By Sonia A. Hall

Managing manure is a big part of what goes on at the “back end” of a dairy. Doing it well is important to avoid impacts on surrounding neighbors due to odors, impacts on air and water quality, or the release of unnecessary amounts of greenhouse gases such as methane or nitrous oxides.

There are multiple technologies being developed, tested, and used to improve manure management in dairies. These include anaerobic digestion, which produces bioenergy and helps reduce odors (we provided an overview about a year ago in this article).

Nutrient recovery technologies are another aspect being studied. These are an array of different technologies that allow us to collect the potentially useful nitrogen and phosphorus found in manure, so it can be used productively rather than contributing to climate change or other issues.

At the Center for Sustaining Agriculture and Natural Resources at Washington State University, we are working on a series of fact sheets focused on different nutrient recovery technologies, their potential for producing value-added products from manure, and for reducing the emissions that naturally arise from its decomposition. We’ll be sharing more on these later this year. In the meantime, this article provides a preview on just one approach to nutrient recovery: worms.

Last month I got the opportunity to visit Royal Dairy, a dairy farm near Royal City, Washington. For the past two years, Royal Dairy has been testing out a vermicompost system (BioFiltro’s BIDA System). As Biofiltro describes it, the system encompasses both biological and physical filtration of the dairy’s liquid manure (after solids have been extracted with a centrifuge).

This wastewater is applied at regular intervals to the system’s surface through sprinklers. The worms — with the help of microbes added when the system was set up — digest the material in the effluent, and the nitrogen, phosphorus and other minerals stay in the worm casts or in the resulting compost-like material.

The water flows out the bottom (having gone through multiple layers of material designed to provide the worms with air and shelter, in addition to capturing the manure) and into a storage lagoon. This water now has a much lower nutrient content… low enough that they can use it to directly irrigate their silage corn and other crops without over-applying nutrients to the fields.

For this dairy, this approach is working. The benefits they gain from improved management of the nutrients in manure pan out economically, since they now don’t have to truck liquid manure to spread it over thousands of acres of crops. The worm castings can potentially be sold as a soil amendment, though Royal Dairy has not done so.

Of course, there are costs as well: the capital investment of setting up the system, the technology provider who tracks conditions and adjusts the flow of liquid manure to optimize how the system works and how long it lasts, and regular maintenance and operating costs.

But here the benefits have outweighed the costs: they are in the process of expanding their pilot into a 2-acre system, which they hope to have operational by summer 2017.

This full-scale system will allow them to take advantage of their existing irrigation network to get the resulting green water piped out to their crops, straight from their storage lagoon. And it fits well with their existing solids separation centrifuge system, a necessary pre-treatment that also produces valuable fiber, which they can use on the dairy or sell.

This description glosses over a lot, including the challenges faced when incorporating a whole other system onto the “back end” of the dairy, the additional work involved, and the risk of testing out new technologies (vermicompost is not new, but systems such as this one have only been installed in dairies in recent years, with Royal Dairy’s being the first we know of in Washington).

But the approach Austin Allred took — installing a pilot system, testing liquid manure going in and green water coming out to calculate reductions in nutrients (their preliminary data estimate 80 to 90% reductions), and then designing an expansion — warms my scientist’s heart. And the fact that they are expanding it suggests the approach is a useful nutrient management tool for them, and could be for other dairies.

As I mentioned, we’ll be sharing more details on nutrient recovery technologies and the challenges and opportunities they face as we complete and share the extension products we are working on — stay tuned for that. In the meantime, let us know if there are particular questions on anaerobic digestion or nutrient recovery technologies you would like us to discuss.

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