Can Biochar Save Lives? The Impact of Surficial Biochar Treatment on Acute H2S and NH3 Emissions During Swine Manure Agitation Before Pump-out

Hydrogen sulfide and ammonia are always a concern in the livestock industries, especially when farmers try to clear their manure storage pits. Agitation of manure can cause dangerously high concentrations of harmful agents such as H2S and NH3 to be emitted into the air. Biochar has the ability to sorb these gases. We hypothesized that applying biochar on top of manure can create an effective barrier to protect farmers and animals from exposure to NH3 and H2S. In this study, two kinds of biochar were tested, highly alkaline, and porous (HAP, pH 9.2) biochar made from corn stover and red oak biochar (RO, pH 7.5). Two scenarios of (6 mm) 0.25” and (12 mm) 0.5” thick layers of biochar treatments were topically applied to the manure and tested on a pilot-scale setup, simulating a deep pit storage. Each setup experienced 3-min of agitation using a transfer pump, and measurements of the concentrations of NH3 and H2S were taken in real-time and measured until the concentration stabilized after the sharp increase in concentration due to agitation. The results were compared with the control in the following 3 situations: 1. The maximum (peak) flux 2. Total emission from the start of agitation until the concentration stabilized, and 3. The total emission during the 3 min of agitation. For NH3, 0.5” HAP biochar treatment significantly (p<0.05) reduced maximum flux by 63.3%, overall total emission by 70%, and total emissions during the 3-min agitation by 85.2%; 0.25” HAP biochar treatment significantly (p<0.05) reduced maximum flux by 75.7%, overall, total emission by 74.5%, and total emissions during the 3-min agitation by 77.8%. 0.5” RO biochar treatment significantly reduced max by 8.8%, overall total emission by 52.9%, and total emission during 3-min agitation by 56.8%; 0.25” RO biochar treatment significantly reduced max by 61.3%, overall total emission by 86.1%, and total emission during 3-min agitation by 62.7%. For H2S, 0.5” HAP biochar treatment reduced the max by 42.5% (p=0.125), overall total emission by 17.9% (p=0.290), and significantly reduced the total emission during 3-min agitation by 70.4%; 0.25” HAP treatment reduced max by 60.6% (p=0.058), and significantly reduced overall and 3-min agitation’s total emission by 64.4% and 66.6%, respectively. 0.5” RO biochar treatment reduce the max flux by 23.6% (p=0.145), and significantly reduced overall and 3-min total emission by 39.3% and 62.4%, respectively; 0.25” RO treatment significantly reduced the max flux by 63%, overall total emission by 84.7%, and total emission during 3-min agitation by 67.4%.

kinds of biochar were tested, highly alkaline, and porous (HAP, pH 9.2) biochar made from corn 23 stover and red oak biochar (RO, pH 7.5). Two scenarios of (6 mm) 0.25" and (12 mm) 0.5" thick 24 layers of biochar treatments were topically applied to the manure and tested on a pilot-scale setup,

Introduction
industries. These gases can be harmful to both humans and livestock, sometimes deadly. The

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Occupational Safety and Health Administration gives the acceptable ceiling concentration for H2S as a maximum duration of 10 min [1]. Although there is no reliable quantitative exposure data available 53 for human fatality due to NH3, people feel unbearable irritation when exposed for 30 min to 2 h at 54 140 ppm [2]. In the mid-western United States, most swine buildings use deep-pits to store tons of 55 manure. When a pit is full, farmers pump out most of the manure to fertilize their fields. This routine 56 seasonal operation can sometimes be very dangerous. Agitating the manure can break the entrapped 57 gas bubbles, which cause a tremendous increase in the concentration of H2S and NH3 (Figure 1

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This led us to explore the possibility of using surficial biochar treatment for short-term mitigation of 76 NH3 and especially H2S emissions from swine manure.

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Biochar is a very stable and lightweight solid, often used as a soil amendment or an alternative 78 source of fuel, but can also be used as a suitable adsorbent [19][20][21]. It can be made from many kinds 79 of inexpensive biomass and waste through pyrolysis with none or a low oxygen level [19][20][21][22][23][24][25]. With 80 different temperature and time of the process, the resulting biochar will have different physical and 81 chemical properties [20][21][22][23][24]. By using the desired chemical and physical properties, it has excellent 82 research potential to benefit our society. Additionally, due to its low specific density, biochar can 83 float on top of swine manure and create a physical barrier.

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The first research question arose: what biochar barrier thickness should be applied. We

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Red oak biochar used in this study was made from red oak and pyrolyzed at 500 to 550°C. It had 103 a pH of 7.5; 6.75 zero-point charge; contained 78.53% dry matter (d.m

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The 0.5" HAP biochar treatment showed a statistically significant reduction in the maximum   (Table 4).
182 183   (Table 5). This study is a proof of concept these treatments with biochar has a possible potential to save 212 people and livestock lives during routine seasonal manure stirring, pump-out, and land application.

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In this study, we showed that biochar applied surficially to manure can be effective for short-term 218 Surprisingly, the 0.25" treatment was a more effective dosage since the percent reduction was 219 slightly higher while using less biochar. The smaller amount of biochar being used could be critical, 220 not only because it is more economical. When the biochar is wetted, it forms 'chunks.' With manure 221 is being agitated, the bigger chunks of biochar in 0.5" treatments started to sink and mix with manure.

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Once the physical barrier on the surface was broken, the maximum concentration of the treatment 223 began to rise and be closer to the control. However, for both treatments, biochar was effective in 224 reducing the overall total emissions for both NH3 and H2S.

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In future research, other kinds of biochar could be tested for their efficacy to mitigate gaseous