LCA supports integrated approach to solid waste management systems

Solid waste management systems need to ensure human health and safety. They must reduce as much as possible the environmental impacts of waste management, including energy consumption, pollution of air, land and water and loss of amenity. The system must operate at a cost acceptable to private citizens, businesses and government. The costs of operating an effective system will depend on existing infrastructure, but ideally should be little or no more than existing waste management costs.

There is an increasing awareness that the waste management “hierarchy”, which ranks treatment options in a descending order of desirability, is of very limited use. There is no scientific basis for ordering waste management treatment options in this way. The hierarchy cannot provide any guidance with respect to using combinations of treatment technologies. This is important as few waste management systems use only one treatment option to handle all the materials in municipal solid waste (MSW) in an environmentally sustainable manner. Finally the waste management hierarchy does not address cost issues.

The waste hierarchy will not identify the best practical environmental option with respect to planning waste management systems.

Integrated waste management

Here “integrated waste management” is defined as a system that deals with all types of solid waste materials and all sources of solid waste. An integrated system includes waste collection and sorting, followed by one or more of the following options: recovery of secondary materials (recycling); biological treatment of organic materials; thermal treatment and landfill (See figure 1). To handle all wastes in an environmentally and economically sustainable way requires a range of these options.

Effective schemes need the flexibility to design, adapt and operate systems in ways which best meet current social, economic and environmental conditions. These are likely to change over time and vary by geography. The need for consistency in quality and quantity of recycled materials, compost or energy, the need to support a range of disposal options and the benefit of economies of scale, all suggest that IWM should be organised on a large-scale, regional basis. Any scheme incorporating recycling, composting or energy-from-waste technologies must be market-orientated. There must be markets for products and energy.

Life cycle assessment

To assess sustainability, a tool that can predict the likely overall environmental burdens of any system is needed. The developing technique of Life Cycle Assessment allows the prediction of the likely environmental burdens associated with a product or service from cradle to grave.

The computer model developed by White et al. (1995), is a Life Cycle Inventory (the goal definition and scoping and inventory analysis stages of a Life Cycle Assessment) of municipal solid waste. An updated version of this model (a Windows based application known as IWM-2) is now available. The model starts the moment a material becomes waste (i.e. loses value) until it ceases to be waste by becoming a useful product, inert landfill material or an emission to either air or water. This Life Cycle approach for modelling waste management has been accepted by both the UK Environment Agency and the US Environmental Protection Agency. These Government organisations are in the final stages of developing their own Life Cycle models for assessing IWM systems.

The inputs for an integrated waste management system are waste, energy and other raw materials.

The outputs from the system are both useful products in the form of reclaimed materials and compost, and emissions to air and water and inert landfill material (see Figure 2).

Once the waste management system has been described, the inputs and outputs of each chosen treatment process must be calculated, using fixed data for each process.

The lack of quality data is a recognised problem in this part of a Life Cycle Inventory methodology.

The results of this Life Cycle Inventory model are expressed as: net energy consumption, air emissions, water emissions, landfill volume (inert), recovered materials and compost.

Use of life cycle tools

Using the technique of Life Cycle Inventory to support an integrated approach to solid waste management requires using the results of several LCI’s to compare different waste management strategies. The existing waste management strategy is used as a “Baseline”, against which all other strategy modifications are measured. This allows the overall performance of different IWM strategies to be compared. For example; a strategy based on recycling compared with one based on incineration with energy recovery. The optimum IWM strategy should be chosen based on the needs of the local environment, economy and population. The LCI tool does not select the “best” waste management strategy but it provides detailed data that can support the decision making process.

Choices are made between different strategy options based on one of four basic approaches.

• Single criterion – where there is a single over-riding concern (eg lack of landfill space)
• Multiple criteria – where more than one issue is important (eg energy consumption and air emissions)
• Less is better – where one option is lower in all categories
• Impact analysis – can combine some categories that contribute to the same effect such as global warming

An example of the results generated by IWM-2 for Happyville 1, a hypothetical town of 500,000 inhabitants living in 250,000 households, each person generating 340kg/year solid waste (with a composition by weight of: 37% paper, 9% glass, 7% metal, 10% plastic, 2% textiles, 19% organics and 16% other material) are presented in Table 1 below.

Similar data tables are generated for costs, fuel use, final solid waste and water emissions.

The model also allows the results of up to six different scenarios to be compared. In Figure 4, six hypothetical Happyville scenarios are compared and the results for Final solid waste arising are presented.

The Happyville scenarios modelled are:

• Happyville 1 – all waste arisings sent to landfill without gas recovery or leachate control.
• Happyville 2 – all waste arisings are sent to landfill with gas recovery with energy generation and leachate control.
• Happyville 3 – operates a single material bank collection system, all restwaste sent to landfill with gas recovery (energy generation) and leachate control.
• Happyville 4 – operates kerbside collection scheme for dry recyclables and a material bank collection scheme for dry recyclables all restwaste sent to landfill with gas recovery (energy generation) and leachate control.
• Happyville 5 – material bank collection system plus a kerbside collection system, with a kerbside sort for selected recyclables. Separate kerbside biowaste collection and composting. Restwaste to landfill with gas collection (with energy generation) and leachate collection and treatment.
• Happyville 6 – material bank collection system plus a kerbside collection system (with a kerbside sort for selected recyclables). Separate kerbside biowaste collection and composting.

Restwaste to incineration with energy recovery. All residues to landfill with gas collection (with energy generation) and leachate collection and treatment.

Conclusions

It is now possible to use life cycle tools to provide environmental data that can be used to support decision making when different combinations of waste treatment and disposal options have to be evaluated.

The IWM-2 model is an entry level LCI tool and is ideal for familiarising users with the approach taken, the data requirements of life cycle work and the results of such models.

Table 1 Sample of results of IWM-2 model – Air emissions