Abstract
With the increasing demand for food worldwide, the use of fertilizers in the agricultural industry has grown. Natural fertilizers derived from the use of animal manure slurry, especially cattle and cow, are responsible for 40% of the agricultural ammonia emission. The EU defined the goal to reduce NH3 emission drastically until 2030, yet until today an overall increase has been observed, making it more difficult to reach the target. In this study, we used two by-products from the dairy industry, namely flushing milk and acidic whey, to lower the pH of cattle manure slurry and therefore mitigate the loss of nitrogen in the form of ammonia into the atmosphere, making it available in the soil. Measurements of pH, ammonium nitrogen, total Kjeldahl nitrogen, and lactic acid bacteria colonies were conducted in a lab-scale experiment to test the hypothesis. Afterwards, pH measurements were conducted on bigger samples. We found that whey effectively reduced the pH of manure below 5, therefore moving the ammonia/ammonium equilibrium strongly towards ammonium. Flushing milk on the other hand lowered the pH to a smaller extent, yet allowed for faster hydrolysis of urea into ammonium. The findings in this study present a suitable and environmentally friendly approach to help reach the climate goals set by the EU by using by-products from the same industry branch, therefore being a suitable example of circular economy.
Highlights
With increasing awareness of climate change and global warming, the role of reducing greenhouse gas (GHG) emissions in all sectors of countries’ economy is becoming increasingly more important
We aimed to show that by mixing cattle manure slurry with by-products of the dairy industry, it is possible (i) to achieve a decrease of pH, shifting the equilibrium towards ammonium, and (ii) to preserve nitrogen within the dairy modified manure to a higher extent compared with untreated control samples
A pH reduction for the manure achieved with acidic whey is in the same range, a similar mechanism can be assumed
Summary
With increasing awareness of climate change and global warming, the role of reducing greenhouse gas (GHG) emissions in all sectors of countries’ economy is becoming increasingly more important. As ammonia converts into various nitrous oxides in the atmosphere, its contribution to global warming is roughly 265 times more severe compared to CO2 [3]. The European Union identified the threat and harmfulness of ammonia emissions on the ozone layer [4], water eutrophication [5], overfertilizing or soil acidification [6], and odor nuisance in 2016 and decided that NH3 emission must be cut by 12% until 2030 compared to 2005 [7]. Until the year 2017, emissions increased moderately every year, which means that roughly 20% of ammonia emissions must be reduced to reach the goals set by the EU25 [8]. The UN defined an even stricter directive to cut ammonia emission by 30–50% to sustain a healthy and undamaged ecosystem [9]
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