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Liquid–liquid displacement porometry (LLDP), is proposed to estimate the molecular weight cut-off value of Ultrafiltration (UF) membranes. Several commercial UF membranes are analysed by using LLDP and their pore size distributions have been used to estimate the molecular weight cut-off as should be obtained by dextran retention. Results compared reasonably with nominal cut-off values given by manufacturers. The method offers a fast and accurate way to assign cut-off values for UF membranes, without having to perform expensive and time consuming solute retention tests, which bring results very often difficult to compare due to the difficulties in the standardization of such methods.

Reverse osmosis (RO) and nanofiltration (NF) processes gain more and more interest in the desalination market. Recently, seawater reverse osmosis (SWRO) has become more widespread, using relatively large plants, whilst NF is being applied before thermal desalination, as an advanced treatment for increased efficiency of thermal processes. A proper and reliable seawater treatment before RO and NF, capable to retain suspended solids that cause fast fouling and plugging of sensitive spiral wound membrane modules, is a key to success of desalination processes. Reliability, high and constant quality of permeate, regardless of changes in seawater characteristics, are major advantages of microfiltration/ultrafiltration (MF/UF) over conventional pre-treatment, allowing a stable and high performance of RO and NF processes. This experimental work evaluates performance of two different UF, hollowfibre membrane modules, when fed directly with raw seawater taken from the industrial harbour of Genoa. The study reports the performance of nanofiltration process fed with UF permeate versus the performance of NF fed with raw seawater.

Several UF membranes with fairly different structure have been characterized by using a liquid–liquid displacement porometer, which has been developed under a close collaboration of our laboratories. Three polysulfone membranes from Millipore and three polycarbonate membranes from Nuclepore–Whatman were studied. The results of pore size distributions showed nice reproducibility and accuracy. The technique is also able to accurately evaluate membrane porosity for membranes with simple cylindrical pore-like structure. In addition the possibility to estimate MWCO, by LLDP results, makes the technique very useful for process selection. Finally SEM pictures of the Millipore membranes show that usual porosimetric liquids do not alter membrane structure.

Membrane bioreactors have been extensively studied for the treatment of domestic wastewater. In this paper we describe the application of membrane bioreactors for the depuration of non-civil wastewater coming from the washing of mineral oil storage tanks. Microfiltration hollow-fibre membranes were submerged in the bioreactor where the biomass used the hydrocarbon as a substrate. The performance of the submerged membrane bioreactor was analysed in terms of COD and hydrocarbon removal during different experiments that showed the high efficiency of the system. Particular care was taken in carrying out the operations in the sub-critical flux region. The reactor performance was very high, with removal efficiencies ranging between 93% and 97%, also when the concentration of hydrocarbon was very high. Moreover, the hydraulic retention times used in this work were lower compared to those used in an activated sludge process. Some kinetic parameters for the COD and the hydrocarbon removal were assessed.

iofouling is the undesirable accumulation of microorganisms on the membrane surface and it is one of themajor problems affecting the performance and the economy of many membrane installations for the treatment ofseawater and wastewater. Unlike inorganic fouling, biological fouling due to microorganisms can be dependent ontheir growth rate. The paper examines from a theoretical point of view the influence of the membrane recoveryratio on the concentration of biomass in the membrane module. An attempt of validation of the model has been triedusing a submerged microfiltration hollow-fibre membrane set-up.

Polyvinylidene fluoride (PVDF) membranes were prepared by water immersion of a binary PVDF-solvent solution cast on the outer surface of a porous tubular support. During immersion the free shrinkage of the cast solution was hindered by the support and consequently the nascent membrane was subjected to a stretching action that caused pore formation. A laboratory scale device was realized for casting operation and some preparative parameters were studied to control the deposition of the PVDF solution on the porous support. Membranes were characterized through scanning electron microscope observations, air permeability measurements, ultrafiltration tests and membrane distillation experiments. These latter were carried out with a laboratory unit fed with 3 w/v% aqueous NaCl solution at 69°C. The membranes were housed in a tubular cell with the feed flowing on the shell side and the sweeping air in the membrane lumen. The effect of feed and gas velocity on the membrane performance was investigated and the obtained results were compared with those of commercial tubular membranes tested on the same unit. The influence of casting parameters on the morphology and permeation properties of the membranes was also studied.

The results of preliminary experiments for the production of new tomato juices based on the introduction of a microfiltration (MF) stage before the reverse osmosis (RO) stage are reported. Ceramic multichannel membranes with an average pore size in the micrometer tenths were used in the MF stage to obtain a clarified serum to be concentrated by RO and a concentrated pulp to be used for remixing with the RO concentrate, in order to formulate new tomato juices. High temperature and pressure resistant spiral-wound RO membranes were used to concentrate the clarified serum up to 14–15 Brix with permeate fluxes around 20 L/m2h..

Poly(vinylidene) fluoride (PVDF)-ZrO2 composite membranes were prepared by casting and immersion into a water bath of ternary suspensions obtained by adding additional amounts of ZrO2 particles to PVDF solutions. Methods to obtain an intimate dispersion of the inorganic particles in the PVDF solutions were developed. A large variety of supported and unsupported membranes were prepared by varying some of the preparative parameters such as: the PVDF solvent (N-methyl-2-pyrrolidone or triethylphosphate), the total concentration and the PVDF/ ZrO2 ratio in the ternary dispersion. Membranes were also cast from a binary solution of PVDF and solvent for comparison purposes. All the obtained membranes were characterized by scanning electron microscope observations and ultrafiltration tests. The effect of the above-mentioned preparative parameters on the structure, flux and dextran retention properties of the membranes is discussed.

In this paper the main techniques (microscopy observations, molecular weight cut-off determinations, porosity measurements) for characterizing ultrafiltration membranes are critically reviewed and discussed. Particular attention is devoted to the problem of evaluating the porosity of the membrane skin layer. Porosity results obtained by testing some commercial ultrafiltration membranes with an automatic instrument based on the combined bubble pressure and solvent permeability method are reported.

In this paper the effect of some preparative parameters on the structure, porosity and UF performances of membranes prepared by the phase inversion, process is shown. The influence of the type of support used to cast solutions on membrane properties is also reported. Some practical aspects in the production of tubular and hollow fiber membranes are finally discussed.

By changing properly the preparation conditions, it is possible starting from the same polymer to obtain asymmetric membranes with different morphology and U.F. performances. The SEM cross-section give us information about the overall structure. Unfortunately these results are not enough, as the membranes properties mainly depend from the thin dense skin layer poorly resolved with the SEM technique. On the other hand, rejection and fluxes investigated with the conventional U.F. pilot units only supply an indirect information about skin layer properties. With the purpose to improve the knowledge on this topics, we have developed an automatic porosimeter based on the combined bubble pressure and solvent permeability method in order to obtain the pore number and radius distribution of the membrane in wet conditions. Despite some problems related to the absolute values we have obtained some interesting results both for new and used membranes.

Microporous polysulfone membranes were prepared from casting solutions of polysulfone, solvent and polyvinylpyrrolidone as additive. The membranes were characterized by scanning electron microscope observations, porosity measurements and ultrafiltration tests. The effect of polyvinylpyrrolidone and its molecular weight on the viscosity of the casting solutions and the properties of the membranes is discussed.