Nanofiltration as tertiary treatment for the reuse of dairy wastewater treated by membrane bioreactor

Due to the growth in the costs of collecting and treating water, and with the treatment and discharge of effluents, reuse has become an increasingly viable option for industries. This study aimed at evaluating the application of membrane bioreactor (MBR) as secondary and nanofiltration (NF) as tertiary treatment for the reuse of dairy wastewater, focusing on determining the best NF operating conditions. MBR showed high removal efficiency for COD (mean of 98%) and nutrients (86% total nitrogen and 89% phosphorus). However, the concentration of dissolved solids in the permeate still prevented its reuse. In order to remove these solids, the MBR permeate was nanofiltrated, and three different cross-flow velocities were evaluated. Due to lower external fouling and better quality of the permeate, the velocity of 7.8 m/s was selected as the most suitable for the NF system. The optimum permeate recovery rate was determined to be 45% since, at values higher than this, the quality of the permeate dropped. The proposed treatment system (MBR + NF) showed overall efficiencies of 99.9% for COD and 93.1% for total solids. The final treated wastewater could be reused as water for cooling, steam generation, or washing of external areas and trucks. (C) 2014 Elsevier B.V. All rights reserved.