# Mitigation of Gaseous Emissions from Swine Manure with the Surficial Application of Biochars
## 4 Discussion
### Effects of Biochar Treatment on Greenhouse Gas Emissions  
On day 1 of Trial 1, HAP and RO treatment had 31% (\(p\) = 0.0001) and 77% (\(p\) = 0.0001) of CH4 reduction, respectively. However, after day 12, both started producing CH4, and the highest production was observed on day 26, where HAP and RO treatment had 415% (\(p\) = 0.0001) and 153% (\(p\) = 0.0001) of increase of emissions. During trial 2, on day 1, HAP and RO reduced CH4 emission up to 35% (\(p\) < 0.0001) and 65% (\(p\) < 0.0001), respectively. However, from day 15, emissions increased up 101% (\(p\) < 0.0001) and 35% (\(p\) < 0.0001), respectively. The highest increase in the CH4 emissions of 176% (\(p\) < 0.0001) and 288% (\(p\) < 0.0001) was measured on the last day of the trial for HAP and RO, respectively. On trial 3, CH4 was reduced to 57.8% (\(p\) < 0.0001) on day 1 due to RO biochar, and the reduction gradually decreased to 20.6% (\(p\) < 0.0001) on day 11. On day 15, RO biochar started the production of CH4, where the highest production was 301.8% (\(p\) < 0.0001) on day 19. HAP increased CH4 emission during the whole trial, where the highest increase was 671% (\(p\) < 0.0001) on day 19 (Figure S10, Table S6). On the first day of trial 1, HAP biochar increased CO2 emission up to 46% (\(p\) = 0.0001) (Figure S11, Table S7). Then again, on day 26, HAP and RO increased CO2 emission up to 42% and 39%, respectively, but they were not statistically significant. Overall, the CO2 reduction was not significant, and % reduction fluctuated between 2% and -9% (except for day 1 and 26). In trial 2, both HAP and RO reduced CO2 emissions till day 11 where it was 17% (\(p\) < 0.0001) and 26% (\(p\) < 0.0001), respectively. No significant reduction of N2O was measured during trial 1. The highest reduction was shown on day 11, where HAP and RO had 9% (\(p\) = 0.2) and 11% (\(p\) = 0.3) reduction, respectively. N2O mitigation was statistically significant for the first 2 weeks, and the highest reductions of 17% (\(p\) < 0.0001) and 16% (\(p\) < 0.0001) were observed on day 5 for HAP and RO, respectively on trial 2. In trial 3, both HAP and RO biochars increased N2O emission up to 28.9% (\(p\) < 0.0001) on day 8 and decreased the emission to 20.8% (\(p<0.0001\)) and 40.5% (\(p<0.0001\)), respectively, on day 22. No statistically significant reductions were observed on other days of the trial (Figure S12, Table S8). [PERSON] et al. and [PERSON] et al. studied that aeration during composting decreased CH\({}_{4}\) emission [50; 51], and in addition to that, [PERSON] et al. stated that biochar improved aeration and methanothrophy of compost [52]. Besides the fact that the headspace of the container with manure was continuously flushed with air, freshly applied biochars might enhance manure surface aeration and so decrease methanogenic activity. However, after biochar started to incorporate into manure, it could be a source of carbon for methanogens for CH\({}_{4}\) production. Moreover, due to high porosity, biochar was not able to capture smaller CH\({}_{4}\) particles. In agreement with the statement, HAP biochar with larger pores was less effective and increased methane emission after 1-2 weeks. Also, in the case of RO biochar, it started producing CH\({}_{4}\) after biochar was incorporated into manure, which can be seen in Figure S10 (part b) where biochar sank after day 15, and high CH\({}_{4}\) emission was observed on day 19. The theory was that biochar was adsorbing CH\({}_{4}\), and after incorporation into manure, it released captured CH\({}_{4}\) out of its pores. RO biochar with less N content (Table 3) and smaller pores showed better performance in CO\({}_{2}\) sorption in comparison with HAP biochar. [PERSON] et al. revealed that micropores of \(<\)0.70 nm were responsible for CO\({}_{2}\) uptake [53]. [PERSON] et al. [54] found that a MgO-activated sugarcane bagasse biochar had a CO\({}_{2}\) adsorption capacity of 733 mg g\({}^{-1}\).