Pressure-driven Membrane Operations Research Articles

Membranes and Integrated Membrane Operations as Clean Technologies in the Leather Industry

The leather industry is characterized by the production of a huge amount of wastewater with a high organic/inorganic charge, causing widespread water and soil pollution. Pressure-driven membrane operations and membrane bioreactors have long been proven to be a valid approach for the treatment of tanning wastewaters aimed at the recovery of raw materials as well as for the removal of toxic and environmentally harmful substances. Such processes, opportunely integrated among themselves and/or with conventional physical-chemical and biological treatments, also provide useful protocols for the treatment of global wastewaters with significant advantages in terms of environmental protection, decrease of disposal costs, simplification of cleaning-up processes and saving of water and chemicals. This paper, as the state of the art, attempts to revise the potential and perspectives of membrane-based technologies in the leather industry with related applications in beamhouse, tanning and post-tanning operations as well as in the treatment of global wastewaters.

Localized Heating to Improve the Thermal Efficiency of Membrane Distillation Systems

Membrane distillation (MD) is a thermal-based membrane operation with high potential for the treatment of aqueous streams. However, its implementation is limited and only few examples of MD pilots can be found in desalination. One of the reasons behind this is that MD requires thermal energy for promoting the evaporation of water, which implies higher energy consumption with respect to pressure-driven membrane operations, like reverse osmosis (RO). Recently, among the different methods investigated to improve the thermal efficiency of MD, attempts for obtaining a localized heating of the feed, close to the membrane surface, were carried out. This work reviews experimental activities on the topic, dealing with both modified membranes, used under solar irradiation or coupled to an electric source, and specifically designed heated modules. The main results are reported and points of action for further optimization are identified. In particular, although at an early stage, this type of approach led to improvements in membrane flux and to a reduction of energy consumption with respect to conventional MD. Nevertheless, long tests to ensure a stable performance time, the optimization of operating conditions, the development of methods to control fouling issues, and the identification of the best module design, together with the scale-up of membranes/modules developed, represent the main research efforts needed for future implementation of localized heating strategy.

Quantification of Selective Transport of Fructose and Glucose During Membrane Filtration of Pomegranate Juice

Pomegranate (Punica granatum L.) is a nutrient-dense fruit with proven health-promoting effects due to the presence of polyphenols. Fructose and glucose are known as the main contributors to the juice sweetness. Pressure-driven membrane operations offer new opportunities and perspectives for efficiently recovering phenolic compounds without losing their activity. We investigated the fractionation of clarified juice with three commercial polyamide-thin film composite membranes having a molecular weight cutoff (MWCO) of 1–3.5 kDa. All selected membranes allowed to concentrate more than 80% of phenolic compounds, while glucose and fructose recovery are more than 60% and 70%, respectively. Among the studied membranes, the General Electric (GE Osmonics, USA) Desal GK membrane (MWCO 3.5 kDa) exhibits highest permeate concentration and selectivity of fructose at 18 bar, in total recycle mode. In the batch concentration mode, the permeate concentration decreases with time. The filtration process is mathematically described as a coupled phenomenon of the mass transport in the polarization layer over the membrane surface and selective transport in the membrane itself, for all three species. The model result is in good agreement with experimental observations under the total recycle and batch operation mode, for both the permeate flux and permeate concentration of three species. The recovery of glucose and fructose is in the range of 60% and 70%, respectively. The permeate is enriched with fructose, which is selectively transported over glucose using the GK membrane, whereas glucose is preferentially transported using GH membrane for the same feed solution. The selectivity of fructose increases with cross-flow rate. Maximum selectivity is obtained at the transmembrane pressure of 18 bar.

Perspective of Membrane Technology in Pomegranate Juice Processing: A Review.

Pomegranate (Punica granatum L.) juice is well recognized for its high content of phytochemicals with proven health-promoting effects. Conventional processing techniques including clarification with fining agents, pasteurization and thermal concentration have significant influences on bioactive compounds and antioxidant activity of the juice. The growing consumers demand for high-quality pomegranate juice as well as the industrial interest for the production of functional foods, nutraceuticals, and cosmetics from its bioactive compounds have promoted the interest for minimal processing technologies. In this context, membrane-based operations represent an innovative approach to improve the overall quality of pomegranate juice production. This review focuses on the recent advances and developments related to the application of membrane technology in pomegranate juice processing. Conventional pressure-driven membrane operations and innovative membrane operations, such as osmotic distillation and pervaporation, are discussed in relation to their potential in juice clarification, fractionation, concentration and aroma recovery. Their implementation in integrated systems offer new opportunities to improve the healthiness and quality of the juice as well as to recover, purify and concentrate bioactive compounds for the formulation of functional ingredients.

Membrane-Based Operations in the Fruit Juice Processing Industry: A Review

The fruit juice industry is one of the food sectors that has invested the most in the implementation of new technologies, such as non-thermal technologies. Among them, membrane processes are considered today well-established separation techniques to support the production and marketing of innovative fruit juices designed to exploit the sensory characteristics and nutritional peculiarities of fresh fruits. Pressure-driven membrane operations, membrane distillation, osmotic distillation and pervaporation have been widely investigated in the last few decades to replace conventional technologies used in fruit juice processing industry (i.e., clarification, stabilization, concentration and recovery of aroma compounds). This paper will review the significant progresses on the use of membrane-based operations in fruit juice processing industry in the light of the growing interest towards products with improved safety, quality and nutritional value and sustainable processes characterized by low energy consumption and low environmental impact.

Sequential pressure-driven membrane operations to recover and fractionate polyphenols and polysaccharides from second racking wine lees

Abstract Wine lees from red wine production are important sources for the recovery of antioxidant compounds, namely polyphenols and polysaccharides. In this work a set of ultrafiltration and nanofiltration membranes was investigated aiming the fractionation of polyphenols and polysaccharides present in wine lees. Permeation fluxes and solute rejection coefficients were evaluated in terms of transmembrane pressure variation. In all the evaluated pressure range (3–15 bar), NF membrane presented a linear increase in permeation fluxes such that the ratio between permeabilities (feed solution/water) stayed constant at 0.72. In contrast, for the UF membranes this ratio decreases by increasing the pressure and the membrane’s MWCO. For membranes with MWCO of 1000 and 10,000 Da, the permeabilities’ ratio is reduced from 0.34 to 0.23 and from 0.29 to 0.17, respectively, as the pressure is increased from 5 to 15 bar. Ultrafiltration has proven to be effective to separate the polysaccharides of the polyphenols, so that the polysaccharides mainly stayed in the retentate stream, while polyphenols preferentially permeated these membranes. Sequentially, considering that the NF270 membrane presented polyphenols rejections higher than 92%, the polyphenols that permeated the ultrafiltration membrane may be concentrated by nanofiltration, and therefore, it can be achieved a concentrated solution having higher antioxidant activity. Thus, the integration of different membrane separation processes emerges as an alternative for the recovery of polyphenols and polysaccharides.

Pressure-driven membrane operations and membrane distillation technology integration for water purification

In the last years, boron and arsenic are gaining wide attention in the water treatment community due to their adverse effects both on human/animal health and on agriculture. As a consequence, nowadays, the number of water treatment plants equipped with boron and arsenic removal facilities is growing. Usually it is difficult to remove them from water due to their size and charge. Therefore, in order to obtain substantial arsenic and boron reduction in the treated water, the most part of the desalination/purification plants have to use chemicals agents and Reverse Osmosis (RO) systems with several pass-stages. In this paper the potentialities of Membrane Distillation (MD) as a new and innovative technique for contaminants removal from water were investigated. The purposes of the present work are as follows: 1) to examine the efficiency of different pressure driven membrane processes for boron and arsenic removal from water; 2) to test experimentally the performance of Membrane Distillation for water purification; 3) to analyse and propose an innovative integrated system for the contaminants removal from water. In the proposed flow sheet, pressure-driven membrane operations have been synergically joined with membrane distillation technology for reaching the Process Intensification goals thanks to the possibility of overcoming the limits of the single units and, thus, to improve the performance of the overall operation. The designed system is constituted by a Reverse Osmosis (RO) step followed by a Membrane Distillation (MD) one. In this process in order to achieve, in the produced fresh water, a boron and arsenic concentration equal or less the maximum recommended values, only 36% of the RO permeate has to be sent to the MD module. Moreover MD operation allows total boron arsenic removal from water without the use of chemical agents, which results in less chemical cost and, above all, in a less environmental impact.

Integrated membrane systems for seawater desalination: energetic and exergetic analysis, economic evaluation, experimental study

Currently over 12,500 industrial desalination plants, with an average production rate of 22.8 million m 3/d, are operating worldwide to alleviate water shortage problem. In this contest, pressure driven membrane operations are today largely utilized. They compete successfully with the more traditional thermal systems due to their lower energy consumption. However, critical issues still remain open: improvement of water quality and plant global recovery factor, reduction of desalted water cost and brine disposal problem. Recent developments make realistic to affirm that integrated membrane systems might offer one of the most reliable solution to solve these problems and also a sustainable development of desalination processes. Integrated membrane processes represent an attractive opportunity because of the synergic effects that can be reached, the simplicity of these units, the possibility of advanced levels of automation and remote control. In this logic well fit in also temperature driven membrane operations, such as membrane distillation and membrane crystallization: they allow increasing fresh water recovery factor, recovery of the crystals naturally present in the concentrated streams of the desalination plants, reduction of brine disposal cost and its negative environmental impact. In this work seven flow sheets for seawater desalination have been proposed, analysed and compared. In each of them different membrane units have been integrated in pre-treatment and post-treatment stages for reaching the process intensification goals, overcoming the limits of the single units and, thus, improving the performance of the overall desalination process.

Integrating Membrane Contactors Technology and Pressure-Driven Membrane Operations for Seawater Desalination: Energy, Exergy and Costs Analysis

Membrane science and technology has nowadays become the dominant technology in water desalination. In this context, Reverse Osmosis, in combination with other pressure-driven membrane operations (i.e., microfiltration, ultrafiltration and nanofiltration), represents the most diffuse practice. Despite this success, specific actions are requested in order to solve problems related to water recovery factors, brine disposal, cost and quality of the water. In this paper, a MF–NF–RO membrane system is integrated with membrane distillation/crystallization units. The use of these membrane contactors devices, operated on the NF and/or RO retentate, permits to increase the water recovery factor up to 92.8% without a significant increase of the costs if waste thermal energy is already available to the process. In addition, the sale of salt crystals grown in high concentrated brines might potentially reduce the overall desalination cost, thus confirming the potential interest for the proposed approach. Energy and exergy analysis permitted to individuate the points of higher entropic losses and low thermodynamic efficiency for the systems, and possible solutions based on the use of energy recovery devices have been discussed in detail.

Saving of Water and Chemicals in Tanning Industry by Membrane Processes

Some results on pressure-driven membrane operations able to improve chromium recovery from spent chromium tanning baths and to desalinate water discharged from filterpress after Cr(III) precipitation are reported. Nanofiltration was employed to concentrate chromium(III) using a spiral-wound module. Chromium concentration and COD in permeate were respectively about zero and 2–3 g/l as compared to initial feed values of 2.8 and 5.2 g/l; the high chloride concentration in the permeate suggested to reuse this solution in the pickling step saving fresh water and salts. The concentrate solution presented a higher chromium purification with respect to initial feed. It was tested in retanning, and after further concentration by chemical precipitation-dissolution method, in tanning operations. Chemical and physical analyses on leather treated with these solutions showed similar characteristics with respect to use of traditional chromium solution. Reverse osmosis was employed to reduce the high salt content in waste water from filter pressing of chromium hydroxide panels. Good rejection of reverse osmosis membrane to chloride and sulphate ions suggested the use of this operation for obtaining water, to be used in washings, or to sent to biological treatment of final waste water.

Saving of water and chemicals in tanning industry by membrane processes

Some results on pressure-driven membrane operations able to improve chromium recovery from spent chromium tanning baths and to desalinate water discharged from filterpress after Cr(III) precipitation are reported. Nanofiltration was employed to concentrate chromium(III) using a spiral-wound module. Chromium concentration and COD in permeate were respectively about zero and 2–3 g/l as compared to initial feed values of 2.8 and 5.2 g/l; the high chloride concentration in the permeate suggested to reuse this solution in the pickling step saving fresh water and salts. The concentrate solution presented a higher chromium purification with respect to initial feed. It was tested in retanning, and after further concentration by chemical precipitation-dissolution method, in tanning operations. Chemical and physical analyses on leather treated with these solutions showed similar characteristics with respect to use of traditional chromium solution. Reverse osmosis was employed to reduce the high salt content in waste water from filter pressing of chromium hydroxide panels. Good rejection of reverse osmosis membrane to chloride and sulphate ions suggested the use of this operation for obtaining water, to be used in washings, or to sent to biological treatment of final waste water.