Abstract
Ammonia (NH3) emissions from animal agriculture can cause eutrophication of water ecosystems and are precursors to secondary particulate matter (PM2.5). NH3 emissions from stored swine manure represent nutrient loss affecting the fertilizing value of manure. The short-term emission bursts occur when farmers agitate manure before emptying storage and fertilizing fields. There is no proven technology to mitigate gaseous emissions during agitation, while the hazards of acute releases (e.g., H2S) are well-known. Biochar mitigates NH3 emissions from manure over the long-term. The objective of this research was to evaluate the mitigation of acute NH3 emissions during/after agitation. Two biochars, highly alkaline and porous (HAP from corn stover) and red oak (RO), were tested. The 6 and 12 mm-thick layers of biochar powder were surficial applied followed by 3 min agitation. NH3 concentrations were measured before/during/after agitation. Mitigation was assessed by comparing: (i) the maximum (peak) flux, (ii) total emission (from agitation start till NH3 concentration returned to the before-agitation), and (iii) the total emissions during agitation. The 12 mm HAP significantly (p < 0.05) reduced (i–iii) by 63, 70, and 85%, respectively. The 6 mm HAP significantly reduced (i–iii) by 76, 75, and 78%, respectively. The 12 mm RO significantly reduced (i–iii) by 9, 53, and 57%, respectively. The 6 mm RO significantly reduced (i–iii) by 61, 86, and 63%, respectively. The NH3 emission kinetics model confirmed that a 6 mm dose was just as effective as the larger dose. More research is needed to optimize and scale-up mitigating emissions and retention of nutrients in manure with biochar.
Highlights
The Midwest United States has a significant presence of pork production
We have reported research on manure additives such as soybean peroxidase, zeolite, and biochar powder that shows the effectiveness of mitigating NH3, H2S, volatile organic compounds (VOCs), and greenhouse gas (GHG) emissions from swine manure over extended periods (Cai et al, 2007; Parker et al, 2016; Kalus et al, 2017; Maurer et al, 2017a,b,c)
We report on the short-term mitigation effect of the same two types of biochar on NH3 emissions during manure agitation
Summary
The Midwest United States has a significant presence of pork production. Many large swine barns use deep-pits to store manure under the slatted floor for up to 1 year. Stored swine manure is a significant source of long-term NH3 emissions for most of the year. The short-term bursts of NH3 emissions can occur when swine farmers agitate manure prior to emptying storage pits before land application. Agitation releases hydrogen sulfide (H2S), with dangerously high concentrations resulting in human and animal fatalities (Chen et al, 2020c). Workers are subjected to chronic exposure to NH3 and other gases released from manure year-round. The United States National Institute for Occupational Safety and Health (NIOSH) recommends the time-weighted average (TWA) 10-h concentration for NH3 at 25 ppm and a short-term exposure limit (ST) 15-min at 35 ppm (NIOSH, 1997)
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