The use of organic wastes at different degrees of maturity as carbon sources for denitrification of landfill leachate

•Denitrification of high strength nitrified landfill leachate.•Organic carbon sources used as cost effective alternative to expensive methods.•Batch tests with commercial garden refuse as carbon sources for denitrification.•Fresh material commercial garden refuse was the most efficient for nitrate removal. In this study different garden refuses were investigated to ascertain their efficiency to act as carbon sources in a denitrification system. Six different garden refuse materials were studied: commercial and domestic garden refuse raw (CGR RAW, DGR RAW), immaturely composted domestic and commercial garden refuse (DGR 10 and CGR 10 respectively), commercial garden refuse composted by Dome Aeration Technology and by “turned windrow” technology (DAT and TW). Different concentrations of synthetic nitrate solution were used to assess the efficiency of each substrate. The results demonstrate that all substrates were able to sustain the denitrification process. However, due to its higher C/N ratio the CGR RAW was the better performing of the materials, reaching 100% removal after 8 and 12h for the 100 and 500mgL−1 respectively and after 11days for 2000mgL−1. Kinetic studies revealed that the zero-order reaction better describes the process indicating a denitrification rate independent from the nitrate concentrations investigated when 100 and 500mgL−1 of nitrate were used. The study demonstrated the suitability of organic municipal solid wastes to sustain denitrification, opening a new scenario towards a low cost and in situ solution for treatment of landfill leachate by using wastes, otherwise disposed of in landfill.