Reuse of tannery wastewaters by combination of ultrafiltration and reverse osmosis after a conventional physical-chemical treatment

Due to the high conductivity of the global wastewater from a tannery industry, wastewater reuse is only possible if a reverse osmosis process is implemented in the wastewater treatment. The supernatant of a physical-chemical treatment is still very polluted, containing high COD values between 3000 mg/l and 4000 mg/l and conductivities of nearly 20 ms/cm. In this work, a combination of filtration, ultrafiltration and reverse osmosis is evaluated as treatment for the physical-chemically treated wastewater. Filtration was carried out using microfilters as a previous stage to ultrafiltration process. Ultrafiltration tests were performed in a laboratory plant. Organic membranes from Orelis with different cut-offs were tested to optimize the rejection and the permeate flux. Finally, the reverse osmosis step was carried out using an ESPA-1 membrane from Hydranautics. Results showed high COD values in ultrafiltration permeates (between 2000 and 3000 mg/l). A polyethersulfone membrane with cut-off of 30 kD was chosen for the pre-treatment of the reverse osmosis membrane. Permeate fluxes of the reverse osmosis membrane reached 40 l/(m2h) at 30 bar. Though membrane fouling was not observed during RO experiments, an industrial scale plant should pay special attention to a probable flux decrease due to the scaling if a high conversion is aimed.