Carbon Footprint of a Dairy Feed Mill In the U.S

Wednesday, October 19, 2011
Exhibit Hall B (Minneapolis Convention Center)
Felix Adom1, Charles Workman1, Greg Thoma2 and David Shonnard1, (1)Chemical Engineering, Michigan Technological University, Houghton, MI, (2)Department of Chemical Engineering, University of Arkansas, Fayetteville, AR

     A carbon footprint analysis was conducted for a single dairy feed mill located in Michigan with the aim of developing a preliminary assessment of feed mill operations in the US.  This choice of milling site is most representative of a northerly US mill which usually has its feed ingredients arriving on site with relatively high moisture content and needing drying.  The main goal is to determine the greenhouse (GHG) emissions on a basis of 1 kg of milled dairy feed (an “average” feed formulation for dairy animal nutrition).

     The major inputs identified in this cradle-to-factory gate analysis specifically includes; the feed ingredients (grains, some processed crop input as well as other inputs such as vitamins, minerals, and supplements), on-site energy usage, and transportation of feed input to both the milling site and various dairy farms after milling.  Data collection has been a combination of a site-visit, peer reviewed journal articles, mill survey and direct communication with feed mill manager.  With the feed mill reporting close to about 170 different types of feed ingredients, different modeling approaches were required for analyzing the GHG impact of the input data.  Upstream GHG burdens for the inputs to the feed mill were estimated using a combination of EcoInvent database unit processes and economic input-output modeling using Economic Input/output Lifecycle Assessment (EIO-LCA) tool.  About 84% (by weight) of feed ingredients (inputs) for the mill was analyzed using GHG emission factors from unit processes in the EcoInvent database while the remaining 16% was estimated by employing EIO-LCA database with Simapro as the computational tool.  SimaPro was also used in estimating both the onsite energy and transportation impacts.

     The relative contribution of the feed mill dairy feed to global warming potential was estimated to be 0.568 kg CO2 equivalents/kg milled dairy rations (economic allocation).  The majority of the GHG footprint of mill feed is due to input crops and other major ingredients to the mill (approximately 85% of mill inputs by mass). The next largest category for GHG emissions is the large number of mineral ingredients, contributing approximately 10% to the total mill carbon footprint.  Supplements, which include highly processed ingredients like vitamins and amino acids, contribute about 4% to the carbon footprint.  Onsite energy consumption contributes only about 3% while transportation impact for both the delivery and distribution of feed to dairies accounted approximately 9% of the footprint.

     Input crops and other major ingredients like distillers grain soluble (DDGS), corn gluten, soybean meal among others were the largest contributors to the overall footprint.  The supplements and minerals together contributes a total of about 14% towards the overall footprint, this is not surprising given that they arrive at the site in a much more processed form. Finally, natural gas for crop drying accounts for 80% of the total onsite energy consumption.

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