Effect of operating conditions on the nanofiltration of landfill leachates: Pilot-scale studies

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 str ict 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 wor k aims at a better expertise of nanofiltration technique to eliminate organ ic (COD) and inorganic pollutions of stabilized landfill leachates. Two org anic membranes (450 Da cut off) are studied for pilot- scare testing. The l andfill leachates of Saint Nazaire CET have been chosen for this study. Fir st, hydrodynamic parameters are optimised to get the best retention and per meation flux. The applied pressure (Delta P) is fixed at 20 x 10(5) Pa and tangential velocity (U) at 3 m s(-1). This investigation shows that nanofil tration may be a good alternative to reverse osmosis for treatment of landf ill leachates, where the COD and ions elimination depends on the membrane u sed. The permeate has a lower COD than the environmental norm applied at Sa int Nazaire (120 mg l(-1) of O-2). The membrane MPT-31 has low retention of monovalent salts, which allows a 75% conversion rate at the permeation ste ady-state flux: of about 60 1 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.