Optimized management of old municipal solid waste landfill with in-situ aeration technique.

The Ph.D. research project was focused on the optimized management of old municipal solid waste (MSW) landfills. In particular, it was supposed to apply the in-situ aeration technique within an old landfill in order to reduce the long-term pollution potential and to maximize the removal of nitrogen and carbon compounds. Previous studies proved that intermittent in-situ aeration is an effective tool to improve the biological stability of a MSW landfill. Considering the economic advantages, the in-situ aeration technique was applied in an intermittent way; two main aspects, not still well understood were considered: 1. the occurrence of denitrification process in old MSW landfills characterized by very low biodegradable organic carbon content, taking advantage of the anoxic conditions of the intermittent aeration. In particular, it was analysed the capacity of an old landfill system to exploit both the heterotrophic and autotrophic pathway for nitrogen removal, according to the available substrate; 2. the possible effects of the intermittent aeration on the potential release of heavy metals into the liquid phase and their behaviour both in the leachate and in the solid waste material, considering that the application of in-situ aeration technique may affect the internal conditions of the landfill system. A further lab-scale experiment was carried out to evaluate the increase of the in-situ aeration efficiency to remove the residual organic carbon within an old landfill. The in-situ aeration was coupled with the microbial fuel cells (MFCs) technology in order to exploit the advantages of both of them. All aspects have been evaluated during several lab-scale tests by means of landfill simulating bioreactors. Results of all experiments carried out during the Ph.D. Course can be summarized as follows. Denitrification process does not seem to be limited in a very old MSW landfill as it can occur in a heterotrophic and/or autotrophic way according to the kind of available substrate. Although the heterotrophic pathway can be considered the preferred one, when the biodegradable organic matter is not available or it is close to zero, nitrate can be removed in a autotrophic way, even if more slowly. The results of the experiments on the behaviour of heavy metals in the leachate and in the solid waste matrix seem to confirm the dominant role of adsorption mechanism within the landfill system that reduces the release of heavy metals in the leachate after aeration and keeps quite constant the metals content in the solid waste material. Therefore, heavy metals in landfill leachate do not seem a major concern in case of in-situ aeration. The preliminary results of the integration of MFCs with landfill bioreactors pointed out some critical aspects of the system, such as the weakness of the cathode material, the great influence of the leachate recirculation mode on the performance of the whole system and the optimal choice of the aeration flux required to keep the cathodic compartment aerated. These considerations highlight the need of slightly modify the configuration of the MFC system within the landfill simulation reactors. The present Ph.D. thesis includes the description of the research activities with the related results and it is divided in two main parts. In the first part, named “Thesis development” the Ph.D. research activity and the main results are briefly summarized. The second part, named “List of Papers” describes in details all the experiments and the related results, listing all the papers written during the Ph.D. course.