Waste to energy, indispensable cornerstone for circular economy: A mini-review.

This mini-review aims at proving that waste-to-energy (WtE) is an essential cornerstone for circular economy (CE). Based on literature, the history of thermal waste treatment over the last 150 years is investigated, from open burning to WtE with resource recovery and final sink function. The results show that in the past incineration solved the issues it was designed for but often created new and sometimes even worse problems: The introduction of incineration in the 19th century improved urban sanitation, decreased waste volume and prolonged operational life of landfills. But it also polluted the environment, triggering an unprecedented scientific and engineering effort of all stakeholders. Today, WtE is one of the best investigated and optimized technologies in waste management. It enables the recovery of energy as heat and electric power and facilitates the 'cleaning' of cycles by the destruction of hazardous organic substances. Recent developments in resource recovery from WtE residues allow to recycle metals and, in the case of sewage sludge, even phosphorus by thermal recycling. Combined with carbon capture and storage technology, WtE stands for a quantifiable contribution to greenhouse gas reduction. Today, WtE is indispensable to reach the goals of CE, namely recycling of energy and materials, supplying safe final sinks for persistent organic substances and minimizing the need for sinks for hazardous inorganic substances.

Improving waste management by focussing on goals: A mini review of the publication sector.

The rationale for this article is that often, decision-makers in waste management (wm) tend to neglect goals and confuse them with means like circular economy or waste hierarchy. Because clear goals are crucial for developing effective wm strategies, the objectives of this mini review are (1) to clarify wm goals in a historical context by a literature review, (2) to investigate how (a) these goals have been observed in general scientific publishing and (b) specifically in Waste Management and Research (WM&R) and (3) to recommend measures for better consideration of wm goals by the publication sector. Based on general as well as specific bibliographic analyses of databases in Scopus and Google Scholar, the study confirms that little attention was given to wm goals in scientific publishing. For instance, during the first 40 years of WM&R, 63 publications and eight editorials were found containing terms related to wm goals, but only 14 respectively and eight explicitly discuss wm goals. We recommend focussing more on wm goals. Editors, authors, reviewers and professional associations in the field of wm should become aware of this challenge and react. If WM&R decides to become a strong platform for the issue wm goals, it will be in a unique selling proposition and more authors, articles and readers are likely to result. This article aims at setting a starting signal for such an endeavour.

Material Flow Analysis as a Tool to improve Waste Management Systems: The Case of Austria.

This paper demonstrates the power of material flow analysis (MFA) for designing waste management (WM) systems and for supporting decisions with regards to given environmental and resource goals. Based on a comprehensive case study of a nationwide WM-system, advantages and drawbacks of a mass balance approach are discussed. Using the software STAN, a material flow system comprising all relevant inputs, stocks and outputs of wastes, products, residues, and emissions is established and quantified. Material balances on the level of goods and selected substances (C, Cd, Cr, Cu, Fe, Hg, N, Ni, P, Pb, Zn) are developed to characterize this WM-system. The MFA results serve well as a base for further assessments. Based on given goals, stakeholders engaged in this study selected the following seven criteria for evaluating their WM-system: (i) waste input into the system, (ii) export of waste (iii) gaseous emissions from waste treatment plants, (iv) long-term gaseous and liquid emissions from landfills, (v) waste being recycled, (vi) waste for energy recovery, (vii) total waste landfilled. By scenario analysis, strengths and weaknesses of different measures were identified. The results reveal the benefits of a mass balance approach due to redundancy, data consistency, and transparency for optimization, design, and decision making in WM.

Waste to energy--key element for sustainable waste management.

Human activities inevitably result in wastes. The higher the material turnover, and the more complex and divers the materials produced, the more challenging it is for waste management to reach the goals of "protection of men and environment" and "resource conservation". Waste incineration, introduced originally for volume reduction and hygienic reasons, went through a long and intense development. Together with prevention and recycling measures, waste to energy (WTE) facilities contribute significantly to reaching the goals of waste management. Sophisticated air pollution control (APC) devices ensure that emissions are environmentally safe. Incinerators are crucial and unique for the complete destruction of hazardous organic materials, to reduce risks due to pathogenic microorganisms and viruses, and for concentrating valuable as well as toxic metals in certain fractions. Bottom ash and APC residues have become new sources of secondary metals, hence incineration has become a materials recycling facility, too. WTE plants are supporting decisions about waste and environmental management: They can routinely and cost effectively supply information about chemical waste composition as well as about the ratio of biogenic to fossil carbon in MSW and off-gas.

Sinks as limited resources? A new indicator for evaluating anthropogenic material flows.

Besides recyclables, the use of materials inevitably yields non-recyclable materials such as emissions and wastes for disposal. These flows must be directed to sinks in a way that no adverse effects arise for humans and the environment. The objective of this paper is to present a new indicator for the assessment of substance flows to sinks on a regional scale. The indicator quantifies the environmentally acceptable mass share of a substance in actual waste and emission flows, ranging from 0% as worst case to 100% as best case. This paper consists of three parts: first, the indicator is defined. Second, a methodology to determine the indicator score is presented, including (i) substance flows analysis and (ii) a distant-to-target approach based on an adaptation of the Ecological Scarcity Method 2006. Third, the metric developed is applied in three case studies including copper (Cu) and lead (Pb) in the city of Vienna, and perfluorooctane sulfonate (PFOS) in Switzerland. The following results were obtained: in Vienna, 99% of Cu flows to geogenic and anthropogenic sinks are acceptable when evaluated by the distant-to-target approach. However, the 0.7% of Cu entering urban soils and the 0.3% entering receiving waters are beyond the acceptable level. In the case of Pb, 92% of all flows into sinks prove to be acceptable, and 8% are disposed of in local landfills with limited capacity. For PFOS, 96% of all flows into sinks are acceptable. 4% cannot be evaluated due to a lack of normative criteria, despite posing a risk for human health and the environment. The examples demonstrate the need (i) for appropriate data of good quality to calculate the sink indicator and (ii) for standards, needed for the assessment of substance flows to urban soils and receiving waters. This study corroborates that the new indicator is well suited as a base for decisions regarding the control of hazardous substances in waste and environmental management.

Combination of material flow analysis and substance flow analysis: a powerful approach for decision support in waste management.

The novelty of this paper is the demonstration of the effectiveness of combining material flow analysis (MFA) with substance flow analysis (SFA) for decision making in waste management. Both MFA and SFA are based on the mass balance principle. While MFA alone has been applied often for analysing material flows quantitatively and hence to determine the capacities of waste treatment processes, SFA is more demanding but instrumental in evaluating the performance of a waste management system regarding the goals "resource conservation" and "environmental protection". SFA focuses on the transformations of wastes during waste treatment: valuable as well as hazardous substances and their transformations are followed through the entire waste management system. A substance-based approach is required because the economic and environmental properties of the products of waste management - recycling goods, residues and emissions - are primarily determined by the content of specific precious or harmful substances. To support the case that MFA and SFA should be combined, a case study of waste management scenarios is presented. For three scenarios, total material flows are quantified by MFA, and the mass flows of six indicator substances (C, N, Cl, Cd, Pb, Hg) are determined by SFA. The combined results are compared to the status quo in view of fulfilling the goals of waste management. They clearly point out specific differences between the chosen scenarios, demonstrating potentials for improvement and the value of the combination of MFA/SFA for decision making in waste management.

Assessment methods for solid waste management: A literature review.

Assessment methods are common tools to support decisions regarding waste management. The objective of this review article is to provide guidance for the selection of appropriate evaluation methods. For this purpose, frequently used assessment methods are reviewed, categorised, and summarised. In total, 151 studies have been considered in view of their goals, methodologies, systems investigated, and results regarding economic, environmental, and social issues. A goal shared by all studies is the support of stakeholders. Most studies are based on life cycle assessments, multi-criteria-decision-making, cost-benefit analysis, risk assessments, and benchmarking. Approximately 40% of the reviewed articles are life cycle assessment-based; and more than 50% apply scenario analysis to identify the best waste management options. Most studies focus on municipal solid waste and consider specific environmental loadings. Economic aspects are considered by approximately 50% of the studies, and only a small number evaluate social aspects. The choice of system elements and boundaries varies significantly among the studies; thus, assessment results are sometimes contradictory. Based on the results of this review, we recommend the following considerations when assessing waste management systems: (i) a mass balance approach based on a rigid input-output analysis of the entire system, (ii) a goal-oriented evaluation of the results of the mass balance, which takes into account the intended waste management objectives; and (iii) a transparent and reproducible presentation of the methodology, data, and results.

The Copper Balance of Cities: Exploratory Insights into a European and an Asian City.

Material management faces a dual challenge: on the one hand satisfying large and increasing demands for goods and on the other hand accommodating wastes and emissions in sinks. Hence, the characterization of material flows and stocks is relevant for both improving resource efficiency and environmental protection. This article focuses on the urban scale, a dimension rarely investigated in past metal flow studies. We compare the copper (Cu) metabolism of two cities in different economic states, namely, Vienna (Europe) and Taipei (Asia). Substance flow analysis is used to calculate urban Cu balances in a comprehensive and transparent form. The main difference between Cu in the two cities appears to be the stock: Vienna seems close to saturation with 180 kilograms per capita (kg/cap) and a growth rate of 2% per year. In contrast, the Taipei stock of 30 kg/cap grows rapidly by 26% per year. Even though most Cu is recycled in both cities, bottom ash from municipal solid waste incineration represents an unused Cu potential accounting for 1% to 5% of annual demand. Nonpoint emissions are predominant; up to 50% of the loadings into the sewer system are from nonpoint sources. The results of this research are instrumental for the design of the Cu metabolism in each city. The outcomes serve as a base for identification and recovery of recyclables as well as for directing nonrecyclables to appropriate sinks, avoiding sensitive environmental pathways. The methodology applied is well suited for city benchmarking if sufficient data are available.

Sustainable resource use requires "clean cycles" and safe "final sinks".

In order to fulfill the objectives of environmental protection, today's focus on quantitative recycling rates must be amended by a more qualitative approach. Because modern products represent a mix of numerous and sometimes hazardous substances, ways must be explored to remove detrimental substances during recycling and to establish "clean cycles". On the one hand, such a "clean cycle" strategy will result in better recycling qualities of secondary products and less dissipation of hazardous substances during further product use. On the other hand, the elimination of hazardous substances during recycling requires sinks for the disposal of the eliminated materials. These topics are presented in general as well as by case studies. In particular, the sink issue is addressed, differentiating between sinks and final sinks and discussing the challenge to supply appropriate final sinks for all materials that cannot be recycled.

Site-specific criteria for the completion of landfill aftercare.

Municipal solid waste (MSW) landfills need to be managed after closure to assure long-term environmental compatibility. Aftercare can be completed when the authorities consider the landfill not likely to pose a threat to humans and the environment. In this work, a methodology for deriving site-specific aftercare completion criteria is presented and its application is illustrated via a case study. The evaluation method combines models addressing waste emission behavior, long-term barrier performance, and pollutant migration to assess the potential impact of landfill emissions on the environment. Based on the definition of acceptable impact levels at certain points of compliance, scenario- and pollutant-specific aftercare completion criteria are derived. The methodology was applied to a closed MSW landfill in Austria and potential aftercare durations were determined. While landfill gas emissions may become environmentally tolerable within decades at the site, leachate-related aftercare measures were expected to be necessary for centuries (primarily as a result of ammonium). Although the evaluation comes with large uncertainties, it allows for linking aftercare intensity and duration with respect to an environmentally compatible state of the landfill in the absence of aftercare. However, further case studies including regulatory review and acceptance are needed to use the methodology in a decision support tool on aftercare completion.

Metals in RDF and other high calorific value fractions from mechanical treatment of MSW: analysis and sampling errors.

RDF and other high calorific value fractions derived from MSW by mechanical treatment processes contain goods such as cans, cables, zippers or batteries which are highly concentrated in metals. The objective of this study was to investigate the importance of these metal carriers (i) for total metal loads and (ii) for sampling errors. Six different products derived from MSW were analysed for carrier bound and total loads of Al, Cd, Cr, Cu, Fe, Ni, Pb and Zn. Sophisticated sample preparation procedures were applied in order to quantify the separate analyte loads from metallic carriers. Typical values for total metal contents and shares of carrier bound loads were found as follows: Al, 20 g kg(-1) (30%); Cr, 0.4 g kg(-1) (50%); Cu, 5 g kg(-1) (80%); Fe, 40 g kg(-1) (80%); Ni, 0.15 g kg(-1) (70%); Pb, 0.4 g kg(-1) (40%); and Zn, 2 g kg(-1) (30%). NiCd-batteries were found in three materials representing 30-70 % of total Cd contents (total 6-20 mg kg(-1)). Sampling errors related to the distribution of analyte carriers were in most cases found in the range of 50-150 % relative standard deviation in spite of the large sample masses of 200-800 kg. The results demonstrate: (1) metal carriers are responsible for significant analyte loads; if they are not adequately considered, total metal contents may be severely underestimated; (2) sampling errors are dominated by the distribution of carriers; (3) correct analysis of total metal contents including loads from metallic components requires expensive sample preparation.

Future landfill emissions and the effect of final cover installation--a case study.

Municipal solid waste (MSW) landfills are potential long-term sources of emissions. Hence, they need to be managed after closure until they do not pose a threat to humans or the environment. The case study on the Breitenau MSW landfill was performed to evaluate future emission levels for this site and to illustrate the effect of final cover installation with respect to long-term environmental risks. The methodology was based on a comprehensive assessment of the state of the landfill and included analysis of monitoring data, investigations of landfilled waste, and an evaluation of containment systems. A model to estimate future emission levels was established and site-specific predictions of leachate emissions were presented based on scenario analysis. The results are used to evaluate the future pollution potential of the landfill and to compare different aftercare concepts in view of long-term emissions. As some leachable substances became available for water flow during cover construction due to a change in the water flow pattern of the waste, a substantial increase in leachate concentrations could be observed at the site (e.g. concentrations of chloride increased from 200 to 800 mg/l and of ammonia-nitrogen from 140 to about 500 mg/l). A period of intensive flushing before the final cover installation could have reduced the amount of leachable substances within the landfill body and rapidly decreased the leachate concentrations to 11 mg Cl/l and 79 mg NH(4)-N/l within 50 years. Contrarily, the minimization of water infiltration is associated with leachate concentrations in a high range for centuries (above 400 mg Cl/l and 200 mg NH(4)-N/l) with low concomitant annual emission loads (below 12 kg/year of Cl or 9 kg/year of NH(4)-N, respectively). However, an expected gradual decrease of barrier efficiency over time would be associated with higher emission loads of 50 kg of chloride and 30 kg of ammonia-nitrogen at the maximum, but a faster decrease of leachate concentration levels.

Environmental compatibility of closed landfills - assessing future pollution hazards.

Municipal solid waste landfills need to be managed after closure. This so-called aftercare comprises the treatment and monitoring of residual emissions as well as the maintenance and control of landfill elements. The measures can be terminated when a landfill does not pose a threat to the environment any more. Consequently, the evaluation of landfill environmental compatibility includes an estimation of future pollution hazards as well as an assessment of the vulnerability of the affected environment. An approach to assess future emission rates is presented and discussed in view of long-term environmental compatibility. The suggested method consists (a) of a continuous model to predict emissions under the assumption of constant landfill conditions, and (b) different scenarios to evaluate the effects of changing conditions within and around the landfill. The model takes into account the actual status of the landfill, hence different methods to gain information about landfill characteristics have to be applied. Finally, assumptions, uncertainties, and limitations of the methodology are discussed, and the need for future research is outlined.