Supported Liquid Membranes (SLMs) have been widely studied as feasible alternative to traditional processes for separation and purification of various chemicals both from aqueous and organic matrices. This technique offers various advantages like active transport, possibility to use expensive extractants, high selectivity, low energy requirements and minimization of chemical additives. SLMs are not yet used at large scale in industrial applications, because of the low stability. In the present paper, after a brief overview of the state of the art of SLM technology the facilitated transport mechanisms of SLM based separation is described, also introducing the small and the big carrousel models, which are employed for transport modeling. The main operating parameters (selectivity, flux and permeability) are introduced. The problems related to system stabilization are also discussed, giving particular attention to the influence of membrane materials (solid membrane support and organic liquid membrane (LM) phase).
Various approaches proposed in literature to enhance SLM stability are also reviewed. Modification of the solid membrane support, creating an additional layer on membrane surface, which acts as a barrier to LM phase loss, increases system stability, but the membrane permeability, and then the flux, decrease. Stagnant Sandwich Liquid Membrane (SSwLM), an implementation of the SLM system, results in both high flux and stability compared to SLM. Finally, possible large scale applications of SLMs are also
reviewed, evidencing that if the LM separation process is opportunely carried out (no production of byproducts),
it can be considered as a green process.
supported liquid membrane; flux; selectivity; stability; application of liquid membranes
Department of Chemical Engineering and Materials, University of Calabria Via P. Bucci, 44/A, I-87036 Rende (CS)-Italy
In this study, response of reversibility of membrane flux during chemically enhanced backwash (CEB) to changes in filtration time, filtration flux and coagulant concentration dosing during ultrafiltration (UF) process was investigated using a regression model. The model was developed via empirical modelling approach using response surface methodology. In developing the model, statistically designed UF experiments were conducted and the results compared with the model output. The results showed that
the performance of CEB, evaluated in terms of the reversibility of the membrane flux, depends strongly
on the changes in coagulant concentration dosage and the filtration flux. Also the response of the reversibility of membrane flux during CEB is independent of the filtration time. The variance ratio, VR << Fvalue and R2 = 0.98 obtained from the cross-validation experiments indicate perfect agreement of the model output with experimental results and also testify to the validity and suitability of the model to predict reversibility of the membrane flux during CEB in UF operation.
ultrafiltration; empirical model; response surface methodology; backwash
M.O. Daramola : Department of Chemical Engineering, Obafemi Awolowo University, Ile-Ife, Nigeria
A.G. Adeogun : National Centre for Hydropower Research and Development, PMB 1515, University of Ilorin, Ilorin, Nigeria
A photovoltaic powered ultrafiltration and reverse osmosis system was tested with a number of natural groundwaters in Australia. The objective of this study was to compare system performance at six remote field locations by assessing the impact of water composition and fluctuating energy on inorganic contaminant removal using a BW30-4040 membrane. Solar irradiance directly affected pressure
and flow. Groundwater characteristics (including TDS, salts, heavy metals, and pH), impacted other performance parameters such as retention, specific energy consumption and flux. During continual system operation, retention of ions such as Ca2+ and Mg2+ was high (> 95%) with each groundwater which can be attributed to steric exclusion. The retention of smaller ions such as NO3 - was affected by weather conditions and groundwater composition, as convection/diffusion dominate retention. When solar irradiance was insufficient or fluctuations too great for system operation, performance deteriorated and retention
dropped significantly (< 30% at Ti Tree). Groundwater pH affected flux and retention of smaller ions (NO3 - and F-) because charge repulsion increases with pH. The results highlight variations in system performance (ion retention, flux, specific energy consumption) with real solar irradiance, groundwater composition, and pH conditions.
brackish groundwater; photovoltaics; reverse osmosis; specific energy consumption; solar energy
Laura A. Richards, Bryce S. Richards : School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh, EH14 4AS, United Kingdom
Andrea I.Schafer : School of Engineering, The University of Edinburgh, Edinburgh, EH9 3JL, United Kingdom
This work deals with the use of High Resolution Scanning Electron Microscopy (HRSEM) to verify ultrafiltration membrane selectivity at the end of the production line as well as membrane ageing. The first part of this work is focused on new membranes. It is shown that it is better to use sputtering metallization than vacuum deposition, as this latter technique entails thermal damage to the skin layer. Moreover, the impact of the metallization layer on the determination of the membrane pore size is studied
and it is observed that no impact of the metallization step can be clearly defined for a metallization layer ranging from 3 to 12 nm. For example, an average pore size of 16.9 nm and a recovery rate of 6.5 % are observed for a 150 kDa cellulose acetate membrane. These results are in agreement with those given by the manufacturer: pore size ranging from 10 to 15 nm and recovery rate ranging from 5 to 10 %. The second part of this work focuses on the study of membrane ageing. A PVDF hollow fibre membrane is studied. It is shown that a 65 % decrease in the permeate flux can be linked to a decrease in the number of pores at the surface of the membrane and a decrease in the recovery rate. In conclusion, a mapping of the pores is performed for several new hollow fibre membranes used to produce drinking water, made of different materials, with different geometries and molecular weight cut-off. These results provide reference data that will help better understand the phenomena of membrane fouling and membrane ageing.
HRSEM; mapping; drinking water; membrane ageing
Y. Wyart, P. Moulin : Laboratoire de Mecanique, Modelisation et Procedes Propres (M2P2-CNRS-UMR 6181),
Universite Paul Cezanne Aix Marseille, Europole de l\'Arbois, BP 80, Bat. Laennec, Hall C, 13545 Aix en Provence cedex 04, France
S. Nitsche, D. Chaudanson : Centre Interdisciplinaire de Nanoscience de Marseille (CINaM-UPR 3138), Campus de Luminy,
13288 Marseille Cedex 09, France
K. Glucina : SUEZ ENVIRONNEMENT, CIRSEE, Pole Qualite Eau, 38, rue du President-Wilson, 78230 Le Pecq, France
At steady state, the simultaneous transport of sulphuric acid and nickel sulphate through an anion-exchange membrane Neosepta-AFN (Astom Corporation, Tokyo, Japan) was investigated in a twocompartment counter-current dialyzer with single passes. The transport was quantified by the recovery yield of acid, rejection of salt and four phenomenological coefficients, which were correlated with the acid and salt concentrations in the feed. The phenomenological coefficients were determined by the
numerical integration of the basic differential equations describing the concentration profiles of the components in the dialyzer. This integration was combined with an optimizing procedure. The experiments proved that the acid recovery yield is in the limits from 63 to 91 %, while salt rejection is in the limits from 79 to 97 % in the dependence on the volumetric liquid flow rate and composition of the feed.