The application of life cycle analysis to compare the environmental performance of solid waste management alternatives provides managers and policy-makers information on the relative levels of emissions associated with waste management alternatives.

By Morton A. Barlaz, P. Ozge Kaplan, and S. Ranji Ranjithan

The demand for waste management strategies that are protective of the environment has increased in response to heightened environmental awareness and major evolution in both environmental policy and regulation over the last 20-30 years. Unfortunately, the quantities of waste that require management have also increased markedly over this period. Per-capita generation of MSW has increased from 2.7 lb./day in 1960 to 4.4 lb./day in 1998 (USEPA 1999). While increases in the quantity of waste recycled and composted have also increased over this period, the mass of MSW buried in landfills has increased from about 55 million to 120 million tpy due to increases in both waste-generation rates and the United States population (USEPA, 1999).

There are multiple alternatives for the collection, recycling, treatment, and disposal of MSW, including collection of mixed waste together with or separate from recyclables and yardwaste, material recovery facilities (MRFs) for recyclables recovery, yardwaste and mixed-waste composting, combustion, and landfills for MSW or the ash remaining after combustion. The total cost of solid waste management is influenced strongly by the particular waste management strategy adopted. For example, waste-to-energy facilities are more expensive than landfills in most regions of the US, and residential curbside recycling programs typically increase the cost of solid waste management above the cost of landfill disposal. While the costs of solid waste management alternatives are reasonably well understood, the environmental burdens associated with these alternatives are not.

The objective of this article is to present estimates of the environmental performance of six alternatives for solid waste management that involve recycling, yardwaste composting, organics composting, and traditional and bioreactor landfills. Environmental emissions and total energy consumption associated with each waste management alternative are calculated using the techniques of life cycle analysis (LCA) as incorporated in a computer tool developed by North Carolina State University in conjunction with the Research Triangle Institute and the US Environmental Protection Agency. The scenarios considered are described in the following section along with a short description of the LCA rationale and approach. Details of the scenarios and a more complete explanation of the solid waste management life cycle model are presented in pdf format here.

Waste Management Scenarios

The alternatives were developed to represent the management of residential MSW from its setout at curbside through its final disposition. Three scenarios were defined, and each scenario was analyzed with both a traditional and bioreactor landfill as follows:

1. The first scenario includes a curbside program for the commingled collection of PET and t-HDPE beverage containers, aluminum and steel cans, newspaper, and three colors of glass. These materials are transported to a MRF for separation and then to appropriate remanufacturing facilities. All other waste, including yardwaste, is disposed of in either a bioreactor or traditional landfill.
2. The second scenario includes a curbside recycling program as described in scenario 1, curbside collection of yardwaste for composting, and a bioreactor or traditional landfill for the residual waste.
3. The third scenario includes a curbside recycling program as in scenarios 1 and 2. The remaining waste is collected in a two-compartment truck for wet and dry fractions. The wet portion of the MSW - i.e., foodwaste, yardwaste, and soiled paper - is composted in a mixed-waste composting facility, while the remaining dry waste is disposed of in either a bioreactor or traditional landfill.

Comparison of the scenarios described above was conducted for a hypothetical community with the waste-generation and composition characteristics. The mass flow from an individual house through the different collection and separation alternatives is governed by a set of participation factors and capture rates for recycling and composting programs.

Brief Description of Life Cycle Analysis

A life cycle inventory (LCI) represents a compilation of a specific set of inputs and outputs associated with a product or a process. More information can be found on the EPA Web site at www.epa.gov/ORD/NRMRL/lcaccess/index.htm and in McDougall et al.'s (2001) book on the application of LCA to solid waste management. LCA may be used to compare a process with an equivalent process - for example, a comparison of solid waste management alternatives. The essential feature of an LCA is to thoroughly identify a set of emissions associated with a process. For example, during refuse collection, energy is consumed as trucks collect refuse and collection vehicles are responsible for a variety of air emissions. In addition, emissions and energy consumption are associated with the extraction, refining, and transportation of fuel to its required location. At a landfill there are emissions associated with the operation of heavy equipment for operation, closure, and postclosure activity as well as emissions associated with landfill gas and leachate management. All emissions are considered after any treatment. Thus, while leachate is produced in landfills, the environmental emission is the leachate after wastewater treatment.

An LCI must also account for the benefits associated with resource recovery, and this is typically done by an offset analysis. In management strategies where some portion of the MSW is recycled, the recyclables are ultimately delivered to a facility for remanufacturing. In the process of collecting and processing recyclables, delivering them to a remanufacturing facility, and converting them to a new product, energy is consumed and some emissions result.

In addition to recycled materials, an offset is appropriate when energy is recovered from a landfill. The emissions associated with the energy recovery device at the landfill are included as a positive number and the avoided emissions associated with energy that was not produced by conventional power production are subtracted. In calculating emissions reductions associated with energy recovery, the user can specify what fuel types the "saved" energy displaced.

Summary

The application of life cycle analysis to compare the environmental performance of solid waste management alternatives has been illustrated for a simple set of scenarios involving residential waste. In making decisions on how to best manage MSW, these results provide solid waste managers and policy-makers with information on the relative levels of emissions associated with solid waste management alternatives. The emissions data can then be evaluated with the costs for each alternative.

References

McDougall, F. et al. Integrated Solid Waste Management: A Life-Cycle Inventory, 2nd Edition. Blackwell Science Ltd. 2001.

USEPA. Characterization of Municipal Solid Waste Generation in the United States: 1998 Update, EPA-530-R-99-021. US Environmental Protection Agency, Research Triangle Park, NC. 1999.

Morton A. Barlaz, P. Ozge Kaplan, and S. Ranji Ranjithan are members of the Department of Civil Engineering at North Carolina State University.

MSW - Elements 2004