Water recovery from textile bath wastewater using combined subcritical water oxidation and nanofiltration

Abstract

Abstract In this study, textile dye bath wastewater was treated by subcritical water oxidation (SCWO) and pressure-driven membrane process. 54.5% of chemical oxygen demand (COD) reduction and 91.7% of color removal were obtained using eco-friendly SCWO method in the presence of H2O2. Box-Behnken design was performed to optimize the SCWO process and precision of the models were evaluated by ANOVA. Two different nanofiltration (NF270 and NF90) membranes were tested before and after SCWO pretreatment. The effect of membrane type (NF270 and NF90) and transmembrane pressure (10, 20, 30, 40 bar) were studied to improve COD reduction and colour removal efficiency. The results showed that steady-state permeate flux increased from 6.6 to 23.5 L/m2.h for NF270 at 30 bar and from 10.0 to 12.4 L/m2.h for NF90 membrane at 40 bar when SCWO was applied as the pretreatment method. The results depicted that SCWO pre-treatment increased the permeate flux almost 2–3 fold. COD was also tested for all permeates and the highest COD reduction efficiency was obtained for SCWO + NF90 combined process. The highest COD reduction and color removal efficiencies were obtained as 96.1% and 99.3%, respectively, for combined SCWO + NF90 process at 40 bar. The proposed combined SCWO + NF90 process was successfully used to recover wastewater from textile dye bath wastewater.