Valorization of agro-food products and by-products by membrane-based processes: a sustainable approach

With a market volume of 800-850 million of Euro/year, the food industry represents the second biggest worldwide industrial market for membranes after water and wastewater treatment with a growth of around 7.5% per year [1]. Pressure-driven membrane operations such as microfiltration (MF), ultrafiltration (UF), nanofiltration (NF) and reverse osmosis (RO) are key technologies in the food industry. The basic properties of these processes make them ideal for the treatment of both food products and by-products; high selectivity, minimization of thermal damage, low energy consumption, modularity and easy scale-up, no phase change and use of chemical additives are typical advantages over conventional separation technologies. Other membrane processes, such as membrane bioreactors (MBRs) and membrane contactors (MCs), have been also investigated in recent years for selected applications in the food industry. The selection of membrane materials and the optimization of operating conditions are key factors in order to improve the efficiency of these processes in terms of productivity and selectivity through the control of concentration polarization and membrane fouling phenomena. Several processes have been investigated at ITM-CNR in the last years in order to improve the quality of food products (i.e. clarification and concentration of fruit juices, wine and must, etc.), as well as to valorise typical wastes of the agro-food production through the recovery of nutri-functional compounds, to be used as supplements or additives in food. Selected applications in different areas of the agro-food processing industry, including olive mill, artichoke, liquorice and citrus wastewaters, are analysed and discussed in relation to separation processes, molecule properties, membrane characteristics and key factors affecting the membrane performance in terms of productivity and selectivity towards target compounds [2,3]. Flow-sheets of integrated membrane processes have been proposed on the basis of experimental results according to a market-competitive and environmentally sustainable way. A conceptual process design in orange juice production is depicted in Figure 1. The implementation of hybrid membrane-based processes in these areas permits to rationalize both direct and indirect energy consumption, with improved product quality, process capacity and selectivity, decreased equipment-size/production-capacity ratio and waste production so resulting in cheaper and sustainable technical solutions.