A new process combination for the treatment of severely contaminated waste water has been developed: powdered adsorbent is injected into the feed of a nanofiltration unit and removed from the concentrate subsequently by a thickener. The powdered adsorbent in the feed has a positive effect on permeate quality, permeate flux and fouling layer in the nanofiltration (NF) unit. Experiments with a semi-continuous pilot plant and biologically pre-treated landfill leachate have shown that a recovery rate of 97% is possible and that the AOX and COD rejection are considerably increased by the powdered adsorbent. Experiments concerning the fouling layer have shown that it can be controlled by a non-chemical flushing procedure consisting of a combination of feed cross flow, air flushing and permeate back flushing. In comparison to reverse osmosis the process combination has higher maximum recovery rate, lower operating pressure and energy consumption which results in lower treatment costs. On the other hand the permeate concentrations are higher than for reverse osmosis but nevertheless still below the legal standards.