Modelling of biogas extraction at an Italian landfill accepting mechanically and biologically treated municipal solid waste.

This paper presents the results of the modelling of the biogas extraction in a full-scale Italian landfill by the USEPA LandGEM model and the Andreottola-Cossu approach. The landfill chosen for this research ('Il Fossetto' plant, Monsummano Terme, Italy) had accepted mixed municipal raw waste for about 15 years. In the year 2003 a mechanical biological treatment (MBT) was implemented and starting from the end of the year 2006, the recirculation in the landfill of the concentrated leachate coming from the internal membrane leachate treatment plant was put into practice. The USEPA LandGEM model and the Andreottola-Cossu approach were chosen since they require only input data routinely acquired during landfill management (waste amount and composition) and allow a simplified calibration, therefore they are potentially useful for practical purposes such as landfill gas management. The results given by the models are compared with measured data and analysed in order to verify the impact of MBT on biogas production; moreover, the possible effects of the recirculation of the concentrated leachate are discussed. The results clearly show how both models can adequately fit measured data even after MBT implementation. Model performance was significantly reduced for the period after the beginning of recirculation of concentrated leachate when the probable inhibition of methane production, due to the competition between methanogens and sulfate-reducing bacteria, significantly influenced the biogas production and composition.

The landfill reinjection of concentrated leachate: findings from a monitoring study at an Italian site.

The membrane-based processes are among the most used techniques for leachate treatment in modern landfills but its environmental, technical and economical sustainability strongly depends on the disposal of concentrated leachate that is produced there. This paper presents the monitoring study of the landfill of the municipality of Monsummano Terme (Pistoia province, Tuscany, Italy) named "Il Fossetto" where concentrated leachate obtained during membrane treatment is recirculated. The findings resulting from the first 30 months of monitoring of concentrated leachate recirculation show that leachate production did not increase significantly and that only a few quality parameters (i.e. COD, Nickel and Zinc) presented a moderate increase. Moreover, the latest data on biogas composition seem to indicate a reduction in methane content that, if confirmed, could be related to the partial inhibition of methanogens due to the competition of sulphate reducing bacteria. The non-accumulation of other conservative pollutants such as Ammonia Nitrogen and Chloride in the leachate is still under investigation and needs to be better clarified. The overall sustainability of the reinjection as a means of disposing of the concentrated leachate produced by membrane treatment should be further analysed and evaluated in the long term.