It’s no secret that livestock manure can be a rich source of nutrients for crops. However, using manure as fertilizer comes with several disadvantages, including the risk of spreading deadly pathogens if not properly treated. But scientists at the University of Wisconsin–Madison (UW) say they’ve figured out a way that could help farmers extract nutrients like ammonia and potassium from livestock waste and efficiently turn it into fertilizer and other useful chemicals.
Unfortunately, farmers don’t have a lot of options for disposing of the manure their livestock generates. Many highly concentrated operations such as dairy farms collect the manure in an open pit, or lagoon where the organic matter breaks down naturally and nutrients like ammonia can eventually be recovered. Unfortunately, this process also releases large amounts of methane into the air.
To reduce their operations’ emissions, some producers use “anaerobic co-digesters,” which are large tanks that can capture the methane produced as the organic matter breaks down and convert it into biogas. But much like manure, these systems can have several disadvantages, including high operating costs and high requirements for the pretreatment of waste.
The new technique described by University of Wisconsin-led team uses electricity and a specially designed electrode to break down the organic matter in animal waste. The nickel-based electrode, which targets ammonium ions, is is placed directly into the manure wastewater. As organic matter in the manure naturally gets oxidized by the electrode, the ammonium, as well as potassium ions, within the wastewater are selectively driven into and captured by the electrode.
In a second step, the nutrient-loaded electrode can be placed into a device that uses electricity to release the recovered ammonium and potassium ions. Those recovered ions can then be used to make nitrogen and potassium-based fertilizers, and simultaneously produce other useful chemical products like hydrogen fuel or hydrogen peroxide.
“Manure has all this stuff in it and we don’t have to do too much extra work,” said Song Jin, a UW–Madison professor of chemistry who led the work. Jin says trial runs with small amounts of manure recovered more than half the ammonia in the first pass, with a recovery of about 85% after two cycles. The next steps will include further improving the materials and processes, as well as scaling up the system to see how it functions at levels closer to a real-world livestock operation.
According to UW, analysis conducted by Rebecca Larson, a professor in the Nelson Institute for Environmental Studies, a 1,000-head dairy farm operation could reduce its ammonia emissions by more than 50% by deploying the system, while also significantly reducing the amount of nitrate entering nearby waters. Additionally, UW says preliminary technical economic analysis shows that a model dairy farm using the system could expect resulting revenues to be higher than operating costs, so long as electricity prices aren’t exorbitant.
Jin notes that renewable power is expected to lower electricity costs in some rural areas to about $0.03 per kWh by 2030. Wind and solar farms often produce more electricity than the power grid can handle, forcing engineers to either dump the power or turn off their turbines. “If we can couple this with wind and solar, we could design it to use electricity only when it is cheap,” Jin says, in turn making it profitable for farmers. The full paper is available at Nature HERE. (Sources: University of Wisconsin–Madison, Science, Feedstuffs)
