Review and meta-analysis of 82 studies on end-of-life management methods for source separated organics

Integrated life cycle assessment of biotreatment and agricultural use of domestic organic residues: Environmental benefits, trade-offs, and impacts on soil application

Extensive agricultural activities have been shown to degrade soils, promoting research into improving soil quality. One such method is to increase the amount of organic matter in the soil, and domestic organic residues (DOR) are commonly used for this purpose. The environmental impact of DOR-derived products, from production to agricultural application, remains unclear in current research. With the aim to have a more comprehensive understanding of the challenges and opportunities in DOR management and reuse, this study extended the boundaries of Life Cycle Assessment (LCA) to include the transport, treatment, and application of treated DOR on a national level while also quantifying soil carbon sequestration that has been less addressed in relevant LCA studies. This study focuses on The Netherlands, where incineration predominates, as a representative case to explore the benefits and trade-offs of moving towards more biotreatment for DOR. Two main biotreatments were considered, composting and anaerobic digestion. The results indicate that biotreatment of kitchen and yard residues generally has higher environmental impacts than incineration, including increased global warming and fine particulate matter formation. However, biotreatment of sewage sludge has lower environmental impacts than incineration. Substitution of nitrogen and phosphorus fertilisers with compost reduces mineral and fossil resource scarcity. In fossil-based energy systems like The Netherlands, replacing incineration with anaerobic digestion yields the highest benefit for fossil resource scarcity (61.93 %) due to energy recovery from biogas and the predominant use of fossil resources in the Dutch energy system. These findings indicate that replacing incineration with biotreatment of DOR may not benefit all impact categories in LCA. The environmental performance of substituted products can significantly influence the environmental benefits of increased biotreatment. Future studies or implementation of increased biotreatment should consider trade-offs and local context.

Life cycle assessment of biowaste and green waste composting systems: A review of applications and implementation challenges

Composting is one of the most widely applied methods for recycling organic waste. This process has been proposed as one option that facilitates the reincorporation of materials into the production cycle. However, composting also generates environmental impacts. Life Cycle Assessment (LCA) is the most common approach to evaluate the environmental impacts of a process at different system stages. Nevertheless, applying LCA in composting facilities is challenging due to the extensive information required, the lack of standardization on the initial assumptions, the definition of system boundaries, and the high diversity of existing composting technologies. This paper systematically reviews LCA studies in biowaste and/or green waste composting. The study highlights the challenges that should be met in order to improving the application of LCA to evaluate the environmental impacts of this type or waste treatment strategy. The review protocol used identified 456 papers published between 2010 and 2022. After the screening, 56 papers were selected, read, and thoroughly analyzed. The results show that: i) about 68% of the studies aimed to compare composting with other solid waste management options; ii) there was a wide diversity among the impact categories considered, which predominantly included climate change and ozone depletion; iii) there was no consensus on the functional unit or the system boundaries; iv) the main gaseous emissions studied were ammonia, methane, and nitrogen oxide, which were generally determined by emission factors; v) the avoided environmental impacts associated with the end-product quality and its application as an organic amendment or soil improver were ignored. This work demonstrates the complexity of conducting credible and valid composting LCA studies and proposes seven recommendations for improving the application of this assessment methodology to analyze this waste management alternative.

Assessing the climate change mitigation potential from food waste composting

Food waste is a dominant organic constituent of landfills, and a large global source of greenhouse gases. Composting food waste presents a potential opportunity for emissions reduction, but data on whole pile, commercial-scale emissions and the associated biogeochemical drivers are lacking. We used a non-invasive micrometeorological mass balance approach optimized for three-dimensional commercial-scale windrow compost piles to measure methane (CH₄), nitrous oxide (N₂O), and carbon dioxide (CO₂) emissions continuously during food waste composting. Greenhouse gas flux measurements were complemented with continuous oxygen (O₂) and temperature sensors and intensive sampling for biogeochemical processes. Emission factors (EF) ranged from 6.6 to 8.8 kg CH₄-C/Mg wet food waste and were driven primarily by low redox and watering events. Composting resulted in low N₂O emissions (0.01 kg N₂O-N/Mg wet food waste). The overall EF value (CH₄ + N₂O) for food waste composting was 926 kgCO₂e/Mg of dry food waste. Composting emissions were 38-84% lower than equivalent landfilling fluxes with a potential net minimum savings of 1.4 MMT CO₂e for California by year 2025. Our results suggest that food waste composting can help mitigate emissions. Increased turning during the thermophilic phase and less watering overall could potentially further lower emissions.

Greenhouse Gas and Air Pollutant Emissions from Composting

Composting can divert organic waste from landfills, reduce landfill methane emissions, and recycle nutrients back to soils. However, the composting process is also a source of greenhouse gas and air pollutant emissions. Researchers, regulators, and policy decision-makers all rely on emissions estimates to develop local emissions inventories and weigh competing waste diversion options, yet reported emission factors are difficult to interpret and highly variable. This review explores the impacts of waste characteristics, pretreatment processes, and composting conditions on CO2, CH4, N2O, NH3, and VOC emissions by critically reviewing and analyzing 388 emission factors from 46 studies. The values reported to date suggest that CH4 is the single largest contributor to 100-year global warming potential (GWP100) for yard waste composting, comprising approximately 80% of the total GWP100. For nitrogen-rich wastes including manure, mixed municipal organic waste, and wastewater treatment sludge, N2O is the largest contributor to GWP100, accounting for half to as much as 90% of the total GWP100. If waste is anaerobically digested prior to composting, N2O, NH3, and VOC emissions tend to decrease relative to composting the untreated waste. Effective pile management and aeration are key to minimizing CH4 emissions. However, forced aeration can increase NH3 emissions in some cases.

Carbon and N conservation during composting: A review

Composting, as a conventional solid waste treatment method, plays an essential role in carbon and nitrogen conservation, thereby reducing the loss of nutrients and energy. However, some carbon- and nitrogen-containing gases are inevitably released during the process of composting due to the different operating conditions, resulting in carbon and nitrogen losses. To overcome this obstacle, many researchers have been trying to optimize the adjustment parameters and add some amendments (i.e., pHysical amendments, chemical amendments and microbial amendments) to reduce the losses and enhance carbon and nitrogen conservation. However, investigation regarding mechanisms for the conservation of carbon and nitrogen are limited. Therefore, this review summarizes the studies on physical amendments, chemical amendments and microbial amendments and proposes underlying mechanisms for the enhancement of carbon and nitrogen conservation: adsorption or conversion, and also evaluates their contribution to the mitigation of the greenhouse effect, providing a theoretical basis for subsequent composting-related researchers to better improve carbon and nitrogen conservation measures. This paper also suggests that: assessing the contribution of composting as a process to global greenhouse gas mitigation requires a complete life cycle evaluation of composting. The current lack of compost clinker impact on carbon and nitrogen sequestration capacity of the application site needs to be explored by more research workers.

Environmental and Economic Life-Cycle Assessments of Household Food Waste Management Systems: A Comparative Review of Methodology and Research Progress

Household food waste (HFW) is the main component of municipal solid waste (MSW). Appropriate HFW management strategies could reduce the environmental burdens and economic costs to society. Life-cycle thinking is an effective decision-making tool for MSW management. This paper compares the three main environmental and economic assessment methodologies, i.e., societal life-cycle costing (societal LCC), environmental cost-effectiveness (ECE) analysis, and multicriteria analysis (MCA) in terms of the definitions, method frameworks, and their advantages/disadvantages. Most reviewed studies applied the environmental life-cycle costing (ELCC) method, a simplified ECE, which does not involve interactive quantitative comparisons between environmental and economic benefits. Further attention should be paid to the coordination between life-cycle assessment (LCA) and life-cycle costing (LCC), the monetization coefficient in external cost calculation of societal LCC, and the standardization and evaluation approaches of ECE. HFW prevention is rarely considered in the reviewed literature but was demonstrated as the best route over treatment or utilization. Anaerobic digestion is environmentally preferable to composting and landfilling; it is comparable to biodiesel production, feeding conversation, and incineration. From the perspective of economic costs (including societal LCC), the ranking of treatment technologies varied a lot from one study to another, attributable to the diverse evaluation methods and different data sources. To improve the environmental and economic assessment approaches to HFW management, an inventory database (e.g., food waste properties, technical treatment parameters, material flow, and fund flow data) suitable for HFW should be constructed. When establishing the system boundaries, the processes of source sorting, collection and transportation, and by-product handling should be coherent with the investigated treatment technology.

Life Cycle Assessment of Existing and Alternative Options for Municipal Solid Waste Management in Saint Petersburg and the Leningrad Region, Russia

A waste reform was recently introduced in Russia to divert waste from landfills. To help advance the reform, this paper presents a life cycle assessment of the municipal solid waste management system in Russia’s second largest city—Saint Petersburg—and its neighboring Leningrad region. Five scenarios were evaluated: the current state of the system (S0), its expected post-reform state in 2024 (S1), and its state improved by increased landfill gas collection (S2), by increased waste incineration (S3), and by separate collection of waste (S4). The environmental impact was assessed in terms of climate change, acidification, eutrophication, and abiotic resource depletion (fossil fuels). The results showed an overall reduction in the environmental impact of the waste management system across all impact categories and all scenarios studied. The largest reduction in all impact categories (except abiotic resource depletion) was achieved through source separation of municipal solid waste. Particularly, global warming potential was reduced from 0.328 kg CO2-eq./kg waste generated in S0 to 0.010 kg CO2-eq./kg waste in S4. Regarding abiotic resource depletion potential (fossil fuels), the incineration scenario is the most beneficial, since it reduces the impact by 573%.

Barriers and Enablers to Food Waste Recycling: A Mixed Methods Study amongst UK Citizens

We aim to identify influences on UK citizens' household food waste recycling as a basis for designing strategies to increase household food waste collection rates via local services. Using a UK dataset (n = 1801) and the COM-B (Capability-Opportunity-Motivation-Behaviour) model as a theoretical framework, we conduct quantitative regression and supporting thematic analyses to investigate influences on citizens' recycling of food waste. Results show that automatic motivation (e.g., emotions and habit) and psychological capability (e.g., knowledge) predict household food waste recycling. Physical opportunity (i.e., dealing with food waste in other ways such as home-composting or feeding pets/strays, time and financial costs) was the main barrier to recycling food waste identified in thematic analyses. Participants also reported automatic motivation-related barriers such as concerns over pests, odour, hygiene and local authorities' food waste collection capabilities. Based on findings we recommend the development of clear, consistent communications aimed at creating positive social norms relating to recycling and increasing knowledge of what can and cannot be put in food waste bins. Improved functional design and free distribution of bins and compostable caddy liners developed according to user-centred needs for cleanliness, convenience and hygiene are also needed. These will not be sufficient without a nationally uniform, efficient and reliable system of household food waste collection.

Microwave-assisted extraction and gas chromatographic determination of thirty priority micropollutants in biowaste fraction derived from municipal solid waste for material recovery in the circular-economy approach

European and national waste directives prioritize recycling of wastes, as well as material and energy recovery from wastes themselves. Bio-waste fraction can be converted into new resources whose quality is strictly dependent upon that of waste feedstock. Methods to evaluate the contamination from organic micropollutants in bio-waste are rarely investigated. The aim of this work was to develop an innovative analytical method for the extraction and quantification of 16 polycyclic aromatic hydrocarbons (PAHs) and 14 polychlorinated biphenyls (PCBs, including dioxin-like compounds) in bio-waste. Through a full-factorial experimental design, a microwave-assisted extraction technique was optimized to extract the thirty targeted micropollutants, studying the effect of cyclohexane and dichloromethane as extraction solvents with or without acetone, and of extraction temperature. Purification of the extract was obtained by a silica-based solid-phase extraction cartridge, followed by a sulfuric acid treatment. The analysis was carried out by gas chromatography coupled with mass spectrometry. The optimized method, validated directly in the bio-waste matrix fortified with isotopically marked surrogates, is characterized by good extraction recoveries, included within 47 and 106% (relative standard deviations <10%), by satisfactory intra-day (<1.1%) and inter-day (<9.3%) precision, and by low matrix effect (<17%), despite the complexity of the matrix. The optimized procedure, applied to the analysis of PAHs and PCBs in a bio-waste sample collected from a local anaerobic digestion and composting plant, showed a total PAHs content of 562 μg/kg. As regards PCBs, the dioxin-like congener PCB 118 was the only compound quantified (25 ± 6 μg kg^-1).

The implications of facility design and enabling policies on the economics of dry anaerobic digestion

Diverting organic waste from landfills provides significant emissions benefits in addition to preserving landfill capacity and creating value-added energy and compost products. Dry anaerobic digestion (AD) is particularly attractive for managing the organic fraction of municipal solid waste because of its high-solids composition and minimal water requirements. This study utilizes empirical data from operational facilities in California in order to explore the key drivers of dry AD facility profitability, impacts of market forces, and the efficacy of policy incentives. The study finds that dry AD facilities can achieve meaningful economies of scale with organic waste intake amounts larger than 75,000 tonnes per year. Materials handling costs, including the disposal of inorganic residuals from contaminated waste streams and post-digester mass (digestate) management, are both the largest and the most uncertain facility costs. Facilities that utilize the biogas for vehicle fueling and earn associated fuel credits collect revenues that are 4-6x greater than those of facilities generating and selling electricity and 10-12x greater than facilities selling natural gas at market prices. The results suggest important facility design elements and enabling policies to support an increased scale of organic waste handling infrastructure.

What Is the Best End Use for Compost Derived from the Organic Fraction of Municipal Solid Waste?

There is increasing interest in diverting the organic fraction of municipal solid waste from landfills to biological treatment processes that result in compost. Due to variations in compost quality and available markets, it is not always possible for compost to be beneficially used on soil. In such cases, compost may be used as alternative daily cover (ADC) in landfills. The objective of this study is to compare the environmental impacts of using compost as a soil amendment, accounting for its beneficial substitutions for fertilizer and peat, to its use as ADC. Monte Carlo simulation and parametric sensitivity analyses were performed to evaluate the effects of uncertainty in input values on the environmental performance. The ADC scenario outperforms the soil amendment scenario in terms of global warming potential, acidification, and eutrophication in ∼63, ∼77, and ∼100% of simulations, respectively, while the soil amendment scenario is better in terms of cumulative energy demand and abiotic resource depletion potential ∼94 and ∼96% of the time, respectively. Therefore, we recommend that using compost as ADC be considered, especially when site-specific factors such as feedstock contamination or a lack of markets make it difficult to find appropriate applications for compost as a soil amendment.

Life-Cycle Greenhouse Gas Emissions and Human Health Trade-Offs of Organic Waste Management Strategies

Waste-to-energy systems can play an important role in diverting organic waste from landfills. However, real-world waste management can differ from idealized practices, and emissions driven by microbial communities and complex chemical processes are poorly understood. This study presents a comprehensive life-cycle assessment, using reported and measured data, of competing management alternatives for organic municipal solid waste including landfilling, composting, dry anaerobic digestion (AD) for the production of renewable natural gas (RNG), and dry AD with electricity generation. Landfilling is the most greenhouse gas (GHG)-intensive option, emitting nearly 400 kg CO_2e per tonne of organic waste. Composting raw organics resulted in the lowest GHG emissions, at -41 kg CO_2e per tonne of waste, while upgrading biogas to RNG after dry AD resulted in -36 to -2 kg CO_2e per tonne. Monetizing the results based on social costs of carbon and other air pollutant emissions highlights the importance of ground-level NH₃ emissions from composting nitrogen-rich organic waste or post-AD solids. However, better characterization of material-specific NH₃ emissions from landfills and land-application of digestate is essential to fully understand the trade-offs between alternatives.

The Use of Life Cycle-Based Approaches in the Food Service Sector to Improve Sustainability: A Systematic Review

With the prevalence of eating out increasing, the food service sector has an increasing role in accelerating the transition towards more sustainable and healthy food systems. While life cycle-based approaches are recommended to be used as reference methods for assessing the environmental sustainability of food systems and supply chains, their application in the food service sector is still relatively scarce. In this study, a systematic review was conducted to examine the use and effectiveness of life-cycle based interventions in improving the sustainability of food services. This review found that life-cycle based approaches are not only useful for identifying hotspots for impact reduction, but also for comparing the performance of different sustainability interventions. In particular, interventions targeting the production phase, such as promoting dietary change through menu planning in which high-impact ingredients (e.g., animal products) are replaced with low-impact ingredients (e.g., plant foods), had the highest improvement potential. Interventions targeting other phases of the catering supply chain (e.g., food storage, meal preparation, waste management) had considerably lower improvement potentials. This review article provides valuable insights on how the sustainability of the food service sector can be improved without the burden shifting of impacts, which interventions to prioritise, and where knowledge gaps in research exist. A key recommendation for future research is to focus on combined life cycle thinking approaches that are capable of addressing sustainability holistically in the food service sector by integrating and assessing the environmental, social and economic dimensions of interventions.

Role of Digestate and Biochar in Carbon-Negative Bioenergy

Digestate and biochar can be land applied to sequester carbon and improve net primary productivity, but the achievable scale is tied to expected growth in bioenergy production and land available for application. We use an attributional life-cycle assessment approach to estimate the greenhouse gas (GHG) emissions and carbon storage potential of biochar, digested solids, and composted digested solids generated from organic waste in California as a test case. Our scenarios characterize changes in organic waste production, bioenergy facility build-out, bioenergy byproduct quality, and soil response. Moderate to upper bound growth in the bioenergy sector with annual byproduct disposal over 100 years could provide a cumulative GHG offset of 50-400 MMTCO₂ equiv, with an additional 80-300 MMTC sequestered in soils. This corresponds to net GHG mitigation over 100 years equivalent to 340-1500 MMTCO₂ equiv (80-350% of California's annual emissions). In most scenarios, there is sufficient working land to apply all available biochar and digestate, although land becomes a constraint if the soil's rest time between applications increases from 5 to 15 years.

Life cycle assessment of garden waste management options including long-term emissions after land application

A life cycle assessment (LCA) was performed on five garden waste treatment practices: the production of mature compost including the woody fraction (MCIW), the production of mature compost without the woody fraction (MCWW), the production of immature compost without the woody fraction (ICWW), fresh garden waste including the woody fraction (GWIW) and fresh garden waste without the woody fraction (GWWW). The assessment included carbon sequestration after land application of the garden waste and composts, and associated emissions. The removed woody fraction was incinerated and energy recovery included as heat and electricity. The functional unit of the assessment was treatment of 1000 kg of garden waste generated in Denmark. Overall, the results showed that composting of garden waste resulted in comparable or higher environmental impact potentials (depletion of abiotic resources, marine eutrophication, and terrestrial eutrophication and acidification) than no treatment before land application. The toxicity potentials showed the highest normalised impact potentials for all the scenarios, but were unaffected by the different garden waste treatments. The choice of energy source for substituted heat and electricity production affected the performance of the different treatment scenarios with respect to climate change. The scenarios with removal of the woody fraction performed better than the scenarios without removal of the woody fraction when fossil energy sources were substituted, but performed worse when renewable energy sources were substituted. Furthermore, the study showed the importance of including long-term emission factors after land application of fresh and composted garden waste products since the greatest proportion of carbon and nitrogen emissions occurred after land application in three out of the five scenarios for carbon and in all scenarios for nitrogen.

Biogas production from the mechanically pretreated, liquid fraction of sorted organic municipal solid wastes

The high liquid content in fruit and vegetable wastes makes it convenient to mechanically separate these wastes into mostly liquid and solid fractions by means of pretreatment. Then, the liquid fraction can be treated using a high-rate anaerobic biofilm reactor to produce biogas, simultaneously reducing the amount of solids that must be landfilled. In this work, the specific composition of municipal solid waste (MSW) in a public market was determined; then, the sorted organic fraction of municipal solid waste was treated mechanically to separate and characterize the mostly liquid and solid fractions. Then, the mesophilic anaerobic digestion for biogas production of the first fraction was evaluated. The anaerobic digestion resulted in a reduced hydraulic retention time of two days with high removal of chemical oxygen demand, that is, 88% on average, with the additional benefit of reducing the mass of the solids that had to be landfilled by about 80%.

A global prospective of income distribution and its effect on life cycle assessment of municipal solid waste management: a review

This study reviewed the municipal solid waste (MSW) composition, the management practices, and the use of life cycle assessment (LCA) tool for MSW management (MSWM) options in the various income group countries. LCA studies require inventory data, which is difficult to procure for any country including higher income group countries, and this issue gets compounded in low-income and lower middle-income group countries, which limits the implementation of LCA. This paper compared the use of LCA for MSWM between high-income and low-income group countries and also highlights the gap in using LCA for MSWM. A very limited number of LCA studies on MSWM were found for low-income group countries in comparison to high-income group countries. The study also provided a critical discussion on the challenges in applications of LCA in MSWM for better solid waste management in low-income and lower middle-income group countries. The study will help in taking up LCA studies in low-income countries to improve the overall MSWM efficiency.

Reviewing the anaerobic digestion and co-digestion process of food waste from the perspectives on biogas production performance and environmental impacts

In this paper, factors that affect biogas production in the anaerobic digestion (AD) and anaerobic co-digestion (coAD) processes of food waste are reviewed with the aim to improve biogas production performance. These factors include the composition of substrates in food waste coAD as well as pre-treatment methods and anaerobic reactor system designs in both food waste AD and coAD. Due to the characteristics of the substrates used, the biogas production performance varies as different effects are exhibited on nutrient balance, inhibitory substance dilution, and trace metal element supplement. Various types of pre-treatment methods such as mechanical, chemical, thermal, and biological methods are discussed to improve the rate-limiting hydrolytic step in the digestion processes. The operation parameters of a reactor system are also reviewed with consideration of the characteristics of the substrates. Since the environmental awareness and concerns for waste management systems have been increasing, this paper also addresses possible environmental impacts of AD and coAD in food waste treatment and recommends feasible methods to reduce the impacts. In addition, uncertainties in the life cycle assessment (LCA) studies are also discussed.

Systematic Evaluation of Industrial, Commercial, and Institutional Food Waste Management Strategies in the United States

New regulations and targets limiting the disposal of food waste have been recently enacted in numerous jurisdictions. This analysis evaluated selected environmental implications of food waste management policies using life-cycle assessment. Scenarios were developed to evaluate management alternatives applicable to the waste discarded at facilities where food waste is a large component of the waste (e.g., restaurants, grocery stores, and food processors). Options considered include anaerobic digestion (AD), aerobic composting, waste-to-energy combustion (WTE), and landfilling, and multiple performance levels were considered for each option. The global warming impact ranged from approximately -350 to -45 kg CO2e Mg(-1) of waste for scenarios using AD, -190 to 62 kg CO2e Mg(-1) for those using composting, -350 to -28 kg CO2e Mg(-1) when all waste was managed by WTE, and -260 to 260 kg CO2e Mg(-1) when all waste was landfilled. Landfill diversion was found to reduce emissions, and diverting food waste from WTE generally increased emissions. The analysis further found that when a 20 year GWP was used instead of a 100 year GWP, every scenario including WTE was preferable to every scenario including landfill. Jurisdictions seeking to enact food waste disposal regulations should consider regional factors and material properties before duplicating existing statutes.

Recovery of essential nutrients from municipal solid waste--Impact of waste management infrastructure and governance aspects

Every year 120-140 million tonnes of bio-waste are generated in Europe, most of which is landfilled, incinerated or stabilized and used as covering material in landfill operation. None of these practices enables the recovery of essential nutrients such as phosphorus (P) and nitrogen (N), which are in great demand for agricultural production. Recovery of these nutrients is a matter of international concern considering the non-renewable nature of P sources and the energy intensive production process required for the synthesis of N fertilizers. The objective of this research is to understand the relation between the municipal solid waste management (MSWM) system, both its the physical components and governance aspects, and the recovery of nutrients in Vitoria-Gasteiz (Basque Country) as a benchmark for European medium-size cities. The analysis shows that the existing physical infrastructure and facilities for bio-waste have high potential for nutrient recovery, 49% for N and 83% for P contained in bio-waste. However, governance aspects of the MSWM system such as legislation and user inclusivity play an important role and decrease the actual nutrient recovery to 3.4% and 7.4% for N and P respectively.

Economic and environmental optimization of waste treatment

This article presents the new systems engineering optimization model, OptiWaste, which incorporates a life cycle assessment (LCA) methodology and captures important characteristics of waste management systems. As part of the optimization, the model identifies the most attractive waste management options. The model renders it possible to apply different optimization objectives such as minimizing costs or greenhouse gas emissions or to prioritize several objectives given different weights. A simple illustrative case is analysed, covering alternative treatments of one tonne of residual household waste: incineration of the full amount or sorting out organic waste for biogas production for either combined heat and power generation or as fuel in vehicles. The case study illustrates that the optimal solution depends on the objective and assumptions regarding the background system--illustrated with different assumptions regarding displaced electricity production. The article shows that it is feasible to combine LCA methodology with optimization. Furthermore, it highlights the need for including the integrated waste and energy system into the model.

Composition variability of the organic fraction of municipal solid waste and effects on hydrogen and methane production potentials

The composition of the Organic Fraction of Municipal Solid Waste (OFMSW) strongly depends on the place and time of collection for a specific municipality or area. Moreover synthetic food waste or organic waste from cafeterias and restaurants may not be representative of the overall OFMSW received at treatment facilities for source-separated waste. This work is aimed at evaluating the composition variability of OFMSW, the potential productions of hydrogen and methane from specific organic waste fractions typically present in MSW and the effects of waste composition on overall hydrogen and methane yields. The organic waste fractions considered in the study were: bread-pasta, vegetables, fruits, meat-fish-cheese and undersieve 20mm. Composition analyses were conducted on samples of OFMSW that were source segregated at household level. Batch tests for hydrogen and methane productions were carried out under mesophilic conditions on selected fractions and OFMSW samples. Results indicated that the highest production of hydrogen was achieved by the bread-pasta fraction while the lowest productions were measured for the meat-fish-cheese fraction. The results indicated that the content of these two fractions in organic waste had a direct influence on the hydrogen production potentials of OFMSW. The higher the content of bread-pasta fraction, the higher the hydrogen yields were while the contrary was observed for the meat-fish-cheese fraction. The definition of waste composition therefore represents fundamental information to be reported in scientific literature to allow data comparison. The variability of OFMSW and its effects on hydrogen potentials might also represents a problematic issue in the management of pilot or full-scale plants for the production of hydrogen by dark fermentation.

Sewage sludge drying by energy recovery from OFMSW composting: preliminary feasibility evaluation

In this paper an original energy recovery method from composting is analyzed. The integrated system exploits the heat available from the aerobic biochemical process in order to support the drying of sewage sludge, using a specific solar greenhouse. The aim is to tackle the problem of organic waste treatment, with specific regard to food waste. This is done by optimizing the energy consumption of the aerobic process of composting, using the heat produced to solve a second important waste management problem such as the sewage waste treatment. Energy and mass balances are presented in a preliminary feasibility study. Referring to a composting plant with a capacity of 15,000 t/y of food waste, the estimation of the power from recovered heat for the entire plant resulted about 42 kW. The results demonstrated that the energy recoverable can cover part of the heat necessary for the treatment of sludge generated by the population served by the composting plant (in terms of food waste and green waste collection). The addition of a renewable source such as solar energy could cover the residual energy demand. The approach is presented in detail in order for it to be replicated in other case studies or at full scale applications.

Review of LCA studies of solid waste management systems--part I: lessons learned and perspectives

The continuously increasing solid waste generation worldwide calls for management strategies that integrate concerns for environmental sustainability. By quantifying environmental impacts of systems, life cycle assessment (LCA) is a tool, which can contribute to answer that call. But how, where and to which extent has it been applied to solid waste management systems (SWMSs) until now, and which lessons can be learnt from the findings of these LCA applications? To address these questions, we performed a critical review of 222 published LCA studies of SWMS. We first analysed the geographic distribution and found that the published studies have primarily been concentrated in Europe with little application in developing countries. In terms of technological coverage, they have largely overlooked application of LCA to waste prevention activities and to relevant waste types apart from household waste, e.g. construction and demolition waste. Waste management practitioners are thus encouraged to abridge these gaps in future applications of LCA. In addition to this contextual analysis, we also evaluated the findings of selected studies of good quality and found that there is little agreement in the conclusions among them. The strong dependence of each SWMS on local conditions, such as waste composition or energy system, prevents a meaningful generalisation of the LCA results as we find it in the waste hierarchy. We therefore recommend stakeholders in solid waste management to regard LCA as a tool, which, by its ability of capturing the local specific conditions in the modelling of environmental impacts and benefits of a SWMS, allows identifying critical problems and proposing improvement options adapted to the local specificities.