The aim of this study was to develop a multiple linear regression (MLR) model to predict the specific methane production (SMP) from dry anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW). A data set from an experimental test on a pilot-scale plug-flow reactor (PFR) including 332 observations was used to build the model. Pearson′s correlation matrix and principal component analysis (PCA) examined the relationships between variables. Six parameters, namely total volatile solid (TVSin), organic loading rate (OLR), hydraulic retention time (HRT), C/N ratio, lignin content and total volatile fatty acids (VFAs), had a significant correlation with SMP. Based on these outcomes, a simple and three multiple linear regression models (MLRs) were developed and validated. The simple linear regression model did not properly describe the data (R² = 0.3). In turn, the MLR including all factors showed the optimal fitting ability (R² = 0.91). Finally, the MLR including four uncorrelated explanatory variables of feedstock characteristics and operating parameters (e.g., TVSin, OLR, C/N ratio, and lignin content), resulted in the best compromise in terms of number of explanatory variables, model fitting and predictive ability (R² = 0.87).

The aim of this study is to investigate the performance of a pilot-scale plug-flow reactor (PFR) as a biorefinery system to recover chemicals (i.e., volatile fatty acids (VFAs)), and biogas during the dry thermophilic anaerobic digestion (AD) of the organic fraction of municipal solid waste (OFMSW). The effects of the hydraulic retention time (HRT) on both outputs were studied, reducing the parameter from 22 to 16 days. In addition, VFA variation along the PFR was also evaluated to identify a section for a further valorization of VFA-rich digestate stream. A particular focus was dedicated for characterizing the community responsible for the production of VFAs during hydrolysis and acidogenesis. The VFA concentration reached 4421.8 mg/L in a section located before the end of the PFR when the HRT was set to 16 days. Meanwhile, biogas production achieved 145 NLbiogas/d, increasing 2.7 times when compared to the lowest HRT tested. Defluviitoga sp. was the most abundant bacterial genus, contributing to 72.7% of the overall bacterial population. The genus is responsible for the hydrolysis of complex polysaccharides at the inlet and outlet sections since a bimodal distribution of the genus was found. The central zone of the reactor was distinctly characterized by protein degradation, following the same trend of propionate production.

In order to study the quality of organic fractions of municipal solid waste (OFMSW), five different municipalities in Tuscany were chosen for sampling according to the peculiarities of their collection systems. The five collection systems selected were sampled four times: during March, June, September and December, for a total of 20 picking analyses. In addition, emphasis was also given to the study of the variability of OFMSW composition related to ultimate, proximate and bromatological analyses. Road container collection systems proved to have a higher content of non-compostable and undesirable fractions (22%±1%) when compared to door-to-door systems (6% ± 1%). During months with lower temperature (March and December), the garden waste content in the OFMSW was negligible, with kitchen waste prevailing. This altered the physical chemical composition of OFMSW, which had a lower lignin content and higher methane production in the months with lower temperatures (272 ± 23 NLCH₄ kg_TVS⁻¹) compared to June and September (238 ± 14 NLCH₄ kg_TVS⁻¹). In general, the Tuscan OFMSW had a higher dry matter content (42%) than observed in previous studies. In conclusion, the result could direct possible future operators of anaerobic digestion plants towards the choice of dry and semi-dry technologies.

Biofiltration systems are emerging technological solutions for the removal of methane and odors from landfill gas when flaring is no longer feasible. This work analyzed and compared two full-scale biofiltration systems: biofilter and biowindows. The emission mitigation of methane, non-methane volatile organic compounds (NMVOCs) and odors during a two-year management and monitoring period was studied. In addition to diluted methane, more than 50 NMVOCs have been detected in the inlet raw landfill gas and the sulfur compounds resulted in the highest odor activity value. Both systems, biofilter and biowindows, were effective for the oxidation of methane (58.1% and 88.05%, respectively), for the mitigation of NMVOCs (higher than 80%) and odor reduction (99.84% and 93.82% respectively). As for the biofilter monitoring, it was possible to define the oxidation efficiency trend and in fact to guarantee that for an oxidation efficiency of 80%, the methane load must be less than 6.5 g CH₄/m²h with an oxidation rate of 5.2 g CH₄/m²h.

This study investigates the influence of moisture content on the potential oxidation efficiency of methane (CH₄) of biofiltration systems treating landfill gas containing high oxygen concentrations. Column tests filled with compost with different moisture contents (20%, 30%, and 40%) loaded with different methane flows were set up on a laboratory scale. Analyzing the results the following evidences can be summarized: With low methane load (<100 g CH₄ m⁻² d⁻¹), a moisture content of 20% was not enough to support bacterial activity, while a moisture content of 40% advantaged the compost respiration assisting it to become the dominating process; with higher methane load (100–300 g CH₄ m⁻² d⁻¹), a moisture content of 30% resulted in an optimal value to support methanotrophic activity showing the highest CH₄ concentration reduction; moving on to a CH₄ load above 300 g CH₄ m⁻² d⁻¹, the inhibition of methanotrophic activity emerged independently to the moisture content of the filter media. The optimal configuration is obtained for a moisture content of 30% and in the case of flows below 200 g CH₄ m⁻² d⁻¹ for which the oxidation efficiency results higher than 80%.