## 3 Results and Discussion
### Identification of Fecal Presence as Related to Degree of Compost Fermentation  
In brief, mature compost is the result of a managed biological process that involves the microbiologically self-heated decomposition of organic residuals and byproducts such as animal feces, food/bedding materials, and landscape trimmings. Through this process, biosolids are stabilized, potential pathogens are reduced, and odors and insect attraction are eliminated [38; 39]. Compost which is not adequately exposed to high temperatures for sufficient time periods may harbor some surviving bacterial pathogens, and these survivors may thrive and multiply under favorable conditions. _Salmonella_ spp. has been reported to persist for 161 and up to 231 days in soils amended with contaminated composts where lettuce and parsley, respectively, were grown. The pathogens were detected on the plants for up to 63 days (lettuce) and 231 days (parsley) [6]. Figure 5a,b show a color photo and a 676 nm fluorescence image, respectively, for the representative compost samples obtained from compost windows aged for one, two, three, and four months. The results show that (hyperspectral) fluorescence imaging was able to detect the fecal presence in the compost samples even though it was not identifiable by the naked eye. As shown in  
Figure 4: (**a**) Photo of representative feces-soil sample matrix where (in clockwise order from upper left) one Petri dish contains only soil, one Petri dish contains a random mixture of soil and fecal particles from all animal species, and two Petri dishes (at bottom) each contain soil topped with larger fecal particulates from each of four animal species; (**b**) Fluorescence image of the representative soil-feces sample matrix acquired at 676 nm; (**c**) Binary feces distribution image obtained by applying automated Otsu threshold (Otsu, 1979) to the 676 nm fluorescence image of soil-feces sample matrix; (**d**) RGB color composite image obtained from a combination of PC2, PC3, and PC4 score images of the soil-feces sample matrix. the F676 nm image, much fecal content was detectable in the one-month compost, but with the passing of time there was significant decomposition. However, the imaging results indicated that some trace fecal presence remained even after four months of composting. This observation was attributable to relatively slow composting rates during the cooler winter months, since all the compost samples were acquired from the outdoor facility in February 2015. Note that compost maturation depends on many factors including ambient temperature and environmental circumstances. To further verify the change in fluorescence intensities based on aged compost samples, mean and standard deviation values for the fluorescence intensities at 676 nm were calculated. The total numbers of pixels acquired from 20 samples for each month were approximately 150,000. The results are plotted in Figure 5c. The average values of fluorescence intensities at 676 nm for the aged compost samples were 2040.2, 914.3, 803.7, and 799.2, respectively. The fluorescence value between the one-month sample and the two-, three- and four-month samples showed a significant difference (\(p<0.0001\)). However, statistically significant differences could not be confirmed between the two-, three- and four-month samples. Nevertheless, the mean and standard deviation of fluorescence intensities decreased with the aged months because the pixels with high fluorescence intensity (676 nm) were reduced. Therefore, these results suggest that the fluorescence value at 676 nm is related to the composting rates of manure. The U.S. Environmental Protection Agency, the U.S. Composting Council, and the FDA stipulate microbial criteria for finished compost to ensure biological safety when it is applied to the land, and the presence and amounts of fecal coliforms and _Salmonella_ spp. must be confirmed as indicators of the total pathogen content [17; 40; 41].