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In the News: Staff Columns

Learning curve: Digesting digesters

Tuesday, May 1, 2018   (0 Comments)
Posted by: Joanna Guza, digital communications manager
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By Clean Fuel Partners

As challenges with nutrient runoff continue to mount across the state, solutions will be sought to support the environment as well as the dairy industry.

We have learned a lot about nutrient management and the digester business since acquiring the Dane County Digester facility in 2015.

Benefits of facilities like ours are reduced odor, nutrient capture and relocation and generation of green energy from the biogas.

The facility processes 90,000 gallons of manure daily, plus 10,000 gallons of substrates to produce biogas. Biogas is converted to electrical energy via generators and fed into the power grid. Specific to our facility is the requirement to remove/relocate phosphorus from the Yahara Watershed.

Digester systems are tanks, pipes, pumps and poop (OK, feedstocks is the more technical term). Once feedstocks are processed in the digesters, the material is put through a screw press or centrifuge, creating two products — liquid centrate and digested manure solids.

Biogas production equipment and solids separation equipment are not necessarily dependent.

They are individual tools, each used for specific purposes.

Our experience has shown us that:

Digesters do not run themselves. The facility requires close monitoring and maintenance. Original plans assumed the facility would run with two full-time people. We employ five full-time employees and have about $160,000 of spare parts to reduce repair time. If we’re not producing electricity, we’re not making money.

Product development and investment is needed to create a product using fiber with market demand. Every ton of digested manure solids/fiber processed contains (in pounds) 13.5 of N, 11 of P205, 5 of K20 and 2 of S. To make a significant impact on watershed nutrient loading, a comprehensive understanding of separation equipment, nutrients and logistics is needed. One option could be working with fertilizer companies to determine how to incorporate renewable nutrients into commercial fertilizer, which would benefit watersheds and enhance soil health.

Digesters provide odor reduction along with altering nutrient availability, giving farmers options in their manure management practices.

The standing digester business model needs to change. Historically, subsidized electric generation made these projects work; however, utility agreements expired and less expensive renewable options are now available. The future of biogas includes natural gas conversion for pipeline injection and gas-to-liquid fuel conversion. Nutrient management options may include a proposal of a nutrient relocation credit, spurring innovation in concentration technology and logistics.

The bottom line is anyone who touches the industry is responsible for finding a sustainable solution. We all want clean water, healthy soil and unpolluted air. Together, we can find solutions that both support the industry and make sense for the environment.

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