Anthropogenic sources of greenhouse gas emissions are known to contribute to global increases in greenhouse gas concentrations and are widely believed to contribute to climate change. A reference carbon dioxide concentration of 383 ppm for 2007 is projected to increase to a nominal 500 ppm in less than 50 years according to business as usual models. This concentration change is equivalent to an increase of 7 billion tonnes of carbon per year (7 Gt C year(-1)). The concept of a stabilization wedge was introduced by Pacala and Socolow (Science, 305, 968-972, 2004) to break the 7 Gt C year(- 1) into more manageable 1 Gt C year(- 1) reductions that would be achievable with current technology. A total of fifteen possible 'wedges' were identified; however, an integrated municipal solid waste (MSW) management system based on the European Union's waste management hierarchy was not evaluated as a wedge. This analysis demonstrates that if the tonnage of MSW is allocated to recycling, waste to energy and landfilling in descending order in lieu of existing 'business-as-usual' practices with each option using modern technology and best practices, the system would reduce greenhouse gas emissions by more than 1 Gt C year( -1). This integrated waste management system reduces CO(2) by displacing fossil electrical generation and avoiding manufacturing energy consumption and methane emissions from landfills.

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A greenhouse gas inventory identifies the sources and quantities of GHG emissions from a facility or a larger organization. Several best practice standards exist that provide guidance for conducting GHG inventories for industrial facilities like a WWTP. Key considerations in a WWTP GHG inventory will include emissions associated with the facility's energy use as well as methane produced from anaerobic digestion processes. GHG inventories can facilitate participation in a voluntary GHG reporting program, assist in preparing for future regulations, or allow the identification of opportunities in emission trading markets.

A carbon offset program is likely to be part of any future federal cap-and-trade program and is included in both the U.S. House of Representatives passed American Clean Energy and Security Act of 2009 and the Kerry-Boxer Senate draft greenhouse gas legislation. Internationally, Energy-from-Waste (EfW) facilities in emerging economies are eligible for carbon offset credits under the Clean Development Mechanism of the Kyoto Protocol. These carbon offset credits can be purchased by developed countries, such as those in Western Europe, to help comply with their obligations under the Kyoto Protocol. Although a similar mandatory market does not yet exist in the United States, there is a growing voluntary market in carbon offsets and a set of standards designed to provide some order to this market. One of the key players in the voluntary market is the Voluntary Carbon Standard (VCS). Project types, such as EfW, that are eligible for credits under the Clean Development Mechanism are also eligible to generate voluntary carbon credits under the VCS. This paper reviews the current methodology for calculating offsets from EfW projects. The current methodology is very conservative, severely restricts the accounting for avoided landfill methane, and significantly underestimates greenhouse gas savings relative to life cycle assessments performed on waste management practices. The current methodology for offsets is compared and contrasted with a more realistic methodology more in line with life cycle assessment calculations. A review of the potential for EfW offsets under evolving state and federal programs and precedents for offsets generated based on avoided landfill methane is also completed.