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 fo od industry could be drastically reduced by water reuse. Boiler make-up wat er or warm cleaning water could be economically produced from low contamina ted process water (electrical conductivity below 3000 muS/cm and COD below 700mgO(2)/l) by membrane desalination and organic removal. Due to varying c oncentrations in impurities in the different types of spent process water ( milk processing and meat processing) experiments were performed with differ ent pre-treatment steps and main membrane treatment stage. The post-treatme nt stage guarantees that the requirements for residual inorganic and organi c concentration in the water are maintained and keeps microorganism concent ration below limit values. A demonstration plant, consisting of the followi ng stages, was set up: (a) pretreatment: belt filtration, cartridge filtrat ion (two stages) and UV predisinfection; (b) main treatment: first stage, n anofiltration with sprial wound modules; (c) post-treatment: second stage, nanofiltration with sprial wound modules and (d) UV disinfection. It was sh own that it was possible to obtain, from the spent process water streams, w ater for reuse e.g. boiler make-up water (electrical conductivity of < 40 m uS/cm at 25 degreesC; Ca2+<0.4mg/l; COD < 10mg O-2/l etc.) or warm cleaning water (el. conductivity below 200 muS/cm, Ca2+< 1mg/l, TOC < 4mg/l etc.).