On the effect of ph and operating conditions on nanofiltration of two-phase olive mill wastewater

In the present work, a thin-film composite polymeric nanofiltration (NF) membrane is examined for the tertiary treatment of secondary-treated two-phase olive mill wastewater (OMW2-ST). Overcoming the deleterious fouling phenomena persistently encountered in membrane processes managing wastewater streams was indeed pursued. With this purpose, the point of zero charge (PZC) of the membrane was determined as a key for the operating conditions. This will determine the intensity of the electrostatic interactions between the organic and inorganic solutes present in the OMW2-ST stream and the active surface of the NF membrane, further to the steric effects. Working above the point of zero charge (pH > 5.8) of the membrane ensured highsteady-state permeate productivity (59.6 L h-1m-2), also economically sustainable in time owed to minimizationof the permeate flux decay (5.5 %). Moreover, these conditions also provided high feed recovery (90%) and significant rejection efficiencies for the electroconductivity (58.1%) and organic matter (76.1%). This led to a purified permeate stream exiting the NF membrane operation exhibiting average EC and COD values equal to1.4 mS cm-1 and 45 mg L-1. This permits complying with the water quality parameters established by different regulations for discharge public waterways and irrigation purposes.