Optimal Recovery of Resources: a Case Study of Wood Waste in the Greater Sydney Region

摘要

In present day society there is an artificial dichotomy between wastes and resources that is perhaps best summed up by the Western Sydney Waste Board slogan 'there is no such thing as waste � only resources in the wrong place and at the wrong time'. Waste management was originally driven by managing the health consequences of wrong time/place materials. This has changed and the significant driver is now the sustainable utilisation of resources, that is, trying to optimally recover as resources (right time/place) those materials that present as wastes requiring management. However, it is not acceptable to justify a resource recovery option purely on the basis that it is diverting material away from landfill. Preferences are emerging for recovery activities that maximise the resource value of a material according to techno-economic, environmental and socio-political criteria; collectively known as the criteria of sustainability. The people and organisations articulating these preferences include owners/operators of resource recovery centres, proponents of alternative waste management technologies, waste planners and managers at both a state and local government level and environmental NGOs representing community interests, in addition to the generators of waste at a domestic, commercial and industrial, and construction and demolition level. It is therefore important to be able to answer the question of 'what is the optimal or most sustainable resource recovery option for materials presenting as waste to landfill in the Greater Sydney Region?' The point of departure for this thesis is twofold. Firstly, that optimal resource recovery options (also known as alternative waste management technologies) can be identified by understanding the context and system drivers and constraints within the system of waste generation and utilisation, by modelling the system using industrial ecology (specifically Materials Flux Analysis) and by using the technology assessment framework developed by the NSW Alternative Waste Management Technologies and Practices Inquiry to evaluate the available options. Secondly, that should the assessment framework from the NSW Inquiry prove to be unsuitable as a framework for evaluation, then an improved and refined assessment framework can be constructed in order to identify optimal resource recovery options and that this process can be successfully demonstrated using wood waste as a case study. The context of waste as an issue has shifted from local government control (pre-1970s) to state government control through the Department of Environment and Conservation. This transition followed experiments with organisations such as the NSW Waste Boards and Resource NSW, in addition to state targets such as a 60% reduction of waste to landfill by the year 2000. In addition to this backdrop of change from a government administrative perspective, there are also a suite of often conflicting drivers and constraints influencing the process of resource recovery. For example, sustainable development is a public policy driver for the integration of environmental and societal concerns, but can also constrain new innovation if competing 'status quo' utilisation options are not subject to the same scrutiny. Similarly, legislation acts as a constraint to resource recovery options by establishing license conditions, prohibiting some energy recovery options and setting recovery criteria; however legislation also acts as a driver for resource recovery options that generate renewable electricity or act to reduce greenhouse gas emissions. Other drivers and constraints include social, technical and economic issues and concerns in addition to environmental impacts such as emissions to air, land and water. Industrial ecology is a model for viewing system components as part of a dependent and interrelated greater whole. Within the context of Industrial Ecology, waste is a by-product of manufacture available as a beneficial input into other processes. Using Materials Flux Analysis as a tool to build a model of waste generation and utilisation, elements within the system are presented as a series of stocks (sources), technology interventions (transformation flows) and sinks (markets). The stocks or sources of materials for resource recovery are categorised as Municipal Solid (MSW), Commercial and Industrial (C&I) or Construction and Demolition (C&D) wastes. Approximately seven million tonnes of waste is generated in the Greater Sydney Region (nearly two and a half million tonnes of materials recovered for recycling and four and a half million tonnes of materials disposed of to landfill). The purpose of technology intervention is to transform the material into a product that is suited to the end market (sink). Markets are grouped according to reuse (same function and form), direct recycling (same supply chain), indirect recycling (different supply chain) and energy recovery (either as process heat, electricity or co-generation, a combination of the two). Landfill is also a potential sink for materials and in this sense can be thought of as a negative value market. The Alternative Waste Management Technologies and Practices Inquiry provided an assessment framework for resource recovery technologies. Each technology was measured and compared against 16 evaluation criteria, resulting in a score out of one hundred. Material sorting scored the highest (81.5), incineration the lowest (50.8) with most of the biological technologies performing �well� (64.6 � 71.7) and with the landfill technologies performing 'moderately well' (60.4 - 61.4). The positive features of the Inquiry included the overview of alternative resource recovery technologies, waste generation and other issues pertinent to decision making and resource recovery. The negatives of the Inquiry arise from the inadequacies of the assessment framework, which lacked technology options, system boundary definition and requisite evaluation criteria in addition to inconsistencies in scoring approaches. By undertaking a sensitivity analysis on the Inquiry�s results, it is shown that rank order reversal results from the allocation of weightings. The improved and refined assessment framework, constructed to overcome identified inadequacies of the Inquiry�s approach, focussed on clearly identifying the problem to be addressed and the primary decision maker involved in the process; ensuring that appropriate options for evaluation were included; defining the system boundary for the assessment; selecting necessary evaluation criteria; adopting a more sophisticated system for scoring; and using a sensitivity analysis to validate the results of the resource recovery option evaluation. Wood waste was used as a case study for this second assessment methodology. Wood waste refers to the end-of-life products, failed products, offcuts, shavings and sawdust from all timber products. Approximately 350,000 tonnes of wood waste are disposed of to landfill each year. This comprises untreated timber (hard wood and soft wood), engineered timber products (particleboard, medium density fibreboard and plywood) and treated timber (predominately copper chrome arsenic). Eight wood resource recovery options are selected for evaluation within the Greater Sydney Region with a different approach to scoring that has the advantage of 'scaling up' the best performers within each attribute (highest score) while 'scaling down' the worst performers (no score). Under this evaluation, an on-site purpose built energy facility is the most preferred option with particleboard manufacture the least preferred option. A sensitivity analysis of the results reveals that the scores of each technology option are sensitive to the weightings of the decision maker. When the change in rankings is examined, it is identified that two eight wood recovery options undergo a large rank reversal. A critique of the results of the wood evaluation reveals five major flaws. Firstly the evaluation produces non-highest resource value results that are non-intuitive (and arguably misleading), for example the poor performance of reuse and particleboard against energy generation options. Secondly, the recording of a single summary score for each recovery option hides unacceptable performance levels in some criteria. For example, the top scorer of Primary Energy On-site hides the fact that such an option is likely to have no political desirability (likely public opposition to 'incineration' within the Sydney air-shed), calling into question its ability to be implemented as a solution. Thirdly there is a reliance on judgement for the scoring of options and weighting of preferences, calling into doubt the accuracy of scores. Fourthly, the rankings of recovery options by the assessment framework are sensitive to the allocation of weightings. Finally and most importantly, the refined evaluation approach suffers from the 'discrete option syndrome', the scoring of each recovery option in isolation with no ability to look at integrated systems with joint recovery options. This is pinpointed as a fundamental flaw in the process of both the Inquiry and the wood evaluation. This leads to the conclusion that the founding assertions of this thesis were false. That is to say that the assessment framework developed by the NSW Alternative Waste Management Technologies and Practices Inquiry is not suitable for use in evaluating resource recovery options. Furthermore a refined assessment framework based on this approach is also unable to identify optimal resource recovery options as demonstrated using wood waste as a case study. The results of this research points to the overall conclusion that any discrete option evaluation and assessment for resource recovery technologies that results in a single summary score for each option will be fundamentally flawed, providing no value in determining optimal resource recovery solutions for the Greater Sydney Region. A systems approach is suggested as an alternative method for the evaluation of optimal resource recovery, the starting point of which is to ask 'what is the highest resource value of the components in the material stream under consideration and how could a network of infrastructure be designed in order to allow materials to flow to their highest resource value use?' A feature of such an integrated approach is a focus on the materials composition of recovered resources, as opposed to recovery technologies, resulting in a 'fit for purpose' as opposed to a 'forced fit' style of resource recovery. It is recommended that further research and public policy efforts be made in logistics planning across the Greater Sydney Region (as opposed to a regional or local government area) in order to create network opportunities for integrated flows of materials to move toward their highest resource value.