Ultraflitration of wastewater with pretreatment: evaluation of flux decline models

Three different mathematical models relating the flux decline were investigated to quantify the effects of pretreatment in a membrane filtration system. The models used are empirical flux decline model, series resistance flux decline model and modified series resistance flux decline model. A cross flow ultrafiltration unit was used to study flux decline and organic removal from synthetic wastewater. Flocculation and adsorption pretreatments were carried out with ferric chloride (FeCl3) and activated carbon of different doses. The three models could predict flux decline after different pretreatments and could be used as a pretreatment index to ultrafiltration. © 2008

Nitrate removal using Purolite A520E ion exchange resin: batch and fixed-bed column adsorption modelling

© 2014, Islamic Azad University (IAU). Removing excessive nitrate from water is essential because it causes eutrophication which in turn has a harmful effect on aquatic life, resulting in a reduction in biodiversity and posing a danger to people’s health when the water is used for drinking. In this study, nitrate removal from aqueous solutions was studied using an ion exchange resin (Purolite A520E) in batch and fixed-bed column experiments. Batch adsorption kinetics was very well described by pseudo-first-order, pseudo-second-order and homogeneous surface diffusion models for resin doses 1.5 and 3.0 g/L at a nitrate concentration 20 mg N/L. Column kinetic data satisfactorily fitted to the empirical Thomas model and a numerical model based on advection–dispersion equation for filtration velocities 2.5 and 5.0 m/h at a column height of 12 cm and inlet concentration 20 mg N/L. The experimental and Thomas model predicted breakthrough adsorption capacity ranges for the two filtration rates were 12.0–13.5 and 8.2–9.7 mg N/g, respectively, whereas the maximum adsorption capacity determined using Langmuir adsorption isotherm model in the batch study was 32.2 mg N/g

Mathematical modelling of nitrate removal from water using a submerged membrane adsorption hybrid system with four adsorbents

© 2018 by the authors. Excessive concentrations of nitrate in ground water are known to cause human health hazards. A submerged membrane adsorption hybrid system that includes a microfilter membrane and four different adsorbents (Dowex 21K XLT ion exchange resin (Dowex), Fe-coated Dowex, amine-grafted (AG) corn cob and AG coconut copra) operated at four different fluxes was used to continuously remove nitrate. The experimental data obtained in this study was simulated mathematically with a homogeneous surface diffusion model that incorporated membrane packing density and membrane correlation coefficient, and applied the concept of continuous flow stirred tank reactor. The model fit with experimental data was good. The surface diffusion coefficient was constant for all adsorbents and for all fluxes. The mass transfer coefficient increased with flux for all adsorbents and generally increased with the adsorption capacity of the adsorbents

Modelling equilibrium adsorption of single, binary, and ternary combinations of Cu, Pb, and Zn onto granular activated carbon

© 2018, Springer-Verlag GmbH Germany, part of Springer Nature. Elevated concentrations of heavy metals in water can be toxic to humans, animals, and aquatic organisms. A study was conducted on the removal of Cu, Pb, and Zn by a commonly used water treatment adsorbent, granular activated carbon (GAC), from three single, three binary (Cu-Pb, Cu-Zn, Pb-Zn), and one ternary (Cu-Pb-Zn) combination of metals. It also investigated seven mathematical models on their suitability to predict the metals adsorption capacities. Adsorption of Cu, Pb, and Zn increased with pH with an abrupt increase in adsorption at around pH 5.5, 4.5, and 6.0, respectively. At all pHs tested (2.5–7.0), the adsorption capacity followed the order Pb > Cu > Zn. The Langmuir and Sips models fitted better than the Freundlich model to the data in the single-metal system at pH 5. The Langmuir maximum adsorption capacities of Pb, Cu, and Zn (mmol/g) obtained from the model’s fits were 0.142, 0.094, and 0.058, respectively. The adsorption capacities (mmol/g) for these metals at 0.01 mmol/L equilibrium liquid concentration were 0.130, 0.085, and 0.040, respectively. Ideal Adsorbed Solution (IAS)-Langmuir and IAS-Sips models fitted well to the binary and ternary metals adsorption data, whereas the Extended Langmuir and Extended Sips models’ fits to the data were poor. The selectivity of adsorption followed the same order as the metals’ capacities and affinities of adsorption in the single-metal systems

Adsorption characteristics of acetaldehyde on activated carbons prepared from corn-based biomass precursor

The ACs (R-1/2 and R-1/4) having two different textual and chemical properties are prepared from corn-based biomass precursor and evaluated together with a wood-based activated carbon (WAC) at room temperature using a gas chromatograph. The results obtained from the correlation studies indicate that the pore size distribution (below 8Å) and the relatively lower energetic heterogeneity of ACs on acetaldehyde adsorption are considerable factors rather than that of a specific surface area and surface chemistry. The adsorption equilibrium of ACs is well correlated with the Sips equation. The pseudo second-order equation was better in describing the ACs' adsorption kinetic of acetaldehyde. © Taylor & Francis Group, LLC

Enhanced removal of nitrate from water using amine-grafted agricultural wastes

© 2016 Elsevier B.V. Adsorption using low-cost adsorbents is a favourable water treatment method for the removal of water contaminants. In this study the enhanced removal of nitrate, a contaminant at elevated concentration affecting human health and causing eutrophication of water, was tested using chemically modified agricultural wastes as adsorbents. Batch and fixed-bed adsorption studies were performed on corn cob and coconut copra that were surface modified by amine-grafting to increase the surface positive charges. The Langmuir nitrate adsorption capacities (mg N/g) were 49.9 and 59.0 for the amine-grafted (AG) corn cob and coconut copra, respectively at pH 6.5 and ionic strength 1 × 10-3 M NaCl. These values are higher than those of many commercially available anion exchange resins. Fixed-bed (15-cm height) adsorption capacities (mg N/g) calculated from the breakthrough curves were 15.3 and 18.6 for AG corn cob and AG coconut copra, respectively, for an influent nitrate concentration 20 mg N/L at a flow velocity 5 m/h. Nitrate adsorption decreased in the presence of sulphate, phosphate and chloride, with sulphate being the most competitive anion. The Thomas model fitted well to the fixed-bed adsorption data from four repeated adsorption/desorption cycles. Plug-flow model fitted well to the data from only the first cycle

W5ater desalination using graphene-enhanced electrospun nanofiber membrane via air gap membrane distillation

© 2016 This study demonstrates the preparation and desalination performance via air gap membrane distillation (AGMD) of a graphene-loaded electrospun nanofiber membrane. Different concentrations of graphene (0–10 wt%) were incorporated in/on electrospun polyvinylidene fluoride-co-hexafluoropropylene (PH) membrane to obtain a robust, and superhydrophobic nanocomposite membrane. The results showed that graphene incorporation has significantly enhanced the membrane structure and properties with an optimal concentration of 5 wt% (i.e., G5PH). Characterization of G5PH revealed membrane porosity of >88%, contact angle of >162° (superhydrophobic), and high liquid entry pressure (LEP) of >186 kPa. These favourable properties led to a high and stable AGMD flux of 22.9 L/m2 h or LMH (compared with ~4.8 LMH for the commercial PVDF flat-sheet membrane) and excellent salt rejection (100%) for 60 h of operation using 3.5 wt% NaCl solution as feed (feed and coolant inlet temperatures of 60 and 20 °C, respectively). A two-dimensional dynamic model to investigate the flux profile of the graphene/PH membrane is also introduced. The present study suggests that exploiting the interesting properties of nanofibers and graphene nanofillers through a facile electrospinning technique provides high potential towards the fabrication of a robust and high-performance AGMD membrane

Graphene/PVDF flat-sheet membrane for the treatment of RO brine from coal seam gas produced water by air gap membrane distillation

© 2016 Elsevier B.V. Brine management of coal seam gas (CSG) produced water is a significant concern for the sustainable production of CSG in Australia. Membrane distillation (MD) has shown the potential to further reduce the volume of CSG reverse osmosis (RO) brine. However, despite its potential, the lack of appropriate MD membranes limits its industrial use. Therefore, this study was aimed on the fabrication of a robust membrane for the treatment of real RO brine from CSG produced water via an air gap MD (AGMD) process. Here, graphene/polyvinylidene fluoride (G/PVDF) membranes at various graphene loadings 0.1-2.0 wt% w.r.t. to PVDF) were prepared through a phase inversion method. Surface characterization revealed that all G/PVDF membranes exhibited favorable membrane properties having high porosity (>78%), suitable mean pore size (3.66 bar). AGMD test results (feed inlet: 60.0±1.5 °C; coolant inlet: 20.0±1.5 °C) for 24 h operation indicated a high water vapor flux and salt rejection of 20.5 L/m2h and 99.99%, respectively for the optimal graphene loading of 0.5 wt%, i.e., G/PVDF-0.5 membrane (compared to 11.6 L/m2h and 99.96% for neat PVDF membrane). Long-term AGMD operation of 10 days further revealed the robustness of G/PVDF membrane with superior performance compared to commercial PVDF membrane (85.3% final normalized flux/99.99% salt rejection against 51.4%/99.95% for commercial membrane). Incorporation of graphene has resulted to improved wetting resistance and more robust membrane that has the potential for the treatment of RO brine from CSG produced water via AGMD

Post-mortem estimation of temperature distribution on a power transformer: Physicochemical and mechanical approaches

Power transformers are electrical machines that allow us to transport electric energy, with reduced losses, from generation stations to consumption points. This definition gives us an idea of the number of transformers that are used in power distribution systems worldwide. The main problem that may affect power transformers is the operation at high temperature. This paper summarizes the results of a postmortem temperature estimation carried out on an 800 kVA distribution transformer. Two methodologies are considered for estimating the temperature distribution in the windings of the machine. The first is based on the calculation of the degree of polymerization and the second is obtained from the tensile strength index. By knowing the value of these two magnitudes for a new and for an aged paper, and the period of operation of a transformer, the temperature distribution along the height of the windings can be estimated. None other previous works have used the tensile strength of winding paper for temperature distribution estimation. With these results and the loading regime records, similar transformers still in operation can be operated in an alternative manner and future designs can be improved