Removal of dye from aqueous solution using a combination of advanced oxidation process and nanofiltration

In order to have energy and cost effective separation of dyes, a combination of advanced oxidation process (AOP) using Fenton's reagent and nanofiltration (NF) is proposed. Three combinations of AOP and NF are studied using a synthetic solution of eosin dye. Scheme-1 is AOP followed by NF. Scheme-2 is NF followed by AOP. And Scheme-3 is two-step NF. The concentration of eosin dye studied in the first step of each of the schemes is in the range of 70-200 mg/l. The operating transmembrane pressures for NF steps are 552, 689 and 828 kPa. The crossflow velocities are 0.46, 0.69 and 0.91 m/s. The schemes are compared for permeate flux, permeate concentration and duration of operation. In Scheme-1, AOP is conducted for 30 min, and then subjected to NF, whereas in Scheme-2, the time needed for AOP is more than 3 h to achieve the concentration level of the dye below 1 mg/l. Thus, it is found that Scheme-1 is superior to Scheme-2 due to lesser time requirement. However, Scheme-3 involving no AOP, is also suitable for dye separation as the final eosin concentration in the permeate falls below 1 mg/l. Scheme-1 is found suitable for dye concentration of 70 mg/l and the most appropriate composition of Fenton's reagent is 1665 mg/l of H2O2 and 347.5 mg/l of FeSO4·7H2O. Suitable NF operating conditions in step 2 of Scheme-1 is transmembrane pressure of 689 kPa and crossflow velocity of 0.91 m/s. In Scheme-3, the suitable operating conditions for NF in both the steps are 828 kPa transmembrane pressure and 0.91 m/s crossflow velocity. Scheme-2 is found to be unsuitable.