Review of LCA studies of solid waste management systems – Part I: Lessons learned and perspectives

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

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.     

Models for waste life cycle assessment: Review of technical assumptions

A number of waste life cycle assessment (LCA) models have been gradually developed since the early 1990s, in a number of countries, usually independently from each other. Large discrepancies in results have been observed among different waste LCA models, although it has also been shown that results from different LCA studies can be consistent. This paper is an attempt to identify, review and analyse methodologies and technical assumptions used in various parts of selected waste LCA models. Several criteria were identified, which could have significant impacts on the results, such as the functional unit, system boundaries, waste composition and energy modelling. The modelling assumptions of waste management processes, ranging from collection, transportation, intermediate facilities, recycling, thermal treatment, biological treatment, and landfilling, are obviously critical when comparing waste LCA models.This review infers that some of the differences in waste LCA models are inherent to the time they were developed. It is expected that models developed later, benefit from past modelling assumptions and knowledge and issues. Models developed in different countries furthermore rely on geographic specificities that have an impact on the results of waste LCA models. The review concludes that more effort should be employed to harmonise and validate non-geographic assumptions to strengthen waste LCA modelling.     

Long-term changes in populations of subtidal bivalves (Abra alba and A. prismatica) from the Bay of Morlaix (Western English Channel)

Two populations of Abra alba (Wood) and one of A. prismatica (Montagu) (Mollusca: Bivalvia) were studied over a 10 yr period (1977–1987) in two muddy fine-sand subtidal communities of the Bay of Morlaix, France. The survey provided an example of long-term changes in the three Abra spp. populations, which displayed synchronized changes, with a regular annual cycle and increasing densities during 1979–1980 related to the higher concentration of organic matter resulting from the Amoco Cadiz oil spill in March 1978. A. alba rapidly adapts its demographic strategy to eutrophic conditions by increasing its reproductive potential, growth, and abundance. During times of eutrophication, A. alba has three spawning periods and three recruitments per year as opposed to two spawning periods and two recruitments per year during oligotrophic conditions. Growth of the juveniles of this species is insignificant until spring for individuals recruited in the autumn, whereas individuals which settle during spring or summer display immediate rapid growth. A. prismatica has a low capacity to adapt to eutrophic conditions. It has one annual period of sexual maturation at the end of the summer, with spawning in September–October and settlement beginning in mid-November. Growth of the juveniles after settlement is also insignificant until April. These results enable comparison of the demographic strategies of these two sympatric species.     

Environmental evaluation of municipal waste prevention

Waste prevention has been addressed in the literature in terms of the social and behavioural aspects, but very little quantitative assessment exists of the environmental benefits. Our study evaluates the environmental consequences of waste prevention on waste management systems and on the wider society, using life-cycle thinking. The partial prevention of unsolicited mail, beverage packaging and food waste is tested for a "High-tech" waste management system relying on high energy and material recovery and for a "Low-tech" waste management system with less recycling and relying on landfilling. Prevention of 13% of the waste mass entering the waste management system generates a reduction of loads and savings in the waste management system for the different impacts categories; 45% net reduction for nutrient enrichment and 12% reduction for global warming potential. When expanding our system and including avoided production incurred by the prevention measures, large savings are observed (15-fold improvement for nutrient enrichment and 2-fold for global warming potential). Prevention of food waste has the highest environmental impact saving. Prevention generates relatively higher overall relative benefit for "Low-tech" systems depending on landfilling. The paper provides clear evidence of the environmental benefits of waste prevention and has specific relevance in climate change mitigation.     

Meso-scale hydrodynamic and reproductive asynchrony affects the source–sink metapopulation structure of the coastal polychaete Pectinaria koreni

The polychaete Pectinaria koreni exhibits a complex life cycle characterized by non-overlapping generations and widespread larval dispersal. To explore how “local” metapopulation genetic structure varies spatially and temporally during population turnover, we combined observations on demography, larval dispersal through hydrodynamic modelling and population genetics of successive age cohorts in the Baie de Seine (eastern English Channel, France). Mature adults (March), newly settled (July) and later-stage juveniles (September) were sampled in 2003 on the edge and in the main demes of the metapopulation. Demes displayed an asynchronous dynamics due to variations in habitat quality affecting reproductive timing (e.g. three distinct spawning events observed) and in local larval supply linked to temporal fluctuations of hydrodynamism. Two-source populations were identified among dense areas with the greatest larval retention and self-recruitment rates: one with a single recruitment event, stable temporal genetic variation and a strong spatial genetic re-homogenization during turnover, and the other with two recruitment events and significant allele frequency changes over time. Sink habitats displayed single recruitment event and experienced strong inter-generational (juveniles vs adults) genetic changes due to genetic drift associated with strong winter mortalities. Altogether, results suggested that adult spawning asynchrony and sweepstakes reproductive success, together with genetic drift, played a greater role than hydrodynamics itself in determining effective recruitment rates at some sites and generating genetic patchiness.