Recycling of washing waters from bottle cleaning machines using membranes

In daily life a large amount of water is used for the cleaning of bottles from the beverage industry. If the amount of fresh water used can be reduced by membrane technology to at least 50% of the starting values, the total costs can be reduced too. During the present work we used different types of membranes, ranging from ultrafiltration (UF) down to reverse osmosis (RO). The membrane properties were studied under cross flow conditions with varying flow rates and different transmembrane pressures. For quality assessment the chemical oxygen demand (COD), conductivity, hardness degree of water and nitrate amount of both feed and permeate solution were measured during the experiments. The most characteristic parameters for the calculation of the energy consumption were permeate flux, energy demand of the pumps and the cleaning procedures and chemicals for membrane recovery. First the experiments were performed at laboratory scale with a small membrane test cell and different types of washing waters. With these basic results a small pilot plant for continuous operation was built. The feed stream could be controlled from 10 up to 400 l/h and the transmembrane pressure could rise to 70 bar. During this part energy consumption and the cleaning possibilities of the membrane system were also studied. The water quality of the first part of the experiments could be confirmed, and the energy and performance data were used for designing a pilot to be connected directly into the water stream of the washing process where the system is to be tested under real conditions. Based on the experiments it was calculated that the amount of fresh water can be reduced by at least 55% by connecting a membrane system into the washing machine.