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Abstract An overview of relevant literature shows how supply chain and network flow models represent useful tools in the area of clean energy generation and processing related waste. This paper deals with a specific network flow problem where the mixed municipal waste as a secondary and partly renewable energy carrier is transported from waste producers (municipalities), through pre-processing facilities, to its final treatment in waste processing units and in which the optimal flow is desired. The results obtained for the minimum total costs, including treatment and transportation, correspond to production and savings of a certain amount of CO 2 and other greenhouse gases which is described by Global Warming Potential (GWP). The average cost was 74 EUR/t and average GWP was 37 kg CO 2eq /t. The GWP contribution varies among the waste producers as a result of treating waste in different places and various technologies. However, to identify the individual contributions, the detailed waste flow identification is required. The flow distribution is unknown due to the effect of merging and splitting waste streams in the network. For this reason, a consequent network flow problem for exact waste flows identification is proposed. The model follows the principle ideas of multi-commodity network flow modelling and it reveals the variability of cost and GWP contribution for all producers in the investigated area. The proposed method has been tested through a case study considering treatment of mixed municipal waste. The results obtained by the original implementation in GAMS are presented and discussed in detail. The GWP contribution varied between −173 and 880 kg CO 2eq /t and significant waste producers were identified in the network regarding GWP. The results are important for setting the target for emission reduction in individual regions and for particular producers. The principle can be applied in general to any commodity and network flow problem. Highlights • Emission, processing and cost analysis in a feasibility study for waste treatment. • Branching network structure lead to the loss of information in producer waste flow. • A new computational approach extends a basic flow and capacity allocation problem. • Waste flows are identified to evaluate GWP contribution of the particular producer. [ABSTRACT FROM AUTHOR]

Abstract: Fossil fuels such as coal still dominate in current energy production plants. However, due to their large carbon footprint caused by combustion, rising prices and the unclear an increased interest in renewable and alternative fuels is observable. By 2020, renewable energy should account for 20% of the EU’s final energy consumption in order to reduce the negative impacts of the utilization of fossil fuels. Biomass-based fuels contribute to this effort. The optimization approach introduced in this article supports sustainable and financially feasible biomass integration into the existing large energy producing system with combined heat and power (CHP) production. The objective is to identify optimal conditions (optimal amount of burned fuels with respect to energy demands and energy flows through key components) with regard to maximum annual financial profit. The general mathematical model of a CHP plant utilizing more types of fuels is introduced and an optimization problem is formulated. The approach application is demonstrated on a case study involving existing CHP plant co-firing coal and biomass. The optimization problem is implemented and solved in GAMS (General Algebraic Modeling System). A sensitivity analysis of crucial parameters is performed and the results are presented and discussed. [Copyright &y& Elsevier]

Abstract: In recent years, renewable energy sources have played an increasingly important role in potential energy production. The integration of renewables into energy production plants has therefore become a major challenge for many organizations. This study concerns the modernization of a small power plant in a large hospital. The design criteria include the possibility of utilizing renewable energy sources and providing a potential increase in heat production (with additional heat being supplied to a nearby university campus). The existing boiler conditions (i.e. controls, efficiency, etc.) are unable to satisfy the desired requirements and therefore require an extensive retrofit. The purpose of this study was to create an effective methodology for the development of an optimal solution to an integrated renewable energy retrofit. This retrofit would supply the current requirements for steam and in addition provide heat to a newly built local facility. Various alternatives were assessed as part of this study including: a retrofit without a complete concept change; a combined heat and power system using natural gas and making use of alternative cogeneration devices; a system utilizing biomass without the production of electricity; and a system producing energy from biomass with combined heat and power. All alternatives were required to maximize the utilization of existing equipment. In considering the combined heat and power production alternative, the plant would be required to reduce the consumption of imported electrical energy in the original building. After considering the technical and economic factors of the various design solutions obtained, and taking into account additional criteria such as the global trend of the price of crude oil and natural gas, electricity costs, and the political support for electric production from renewable sources, the two best alternatives were determined. The preferred design utilizes an energy production plant with a biomass boiler. An alternative choice includes the use of a combined heat and power energy plant that utilizes biomass as a fuel combined with a backpressure steam turbine for extraction. [Copyright &y& Elsevier]

Biowaste represents a significant fraction of municipal solid waste (MSW). Its separate collection is considered as a useful measure to enhance waste management systems in both the developed and developing world. This paper aims to compare the environmental performance of three market-ready technologies currently used to treat biowaste—biowaste composting, fermentation, and biowaste incineration in waste-to-energy (WtE) plants as a component of residual municipal solid waste (RES). Global warming potential (GWP) was applied as an indicator and burdens related to the operation of facilities and credits obtained through the products were identified. The environmental performance of a WtE plant was investigated in detail using a model, implementing an approach similar to marginal-cost and revenues, which is a concept widely applied in economics. The results show that all of the treatment options offer an environmentally friendly treatment (their net GWP is negative). The environmental performance of a WtE plant is profoundly affected by its mode of its operation, i.e., type of energy exported. The concept producing environmental credits at the highest rate is co-incineration of biowaste in a strictly heat-oriented WtE plant. Anaerobic digestion plants treating biowaste by fermentation produce fewer credits, but approximately twice as more credits as WtE plants with power delivery only. [ABSTRACT FROM AUTHOR]

This paper introduces a novel approach to forecasting future commodity production in hundreds of nodes, which represents a key input for many applications of supply-chain models. A mathematical model was proposed to handle the problem of forecasting with spatially distributed and uncertain data. It is derived from the principle of regression analysis and extended by a data reconciliation technique. Additional areal constraints guarantee mass conservation in a tree-like structure, which reflects the organisational arrangement of an investigated region. The proposed model was tested through a case study, where future production of hazardous waste suitable for thermal treatment was forecasted in 206 base-nodes, 14 superior nodes and one apex. Based on an extensive investigation of historical data, it was revealed that extrapolations carried out at different levels of the hierarchical organisational structure lead to inconsistent forecasts. The differences between forecasts reached up to 50%. In addition to this, mass conservation was violated. Significant corrections were performed by computations utilizing the formulated model. The corrections ranged from between 0% and 12% for 90% of nodes. There were 17 nodes, where massive adjustments of up to 30% were inevitable. [ABSTRACT FROM AUTHOR]

Changing the fuel mix used in the heating industry, i.e., switching to greener fuels, is one of the possible solutions to prevent rising costs for final consumers in the context of rising emission allowance prices. This paper presents a methodology that offers the possibility to perform a comprehensive technical and economic assessment of a theoretical solution—changing the fuel mix of centralized heating sources—and other strategic decisions within a district's heating systems. Emphasis is placed on fuels with a negative price, such as municipal waste. The presented approach can also be used to assess the effect of other significant changes related to the configuration of district heating systems on the economy of the plant, such as the impact of a decrease in heat demand and implementation of a steam turbine. The key benefit of this paper is an approach based on mathematical modelling of the operation of individual boilers with different operating parameters in terms of their start-up, shutdown, and mode of operation. A unique approach of optimizing an operation's schedule using dynamic programming is presented, which enables the selection of a suitable solution for the configuration of binary variables in consecutive time steps. In this way, it is possible to achieve a more accurate estimate of the economics of the facility at the strategic planning stage that will consider the real operational capabilities of the heat source given its technical limitations. Using this approach, up to a 4% reduction in variable operating costs was achieved in the model case, when compared to static time interval planning. [ABSTRACT FROM AUTHOR]

In Europe, most of the district heat is produced from fossil energy sources such as coal or natural gas. Together with the intention to divert municipal waste from landfill, which is still the main way of treatment in approximately half of the EU countries, there is a potential for the construction of waste-to-energy plants (WtEP) that can partially replace fossil fuels. An important factor in planning the construction of new WtE plants is the assessment of the project's economy. However, the ecological aspect of the project, namely the greenhouse-gas (GHG) savings, is becoming a topic of discussion nowadays. In terms of GHG savings, WtE plant integration into an existing district heating system (DHS) has a positive impact, but its level is often only roughly estimated. The paper presents a comprehensive mathematical optimization tool working on a daily time interval that is able to evaluate the impact of changing current technology or WtE plant construction on global warming potential. The technical parameters such as boiler output range, energy efficiency, etc. are considered. The tool also allows to put in the context the GHG savings and economic benefits of the project. These two factors are very difficult to compare. The study answers the question of how to deal with this issue and presents the possibility of comparison, which is generally transferable to any two parameters. Due to two poorly comparable criteria, the result does not include a single optimal solution, but clearly illustrates the view of the overall issue and gives a good basis for the final decision. The method used are illustrated in real-world DHS with various parameters where the relationship between GHG savings and the economic benefits of the integration of a WtE plant is evaluated. The whole problem is the task of linear integer programming and is implemented in the GAMS programming environment. • A multi-criteria optimization tool for WtE plant integration is introduced. • Economic and environmental aspects are put into context. • The optimal capacity is determined depending on the emphasis on both aspects. • The cost of removing a tonne of CO 2 by WtE in a particular location is calculated. [ABSTRACT FROM AUTHOR]

The data regarding the current potential of unrecyclable waste and its spatial distribution play an essential role in the planning process. As per the circular economy strategies, especially the bulky waste streams suitable for energy recovery are to be identified. The public databases, however, collect data from a variety of sources (production and handling reports), which implies the presence of errors. This paper therefore proposes a multi-objective approach to identification and elimination of such errors to improve the accuracy of the assessment of potential energy recovery. The discussed model tracks the flow of waste from producers to processing nodes and minimises the deviation from the original data. Economic aspects are considered as well by preferring the shortest transport distance. The combination of data reconciliation and network flow enhances performance, as objective functions are solved separately, and only then the normalised individual optima are used in the multi-objective function. The model was tested using a Czech Republic regional-level dataset from 2015. A new perspective on the current state of waste management was provided, and valuable information for future planning was revealed, which can be useful for modelling of flows of other commodities. Image 1 • Novel supply chain model for transportation and treatment reconciliation is presented. • Large amount of bulky waste is identified as suitable for energy recovery. • Region-specific waste potential for an environmental treatment option is analysed. [ABSTRACT FROM AUTHOR]

The contribution of supporting tools developed for logistic optimization and processing infrastructure planning is highly dependent on the quality of input data. Databases containing reports on waste production and treatment are often used for waste management case studies and in the aggregated form at the national level provide sufficient information with negligible errors. On the other hand, analysis in greater detail at the smallest administrative unit usually reveals significant inconsistencies, especially in the case of mass balance control. This often results in the impossibility to track waste flows in the system and evaluate final treatment. This paper aims to present a tool for database verification in order to satisfy mass balances at all levels of the investigated system. As part of the mathematical modelling, the database is first subjected to a statistical analysis where selected inconsistencies between records can be removed. Subsequently, data reconciliation is applied with appropriate weights assigned to each entity in the system. The weights represent credibility and reflect various errors, which are identified in the previous stage of the approach. The correction of mass balances enables an evaluation of quality or composition in greater detail of individual entities and also determines the feasible interval of monitored properties. The tool is applied to the treatment evaluation of dry matter in wastewater sludge in the Czech Republic. Thanks to the developed tool, disposal and material or energy recovery can be quantified at micro-regional. [Display omitted] • National waste management database controlling in the detail of single entities. • Mass balance correction in every level of monitored territory. • Combination of statistics, data reconciliation and network flow problem. • Point and interval estimates of waste flow properties within the system. • Application of the developed approach to a case of wastewater sludge treatment. [ABSTRACT FROM AUTHOR]

Abstract The paper deals with the issue of fluctuations in heat demand and how they are dealt with when planning investments in the field of energy recovery of waste. The lifetime of Waste to Energy plants (WtEP) is typically 20–30 years. Their construction is also a time and investment-intensive business and requires a robust design with low sensitivity to future changes in key parameters. The paper analyses the effect of fluctuations in heat demand on the accuracy of techno-economic models and their outputs. The aim is to determine the sensitivity of optimisation models to the applied time step. The sensitivity of two different models is compared – a simple model of a WtEP cooperating with a gas boiler and a complex model of a WtEP integrated with a combined heat and power plant. Optimisation models, commonly used to design these facilities, perform calculations in certain time steps, typically on an annual or monthly basis. The simplification from hour to month time step may cause inaccuracies. The paper offers alternative solutions to modelling methods of WtEP, using so-called correction coefficients. They help to increase the accuracy of the models while maintaining acceptable calculation time. Highlights • Tracking short-term changes to important parameters for the WtE plant economy. • Modelling the operation of an existing and newly considered thermal facility. • Creating and applying correction coefficients for fluctuation parameters. [ABSTRACT FROM AUTHOR]

Waste management has still been a developing and progressing field, which demands continual improvements in waste transportation as well as proper selection of locations and technical operation of new treatment facilities. Most of research papers on waste management planning have been dealing with optimisation of network flows, thus minimising the cost and improving economic criteria. The shortest paths to treatment facilities are considered together with detailed analysis of their operation including heat and electricity demands in their vicinity. The tasks sometimes include social and global environmental criterions, however, the direct local consequences also play an important role and should be examined. A decision-making strategy in waste management updated with the local emission impact on the population is proposed in this paper. The paper focuses on the first move in analysing the production, dispersion, and impact of pollutants, originating in transport, with regards to the population living close to routes. The calculation of emission produced during the transport of waste takes into consideration the altitude profiles of routes, container loads, and specific types of vehicles. The consecutive estimated impact on the population reckons with the distances between routes and municipalities as well as their sizes in terms of the numbers of inhabitants, where the transportation routes are divided into smaller segments and dispersion is limited with threshold value. The proposed approach describing the emission effect has been tested using real-life operating data corresponding to the specific, 81 km long route along which approximately 25 t of waste is transported 800 times a year. The impact of pollutants on the population was evaluated and discussed. Results of the analysis were quantified for this route to create an edge characterisation needed for further calculations. This approach applied to the whole network then yields input data needed for future research of novel strategies in facility location problems. Other possible extensions of the presented approach include more accurate dispersion function or detailed calculation of the impact of pollutants with respect to specific locations of residential houses. [ABSTRACT FROM AUTHOR]

Bottom ash (BA) from waste-to-energy (WtE) plants contains valuable components, particularly ferrous (Fe) and non-ferrous (NFe) metals, which can be recovered. To assess the resource recovery potential of BA in the Czech Republic, it was necessary to obtain its detailed material composition. This paper presents the material composition of BA samples from all three Czech WtE plants. It was found that the BA contained 9.2–22.7% glass, 1.8–5.1% ceramics and porcelain, 0.2–1.0% unburnt organic matter, 10.2–16.3% magnetic fraction, 6.1–11.0% Fe scrap, and 1.3–2.8% NFe metals (in dry matter). The contents of individual components were also studied with respect to the BA granulometry and character of the WtE waste collection area. [ABSTRACT FROM AUTHOR]

With the increasing share of waste material recovery, household plastic waste is one of the biggest problems. In most countries, mainly manual sorting is used. Meanwhile, new automated technologies are being developed to expand the range of classifiable types to increase material recovery. The overall automation of the sorting process can help the EU's established recycling targets to be effectively met. However, the new technologies are feasible only in the case of large-capacity centers, which must be conveniently located in the existing infrastructure. This paper presents a two-stage model aiming to modernize the current sorting infrastructure for plastic waste. The approach uses multi-criteria optimization to minimize environmental impact at a reasonable price. The result is the optimal location of new automatic sorting centers, and waste stream flows using existing manual sorting facilities. The model is applied through an initial case study inspired by the Czech Republic data. Optimization output proposes four new automatic sorting lines with a total capacity of 158 kt per year. In most cases, manual sorting is used to reduce the transported weight of plastic waste, while automatic sorting lines separate the remaining, hardly recognized part. More than 60% of separately collected plastic is sorted and determined for material recovery. • Implementation of new sorting technologies into existing infrastructure. • Multi-criteria model for reducing environmental impact with a cost estimate. • Model tested through a case study inspired by conditions in the Czech Republic. • The results recommend four new high-tech centers with a total capacity of 158 kt. • The emission savings are 264 kt CO 2eq , costing 74 EUR per tonne of CO 2eq. [ABSTRACT FROM AUTHOR]

The fundamental knowledge at all levels of decision-making related to waste management is the quantity and composition of waste. Many articles deal with methods for estimating the composition of municipal waste, but most details are given as to how many categories should be chosen and what technical procedure should be followed. In order to obtain a broader view and a reasonable evaluation of the results, it is necessary to select the areas where the analyzes will be performed effectively. Current approaches have insufficiently addressed this issue at the regional and national levels. This paper presents a method that uses multi-level stratification to divide municipalities into similar groups to reduce the number of observations needed to obtain an estimate of the composition of waste in a selected area (region or state level). The method combines expert knowledge with statistical considerations and makes use of cluster analysis. Socio-economic and waste-related parameters are used within the individual steps. Regarding the available financial resources and the required accuracy of the results, the municipalities in which the analyzes should take place are selected. These representative municipalities represent other municipalities in the created groups, and thanks to them, it is possible to estimate the composition of waste in any municipality, region, or larger territory. Waste analysis planning is an essential procedure for waste management, but the respective costs represent a crucial factor at the national level and even more for individual municipalities. Estimating waste composition impacts the transition to sustainable waste management and is thus a key element for further development in this sector. The presented method demonstrates the selection of 10 representative municipalities from the Czech Republic, but an arbitrary number can be set respecting the financial resources. Estimating the composition of the mixed municipal waste for the Czech Republic should cost around 72,000 euros for ten representatives with different distribution of dwelling types. The method is described in general and can be applied to any territory/country in the world, considering local conditions and possibilities. • Stratification of municipalities reduces the cost of waste composition analysis. • Socio-economic parameters applied in multi-level stratification of a large territory. • Country/region composition estimates of mixed municipal waste can be accomplished. • A guideline on how to select representative municipalities was proposed. [ABSTRACT FROM AUTHOR]

A circular economy is a trendy word, which encompasses reaching of closed-loop in all industries. This also applies to the waste management sector, where new regulations and directives have been issued. Given milestones, however, do not have to correspond with economic or even environmental sustainability. Thus, it is more than necessary to evaluate waste management system using these criteria and present supportive or contradictory statements. An approach for such a complex assessment is proposed. It uses mathematical programming models and multi-objective strategy to suggest a suitable number and locations for waste treatment and pre-treatment facilities. Only main fractions of municipal solid waste are considered – plastic, paper, glass and mixed municipal waste. The environmental part covers the production of greenhouse gases respecting all processes in the system, excluding transportation. Based on comprehensive research, non-linear dependencies were estimated for costs and sorting efficiencies. The mathematical model uses an iterative procedure to avoid non-linearity. Afterwards, the case study of Czech treatment infrastructure is designed. The approach resulted in the establishment of 14, and 42 sorting lines for plastics and paper, respectively, supported by 20 Waste-to-Energy plants with different capacity. An interesting output says that in an optimal situation, out of total sorted plastics and paper, only 25% and 79% will be recycled, while the remaining amount ends up in Waste-to-Energy plant. Further research will include additional fractions, such as bio-waste, oils or textile, as it is being collected these days separately. Other directions involve new targets from the real-operated sorting lines and new conditions related to investment for more fractions treated at a single site. Image 1 • Optimal separation rate determined by the economic performance of sorting line. • Municipal solid waste treatment infrastructure and transportation were designed. • Economic and environmental balances were used for each process component. • The waste management system was updated by a complex network flow model. • Case study results: 100% separation rate of paper and 52% of plastic. [ABSTRACT FROM AUTHOR]

The paper presents a new model for integration of circular economy strategies into the municipal solid waste management. The goals are to reduce the waste produced, recycle at the highest rate as possible (material recovery) and to use the resultant residual waste for energy recovery. Such a strategy utilizes both pricing and advertising principles in the mixed integer linear programming model while accounting two criterions - assessment of greenhouse gas (GHG) and cost minimization. The aim is to design the optimal waste management grid to suggest a sustainable economy with environmental concerns. The government, municipalities and/or authorized packaging company decide about the investments to the propagation of waste prevention and to advertising of waste recycling, while investors decide about new facility location and technological parameter. The availability of waste is projected in pricing method as well as in the location of the facility. The mathematical model will consider randomness in the form of waste production. The suggested non-linear functions of pricing and advertising are replaced by piecewise linear approximation to reduce computational complexity. The proposed multi-objective model is applied in a case study for the Czech Republic in the area of waste treatment infrastructure planning to support decision-making at the micro-regional level. The integration of circular economy principles, considering also the total amount of produced GHG, revealed the existing potential in waste prevention. On the other hand, the increase of recycling is limited, landfills are not supported and the energy recovery is preferred. However, the planning of the complex system relies on the decision-maker. Image 1 • Waste treatment hierarchy principles utilized in mathematical modelling. • Pricing and advertising as the features of waste prevention and recycling. • Investor point of view for the evaluation of sustainable facility location. • Greenhouse gases and cost minimization as the decision-making criterions. [ABSTRACT FROM AUTHOR]

Municipal solid waste treatment leads to the production of a considerable amount of mixed municipal waste, in case of which material recovery is difficult. Its treatment represents a worldwide challenge since landfilling is still a major treatment method and the respective emissions of greenhouse gases are significant. Approximately 126 Mt of municipal solid waste were landfilled or incinerated within the EU-28 in 2017, while the waste management sector produced 3% of the overall greenhouse gases emissions. Regarding mixed municipal waste, Waste-to-Energy plants seem to be a suitable disposal option as they substitute both landfills and energy production from fossil fuels in combined heat and power plants. However, new treatment facilities of this type need to take into account also the heat and electricity demands in their vicinity to ensure economic stability. This paper therefore analyses the relationship between greenhouse gases emissions and the cost of mixed municipal waste treatment, while considering environmental impact of different treatment options. A reverse logistic (mixed integer programming) model has been developed to optimise future strategies of mixed municipal waste treatment in a large geographical area. The model is nonlinear because of the nonlinear nature of the cost of mixed municipal waste treatment as well as the economic incentive associated with the avoided greenhouse gases emissions. These, in turn, are influenced by plant capacities, locations, and other location-specific parameters (such as the yearly heat demand profile) that must be considered during the integration of a future plant into the existing district heating systems. The results are presented through a case study for the Czech Republic, with 206 micro-regions (waste producers), 148 landfills, 113 potential mechanical-biological treatment plants, 24 potential locations for plants utilising refuse-derived fuels, 4 existing Waste-to-Energy plants, and 32 candidate locations for new Waste-to-Energy plants have been considered. The proposed future concepts involving various processing chains (small Waste-to-Energy plant, large Waste-to-Energy plant with the necessary complex logistics, mechanical biological treatment prior to incineration), are compared with the current (2016) waste treatment strategy, in which 73% of mixed municipal waste is landfilled. The trade-off between economically viable and environmentally acceptable solution is also targeted. The obtained data suggest a possible reduction in greenhouse gases emissions by almost 150% with the cost of waste treatment being increased only by approx. 2.5 EUR/t. Image 1 • Cost of reducing greenhouse gas emissions is evaluated using the proposed method. • Emissions of the Waste-to-Energy strategy are assessed and implemented in model. • Locations of new plants are suggested to reduce greenhouse gases at a viable cost. • Reduction in greenhouse gases by 150% causes only 2.5 EUR/t increase in the cost. [ABSTRACT FROM AUTHOR]