Technical set-up of a reverse osmosis membrane unit in continuous operation for final purification of two-phase olive oil mill wastewater

In the present work, the final purification of olive mill wastewater from two-phase extraction mills, previously subjected to a secondary treatment (OMW2ST), was performed by means of a RO operation stage in continuous operation. Within this framework, it was found that the performance of the membrane with regard to the steady-state permeate flux started to decrease over an applied net pressure of 25 bar, such that further increments of the net operating pressure did not lead to increased stable flux values. Results point that above 2.5 m s−1 cross flow the flux tends to be asymptotic. Moreover, the flux loss due to membrane fouling was similar disregarding the temperature, which would have important implications in the cost-efficiency of the process, offering the possibility of working efficiently at ambient temperature conditions, thus giving a sensible economic boost to the OMW2ST purification. The ratio between the cleaning time, consisting in 15 minutes acid cleaning plus 15 minutes alkaline/detergent cleaning, and the operating cycle (46.8-48 h) was equal to ɳtc/top (%) = 1.04 %, recovering satisfactorily the membrane permeability. Finally, the standards for discharging in public waterways or reusing the final treated effluent in the proper production process were accomplished.