Concentrate reduction in NF and RO desalination systems by membrane-in-series configurations-evaluation of product water for reuse in irrigation

Wastewater reclamation and reuse became essential to meet the more restrictive discharge limits and to overcome the water scarcity issue. Industrial wastewaters treated by membrane bioreactor (MBR)systems generally include high amounts of salinity, nutrients as nitrogen and phosphorus, heavy metals, hardness, etc. which in most cases, do not fit with discharge and reuse limits. Membrane processes like nanofiltration (NF)and reverse osmosis (RO)are widely adopted for secondary effluent treatment producing high-quality water. Since untreated brine can damage the environment, this work focused on reduction of amount of concentrate by working in membrane-in-series configuration. Tests with two membrane-in-series (NF90 + NF90, BW30 + BW30, BW30 + NF270 combinations)were performed as the concentrate stream of the first one was fed to the second one. Water recoveries were over 80% in each experiment. Water fluxes of 44.0, 41.4 and 73.4 L/m2.h were obtained with NF90 + NF90, BW30 + BW30, BW30 + NF270 combinations, respectively. Also, salinity rejections represented by electrical conductivity were 92.9%, 97.4% and 42.9% for NF90 + NF90, BW30 + BW30, BW30 + NF270 configurations, respectively. Permeates of BW30 + BW30 and NF90 + NF90 combinations seem to be useable for agricultural irrigation although soil permeability is an important issue, not only ion concentrations and salinity of water used.