## 3 Results and Discussion
### Greenhouse Gas Emissions Comparison  
There are many factors that affect the composition of the biogenic emissions from the production of Class A biosolids, including oxygen availability, moisture content, the activity of methanotrophic bacteria, and the C/N ratio of the biosolids. Oxygen levels can be increased during Composting by adding a bulking agent to the biosolids and by turning Composting and Air Drying windows. The resulting increase in oxygen availability leads to greater aerobic and less anaerobic microbiological activity and is thus associated with lower methane emissions and greater carbon dioxide emissions. Methanotrophic bacteria oxidize methane to carbon dioxide using oxygen as an electron acceptor, and their activity is also stimulated by increased oxygen availability [34]. Composting and Air Drying methane emissions are also dependent on the level of moisture present in the windows because as the windows dry, a greater percentage of the pore spaces is filled with air rather than water [34]. In addition, [PERSON] [20] showed that as the C/N ratio of manure increased, less methane and nitrous oxide were produced. The estimated composition and quantity of biogenic emissions from Class A biosolids treatment via Air Drying, Composting, and Lagoon Storage are summarized in Figure 7. Air Drying produces more nitrous oxide compared to Composting, presumably because  
Figure 6: Transportation sensitivity analysis results for five Class A biosolids treatment processes. Transport distances listed are one-way distances. biosolids treated via Air Drying are not amended with a carbon feedstock and thus have a lower C/N ratio compared to biosolids that are amended with sawdust and composted. Methane is present in Air Drying and Composting because the two processes are not completely aerobic [11]. For example, anaerobic conditions may develop within biosolids aggregates. The emissions from Lagoon Storage Plus Air Drying are dominated by the carbon dioxide and methane produced during the Air-Drying stage. This explains why the total emissions and their composition are so similar for Air Drying and Lagoon Storage Plus Air Drying. It should be noted that, in general, there is relatively little information available in the literature on biogenic gas emissions from biosolids during treatment via Air Drying or Lagoon Storage Plus Air Drying. Therefore, data were used from a study [23] in which the operating conditions and parameters were most consistent with the assumptions made in the current study. Even so, there were some key differences between the two studies. First, the comparison study [23] maintained biosolids in stockpiles that were 20 ft to 30 ft deep, while the current study assumed the biosolids were stored in lagoons that are 5 feet deep. Furthermore, in the comparison study, the biosolids were treated sequentially in anaerobic and aerobic lagoons before being air-dried and then stockpiled. Finally, the percentage of solids in the stockpiles used by the comparison study was twice as great as the percentage of solids assumed for Lagoon Storage in this research. Thus, to improve the accuracy of future LCA studies in this area, more data on emissions from biosolids under a wide range of treatment and storage conditions are needed. Unfortunately, obtaining comprehensive emissions data will be challenging given the many environmental and biosolids characteristics (e.g., carbon and nitrogen content, moisture, and temperature) that vary from one WRRF to another and affect the composition of the emissions from Class A biosolids treatment processes. The results of this study have important implications for stakeholders involved in, and impacted by, decisions about technologies for the treatment and recovery of resources from wastewater [35].