Spent process water desalination and organic removal by membranes for water reuse in the food industry

In this study, it could be shown that, drinking water consumption in the food industry could be drastically reduced by water reuse. Boiler make-up water or warm cleaning water could be economically produced from lowcontaminated process water (electrical conductivity below 3000 µS/cm and COD below 700 mgO2/l) by membrane desalination and organic removal. Due to varying concentrations in impurities in the different types of spent process water (milk processing and meat processing) experiments were performed with different pre-treatment steps and main membrane treatment stage. The post-treatment stage guarantees that the requirements for residual inorganic and organic concentration in the water are maintained and keeps microorganism concentration below limit values. A demonstration plant, consisting of the following stages, was set up: (a) pretreatment: belt filtration, cartridge filtration (two stages) and UV predisinfection; (b) main treatment: first stage, nanofiltration with sprial wound modules; (c) post-treatment: second stage, nanofiltration with sprial wound modules and (d) UV disinfection. It was shown that it was possible to obtain, from the spent process water streams, water for reuse e.g. boiler make-up water (electrical conductivity of < 40µS/cm at 25°C; Ca2+ < 0.4 mg/l; COD < 10 mg O2/l etc.) or warm cleaning water (el. conductivity below 200 µS/cm, Ca2+ < 1mg/l, TOC < 4 mg/l etc.)

In this study, it was possible to illustrate, using a demonstration plant with a capacity of 1– 2 m3/h, on the basis of the treatment of two lowcontaminated process water streams in the food industry that by a combination of pretreatment, membrane filtration and UV disinfection, treated water of a defined quality could be obtained. It was shown by numerous chemical and microbiological analyses that with a two-stage membrane combination of nanofiltration, appropriate design and build-up of the treatment plant and suitable cleaning procedure for the plant that the limit values for water reuse i.e. boiler makeup water or warm cleaning water could be adhered to at all times.