Effect of Operating Conditions on the Nanofiltration of Landfill Leachates: Pilot-Scale Studies

Abstract

Landfill leachate is the name given to water that has passed through solid waste and contains organic, metal and mineral contaminants. Therefore, this effluent must be treated before being discarded. Owing to increasingly strict requirements of rejection norms and stabilization of landfill leachates with time, new techniques have now appeared in this field. Reverse osmosis has been developed in many European countries. However, this selective and costly technique is only justified when norms are drastic. The present work aims at a better expertise of nanofiltration technique to eliminate organic (COD) and inorganic pollutions of stabilized landfill leachates. Two organic membranes (450 Da cut off) are studied for pilot- scale testing. The landfill leachates of Saint Nazaire CET have been chosen for this study. First, hydrodynamic parameters are optimised to get the best retention and permeation flux. The applied pressure (ΔP) is fixed at 20 × 105 Pa and tangential velocity (U) at 3 m s−1. This investigation shows that nanofiltration may be a good alternative to reverse osmosis for treatment of landfill leachates, where the COD and ions elimination depends on the membrane used. The permeate has a lower COD than the environmental norm applied at Saint Nazaire (120 mg l−1 of O2). The membrane MPT-31 has low retention of monovalent salts, which allows a 75% conversion rate at the permeation steady-state flux of about 60 l h−1 m−2, and the conditions cited above. The comparison of hydraulic resistances shows flux drop is essentially due to reversible phenomena (concentration polarization). Irreversible fouling results mainly from the adsorption of some landfill leachates components on membranes.