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

Abstract

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 low-contaminated process water (electrical conductivity below 3000μS/cm and COD below 700mgO 2/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; Ca 2+<0.4mg/l; COD<10mg O 2/l etc.) or warm cleaning water (el. conductivity below 200 μS/cm, Ca 2+<1mg/l, TOC< 4mg/l etc.)