Investigating reverse osmosis membrane fouling and scaling by membrane autopsy of a bench scale device

In response to the escalating world water demand and aiming to promote equal opportunities, reverse osmosis desalination has been widely implemented. Desalination is however constantly subjected to fouling and scaling which increase the cost of desalination by increasing the differential pressure of the membrane and through decline in permeate flux. A bench-scale desalination equipment has been used in this research to investigate the mitigation of fouling and scaling. This study also involved the performance of membrane autopsy for fouling characterisation with special attention to flux decline due to sulphate precipitation and biofouling. Visual inspection, scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR) and microbiology tests (API) were performed. Results obtained showed the presence of diatoms, pseudomonas and polysaccharides as the main foulants causing biofouling. Analysis revealed sulphate deposits as well as aluminium, calcium and silica as the main elements contributing to inorganic scaling. Findings pointed out that the pretreatment system of the small-scale reverse osmosis water treatment was inefficient and that selection of pretreatment chemicals should be based on its compatibility with the membrane structure. The importance of characterization for the verification of fouling mechanisms is emphasized

OPTIMIZATION OF THE ALKALINE ACTIVATION PROCESS OF DIFFICULT-TO-TREAT INORGANIC WASTES

Abstrac

Mineralized alginate hydrogels using marine carbonates for bone tissue engineering applications

The search for an ideal bone tissue replacement has led to the development of new composite materials designed to simulate the complex inorganic/organic structure of bone. The present work is focused on the development of mineralized calcium alginate hydrogels by the addition of marine derived calcium carbonate biomineral particles. Following a novel approach, we were able to obtain calcium carbonate particles of high purity and complex micro and nanostructure dependent on the source material. Three different types of alginates were selected to develop inorganic/organic scaffolds in order to correlate alginate composition with scaffold properties and cell behavior. The incorporation of calcium carbonates into alginate networks was able to promote extracellular matrix mineralization and osteoblastic differentiation of mesenchymal stem cells when added at 7 mg/ml. We demonstrated that the selection of the alginate type and calcium carbonate origin is crucial to obtain adequate systems for bone tissue engineering as they modulate the mechanical properties and cell differentiation

Particle motion and heat transfer in an upward-flowing dense particle suspension: application in solar receivers

Concentrated solar power (CSP) plants conventionally make use of molten salt as the heat transfer medium, which transfers heat between the solar receiver and a steam turbine power circuit. A new approach uses particles of a heat-resistant particulate medium in the form of many dense upward-moving fluidised beds contained within an array of vertical tubes within the solar receiver. In most dense gas-solid fluidisation systems, particle circulation is induced by bubble motion and is the primary cause of particle convective heat transfer, which is the major contributing mechanism to overall heat transfer. The current work describes experiments designed to investigate the relationship between this solids convection and the heat transfer coefficient between the bed and the tube wall, which is shown to depend on the local particle concentration and their rate of renewal at the wall. Experiments were performed using 65 µm silicon carbide particles in a tube of diameter 30mm, replicating the conditions used in the real application. Solids motion and time-averaged solids concentration were measured using Positron Emission Particle Tracking (PEPT) and local heat transfer coefficients measured using small probes which employ electrical resistance heating and thermocouple temperature measurement. Results show that, as for other types of bubbling beds, the heat transfer coefficient first increases as the gas flow rate increases (because the rate of particle renewal at the wall increases), before passing through a maximum and decreasing again as the reducing local solids concentration at the wall becomes the dominant effect. Measured heat transfer coefficients are compared with theoretical approaches by Mickley and Fairbanks packet model and Thring correlation. The close correspondence between heat transfer coefficient and solids movement is here demonstrated by PEPT for the first time in a dense upward-moving fluidised bed

Use of organic byproducts as binders in the roll compaction of caustic magnesia

This paper presents an improvement of the roll compaction process of dusty caustic magnesia carried out by using vinasses and molasses from the sugar beet industry as organic binders. The objective of this industrial study is to verify the possibility of increasing the particle size of the powdery raw material by granulation. It involved an instrumented pilot scale roller press (corrugated surface) to set the operating parameters and control the agglomeration process assessing the quality of the product established on a lot of final granules. As result, the effect of the addition of 5% (w/w) of binder by a spray nozzle atomizer on the caustic magnesia and the intensive mixing in a high shear mixer reduces notably the proportion of fines (by 30%) and increases significantly the rate of granules greater than 2. mm formed when the "moist powders" are compacted in the subsequent pressure agglomeration unit. This furtherance represents a process optimization strategy which increases the productivity and achieves a significant reduction in the quantum of failures. © 2012 Elsevier B.V. All rights reserved

Finite element analysis of thermomechanical behaviour of powders during tabletting.

In the current paper, a systematic finite element (FE) analysis of the thermo-mechanical behaviour of pharmaceutical powders during die compaction is performed using the FE solver ABAQUS. The transformation of irreversible compression work to heat during compaction is considered, so is the energy dissipated by the particle-particle friction, and die-wall friction. Die compaction with various shaped punches to produce flat-face (FF), shallow convex (SC) and standard convex (STC) tablets at different compression speeds are then analysed. Evolutions of density and temperature distributions during compaction are examined. The effect of die wall friction on thermo-mechanical behaviours is also explored. It is shown that the punch shape, the compression speed and die-wall friction significantly affect the thermo-mechanical behaviour. The maximum temperature and temperature distribution of the compressed powder changes dramatically when different shaped punches are used. The maximum temperature of the tablet upon ejection can be reduced by decreasing the die-wall friction or the compression speed

Use of organic byproducts as binders in the roll compaction of caustic magnesia

This paper presents an improvement of the roll compaction process of dusty caustic magnesia carried out by using vinasses and molasses from the sugar beet industry as organic binders. The objective of this industrial study is to verify the possibility of increasing the particle size of the powdery raw material by granulation. It involved an instrumented pilot scale roller press (corrugated surface) to set the operating parameters and control the agglomeration process assessing the quality of the product established on a lot of final granules. As result, the effect of the addition of 5% (w/w) of binder by a spray nozzle atomizer on the caustic magnesia and the intensive mixing in a high shear mixer reduces notably the proportion of fines (by 30%) and increases significantly the rate of granules greater than 2. mm formed when the "moist powders" are compacted in the subsequent pressure agglomeration unit. This furtherance represents a process optimization strategy which increases the productivity and achieves a significant reduction in the quantum of failures. © 2012 Elsevier B.V. All rights reserved

Study on the mechanical strength of primary carbonate tablets

The mechanical strength of three carbonate tablets constructed by uniaxial compaction is evaluated using a simple tester, specially designed, as a comparative method, to classify and establish correlations between the measured resistance and the physical and flow properties of each carbonate. The net compression work required to construct the tablets is also compared with the strength of the samples in order to relate it to powder's ability to convert the force applied into effective solid-solid bonds. © 2010 Elsevier B.V. All rights reserved

Development of alkali activated cement from mechanically activated silico-manganese (SiMn) slag

Silico-manganese (SiMn) slag has been used to develop alkali activated cement binder. The reactivity of SiMn slag was altered by mechanical activation using eccentric vibratory and attrition mill. The reaction kinetics during alkali activation of SiMn slag and structural reorganization were studied using isothermal conduction calorimetry and Fourier transform infrared spectroscopy. The particle size after milling was smaller in attrition milled samples but reaction started earlier in vibratory milled samples due to more reactivity. This observation was further supported by compressive strength which was highest in samples prepared from vibratory milled slag. The main reaction product was C-S-H (C= CaO, S = SiO2, H = H2O) of low crystallinity of different types with varying Si/Al and Ca/Si ratio. An attempt has been made to relate the microstructure with mechanical properties. The results obtained in this study establish technical suitability of SiMn slag as raw material for alkali activated cement © 2013 Elsevier B.V. All rights reserved

Study on the mechanical strength of primary carbonate tablets

The mechanical strength of three carbonate tablets constructed by uniaxial compaction is evaluated using a simple tester, specially designed, as a comparative method, to classify and establish correlations between the measured resistance and the physical and flow properties of each carbonate. The net compression work required to construct the tablets is also compared with the strength of the samples in order to relate it to powder's ability to convert the force applied into effective solid-solid bonds. © 2010 Elsevier B.V. All rights reserved