Last fall, despite strong opposition from farmers, California became the first state to pass legislation to curbing cow-produced methane. The so-called “anti-flatulence” bill aims to mitigate climate change by calling for a 40% reduction in methane–created mostly in the cow’s manure though yes, also in their farts and burps–by 2030. Farmers were dismayed: Short of reducing the size of their livestock operations, which can, in some cases, number more than 3,000 cows, what could they do to limit the emissions from their farms?
Eungsung Kan, a chemical and environmental engineer at Texas A&M University, is working on what might prove to be a solution to California farmers’ woes. Last year, Kan has received a $1 million grant from the university to research the viability of his concept for a “closed-loop” dairy farm, which reuses wastewater, emits zero waste, and powers itself using the damaging methane from the manure. Kan’s concept has three main goals: to treat wastewater with dairy manure-derived biochar (a carbon material similar to charcoal, which is produced by gasifying manure); to produce bioenergy from manure; and to capture greenhouse gasses with biochar.
In addition to the climate-change repercussions of dairy farms, “farm operations have been implicated in higher-than-normal levels of nitrogen and phosphorous, antibiotics, heavy metals and hormones in surface and groundwater downstream from facilities,” Kan tells Fast Company. Too much nitrogen and phosphorous in surface water produce algae, which reduces water quality and wrecks aquatic ecosystems; dairy wastewater also contains pathogens like E.coli that can cause endocrine disruption in humans. That is unpleasant enough but then consider the fact that the USDA has estimated that the manure from 200 milking cows produces as much nitrogen as the sewage from a community of 5,000 to 10,000 people, and the magnitude of the issue becomes even more obvious.
Currently, manure is generally stored in giant outdoor pits called lagoons, where it’s treated with water and repurposed as fertilizer. However, this system is flawed: Contaminants escape from the lagoons and into the surrounding environment, and the lagoons fail to capture the greenhouse gasses created by the decomposing manure.
For dairy farms to be sustainable in the long term, Kan says, they need to more effectively treat and repurpose wastewater, and efficiently minimize emissions.
Kan’s closed-loop concept, which he’s currently developing at lab scale, will address both requirements. In the closed-loop system, the first step is to separate out solid dairy manure from liquid wastewater. The dairy manure is converted to syngas (energy-rich gas) and biochar by gasifying the manure in an on-site reactor at temperatures of nearly 1,000 degrees Fahrenheit. Using an installed on-site combined heat and power (CHP) system, the syngas is converted to heat and power for the dairy farm; excessive power could be sold to a local utility company, Kan says.
The gasification process creates biochar–a fine-grain charcoal which effectively absorbs nutrients. Columns filled with biochar would act as a water purification system that would filter out nitrogen, phosphorous, and other harmful contaminants from the liquid as it passes through. The water could be used for agricultural irrigation and washing and watering cows; the biochar, Kan says, can then be repurposed as fertilizer because it so effectively traps soil nutrients (it also traps greenhouse gasses from the ground that otherwise would be released into the atmosphere)
After Kan completes the lab-scale demonstration of the closed-loop system, he’ll apply the process to the Tarleton Southwest Regional Dairy Center in Stephenville, Texas, a facility with around 400 dairy cows. Testing at Tarleton for two to three years, Kan says, will help his team at Texas A&M anticipate any problems that might arise before scaling the system up to commercial farms.
Apart from the installation cost to the Tarleton dairy farm of roughly $300,000 for the pyrolysis reactor and the CHP system, the annual operation of the closed-loop dairy concept is not expensive, Kan says. The whole process will require around two people to operate the system over the course of a year, and the concept will actually result in savings for the farm. Because a medium-sized dairy like Tarleton spends roughly $3,000 per month on energy, it will reclaim that money through generating power on-site. The same is true for water: Kan estimates that a farm goes through around 170 pounds of water per cow each day (accounting for irrigation, washing, and watering); the closed-loop dairy will recycle as much as 70% of that water.
Dairy farms continue to grapple with how best to curb emissions without scaling down operations; California is doing its part to assist farmers in reducing emissions by directing $50 million in fees collected through its cap and trade program toward supplying dairy farmers with methane digesters, which, like in Kan’s model, convert manure into energy. Currently, only 12 of the state’s 1,500 dairies are equipped with digesters. Kan believes that his more comprehensive closed-loop dairy system could play a significant role in making the dairy industry more sustainable.
However, it’s important to keep in mind that advancements in mitigation technology are not enough to curb the massive environmental burden posed by the dairy and livestock industries: A 2014 study found that even if farms become more productive and implement technical mitigation measures, the livestock and dairy industries would still account for over half the acceptable volume of greenhouse gases by 2070. The thing that will really tip us toward sustainability? Cutting down how much meat and dairy we consume. That might be a tough pill for non-vegans to swallow, but that’s what embattled plant-based milk and the Impossible Burger are for.
Source: FastCompany
Link: https://www.fastcompany.com/3069268/this-revolutionary-concept-could-make-dairy-farms-more-sustainable