Recycling of spent process water in the food industry by an integrated process of biological treatment and membrane separation

An integrated membrane filtration process was developed to produce water of drinking quality out of polluted process water from small and medium-sized enterprises in the food and beverage industries. It comprised a membranesupported bioreactor and a combined nanofiltration/UV disinfection stage. The process was implemented in demonstration scale (up to 1.5 m3/h) at a fruit juice production plant. In the bioreactor, COD removal rates >95% were achieved. After the second treatment step, the chemical and bacteriological parameters of the treated water met the limits of the German Drinking Water Act (DWA). After authorisation procedure by the responsible authorities, the technology tested was granted approval for water reuse in the food industry. The influence of biological process parameters on the flux of the bioreactor membranes was investigated as well as backflushing and CIP cleaning procedures. In the second treatment step membrane permeability depending on different operating conditions was investigated. The treated water can be re-used for various purposes, e.g. boiler make-up water, cooling water. Amortisation periods of less than 3 years are possible, depending on the water re-use potential.