Sarker, N.; Rahman, S.; Borhan, M.; Rajasekaran, P.; Santra, S.; Ozcan, A. (2019). Nanoparticles in mitigating gaseous emissions from liquid dairy manure stored under anaerobic condition. Journal of Environmental Sciences, 76, 26-36. https://doi.org/10.1016/j.jes.2018.03.014
Greenhouse gases trap heat in the Earth’s atmosphere. This is partly what keeps Earth at a livable temperature for humans. Unfortunately, if the concentration of greenhouse gases in the atmosphere increases, the temperature will also increase, resulting in a negative impact on the climate. Humans contribute to an increase in atmospheric greenhouse gases concentration in many ways including livestock production operations. In the United States, the agricultural sector contributes about 9% of the total greenhouse gas emissions for the country. Two common greenhouse gases produced during the anaerobic digestion phase of livestock manure are methane and carbon dioxide. Anaerobic digestion is when microorganisms break down material such as manure to gain energy without the presence of oxygen.
Scientists have been trying to find a way to reduce emissions from this process and believe nanoparticles might be the answer. Nanoparticles are very small particles and could be used to absorb the greenhouse gases or kill the microorganisms that produce the gases. Niloy Sarker and colleagues wanted to determine if nanoparticles could be used to reduce greenhouse gas emissions from manure on a dairy farm.
The scientists compared the effectiveness of three different nanoparticles in minimizing carbon dioxide, methane, and hydrogen sulfide emissions from liquid dairy manure. The three nanoparticles studied were zinc silica nanogel liquid, copper silica nanogel liquid, and n-acetylcystein liquid coated zinc oxide quantum dots. The researchers collected dairy manure from the dairy research unit of North Dakota State University. Back in the lab they set up bottles containing the raw manure and one type of nanoparticle, as well as a control that had raw manure and no nanoparticles. Because the greenhouse gas emissions are produced during anaerobic digestion, all the oxygen was removed from each bottle before sealing it. Then, the bottle was connected to a bag where the greenhouse gas produced from the manure could be collected. The scientists collected gas from the bags every 2 to 14 days for 56 days.
The researchers found that all three types of nanoparticles significantly reduced gas production by over 90%. Additionally, the scientists also found that there were less bacteria in nanoparticle treatments indicating that the nanoparticles may be killing the microorganisms that produce the greenhouse gases.
What’s the catch?
This study demonstrated that nanoparticles may be an option for reducing greenhouse gas emissions from manure. However, nanoparticles might also negatively impact the environment. If nanoparticles were to make their way into the environment they could kill bacteria in the soil and neighboring ecosystems. Also, because nanoparticles contain metals, they can lead to heavy metal accumulation in the surrounding environment. However, if the load used in this study was scaled for a farm, the nanoparticle load would be within the allowable limit for heavy metals. The paper did indicate that nanoparticles could be indirectly applied using filters. Future studies will be needed to fully understand the impacts of nanoparticles on the environment and determine the feasibility of using them to treat manure.