In the last 30 years, membrane processes have become major tools in the food industry. This industry represents the second sector of membrane applications, after water treatment, and on equal terms with pharmaceutical and biotechnology applications.Among the food sector, the dairy industry has undoubtedly developed the most advanced filtration procedures for concentration and fractionation of molecules from milk and its derivates. The first membrane development in the separation procedures of milk components occurred in the late 1960’s with the advent of membrane separation. This has spawned a new industry for whey treatment as well as new avenues for cheese-making. Since then, the membrane equipment has been implemented throughout the dairy processing chains: milk reception, cheese-making, whey protein concentration, fractionation of protein, effluents treatment. Nowadays, 40 percent of the membrane food applications are developed in the dairy industry.
INFLUENT TREATMENT FOR DAIRY INDUSTRY
Concentration of whey on its production site is the major application of reverse osmosis (RO) owing to its flexibility and energy consumption (9-20 kWhm-3 water removed) compared to vacuum evaporation (almost equal to 100 kWhm-3). The maximum concentration that can be obtained by RO is 18-27 per cent dry matter, limited by high osmotic pressure, high retentive viscosity, calcium phosphate precipitation and lactose crystallisation.
Because of the high salt content of whey (8-20 per cent dry matter), which generates numerous processing difficulties and nutritional imbalance (particularly in infant food), it became advantageous to demineralise whey before evaporation. Whey was demineralised in the range 50-95 per cent by electro dialysis and/or ion exchange, but these operations led to a large volume of polluting effluents, high investment and running costs.
Nano-filitration became therefore an industrial alternative, making it possible to reach simultaneously the concentration of dry matter (20-22 per cent at VRF 4-5) and demineralisation (25-50 per cent and even 90 per cent with di-filtration). The process is competitive to RO and electro dialysis.
Demineralisation is more selective (high reduction of monovalent ions and low reduction of divalent nutrition value ions like calcium). NF selectivity remains satisfactory even at the highest demineralisation rate; losses of lactose and nitrogen are low. In addition, the NF step significantly improves the technological characteristics of the concentrate and gives it higher value (increase in yield of lactose crystallisation, and low hygroscopy of obtained powders).
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EFFLUENT TREATMENT FOR DIARY INDUSTRY
The treatment of effluents strongly benefits from the potentialities of filtrations. Several types of effluents are currently treated in the industry: washing waters of rennet casein precipitate (NF); white (flushing) and pre-rinsing waters (UF, NF, RO). The outcome is a highly significant improvement of water quality after treatment and the re-use of milk components (either as recycling back to the production unit or animal feed). Cheese brines are widely recycled after a MF or UF step, which strongly reduces microbiological counts, without altering the chemical composition (nitrogen, ash) contrarily to conventional pasteurisation. Alkaline and acid Cleaning-in-place solutions, which are periodically drained to waste due to their pollution load, can be regenerated using NF, UF or MF.