Sustainable Carbon Management at Treatment Facilities for Enhanced Nutrient Removal using LCA
- Joyeeta Banerjee, P.E., Brian Henn, Katya Bilyk, P.E, Joe Rohrbacher, P.E., and Sandeep Mehrotra P.E. - Hazen and Sawyer
Under stricter new total nitrogen and phosphorus limit regulations, treatment plants are considering external carbon sources for low effluent limits. Methanol has been the most popular supplemental carbon choice. However, there are several alternative carbon sources such as ethanol corn syrup waste, glycerin/glycerol-based products resulting from biodiesel production.
To determine a holistic, triple bottom line approach, a Life Cycle Assessment (LCA) was completed of a cradle-to-grave environmental impact of these carbon alternatives. The South Durham Water Reclamation Facility (SDWRF) was selected as the basis for the analysis. SDWRF is a 20-mgd five-stage BNR plant. Data derived from literature along with bench and full-scale investigations of corn-syrup and glycerin products were used to develop comparative dosage requirements. Results indicate that while Methanol is economical, it may not be the most sustainable carbon source from an environmental perspective. Production, transportation, process impacts and effect on biosolids production and methane emissions were modeled to compare carbon source sustainability.
The environmental impacts of each of the carbon sources were aggregated into impact categories including global warming, greenhouse gas emissions, and land use utilizing Sima-Pro software implementing the Impact 2002, Eco-Indicator and Intergovernmental Panel on Climate Change (IPCC) evaluation methodologies. The LCA results provide a valuable tool to quantify greenhouse gas emissions, carbon footprint among other environmental impacts that are associated with process decisions at a treatment plant.
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