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Purpose

Improving the economic feasibility of anaerobic digestion projects for processing dairy manure.

What did we do?

We completed a study that evaluated the economics of dairy manure granulation as means to export phosphorus from P-sensitive watersheds. To achieve this goal we developed a techno-economic optimization model that considers all dairy farms within the watershed simultaneously to determine the minimum break-even price for the granulated manure.

A second study was developed to assess the economics of anaerobic digestion using a techno-economic optimization model. We incorporated different revenue sources (power sale, methane destruction credits, renewable energy certificates (RECs) and tipping fee (if co-substrate is available). The model evaluated the project feasibility over ranges of values for technical and economic parameters to quantify the project resilience to uncertainty in process conditions.

What have we learned?

The results from the first study indicated that multi-farm participation can significantly improve feasibility and overall economics of manure granulation. Herd sizes were found to be a critical parameter in deciding whether a farm can economically participate in coordinated management. For manure granulation projects, liquid-solid separation followed by transportation of separated solids was always more economical than transporting raw manure from satellite farm to central processing facility. In the second study, electricity sale price was found to be the key parameter that determines the feasibility of anaerobic digesters. The hub-spoke configuration, where a large central farm hosts the digester and smaller surrounding farms contribute to it was found to be the most favorable arrangement. The size of the hub farm was critical to the feasibility of the project. Similarly, transportation distance was a critical factor that constrained the extent of cooperative digesters.

Future Plans

The information generated from these studies is being written into peer-review publications and factsheets to share insights of collaborative manure management with a wider audience.We are currently expanding the model by adding the option for manure transportation via pipelines. Furthermore, we are also incorporating additional biogas utilization technologies,i.e., natural gas sale over pipelines and also the utilization of power/heat on-site in manure upgrading and processing.

Corresponding author, title, and affiliation

Troy M. Runge, Associate Professor, University of Wisconsin-Madison

Corresponding author email

trunge@wisc.edu

Other authors

Mahmoud A. Sharara, Rebecca Larson

Additional information

1. http://www.are.wisc.edu/

2. Sharara, Mahmoud, Apoorva Sampat, Laura W. Good, Amanda S. Smith, Pamela Porter, Victor M. Zavala, Rebecca Larson, and Troy Runge. “Spatially explicit methodology for coordinated manure management in shared watersheds.” Journal of Environmental Management 192 (2017): 48-56.

3. Sharara, Mahmoud, Qiang Yang, Thomas L. Cox, and Troy Runge. “Techno-economic assessment of dairy manure granulation.” In 2016 ASABE Annual International Meeting, p. 1. American Society of Agricultural and Biological Engineers, 2016.

Acknowledgements

This work is based on research supported by the USDA National Institute of Food and Agriculture for its financial support (USDANIFABRDI Grant No. 2012-10006-19423) and funding from Dane County, Wisconsin under Award Number 12486.