Life Cycle Assessment

Dr Neil Kirkpatrick

The 'solid waste management hierarchy' is often cited as a means of justifying the desire to process solid waste by any means other than landfill.

Solid waste management hierarchy

This hierarchy places alternative waste treatment options in a fixed order of preference with waste minimisation at source as the most environmentally preferred (least environmental impact) option and landfill as the least environmentally preferred (most environmental impact) option.

Whilst the solid waste management hierarchy serves a useful purpose, many have come to argue that the hierarchy should not be viewed as fixed and that one should exercise a degree of caution before coming to any immediate conclusions as to what represents the most environmentally preferred solid waste disposal practice.

The UK Department of the Environment (DoE) has recently initiated a programme of research aimed at adopting a more holistic approach to solid waste disposal. In this work, the DoE is seeking to employ the techniques of Life Cycle Assessment (LCA) to assist it to evaluate waste management practices in a more Ôscientific¹ fashion.

Overview of life cycle assessment

Life Cycle Assessment (LCA) is defined as 'an objective process to evaluate the environmental burdens associated with a product, process or activity by identifying and quantifying energy and materials used and wastes released to the environment, and to evaluate and implement opportunities to effect environmental improvements' (Society of Toxicology and Chemistry, SETAC, Code of Practice, 1991).

LCA may be broken down into three stages:

1 Inventory analysis

Life Cycle Inventory Analysis (LCI) quantifies the raw material and energy consumption together with all solid wastes, emissions to air and water (the environmental burdens) for all of the processes within the system boundary. The results of such a study generate an inventory of the environmental burdens associated with the functional unit.

Examples of functional units used most often in the context of waste management include:

A difference between 'waste management LCAs' and LCAs for conventional 'single product systems' (eg packaging), is that waste management LCAs necessarily deal with a much wider range of material types. Accordingly, the functional unit will need to reflect the composition of waste both with respect to material type and relative weight. Studies will then allocate on a mass-by-mass basis the environmental burdens specific to those material types present.

Having defined the functional unit, it will then be necessary to identify those activities, or unit operations, which collectively define the 'system' to be studied.

System boundaries generally include:

System boundaries generally exclude:

In the context of waste management practices, the systems boundary definition can become extremely complex. At the simplest level one can define the boundaries artificially by defining the 'beginning of the life cycle' as, for example, the kerbside or kerbside collection (the curtilage).

The 'end' of the life cycle may be defined, as is commonly stated, when all residues from the system are returned to land. In the case of evaluating recycling and incineration, both practices should be considered on the basis of 'what if' scenarios. In other words, recycling needs to be considered in the context of those environmental burdens/impacts avoided through displacing virgin materials. Similarly, incineration with energy recovery should be evaluated by considering those environmental burdens/impacts which are avoided by generating heat and power from an alternative means such as burning fossil fuels.

It should be noted that using the systems boundaries outlined here, waste minimisation at source and re-use are excluded. In most cases, waste minimisation at source will be the preferred waste management option although in the case of re-use, the outcome of comparative LCAs studies is often less clear. There are of course always exceptions to the rules and depending on the scope of a given study, waste minimisation at source may not be preferred if savings at one point in the system give rise to greater losses elsewhere (eg lightweighting of packaging at the expense of greater loss of those products packaged therein through breakage/damage).

Once the boundaries for a given study have been set, the next stage is to gather the data that will form the basis for all calculations. The UK DoE has identified data quality as a key issue for the evaluation of the relative merits of solid waste management practices and accordingly have given this topic a high priority, intending to spend £850,000 over the next three years to support the compilation of a comprehensive up-to-date database specific to waste management practices. There will inevitably be a lot of competition to access this pool of funding!

2 Impact assessment

Impact assessment facilitates the interpretation and aggregation of inventory data into forms that are more manageable and meaningful to the decision maker.

In the problem-oriented approach, data in the inventory are aggregated according to the relative contributions made to a surveyable number of environmental concerns. The following environmental impact categories are generally included in an impact assessment determination:

The following list includes environmental impact categories less well defined or used by only a few practitioners:

The impact potential factors derived from this process may then be assigned weighting factors, thereby enabling them to be reduced to a single score. The development of valuation methods is still in its early stages and fraught with controversy.

Impact assessment in the context of solid waste management

The 'treatment' of waste management LCA data is no different compared to conventional single product or service systems LCAs. Once again, all previous comments concerning the complexity of solid waste management LCAs are applicable with waste being considered as a collection of discrete but often inter-mingled used products which themselves can be composed of a wide variety of material types.

3 Improvement assessment

This 'stage' of LCA is invariably cited as being an integral part of LCA methodology although, in reality, improvement assessment is what one does with the results. According to the BSI Technical Committee on Life Cycle Assessment (which the author chairs) Improvement Assessment is not a part of the methodology which can be standardised since each and every application of LCA will vary. That being the case, there are no absolute rules to describe here. Suffice it to say that one needs to have a clear focus in mind at the outset of a study or else the scope will shift continually, which will increase the chance of making an error or employing an incorrect assumption dependent on the 'final' scope of the application as reached.

Interpretation of the results

A detailed discussion of the results of LCA studies generated for solid waste management scenarios is beyond the scope of this paper.

However, it is clear that the solid waste management hierarchy is not fixed and, based on experience, in some cases there is a very clear case for incineration with energy recovery over material recycling. It is dangerous to make generalised conclusions in this respect and each scenario will yield its own results which may differ - even for studies which appear similar - depending on the assumptions made. This emphasises the need to exert caution when interpreting the results of LCA studies - a fact which causes much friction politically when people seek to use the results of LCA studies for marketing applications.

Let me make a plea at this stage!

All processes and 'product systems' impact on the environment.

Use the results of LCA studies (and other environmental management tools) to quantify environmental impacts to enable you to identify where to prioritise your efforts to minimise those impacts, eg through the implementation of an environmental management system. We should all remember that sustaina-bility - both economically and environmentally - is where our attentions should be focused, not on trying to use the results of complex LCA studies to justify a market claim that might be easily challenged if aspects of the LCA studies were conducted in a slightly different way or using different assumptions!!

Conclusions

The main conclusions reached are as follows:

Life Cycle Inventory Analysis (LCI) serves to quantify the consumption of raw materials and energy as well as releases to air, water and solid waste for a defined system (theoretically 'cradle to grave')

Life Cycle Impact Assessment seeks to relate those parameters quantified at the inventory stage to measures of environmental concern such as global warming or depletion of reserves

Solid waste management practices are themselves processes requiring inputs of energy consumption and resulting in the generation of atmospheric emissions as well as discharges to a receiving water and solid waste for further disposal and/or processing

Waste minimisation at source is recognised most often to be the most common sense approach to minimising environmental impact associated with solid waste management practices

To determine the advantages (or disadvantages) of waste management options relative to each other requires an investigation of 'complete life cycles' in which the potential advantage(s) of recycling/incineration are balanced against those environmental burdens offset from the avoidance of the use of so much of the virgin material or energy source

Life Cycle Assessment (LCA) is an effective tool for bench marking environmental performance and can be used in comparative studies to determine the relative environmental advantages and disadvantages of products able to carry out the same function

LCA is being used now to assist companies to quantify and assess their impacts to the environment, to identify opportunities to minimise that impact and, significantly to realise cost savings by making more effective use of available resources

There is - presently - no universally accepted and scientifically defensible way of prioritising environmental concerns!

Dr Neil Kirkpatrick is Chairman of the British Standards Institution (BSI) Technical Committee on Life Cycle Assessment. Further information and a longer version of this article are available from Warmer Bulletin's UK office. Extract from Warmer Bulletin No 47, November, 1995

Moving On
To the home page of PRISM To the WRF archive To Warmer Bulletin - WRF's journal
To WRF's library request service
To Mail us at WRF
 To the Waste Web