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.

Three plastics, high density polyethylene (HDPE), polypropylene (PP) and polystyrene (PS), were individually co-pyrolysed with deoiled cake of jatropha (JC) at 400 and 450°C in a batch reactor in the presence of nitrogen under atmospheric pressure to produce modified liquid fractions. At higher temperature (450°C), the yield of liquid fractions by the pyrolysis of plastics (HDPE, PP and PS) alone was found to increase by 11, 12.5 and 11% for HDPE, PP and PS, respectively. Furthermore, the gaseous fraction increased by 1.3 to 2.6% while the residue generation reduced by 12.3 to 15.1%. In comparison with only plastics pyrolysis, the yield of the liquid fraction improved by 2.0 to 4.9% for their co-pyrolysis with JC. Gas chromatography–mass spectrometry analyses demonstrated that the co-processing afforded a reduction of paraffin and olefins in the liquid fractions for all of the experiments. This reduction was found to be in the order of PS > PP > HDPE. Furthermore, the proportion of oxygenates in the liquid product increased in the order of PP > HDPE > PS. Physical characteristics such as oxygenates, water contents, acid values and viscosity increased during the co-pyrolysis of plastics and JC in contrast to the liquid fractions obtained from the pyrolysis of pure plastics. Furthermore, co-pyrolysis offered a reduction in calorific values.

There is increasing concern regarding the fate of methyltins in the environment, particularly since large amounts of polyvinyl chloride (PVC) plastics are deposited in landfills. The potential transformation of methyltin chlorides and stannic chloride in landfills was investigated, by incubating the target substances at concentrations relevant to landfill conditions (100 and 500 µg Sn L^–1). The amounts of methane formed in all treatment bottles, and controls, were measured to evaluate the general microbial activity of the inocula and possible effects of methyltins on the degradation of organic matter. The methyltins and stannic chloride were found to have no significant inhibitory effects on the activity of landfill micro-organisms, and the methanol used to disperse the tin compounds was completely degraded. In some experimental bottles, the methanol degradation gave rise to larger methane yields than expected, which was attributed to enhanced degradation of the waste material. Alkyltin analyses showed that monomethyltin trichloride at an initial concentration of 500 µg Sn L^–1 promoted methylation of inorganic tin present in the inoculum. No methylation activities were detected in the incubations with 100 µg Sn L^–1 methyltin chlorides (mono-, di- or tri-methyltin), but demethylation occurred instead. Levels of soluble inorganic tin increased during the incubation period, due partly to demethylation and partly to a release of tin from the waste inocula.