Study On Gases Emissions From Pig Digested Slurry

Vast animal wastes from Livestock production have proved to be a significant contributor to air pollution in agriculture. Anaerobic fermentation is a promising technology for its resource utilization of animal manure; however, its by-product digested slurry still emission gaseous pollutants without appropriate management. Nowadays, studies on greenhouse gases and ammonia (NH3) emissions and mitigation technologies from digested slurry are rare in China, and the emission inventory lacks solid scientific supports. The gases emission characterstics and reduction effects of acidification on gases from pig digested slurry storage were investigated in this thesis.1. Methane (CH4) and NH3emissions from and pH changes in digested slurry during storage were monitored for46days. The results showed that CH4and NH3emissions increased rapidly to day12, and were high during the first15days and25days respectively. The result suggested that emission mitigation is best carried out during the first15days and25days respectively for CH4and NH3. The pH value increased from7.2at the beginning and to7.89at the end of the study.2. The effects of different initial pH adjustments on emissions of CH4, NH3and hydrogen sulfide (H2S) during digested pig slurry storage were studied. The following conclusions were made:(1) Digested pig slurry from different biogas projects presented different gas emissions potential because of the different physicochemical properties. In the control group, the daily mean emissions of CH4and NH3reached up to21.5mg m2min-1and3.48mg m2min-1respectively, which were significantly higher than the result in1and14.13μg m2min-1for H2S.(2) Most of the CH4emission occurred during the first21days of the storage for the control group. There were large variations of NH3emission during the whole storage period. At the end of the test, the NH3emission still remained0.74mg m2min-1, which was different from the first test. Similar to CH4, the H2S emission was reduced to0.35μg m2min-1after first13d of storage, and then kept steady at low levels.(3) Temperature and pH were crucial factors that influenced CH4and NH3emissions from digested pig slurry. The results showed that CH4emission had a strong negative correlation with pH value (r=0.931), and a positive correlation with temperature (r=0.607). Similarly, negative correlation and positive correlation were found between NH3emission and pH (r=0.814) and between NH3emission and temperature (r=0.785) respectively. No significant correlation was found between H2S emission and temperature (r=0.463). However, H2S emission had strong negative correlation with pH (r=0.795).(4) Adjustment of initial pH to5.5significantly reduced CH4concentrations by80.8%and NH3concentrations by40.2%compared with the control group (P<0.01). However, it also increased H2S emission by11,324%. There were considerable variations in H2S emission during the whole storage. Acidification with pH adjustment to6.5reduced CH4emission by31.2%, but did not affect NH3and H2S emissions significantly.