# Mitigation of Gaseous Emissions from Swine Manure with the Surficial Application of Biochars
## 5 Conclusions  
This laboratory-scale experiment evaluated two biochar treatments and their effective duration on mitigating targeted gases and odor emissions (as the percent reduction, % \(R\)) from swine manure surface in three trials. Overall, both biochars were effective in mitigating NH\({}_{3}\), H\({}_{2}\)S, and odorous phenolic VOCs. The impact on GHGs, isobutyric acid, and the odor was mixed with some mitigation and generation effects. The manure and biochar type and properties had an impact on the mitigation effect and its duration. In the case of RO treatment, there was a:  
1. significant percent reduction (% \(R\)) that ranged from 19-39% for NH\({}_{3}\) in all three trials, and the types of manure tested. 2. H\({}_{2}\)S was mitigated (16-23% reduction), but not significantly for all trials. 3. CH\({}_{4}\) was generated (\(-\)26 to \(-\)104%), but not significantly for all trials. CO\({}_{2}\) trended toward mitigation (0-25%), but not significantly for all trials. There was no significant effect on N\({}_{2}\)O (\(-\)1-7%). 4. Overall, the phenolic VOCs had relatively high % \(R\) in most trials. Significant (66-78%) reductions for \(p\)-cresol were observed for all trials. The % \(R\) for skatole ranged from 29-72%, but not significantly for all trials. The % \(R\) for phenol and indole ranged from (\(-\)13-94%) and (\(-\)11-84%) but not significantly for all trials. The % \(R\) for isobutyric acid ranged from (9-26%) but not significantly for all trials. 5. Finally, the odor was mitigated in all trials (17-30%) but not significantly for all trials. The RO treatment resulted in the decreasing effectiveness (% \(R\)) for NH\({}_{3}\) mitigation, consistently for the first week, the first 2 weeks, the first 3 weeks, and the entire trial for all three trials (Table 4). The % \(R\) for \(p\)-cresol was relatively steady. However, % \(R\) for several targeted gases (H\({}_{2}\)S, phenol, skatole, indole) were relatively steady in at least one of the trials. In the case of HAP treatment:  
1. the % \(R\) for NH\({}_{3}\) ranged from 4-21% but not significantly for all trials. 2. H\({}_{2}\)S was mitigated (2-22% reduction), but not significantly for all trials. 3. CH\({}_{4}\) was generated (\(-\)41 to \(-\)221%), but not significantly for all trials. CO\({}_{2}\) trended toward generation (\(-\)57-2%), but not significantly for all trials. There was no significant effect on N\({}_{2}\)O (\(-\)6-46%). 4. Overall, the phenolic VOCs had relatively high % \(R\) in most trials. Significant (91-97%) reductions for \(p\)-cresol were observed for all trials. The % \(R\) for skatole ranged from 74-95% and was significant for all trials. The % \(R\) for phenol and indole ranged from (60-99%) and (29-94%) but not significantly for all trials. The % \(R\) for isobutyric acid ranged from (8-88%) but not significantly for all trials. * Finally, the odor was generated in all trials (\(-12\) to \(-59\%\)) but not significantly for all trials. It is important to mention that the odor measurement does not capture odor character. The HAP treatment resulted in the decreasing effectiveness (% \(R\)) for NH3 mitigation, consistently for the first week, the first 2 weeks, the first 3 weeks, and the entire trial for all three trials. The % \(R\) for \(p\)-cresol and skatole were relatively steady. However, % \(R\) for several targeted gases (H2S, phenol, indole) were relatively steady in at least one of the trials. CH4 generation increased with the duration of most of the trials. This lab-scale experiment showed that treatments of biochars with different properties result in different mitigation or generation effects for the targeted gases over the duration of trials. In future studies, various types of biochar can be explored based on the desired mitigation or generation effect of targeted gases. The opportunity of biochar reapplication can also be evaluated since the greatest reduction for NH3 and some phenolics were observed within the first few weeks of the study.