An environmental analysis for comparing waste management options and strategies

Assessing the food recovery hierarchy concept from an eMergy accounting perspective: Validation and theoretical insights

The food recovery hierarchy (FRH) is an important concept widely used worldwide as a guideline for food waste management policies. It consists of different options for food waste management hierarchically organized, in which source reduction is the most preferable option, followed by food donation, feeding animals, industrial use, composting, energy recovery, and landfilling. The most common approaches used in the literature to validate the FRH concept consider both, a user-side and donor-side perspectives. While the former are typical of methods such as life cycle assessment and ecological footprint that are extensively explored in the literature, the latter is typical of methods such as eMergy accounting (EMA), a perspective that remains unexplored. This study aims to overcome that literature gap by discussing: (i) The validity of FRH concept under an EMA perspective; (ii) The differences on saving natural resources depending on the adopted FRH option; (iii) Obtaining a mathematical model representing the saved emergy as a function of invested emergy. Results show that the FRH is confirmed under the EMA lens as expressed by the proposed emergy return index (ERI). The most preferable options within FRH are by far more efficient in saving emergy than the least preferable options (about 250 times better). The obtained model EMS=2.44E+22/EMI 0.51 describes the relation between the invested and saved emergy along the FRH hierarchy. Insights are presented to promote discussions on existing ERIs cluster within the FRH.

Mapping the knowledge domain of the evolution of emergy theory: a bibliometric approach

Bibliometric and visualization tools are effective for uncovering information contained in vast amounts of literature data. We retrieved publications from the Web of Science (2008-2020) and used the Statistical Analysis Toolkit for Informetrics (SATI) and CiteSpace to conduct a bibliometric analysis of emergy studies, review the focus of the studies, summarize current research, and identify academic trends. The SATI-based charts provided an overall description of yearly published articles, literature sources, high-frequency keywords, authors, institutions, and highly cited papers. CiteSpace was applied to determine the frontiers and hotspots of emergy theory. A dual-map analysis was used to reveal the connection between multiple disciplines. Keyword clustering analysis was performed to evaluate research hotspots. Moreover, burst analysis and timeline maps presented a holistic picture of cutting-edge issues and the evolutionary trajectory of emergy studies in recent years. An alluvial flow map analysis of the landmark literature depicted the transmission of knowledge in the emergy field. In addition, this article also evaluated the current status of collaborative research in emergy-related fields. The results can provide a reference for researchers to explore hot issues or target a specific field of study.

Evaluation of the environmental costs of tourism based on an emergy analysis of tourism waste disposal: a case study of Yarlung Zangbo Grand Canyon National Park in Motuo County, Tibet

Eco-tourism has become increasingly popular in the postmodern era. However, the management of tourism waste remains a major challenge for tourist destinations worldwide. Here, a non-participatory survey was conducted in five famous scenic spots in Yarlung Zangbo Grand Canyon National Park in Motuo County, Tibet, to characterize the waste composition and the amount of average daily production per capita during sightseeing. In addition, interviews were conducted at 26 restaurants and 32 hotels in Motuo Town (the administrative center of Motuo County), and data on the composition and amount of average daily production per capita of waste generated by tourists during accommodation and meals were obtained. The total amount of tourism waste in Motuo County in 2018 was approximately 172,108.82 kg. Based on the data collected, an emergy analysis was applied to emergy calculations of the pollution and losses generated during two conventional and locally used tourism waste disposal methods. According to China's emergy to money ratio (EMR) of 2018, the emergy was converted into its monetary value. The theoretical ecological compensation standard for Motuo County was 4,293,568.99 CNY (equivalent to 648,830.20 USD), and the average ticket price for a single tourist was 18.87 CNY (equivalent to 2.85 USD) in the absence of government fiscal transfer payments. These findings should be utilized by local national park authorities to establish a market-oriented ecological compensation mechanism that is capable of alleviating environmental pressure.

Life cycle assessment of municipal waste management options

To date, landfilling remains the most common waste management practice in Greece in spite of enforced regulations aiming at increasing recycling, pre-selection of waste and energy and material recovery. In this study, selected alternative scenarios aiming at minimizing the unused material fraction to be disposed of in landfills are analyzed, using the life cycle assessment methodology. The methodology was applied in the case of municipal solid waste (MSW) management in Athens and Thessaloniki, with a special focus on energy and material balance, including potential global and local scale airborne emissions. Results are given in the form of indices efficiency, effectiveness, environmental and public health impacts. Material flow accounting, gross energy requirement, emergy intensity, emission and release intensity and morbidity or mortality indicators have been used to support the comparative assessment. However, not all options are equally benign to the local environment and to the health of the local population, since both the former and the latter are still affected by non-negligible local emissions. With regard to public health impacts, adverse effects on respiratory health, congenital malformations, low birth weight and cancer incidence were estimated. A significant and not intuitive result is the fact that life cycle analysis produces different conclusions than a simple environmental impact assessment based only on estimated or measured emissions. Taking into account the overall life cycle of both the waste streams and of the technological systems and facilities envisaged alters the relative attractiveness of the solutions considered.

A multidisciplinary perspective on the evolution of municipal waste management through text-mining: A mini-review

The unprecedented urbanization that is occurring worldwide brings with it a vast amount of solid waste, leading to a rapid increase in study of municipal waste management (MWM) worldwide. This mini-review assessed this body of research both quantitatively and qualitatively. The data for the review were 9711 publications indexed by the Science Citation Index Expanded and the Social Sciences Citation Index for the period 2000-2019. The analysis showed that developed countries, the United States in particular, led trends in research during the first part of the period, and developing countries made substantial contributions to the literature more recently. For all years since 2009 except for 2014, China produced more research than the United States, becoming the most productive country in the study of MWM. Home to five of the ten most productive global research institutes on this subject, China is also a hub for collaboration among countries and institutes, as is the United States. Using content analysis and keyword visualization, this study characterized two decades of study of MWM. This study found that the keywords "sustainability," "waste-to-energy," "life-cycle assessment," and "China" exhibited an upward trend in research. This study seeks the pathway to successful scientific research, helping guide researchers as they innovate in and contribute to the field, and proposes pathways that governments can take to build sustainable MWM systems.

A comparison between a natural gas power plant and a municipal solid waste incineration power plant based on an emergy analysis

This paper performs an emergy analysis (EmA) to compare two real power plants include a conventional natural gas steam power plant (NGPP) with one that burns municipal solid waste (MSWPP). For this purpose, the EmA is used to investigate the sustainability, renewability, environmental impacts, and economic issues. The capacity of the NGPP and MSWPP are 247.5 and 3 MW, respectively. Results from this study show that the percent of renewability (PR) and emergy sustainability index (ESI) of the MSWPP are much more than those of the NGPP. The PR and ESI of the MSWPP are 46.81 and 1.65, while for the NGPP are 5.01 and 0.05, respectively. It is proved that the MSWPP is more efficient and has the better environmental impacts compared to the NGPP. Moreover, a hypothetical MSWPP with the same electricity output of the NGPP is studied using the EmA. A more efficient system with the higher PR and ESI is observed compared to the other case studies. Beside of these advantages, use of the MSW has other benefits such as reducing the greenhouse gases released in the atmosphere, saving fossil fuels, low land area required compared to the landfill, speed and ease of disposal, and production of clean and useful ash.

Methodology to Evaluate the Embodied Primary Energy and CO2 Production at Each Stage of the Life Cycle of Prefabricated Structural Systems: The Case of the Solar Decathlon Competition

The construction industry is responsible for a high percentage of the energy consumed on the planet and the emission of greenhouse gases, therefore it is considered necessary to rethink many of the processes that this industry carries out in order to reduce its environmental impact. For this, one of the paths could take into account the Life Cycle Assessment of the used materials, for which it is necessary to evaluate this aspect through indicators that allow the qualification and quantification of the weight of these environmental impacts. In this context, this article presents a methodological proposal for the quantitative evaluation of the embodied primary energy and CO2 production at each stage of the life cycle of prefabricated structural systems, taking as case studies eight prototypes from the “Solar Decathlon” competition in its editions of Europe (2014), United States (2015) and Latin America (2015), through a Simplified Life Cycle Analysis, using the Eco Audit tool from CES Edupack. Through this analysis, conclusions are drawn about the optimization of a structural system with lower environmental demand and the possibilities of transferring knowledge from this competition to be applied in innovative systems of new housing models.

Externalities of energy sources: The operation of a municipal solid waste-to-energy incineration facility in the greater Thessaloniki area, Greece

There is much debate around promoting waste to energy incineration facilities in many communities globally, mainly because of social opposition against potential negative health effects of the operation of these installations close to urban areas. In this paper, a novel decision support approach is developed and its applicability is demonstrated for the greater Thessaloniki area, Greece. In this area, the incineration facilities are hotly debated, mainly due to the "Not In My Back Yard" syndrome related with health considerations. The exclusive method of treatment is landfilling. Health impacts and corresponding externalities attributed to the operation of an incineration facility are reliably estimated. Three potential alternative sites and three scenarios of emission rates are considered, depending on the abatement technology used. The estimated externalities are compared to the corresponding ones attributed to other pressures in the area. The "Years of Life Lost (YOLL)" indicator attributed to the operation of the facility is 2.8 YOLL in the worst-case scenario. This corresponds to a minimal added implication in comparison with the 11,044 YOLL estimated for the area due to the other environmental pressures (road traffic, space heating, industrial activity). The externalities ratio (externalities due to incineration facility/total externalities) for the region is approximately 0.03%. Thus, the impact of this operation on human health is negligible -and preferable to landfilling- even in the case that maximum emission rates are considered. Efforts should be targeted towards enhancing public awareness and militating the widely acknowledged "Not In My Back Yard" syndrome by local communities.

Pinch Methods for Efficient Use of Water in Food Industry: A Survey Review

The implementation of sustainable water management practices, through the recycling and reuse of water, is essential in terms of minimizing production costs and the environmental impact of the food industry. This problem goes beyond the classical audit and housekeeping practices through developing a systemic water-using reduction strategy. The implementation of such an approach needs R&D development, especially for the food industry, where there is a lack of knowledge on: (a) process integration and (b) data on the pollutant indicators or (c) volumes of water used and discharged at specific steps of the food processing line. Since energy pinch analysis emerged, different variations of pinch methods have been developed. As a variation of pinch, Water pinch analysis is a global and systematic approach to minimize water consumption and discharges, especially for the most energy-intensive and water-consuming factories. Based on the nature of the food industry, the real systems are complex, multi-source multi-contaminant systems, the problem should be well formulated, including mathematical constraints (inequalities thresholds). Current work has reviewed comprehensive literature about different variations of pinch analysis. In continue, water pinch method deeply discussed and some relevant data concerning the water using process and pollutant indicators have been reviewed with emphasis on the food industry sector.

Investigating impact of waste reuse on the sustainability of municipal solid waste (MSW) incineration industry using emergy approach: A case study from Sichuan province, China

China has become the largest generator of municipal solid waste (MSW) in the world with its rapid urbanization, population growth and raising living standard. Among diverse solid waste disposal technologies, MSW incineration has been becoming an attractive choice. In terms of systematic point, an integrated MSW incineration system should include an incineration subsystem and a bottom ash (BA) disposal subsystem. This paper employed an extend emergy assessment method with several improved indicators, which considers the emissions' impact, to evaluate the comprehensive performances of an integrated MSW incineration system. One existing incineration plant in Yibin City, Sichuan Province, China, as a case study, is evaluated using the proposed method. Three alternative scenarios (scenario A: the incineration subsystem + the BA landfill subsystem; scenario B: the incineration subsystem + the concrete paving brick production subsystem using BA as raw material; scenario C: the incineration subsystem + the non-burnt wall brick production subsystem using BA as raw material) were compared. The study results reveal that the ratio of positive output is 1.225, 2.861 and 1.230, the improved environmental loading ratio is 2.715, 2.742 and 1.533, and the improved environmental sustainability index is 0.451, 1.043 and 0.803 for scenario A, B and C respectively. Therefore, reuse of BA can enhance the sustainability level of this integrated system greatly. Comparatively, scenario B has the best comprehensive performance among the three scenarios. Finally, some targeted recommendations are put forward for decision-making.

Production of sorbent from paper industry solid waste for oil spill cleanup

The aim of the study is to select a cellulosic waste material from paper industry solid wastes and process it for sorbent production. Four different solid wastes were collected from a local paper production facility and rejects were selected due to its sorption capacity and processability. Oil sorption experiments were conducted according to the ASTM F 726-12 method. Effect of sorbent dosage, contact and dripping time, recovery of the oil, reusability of the sorbent and sorption from the water surface were also determined. Maximum oil sorption capacity was determined as 9.67, 12.92 and 12.84g/g for diesel oil, 0W30 and 10W30 motor oils respectively for the static test and 8.27, 10.45 and 11.69g/g for the dynamic test. An efficient and low-cost sorbent was produced from paper industry rejects that can be used on land and on water.

A review on technological options of waste to energy for effective management of municipal solid waste

Approximately one-fourth population across the world rely on traditional fuels (kerosene, natural gas, biomass residue, firewood, coal, animal dung, etc.) for domestic use despite significant socioeconomic and technological development. Fossil fuel reserves are being exploited at a very fast rate to meet the increasing energy demands, so there is a need to find alternative sources of energy before all the fossil fuel reserves are depleted. Waste to energy (WTE) can be considered as a potential alternative source of energy, which is economically viable and environmentally sustainable. The present study reviewed the current global scenario of WTE technological options (incineration, pyrolysis, gasification, anaerobic digestion, and landfilling with gas recovery) for effective energy recovery and the challenges faced by developed and developing countries. This review will provide a framework for evaluating WTE technological options based on case studies of developed and developing countries. Unsanitary landfilling is the most commonly practiced waste disposal option in the developing countries. However, developed countries have realised the potential of WTE technologies for effective municipal solid waste management (MSWM). This review will help the policy makers and the implementing authorities involved in MSWM to understand the current status, challenges and barriers for effective management of municipal solid waste. This review concluded WTE as a potential renewable source of energy, which will partly meet the energy demand and ensure effective MSWM.

Improving agricultural straw preparation logistics stream in bio-methane production: experimental studies and application analysis

Long-term production in commercial straw biogas plants has been rare in China due to inefficiencies in the logistics stream. Biomass densification could be a potential solution to this issue. Therefore, we conducted a study to evaluate whether biomass densification is a more efficient and sustainable option. We performed methane production experiments to investigate fermentation characteristics of briquettes (with a new pretreatment, model II) and rubs (with a common pretreatment, model I). A 3000-m³ biogas plant was used to conduct a comparative analysis with solar eMergy joules. Results showed that the methane yield of briquettes of corn stover was 66.74% higher than that of rubs, and the briquettes had better digestion performance in terms of CH₄ content, VFA, and alcohol. The two models required almost the same eMergy investment input, while model II obtained a greater quantity of net eMergy (16.5% higher) in comparison with model I. The net eMergy yield ratio (EYR) (biogas only) of model I and model II was 0.99 and 1.67, respectively, showing less market competitiveness for commercial operations with model I. Meanwhile, the logistic costs of model II could be reduced to approximately US $34,514 annually.

Generation, characterization and reuse of solid wastes from a biodiesel production plant

The aim of this study was to identify and characterize industrial solid wastes generated by a biodiesel production plant in Brazil, as well as to present strategies for the management of these materials. This plant produces every year around 100,000tons of biodiesel from vegetable oils and animal fats. The methodology of the study included technical visits, interviews with the operational and environmental management staff as well as analysis of documents, reports and computerized data systems. An approach to reduce the generation of hazardous waste was investigated. It was take into account the amount of raw material that was processed, reduction of landfill disposal, and the maximization of the their recycling and reuse. The study also identified the sources of waste generation and accordingly prepared an evaluation matrix to determine the types of waste with the higher potential for minimization. The most important residue of the process was the filter material impregnated with oil and biodiesel, requiring, therefore, measures for its minimization. The use of these residues in the production of ceramic artefacts (light bricks) was considered to be very promising, since no significant effect on the physico-chemical and mechanical properties of the artefacts produced was observed. Phytotoxicity test using seeds of Lactuva sativa (lettuce), Brassica juncea (mustard), Abelmoschus esculentus (okra), Chrysanthemum leucanthemum (daisy), Dendranthema grandiflorum (chrysanthemum) and Allium porrum (leek) were carried out. The results clearly show incorporation of the waste material into bricks did not influence relative germination and relative root elongation in comparison to control tests.

'Wasteaware' benchmark indicators for integrated sustainable waste management in cities

This paper addresses a major problem in international solid waste management, which is twofold: a lack of data, and a lack of consistent data to allow comparison between cities. The paper presents an indicator set for integrated sustainable waste management (ISWM) in cities both North and South, to allow benchmarking of a city's performance, comparing cities and monitoring developments over time. It builds on pioneering work for UN-Habitat's solid waste management in the World's cities. The comprehensive analytical framework of a city's solid waste management system is divided into two overlapping 'triangles' - one comprising the three physical components, i.e. collection, recycling, and disposal, and the other comprising three governance aspects, i.e. inclusivity; financial sustainability; and sound institutions and proactive policies. The indicator set includes essential quantitative indicators as well as qualitative composite indicators. This updated and revised 'Wasteaware' set of ISWM benchmark indicators is the cumulative result of testing various prototypes in more than 50 cities around the world. This experience confirms the utility of indicators in allowing comprehensive performance measurement and comparison of both 'hard' physical components and 'soft' governance aspects; and in prioritising 'next steps' in developing a city's solid waste management system, by identifying both local strengths that can be built on and weak points to be addressed. The Wasteaware ISWM indicators are applicable to a broad range of cities with very different levels of income and solid waste management practices. Their wide application as a standard methodology will help to fill the historical data gap.

The Sustainability Cycle and Loop: models for a more unified understanding of sustainability

In spite of the considerable research on sustainability, reports suggest that we are barely any closer to a more sustainable society. As such, there is an urgent need to improve the effectiveness of human efforts towards sustainability. A clearer and more unified understanding of sustainability among different people and sectors could help to facilitate this. This paper presents the results of an inductive literature investigation, aiming to develop models to explain the nature of sustainability in the Earth system, and how humans can effectively strive for it. The major contributions are two general and complementary models, that may be applied in any context to provide a common basis for understanding sustainability: the Sustainability Cycle (S-Cycle), and the Sustainability Loop (S-Loop). Literature spanning multiple sectors is examined from the perspective of three concepts, emerging as significant in relation to our aim. Systems are shown to provide the context for human action towards sustainability, and the nature of the Earth system and its sub-systems is explored. Activities are outlined as a fundamental target that humans need to sustain, since they produce the entities both needed and desired by society. The basic behaviour of activities operating in the Earth system is outlined. Finally, knowledge is positioned as the driver of human action towards sustainability, and the key components of knowledge involved are examined. The S-Cycle and S-Loop models are developed via a process of induction from the reviewed literature. The S-Cycle describes the operation of activities in a system from the perspective of sustainability. The sustainability of activities in a system depends upon the availability of resources, and the availability of resources depends upon the rate that activities consume and produce them. Humans may intervene in these dynamics via an iterative process of interpretation and action, described in the S-Loop model. The models are briefly applied to a system described in the literature. It is shown that the S-Loop may be used to guide efforts towards sustainability in a particular system of interest, by prescribing the basic activities involved. The S-Cycle may be applied complementary to the S-Loop, to support the interpretation of activity behaviour described in the latter. Given their general nature, the models provide the basis for a more unified understanding of sustainability. It is hoped that their use may go some way towards improving the effectiveness of human action towards sustainability.

The Emergy Value Assessment of Municipal Waste Management in Yogyakarta, Indonesia

The emergy values of three different scenarios for the new landfill in Yogyakarta City were calculated to evaluate the sustainability and efficiency. The assessment included the environmental parameters which are Environmental Yield Ratio (EYR), Net Emergy, Environmental Loading ratio (ELR) and Emergy Sustainability Index (ESI).The calculation of emergy indices showed that treatment in landfill requires the largest emergy input for all scenarios with the percentage between 92% and 97%. Scenario 0 contains the lowest total solar emergy implying that it requires lower emergy input compared to other scenarios. Scenario 1 needs the lowest emergy investment. Meanwhile, Scenario 2 offers the highest emergy recovery contributed mainly by the output from higher scavenging rate. Scenario 2 is the best option for the municipal waste management in Yogyakarta since it meets more criteria for sustainability and efficiency.

Improvements to Emergy evaluations by using Life Cycle Assessment

Life Cycle Assessment (LCA) is a widely recognized, multicriteria and standardized tool for environmental assessment of products and processes. As an independent evaluation method, emergy assessment has shown to be a promising and relatively novel tool. The technique has gained wide recognition in the past decade but still faces methodological difficulties which prevent it from being accepted by a broader stakeholder community. This review aims to elucidate the fundamental requirements to possibly improve the Emergy evaluation by using LCA. Despite its capability to compare the amount of resources embodied in production systems, Emergy suffers from its vague accounting procedures and lacks accuracy, reproducibility, and completeness. An improvement of Emergy evaluations can be achieved via (1) technical implementation of Emergy algebra in the Life Cycle Inventory (LCI); (2) selection of consistent Unit Emergy Values (UEVs) as characterization factors for Life Cycle Impact Assessment (LCIA); and (3) expansion of the LCI system boundaries to include supporting systems usually considered by Emergy but excluded in LCA (e.g., ecosystem services and human labor). Whereas Emergy rules must be adapted to life-cycle structures, LCA should enlarge its inventory to give Emergy a broader computational framework. The matrix inversion principle used for LCAs is also proposed as an alternative to consistently account for a large number of resource UEVs.

Examining the effectiveness of municipal solid waste management systems: an integrated cost-benefit analysis perspective with a financial cost modeling in Taiwan

In order to develop a sound material-cycle society, cost-effective municipal solid waste (MSW) management systems are required for the municipalities in the context of the integrated accounting system for MSW management. Firstly, this paper attempts to establish an integrated cost-benefit analysis (CBA) framework for evaluating the effectiveness of MSW management systems. In this paper, detailed cost/benefit items due to waste problems are particularly clarified. The stakeholders of MSW management systems, including the decision-makers of the municipalities and the citizens, are expected to reconsider the waste problems in depth and thus take wise actions with the aid of the proposed CBA framework. Secondly, focusing on the financial cost, this study develops a generalized methodology to evaluate the financial cost-effectiveness of MSW management systems, simultaneously considering the treatment technological levels and policy effects. The impacts of the influencing factors on the annual total and average financial MSW operation and maintenance (O&M) costs are analyzed in the Taiwanese case study with a demonstrative short-term future projection of the financial costs under scenario analysis. The established methodology would contribute to the evaluation of the current policy measures and to the modification of the policy design for the municipalities.

Usefulness of TAO model to predict and manage the transformation in soil of carbon and nitrogen forms from West-Africa urban solid wastes

The TAO model of Transformation of Added Organic materials (AOM) calibrated on AOMs and substrates of temperate areas was used to assess the transformations in soil of carbon and nitrogen forms of AOMs: raw materials, selected mixtures and composts from Ouagadougou urban wastes. AOMs were studied in terms of chemical and biochemical contents and for their C and N mineralization during incubations in a typical Ferric Lixisol of the sub-urban agriculture of Ouagadougou. The TAO model was used to predict the transformations of C (very labile, resistant and stable organic C) and N (very labile, resistant and stable organic N, produced and immobilized inorganic N) forms driven by AOM biochemical data. Without any change in calibration formulae, TAO predicted accurately the C transformations and inorganic N production of most of the tested AOMs, with a tendency to slightly overestimate C mineralization of previously well-composted materials and re-mineralization of immobilized N. Complementary adjustments using more complete data from laboratory experiments are suggested, but the model agrees with other data collected in the field and appears as a promising tool to optimise the management of urban wastes in the tropical area as well as for agro industrial organic fertilizers of the temperate zone. This application suggests ways to improve the management of urban wastes aiming to optimize agricultural yields, system sustainability and C sequestration in soil.

Dynamic emergy evaluation of a fish farm rearing process

The environmental sustainability of a fish farm rearing process was examined by means of emergy analysis. Many emergy analyses integrate data for a whole year smoothing short term variations and sometimes losing meaningful information (aliasing). For this reason we developed a model for an instantaneous emergy evaluation in an aquacultural system so that transformities, efficiency and effort spent at each moment during the fish rearing activity could be calculated. By means of the model and dynamic emergy calculations it is possible to recognize step by step the importance of the various emergy contributions and verify where and when to modify the system to move toward optimum production of a sustainable product. By the application of the model we confirmed that the emergy trends in a fish farm installation follow wide oscillations during a year due to variations in both internal and external emergy contributions. Among the fluxes considered, those due to the introduction of fingerlings represented the highest contributions to the total emergy budget. Thus, to improve the sustainability of the analyzed system the amount, frequency and timing of these fluxes must be carefully considered. For this purpose, a comparison between two different fry introduction schedules was performed to evaluate differences in the efficiency of the rearing process.

Municipal wastes and their solar transformities: an emergy synthesis for Macao

The debate over waste management practices has become increasingly important as human activities have begun to overload the biosphere's assimilative capacity. An effective waste management policy should be based on the principles of sustainable development, with wastes regarded as a potential resource rather than solely as something to eliminate. This approach requires an integrated waste management plan that makes full use of all available technologies. Macao is a highly populated consumer society that lacks natural resources and must therefore import almost all of its life-supporting goods and raw materials from regions outside the city. During the past 20 years, Macao has experienced an economic boom, accompanied by rapid socioeconomic development. Its discharged wastes have increased steadily during this period. This paper employs emergy analysis to investigate Macao's waste treatment in 1995, 1999, 2003 and 2004. The emergy of gaseous emissions was estimated to be 4.76 x 10(21) sej in 2004. Since 1992, Macao's municipal solid waste (MSW) has been incinerated to reduce its volume. The transformity of the fly ash and slag produced by this treatment in 2004, and the electricity generated by the incinerator, equaled 5.11 x 10(11) sej/g, 6.01 x 10(10) sej/g, and 7.61 x 10(6) sej/J, respectively. A large investment of natural resources and technology is required for the treatment of wastes; the feedback ratio of wastes, which represents the scale of the treatment of inputs, equaled 0.02 for MSW, 0.11 for sewage, and 0.06 for gaseous emissions.