Landfill leachate is highly loaded, toxic and is bad for the sanitation of wastewater. The management of leachate can be carried out by applying treatment or pre-treatment, recirculation (spraying), evaporation to the solid phase and discharge into sewer systems or transfer to a wastewater treatment plant. Research is presented into the biodegradation of leachate collected from the municipal landfill in Gliwice, which was added to a medium that simulated municipal wastewater. The tests were carried out in two systems: a laboratory bioreactor with activated sludge and a membrane bioreactor. The biodegradation of organic compounds was assessed on the basis of reduction in the contaminants denoted by BOD, COD, TOC and changes in IC. The results revealed a considerable impact of the amount of added leachate (2.5, 5 and 10%) on the effectiveness of biodegradation. The application of membrane operations instead of the conventional secondary tank enhanced the treatment of wastewater that contained municipal landfill leachate.