Effect of concentrate recirculation on the product water quality of integrated MBR – NF process for wastewater reclamation and industrial reuse

Abstract

In this study, field tests were performed at the wastewater treatment plant of ITOB-Organized Industrial Zone located in Menderes, Izmir where membrane bioreactor (MBR) process has been employed for wastewater treatment. For advanced treatment of MBR effluent, a mini pilot scale membrane test unit having nanofiltration (NF) membranes was employed. For this study, only NF90 membrane was used for tertiary treatment of different feed mixtures. The feed mixtures were obtained by mixing MBR effluent and concentrate stream of NF90 membrane at different proportions. During field tests, while some amount of concentrate stream of NF90 membrane was sent to the feed tank with MBR effluent to obtain feed mixtures, the remaining part of concentrate stream was discharged to the MBR pool.Water qualities of permeate and feed were investigated by measuring various physicochemical parameters such as total dissolved solid (TDS), salinity, conductivity, pH, turbidity, chemical oxygen demand (COD), total suspended solid (TSS), color, Na+, Ca2+, K+, Mg2+, HCO3−, SO42−, Cl−,PO4-P, NH4-N, NO3-N, NO2-N, total nitrogen (TN), CaCO3 hardness, total organic carbon (TOC) and SiO2 concentrations. By increasing the ratio of NF90 concentrate to MBR effluent ratio in the feed mixture, permeate flux and average rejections of some parameters slightly decreased although some of the rejections slightly increased. Quality of product water obtained from various combinations of feed water was investigated and compared with the standards of cooling and boiling feed water for industrial usage. Also, reuse of product water as process water in paper and textile industries was discussed.