristobalite and restrained the reaction of mullite and silica. Muscovite in K-SZ acted as a fluxing agent for silica and mullite before 1400 °C and accelerated the formation of cristobalite. The FTIR band at 896.8 cm^− 1 was used to monitor the formation of orthorhombic mullite.     

Removal of boron from seawater by selective ion exchange resins

Reverse osmosis (RO) desalination process is an efficient and reliable membrane technology for the production of drinking water from seawater. However, some serious limitations had recently been discovered during the field practice. Boron problem is one of them. According to the WHO regulations, the boron concentration should be lower than 0.5 mg/L in drinking water. It is still difficult to reduce boron level to 0.5 mg/L or lower with the conventional reverse osmosis desalination plants equipped with commercially available RO membranes. Therefore, more efficient separation technologies are needed for boron removal.In this study, the performance of the boron-selective ion exchange resins containing N-methyl glucamine groups, as Diaion CRB 02 and Dowex XUS 43594.00, have been tested for boron removal from model seawater. The kinetic performances of these resins were compared. The kinetic data obtained were evaluated using Lagergren pseudo-first-order and second-order models. Also, the process kinetics were predicted by using diffusion models. In addition, column-mode tests have been carried out for boron removal from model seawater.