Assessing Greenhouse Gases from a Triple Bottom Line Approach

The St. Louis Metropolitan Sewer District (MSD) operates seven wastewater treatment facilities ranging in size from 40 mgd average daily flow (ADF), to over 120 mgd ADF. MSD's biosolids disposal options have included land application, composting, landfilling, and landfill disposal of incinerated ash. In 2009, MSD faced the daunting prospect of needing to undertake major structural renovations to the incineration facilities at its two largest treatment plants at a time when pending regulatory revisions to the Clean Air Act (CAA) were going to significantly impact the continued use of existing multiple hearth furnace (MHF) incineration technology. As part of a comprehensive assessment of its entire biosolids system, MSD undertook a triple-bottom line assessment that also incorporated the impact greenhouse gas (GHG) production would have on its future decision-making process, including opportunities to partner with energy utilities as part of its future operations. This paper addresses the overall GHG evaluation process, the assessment of GHG emissions for various alternatives, and the reconciliation of GHG's as part of the triple-bottom line (TBL) evaluation and selection process at the District's largest facility.