KYU HO SO, Jong-Sik Lee, Ki-Seog Seong, and Gun-Yeob Kim. National Institute of Agricultural Science and Technology, 249 Seodun-dong Kwonsun-gu, Suwon, 441-707, South Korea
In Korea, the characteristic of food waste was its high contents of moisture and salt. It is one of the limiting factors of its composting. This study was conducted to find out the chemical properties of mixture of Food Waste Slurry (FWS) and Pig Manure Slurry (PMS). The initial pH of these two slurries didn't show big difference. With proceeding of fermentation, however, it was changed. It was increased at slurry mixture with a higher ratio of FWS. Meanwhile, it was decreased at the mixture with higher ratio of PMS. The difference of EC value was decreased with fermentation. It was stabilized with 21-23 dS/m after 180 days of fermentation. After 180 days, total nitrogen had dramatically decreased up to 20% of initial contents. Furthermore, compound with higher than 50% of FWS had decreased total nitrogen up to 0.1%, which is lower than the standard of fertilizer processing nitrogen content of 0.3%. This result showed that compound with higher ratio of FWS was not suitable. As fermentation was continued, chemical properties such as organic content, total nitrogen, total phosphors, calcium and magnesium were decreased while contents of potassium and salinity were increased. The increase of salinity was probably caused by evaporation. Results of the study revealed that compound with PMS and FWS could reduce offensive odor, and increase salinity and total nitrogen. The ammonia, which was offensive odor was produced at the initial fermentation periods until 30 days. However, it decreased steadily except in the mixture with high ratio of PMS. For generation of ammonia gas less than 50 ppm in the fermentation tank, FWS took 30 days, and it took longer periods with increase of PMS ratio in the mixture. R.NH2 showed the same tendency with ammonia. However, it took a little longer period. It was needed 45 days for FWS. In case of C2H5SH, it was not generated at FWS. It was produced at PMS and its mixture. In sensory tests for offensive odor, FWS showed lower than 1 degree after 30 days of fermentation while PMS had offensive odor even after 180 days of fermentation. It is probably affected by the continuous production of C2H5SH and R.NH2 with fermentation.