Treatment of spent process water from a fruit juice company for purposes of reuse: hybrid process concept and on-site test operation of a pilot plant

In order to treat spent process water from companies of the food and beverage industries up to drinking water quality, a process concept was developed consisting of the following two treatment steps: (1) biological COD reduction using a membrane bioreactor (MBR) in which the active biomass as well as other particulate matter were completely retained by means of immersed hollow-fibre MF membranes, and (2) subsequent reduction of bacterial germs, residual organics as well as of inorganic constituent compounds by means of downstream two-stage nanofiltration with integrated UV disinfection. This hybrid process was tested by operating a pilot plant (capacity 100 l/h) for 6 months at a fruit juice company in order to treat spent process water (COD: 2,500-6,500 mg/l; electrical conductivity: 2,300-4,700 muS/cm) from the on-site mixing and equalising tank. The process under study proved to be technically feasible and reliable. The treated water was partially desalted and fulfilled both the chemical and bacteriological standards required by the German Drinking Water Act. Therefore, it can be reused, for example, as cooling or boiler make-up water as well as for pasteurisation, preparation of conveyor belt lubricants and bottle washing. Based on the results obtained, a preliminary evaluation was conducted to determine the investment and operating costs required for implementation of the tested hybrid process.