Influence of nanofiltration concentrate recirculation on performance and economic feasibility of a pilot-scale membrane bioreactor-nanofiltration hybrid process for textile wastewater treatment with high water recovery

The membrane bioreactor-nanofiltration hybrid process has been proven to be promising for textile wastewater treatment. High water recovery could be achieved through the recirculation of nanofiltration concentrate to the membrane bioreactor. However, its influence on both the performance and economic feasibility of the membrane bioreactor-nanofiltration was not fully investigated, especially at larger scale. In this study, a pilot-scale membrane bioreactor-nanofiltration system was used for the on-site treatment of textile wastewater. The hydraulic retention time of membrane bioreactor was first optimized (Stage A), then the membrane bioreactor-nanofiltration system was operated at different water recovery rates (Stage B). The results showed that the sludge activity was relatively stable, but the nanofiltration concentrate recirculation significantly influenced the pollutants removal efficiencies of membrane bioreactor. The membrane bioreactor-nanofiltration effluent is suitable for reuse and the high water recovery could bring considerable benefits that enhance the economic feasibility of the process with a net income of 1.24 M USD/y and a payback period of 3.11 y.