Review of LCA studies of solid waste management systems – Part II: Methodological guidance for a better practice

Life cycle assessment (LCA) is increasingly used in waste management to identify strategies that prevent or minimise negative impacts on ecosystems, human health or natural resources. However, the quality of the provided support to decision- and policy-makers is strongly dependent on a proper conduct of the LCA. How has LCA been applied until now? Are there any inconsistencies in the past practice? To answer these questions, we draw on a critical review of 222 published LCA studies of solid waste management systems. We analyse the past practice against the ISO standard requirements and the ILCD Handbook guidelines for each major step within the goal definition, scope definition, inventory analysis, impact assessment, and interpretation phases of the methodology. Results show that malpractices exist in several aspects of the LCA with large differences across studies. Examples are a frequent neglect of the goal definition, a frequent lack of transparency and precision in the definition of the scope of the study, e.g. an unclear delimitation of the system boundaries, a truncated impact coverage, difficulties in capturing influential local specificities such as representative waste compositions into the inventory, and a frequent lack of essential sensitivity and uncertainty analyses. Many of these aspects are important for the reliability of the results. For each of them, we therefore provide detailed recommendations to practitioners of waste management LCAs.     

Pyrolysis of waste animal fats in a fixed-bed reactor: Production and characterization of bio-oil and bio-char

Several animal (lamb, poultry and swine) fatty wastes were pyrolyzed under nitrogen, in a laboratory scale fixed-bed reactor and the main products (liquid bio-oil, solid bio-char and syngas) were obtained. The purpose of this study is to produce and characterize bio-oil and bio-char obtained from pyrolysis of animal fatty wastes. The maximum production of bio-oil was achieved at a pyrolysis temperature of 500 °C and a heating rate of 5 °C/min. The chemical (GC–MS analyses) and spectroscopic analyses (FTIR analyses) of bio-oil showed that it is a complex mixture consisting of different classes of organic compounds, i.e., hydrocarbons (alkanes, alkenes, cyclic compounds…etc.), carboxylic acids, aldehydes, ketones, esters,…etc. According to fuel properties, produced bio-oils showed good properties, suitable for its use as an engine fuel or as a potential source for synthetic fuels and chemical feedstock. Obtained bio-chars had low carbon content and high ash content which make them unattractive for as renewable source energy.     

Recycling of high purity selenium from CIGS solar cell waste materials

Copper indium gallium diselenide (CIGS) is a promising material in thin film solar cell production. To make CIGS solar cells more competitive, both economically and environmentally, in comparison to other energy sources, methods for recycling are needed. In addition to the generally high price of the material, significant amounts of the metals are lost in the manufacturing process. The feasibility of recycling selenium from CIGS through oxidation at elevated temperatures was therefore examined. During oxidation gaseous selenium dioxide was formed and could be separated from the other elements, which remained in solid state. Upon cooling, the selenium dioxide sublimes and can be collected as crystals. After oxidation for 1 h at 800 °C all of the selenium was separated from the CIGS material. Two different reduction methods for reduction of the selenium dioxide to selenium were tested. In the first reduction method an organic molecule was used as the reducing agent in a Riley reaction. In the second reduction method sulphur dioxide gas was used. Both methods resulted in high purity selenium. This proves that the studied selenium separation method could be the first step in a recycling process aimed at the complete separation and recovery of high purity elements from CIGS.     

Recycled sand in lime-based mortars

The increasing awareness of the society about safe guarding heritage buildings and at the same time protecting the environment promotes strategies of combining principles of restoration with environmentally friendly materials and techniques. Along these lines, an experimental program was carried out in order to investigate the possibility of producing repair, lime-based mortars used in historic buildings incorporating secondary materials. The alternative material tested was recycled fine aggregates originating from mixed construction and demolition waste. Extensive tests on the raw materials have been performed and mortar mixtures were produced using different binding systems with natural, standard and recycled sand in order to compare their mechanical, physical and microstructure properties. The study reveals the improved behavior of lime mortars, even at early ages, due to the reaction of lime with the Al and Si constituents of the fine recycled sand. The role of the recycled sand was more beneficial in lime mortars rather than the lime–pozzolan or lime–pozzolan–cement mortars as a decrease in their performance was recorded in the latter cases due to the mortars’ structure.     

Effects of fly ash addition on physical properties of porous clay-fly ash composites via polymeric replica technique

The porous composites of clay and fly ash have the potential to be used in many fields, such as catalyst support and gas adsorbents. In this study, various ratios of fly ash (1–2) with different percentage of suspension (50–70 wt%) were applied to produce porous clay-fly ash composites via polymeric replica technique. Fabrication process starts by mixing clay and fly ash in distilled water to form slurry. The process is followed by fully immersing polymer sponge in slurry. The excess slurry is then removed through squeezing. Finally, the sponge coated with slurry is sintered at 500 and 1250 °C for 1 h. It is found that the compressive strength of porous composites improves significantly (0.178–1.28 MPa) when the amount of clay-fly ash suspension mixture (50–70 wt%) increases. The compressive strength of porous composites is mainly attributed to the mullite, quartz and amorphous phase formations. These results are supported by X-ray diffraction analysis. On the other hand, increase in the amount of suspension reduces the apparent density (from 2.44 to 2.32 g/cm³) and porosity (from 97 to 85 %). The reduction in apparent density is believed to be caused by the presence of high fly ash content in porous composites. The melted fly ash cenospheres have closed the internal pores and increased density of samples. Higher suspension level not only reduces porosity, but also increases close pores of the porous composites. The results are justified through the observation from the structures of porous clay-fly ash composites.     

Inexact fuzzy-stochastic mixed-integer programming approach for long-term planning of waste management – Part A: Methodology

In this study, an inexact fuzzy chance-constrained two-stage mixed-integer linear programming (IFCTIP) approach is proposed for supporting long-term planning of waste-management systems under multiple uncertainties in the City of Regina, Canada. The method improves upon the existing inexact two-stage programming and mixed-integer linear programming techniques by incorporating uncertainties expressed as multiple uncertainties of intervals and dual probability distributions within a general optimization framework. The developed method can provide an effective linkage between the predefined environmental policies and the associated economic implications. Four special characteristics of the proposed method make it unique compared with other optimization techniques that deal with uncertainties. Firstly, it provides a linkage to predefined policies that have to be respected when a modeling effort is undertaken; secondly, it is useful for tackling uncertainties presented as intervals, probabilities, fuzzy sets and their incorporation; thirdly, it facilitates dynamic analysis for decisions of facility-expansion planning and waste-flow allocation within a multi-facility, multi-period, multi-level, and multi-option context; fourthly, the penalties are exercised with recourse against any infeasibility, which permits in-depth analyses of various policy scenarios that are associated with different levels of economic consequences when the promised solid waste-generation rates are violated. In a companion paper, the developed method is applied to a real case for the long-term planning of waste management in the City of Regina, Canada.     

Inexact fuzzy-stochastic mixed integer programming approach for long-term planning of waste management–––Part B: Case study

In this study, a solid waste decision-support system was developed for the long-term planning of waste management in the City of Regina, Canada. Interactions among various system components, objectives, and constraints will be analyzed. Issues concerning planning for cost-effective diversion and prolongation of the landfill will be addressed. Decisions of system-capacity expansion and waste allocation within a multi-facility, multi-option, and multi-period context will be obtained. The obtained results would provide useful information and decision-support for the City's solid waste management and planning. In the application, four scenarios are considered. Through the above scenario analyses under different waste-management policies, useful decision support for the City's solid waste managers and decision makers was generated. Analyses for the effects of varied policies (for allowable waste flows to different facilities) under 35 and 50% diversion goals were also undertaken. Tradeoffs among system cost and constraint-violation risk were analyzed.Generally, a policy with lower allowable waste-flow levels corresponded to a lower system cost under advantageous conditions but, at the same time, a higher penalty when such allowances were violated. A policy with higher allowable flow levels corresponded to a higher cost under disadvantageous conditions. The modeling results were useful for (i) scheduling adequate time and capacity for long-term planning of the facility development and/or expansion in the city's waste management system, (ii) adjusting of the existing waste flow allocation patterns to satisfy the city's diversion goal, and (iii) generating of desired policies for managing the city's waste generation, collection and disposal.     

A Pluralist–Expressivist Critique of the Pet Trade

Elizabeth Anderson’s “pluralist–expressivist” value theory, an alternative to the understanding of value and rationality underlying the “rational actor” model of human behavior, provides rich resources for addressing questions of environmental and animal ethics. It is particularly well-suited to help us think about the ethics of commodification, as I demonstrate in this critique of the pet trade. I argue that Anderson’s approach identifies the proper grounds for criticizing the commodification of animals, and directs our attention to the importance of maintaining social practices and institutions that respect the social meanings of animals. Her theory alone, however, does not adequately address the role of the state in this project. Drawing on social contract theory to fill this gap, I conclude that the state’s role in regulating the pet trade should be limited to ensuring the welfare of animals in the stream of commerce, not prohibiting their mass marketing altogether.     

Inexact fuzzy-stochastic constraint-softened programming – A case study for waste management

In this study, an inexact fuzzy-stochastic constraint-softened programming method is developed for municipal solid waste (MSW) management under uncertainty. The developed method can deal with multiple uncertainties presented in terms of fuzzy sets, interval values and random variables. Moreover, a number of violation levels for the system constraints are allowed. This is realized through introduction of violation variables to soften system constraints, such that the model’s decision space can be expanded under demanding conditions. This can help generate a range of decision alternatives under various conditions, allowing in-depth analyses of tradeoffs among economic objective, satisfaction degree, and constraint-violation risk. The developed method is applied to a case study of planning a MSW management system. The uncertain and dynamic information can be incorporated within a multi-layer scenario tree; revised decisions are permitted in each time period based on the realized values of uncertain events. Solutions associated with different satisfaction degree levels have been generated, corresponding to different constraint-violation risks. They are useful for supporting decisions of waste flow allocation and system-capacity expansion within a multistage context.     

Regulating the hydrolysis of organic wastes by micro-aeration and effluent recirculation

In this study, the effects of micro-aeration and liquid recirculation on the hydrolysis of vegetable and flower wastes during two-phase solid–liquid anaerobic digestion were assessed. To accomplish this, we evaluated the hydrolysis of five batches of waste that were treated under the following conditions: anaerobic, insufficient micro-aeration (aeration for 5 min every 24 h), and sufficient micro-aeration (aeration for 5 min every 12, 4 and 1 h). Hydrolysis was found to depend on the level of micro-aeration. Specifically, insufficient micro-aeration led to unstable and decreased performance. Conversely, sufficient micro-aeration promoted the hydrolysis of easily biodegradable carbohydrates and proteins, but the microbial activity was later impaired by liquid recirculation using methanogenic effluent. The hydrolysis efficiency under anaerobic conditions was comparable to the efficiency observed under sufficient micro-aeration, while the cumulative TOC of the anaerobic batch was 1.4–2.4 times higher than that of the micro-aerated batches. In addition, liquid recirculation did not have a negative effect on the development of microbial activity under anaerobic conditions, which resulted in the lignocelluloses having a higher hydrolysis efficiency.