Advanced biomethane potential from local sources in Italy.

Anaerobic Co-digestion of sewage sludge and organic fraction of municipal solid waste: Focus on mix ratio optimization and synergistic effects

Anaerobic co-digestion of organic fraction of municipal solid waste, with thickened waste activated sludge and primary sludge has the potential to enhance biodegradation of solid waste, increase longevity of existing landfills and lead to more sustainable development by improving waste to energy production. This study reports on mesophilic batch and continuous studies using different concentrations and combinations (ratios) of organic fraction of municipal solid waste, thickened waste activated sludge (microwave pre-treated and untreated) and primary sludge to assess the potential for improved biodegradability and specific biogas production. Improvements in specific biogas production for batch assays, with concomitant improvements in total chemical oxygen demand and volatile solid removal, were obtained with organic fraction of municipal solid waste:thickened waste activated sludge:primary sludge mixtures at a ratio of 50:25:25 (with and without thickened waste activated sludge microwave pre-treatment). This combination was used for continuous digester studies. At 15 d hydraulic retention times, the co-digestion of organic fraction of municipal solid waste:organic fraction of municipal solid waste:primary sludge and organic fraction of municipal solid waste:thickened waste activated sludge microwave:primary sludge resulted in a 1.38- and 1.46-fold increase in biogas production and concomitant waste stabilisation when compared with thickened waste activated sludge:primary sludge (50:50) and thickened waste activated sludge microwave:primary sludge (50:50) digestion at the same hydraulic retention times and volumetric volatile solid loading rate, respectively. The digestion of organic fraction of municipal solid waste with primary sludge and thickened waste activated sludge provides beneficial effects that could be implemented at municipal wastewater treatment plants that are operating at loading rates of less than design capacity.

Disposal of biodegradable waste has become a stringent waste management and environmental issue. As a result, anaerobic digestion has become one of the best alternative technology to treat the organic fraction of municipal solid wastes and can be an important source of bioenergy. This study focuses on the evaluation of biogas and methane yields from the digestion and co-digestion of mixtures of waste untreated sludge and the organic fraction of municipal solid wastes. These are compared with the results obtained from the digestion and codigestion of mixtures containing waste active sludge and the organic fraction of municipal solid wastes. The two types of substrates were used to perform biomethanation potential tests, in mesophilic conditions (35 °C) at lab scale. It was observed a maximum biogas yield for 100% of untreated sewage sludge, corresponding to 0.644 Nm 3 /kg VS and 0.499 Nm 3 /kg VS of biogas and methane production respectively. The study also demonstrates the possibility of increasing biogas production up to 36% and methane content up to 94% using waste untreated sludge substrate in both digestion and codigestion, compared to waste active sludge substrate.

The influence of spent household batteries to the organic fraction of municipal solid wastes during composting

Anaerobic Digestion (AD) technologies have been developed and implemented in Brazil and Mexico to treat the organic fraction of municipal solid waste (OFMSW). However, they are still far away to significantly contribute to treating the ever-increasing waste volumes in the region and supply the regional energy demand, recuperate nutrients, and meet national carbon emission goals. This study aims to determine the feasibility of implementing AD, and more specifically dry anaerobic digestion (DAD) technologies, to treat the OFMSW evaluating the technical and environmental benefits and advantages these technologies offer, and secondly to propose the policy guidelines for implementing and disseminating AD technologies based on the existing regulatory framework in Brazil and Mexico. For this purpose, the research uses mixed methods research (MMR). It firstly performs an environment and resource use analysis to compare two case studies in Brazil: A wet anaerobic digester in Foz de Iguau and a dry anaerobic digester localized in Rio de Janeiro. This analysis includes an assessment of the water, material, and nutrients flow, energy efficiency, and mitigation of greenhouse gas emissions (GHG) as the most relevant categories, seeking the most efficient technology. A literature and public policy review and a series of interviews with researchers and public policy specialists to identify the limitations, challenges, and opportunities to apply AD from a governmental perspective complemented the case study analysis.

The Mediterranean region is increasingly confronted with intersecting environmental, ag-ricultural and socio-economic challenges, including biowaste accumulation, soil degra-dation and high dependency on imported fossil fuels. Biomethane, a renewable substitute for natural gas, offers a strategic solution that aligns with the region's need for sustainable energy transition and circular resource management. This review examines the current state of biomethane production in the Mediterranean area, with a focus on Anaerobic Di-gestion (AD) technologies, feedstock availability, policy drivers and integration into Cir-cular Bioeconomy (CBE) framework. Emphasis is placed on the valorisation of regionally abundant feedstocks such as olive pomace, citrus peel, grape marc, cactus pear (Opuntia ficus-indica) residues, livestock manure and the Organic Fraction of Municipal Solid Waste (OFMSW). The multifunctionality of AD—producing renewable energy and nutrient-rich digestate—is highlighted for its dual role in reducing Greenhouse Gas (GHG) emissions and restoring soil health, especially in areas threatened by desertification such as Sicily (Italy), Spain, Malta and Greece. The review also explores emerging innovations in biogas upgrading, nutrient recovery and digital monitoring, alongside the role of Renewable En-ergy Directive III (RED III) and national biomethane strategies in scaling up deployment. Case studies and decentralised implementation models underscore the socio-technical feasibility of biomethane systems across rural and insular territories. Despite significant potential, barriers such as feedstock variability, infrastructural gaps and policy fragmen-tation remain. The paper concludes with a roadmap for research and policy to advance biomethane as a pillar of Mediterranean climate resilience, energy autonomy and sus-tainable agriculture within a circular bioeconomy paradigm.

The Mediterranean region is increasingly confronted with intersecting environmental, agricultural, and socio-economic challenges, including biowaste accumulation, soil degradation, and high dependency on imported fossil fuels. Biomethane, a renewable substitute for natural gas, offers a strategic solution that aligns with the region’s need for sustainable energy transition and circular resource management. This review examines the current state of biomethane production in the Mediterranean area, with a focus on anaerobic digestion (AD) technologies, feedstock availability, policy drivers, and integration into the circular bioeconomy (CBE) framework. Emphasis is placed on the valorisation of regionally abundant feedstocks such as olive pomace, citrus peel, grape marc, cactus pear (Opuntia ficus-indica) residues, livestock manure, and the Organic Fraction of Municipal Solid Waste (OFMSW). The multifunctionality of AD—producing renewable energy and nutrient-rich digestate—is highlighted for its dual role in reducing greenhouse gas (GHG) emissions and restoring soil health, especially in areas threatened by desertification such as Sicily (Italy), Spain, Malta, and Greece. The review also explores emerging innovations in biogas upgrading, nutrient recovery, and digital monitoring, along with the role of Renewable Energy Directive III (RED III) and national biomethane strategies in scaling up deployment. Case studies and decentralised implementation models underscore the socio-technical feasibility of biomethane systems across rural and insular territories. Despite significant potential, barriers such as feedstock variability, infrastructural gaps, and policy fragmentation remain. The paper concludes with a roadmap for research and policy to advance biomethane as a pillar of Mediterranean climate resilience, energy autonomy and sustainable agriculture within a circular bioeconomy paradigm.

Two biological treatments for biodegradable substrates were assessed: (i) conventional co-digestion of source sorted organic fraction of municipal solid waste (SS-OFMSW) and sewage sludge (SS); (ii) preliminary dark-fermentation pre-treatment of the mixture of SS-OFMSW and SS, followed by a second step of anaerobic digestion. The produced biogas and hydrogen-rich gas are assumed to be used in an internal combustion engine to produce electricity and thermal energy. Life Cycle Assessment and Life Cycle Costing were implemented to assess the two biological treatments, which were also compared with the current treatments (separate aerobic composting of SS-OFMSW and anaerobic digestion of SS). The selected functional unit is the total annual amount of entering waste (189,000 t/y of SS-OFMSW and 15,500 t/y of SS) to an actual Italian plant, which was used as case study for this work. The Life Cycle Assessment results show that the co-treatments of SS and SS-OFMSW provide general environmental improvements with respect to the reference case study of separate SS anaerobic digestion and SS-OFMSW aerobic composting. The case based on the preliminary dark fermentation of the mixture of SS-OFMSW and SS followed by digestion always shows better indicator values than the co-digestion one. This result is mainly influenced by the higher energy recovery, which, in turn, is due to the improved specific gas production of the digestion step, after the co-fermentation pre-treatment. The Life Cycle Costing shows that both the studied systems are economically sustainable, however the case based on the preliminary dark fermentation of the mixture of SS-OFMSW and SS followed by digestion has a shorter time of return of investment and a higher net present value than the co-digestion one. For the considered study case, the preliminary dark-fermentation pre-treatment of the mixture of SS-OFMSW and SS, followed by a second step of anaerobic digestion is preferable to their simple co-digestion process both from the environmental and economic points of view.

Wastewater treatment plants (WWTPs) aim to increase energy independence by intensifying biogas production. The study involved Life Cycle Assessment (LCA) comparing sewage sludge (SS) anaerobic co-digestion (AcD) with the organic fraction of municipal solid waste (OFMSW) at WWTP against SS anaerobic mono-digestion (AD). The LCA was based on the authors' research showing that methane production related to wet mass in AcD was higher than in AD by 86.4, 225.8, and 354.3 % for SS:OFMSW mixing ratios of 75:25, 50:50, and 25:75, respectively. The LCA was conducted for 1 kWh of biogas energy produced at a WWTP and included two subsystems: energy production (AD/AcD and CHP) and associated digestate management (drying, incineration with energy reuse, residual landfilling). CML-IA baseline 2013 and Recipe 2016 Midpoint (H) LCIA methodologies indicated the environmental impacts on abiotic depletion - fossil fuels (fossil resource scarcity), global warming, human toxicity (non-carcinogenic), freshwater, and marine aquatic ecotoxicity. AD of SS in all categories was characterized by the highest impact. The impact decreased with an increase in the OFMSW rate. Both methodologies showed a significant impact of AD and AcD on global warming, which indicated the need for the determination of the carbon footprint (CF) of 1kWh biogas energy production (gCO2 kWh−1) at WWTP, using IPCC 2021 GWP100 (incl. CO2 uptake). The CF was the highest for biogas energy production in SS AD (1509 gCO2 kWh−1) and it decreased with the increase of OFMSW content in AcD (872–481 gCO2 kWh−1). This was also observed for the management of associated digestate. CF changed from 1508 gCO2 kWh−1 for SS AD to 396 gCO2 kWh−1 for SS: OFMSW mixing ratio of 25: 75 in AcD. The environmental burdens associated with biogas energy production and digestate management were equally significant. Finally, the formula for economic and ecological comparison of SS AD and AcD with OFMSW was proposed.

Advanced steam explosion of mixed organic fraction of municipal solid waste and sewage sludge to determine biomethane potentials

Revisiting the elemental composition and the calorific value of the organic fraction of municipal solid wastes

Enhancement in hydrogen production by thermophilic anaerobic co-digestion of organic fraction of municipal solid waste and sewage sludge--optimization of treatment conditions.

Co-biodrying of sewage sludge and organic fraction of municipal solid waste: A thermogravimetric assessment of the blends

An attempt is presented and discussed to adapt a well-known process successfully employed in the U.S.A. for the simultaneous treatment of the organic fraction of municipal solid waste (MSWOF) and sewage sludge to the particular situation of water works in Italy. It consists of preliminary domestic grinding of MSWOF, its discharge into the sewer, screening, and final digestion of the resulting residue together with sewage sludge. In order to avoid extension work of the present activated sludge sections necessary to face the organic load increase, a fine screening is necessary, while the efficiency of anaerobic digestion can be improved by shifting the system from mesophilic (37 °C) to thermophilic (55 °C) conditions. The effects of thermal, chemical, and biological pretreatments of both MSWOF and sewage sludge on methane, carbon dioxide, and biogas productions are investigated either separately or jointly. During these pretreatments, volatile suspended solid (VSS) concentration remarkably decreased while soluble chemical oxygen demand (COD) increased as the result of the progressive hydrolysis of the polymeric materials present in the feed. Finally, the kinetic parameters of the hydrolysis of these materials are estimated and compared in order to provide useful information on the factors limiting the anaerobic digestion as well as to suggest the best way to carry out the process on a large scale.

The aim of this study was to evaluate the effect of the inoculum to substrate ratio (ISR) and the mixture ratio between organic fraction of municipal solid waste (OFMSW) and sewage sludge (SS) on the methane production potential achievable from anaerobic co-digestion (AcoD). Biochemical Methane Potential (BMP) assays at mesophilic temperature were used to determine the best AcoD configuration for maximizing methane yield and production rate, as well as to address possible synergistic effects. The maximum methane yield was observed at ISR of 1 and 60% OFMSW: 40% SS as co-digestion mixture, whereas the highest methane production rate was achieved at ISR of 2 with the same mixture ratio (207 mL/gVS/d). Synergistic effects were highlighted in the mixtures having OFMSW below 60%, determining an increase of approximately 40% in methane production than the OFMSW and SS digestion as a sole substrate. The experimental data demonstrated that co-digestion of OFMSW and SS resulted in an increase in the productivity of methane than anaerobic digestion using the sole substrates, producing higher yields or production rates while depending on the ISR and the mixture ratio.