An alternative process consisting of a pre-treatment step for nitrogen recovery as struvite followed by ozone enhanced biological degradation carried out in a SBBGR system (sequencing batch biofilter granular reactor) is proposed. The efficiency of the process in treating a mature municipal landfill leachate was tested at laboratory scale. The results show that for the same applied ozone dose, the plant performance was improved by shortening the ozonation phase time, due to higher ozone transfer efficiency. After optimization, the process was able to meet the COD limits for discharging into water bodies and sewer systems when a specific ozone dose of 2 and 0.6g O-3/L-influent, respectively, was used. The process was characterized by a negligible biological sludge production. The economic evaluation of the process showed operating costs of 9 and 6.5(sic) per m(3) of leachate for discharging into water bodies and sewer system, respectively. Additionally, in situ hybridization and staining techniques allowed the microbial composition and structure of the biomass growing under the different operating conditions of the SBBGR system to be defined. Microscopic analysis showed that ozone improves the biomass aggregation and lead to a substantial increase in biomass concentration (i.e., from 18 to 30 gTSS/L-bed) and EPS content. SBBGR biomass was dominated by Gammaproteobacteria. (C) 2011 Elsevier B.V. All rights reserved.