Single- and multi-stage dairy wastewater treatment by vibratory membrane separation processes

Before discharge into sewage or living waters, dairy effluents need to be effectively treated to meet the requirements defined by environmental protection regulations. In addition to the commonly used technologies, membrane separation might offer a novel solution with many remarkable advantages. Although membrane fouling often limits its industrial scale application, module vibration can reduce membrane fouling. In this study, multi-stage membrane separations with ultrafiltration (UF), as pre-filtration, and nanofiltration (NF) were investigated. On the one hand, our aim was to separate the wastewater to reach the cleanest permeate possible, on the other hand to achieve the highest organic content in the smallest volume for further energetic utilization. Firstly, with one-stage separations the effects of Vibratory Shear Enhanced Processing (VSEP) on shear rate, fluxes and rejections were investigated. These tests revealed that vibration has a positive effect on fluxes and rejections. Secondly, two types of multi-stage UF/NF separation experiments were carried out and membrane fluxes, COD rejections and flux decreasing rates were examined. In type 1, permeates of nanofiltered UF permeates achieved the lowest organic load in purified wastewater to meet European environmental threshold limits for living waters. In type 2, concentrates of nanofiltered UF concentrates reached the highest possible volume reduction ratio (VRR) resulting in higher organic content in a smaller volume, which could increase the efficiency of biogas production as an alternative post-treatment for waste management.