In all treatments of the primary treatment experiment, the production of organic acids (volatile fatty acids) was highest four days after treatment. KBM-1 and BM-S-1 showed the highest production rates (17.2mM and 16.2 mM, respectively), and the rates were highest in the order of acetic acid, propionic acid, butyric acid, and isobutyric acid (data not shown). It was assumed that these organic acids were used as electron donors in the denitrification process because they were observed to be consumed after eight days of treatment during which a significant removal of nitrates occurred. Considering its good nitrate removal rate, KBM-1 was selected as an optimal microbial agent candidate for the secondary treatment experiment to understand the degradation process and organic acid production process during the valorization of RAS solid wastes.In the KBM-1 treatment of the secondary experiment, the total organic acid production reached a maximum (230 mg L−1, 3.5 mM, 0.018 kg m-3 d-1) after two days, while little production occurred in the control in the same period (Fig. 5). However, the total acid production of the control reached a maximum level (268 mg L−1, 4.0 mM, 0.040 kg m-3 d-1) after four days. In increasing order, the production of acetic acid, butyric acid, and propionic acid was significantly higher. The removal of organic acids in the KBM-1 treatment was notable after four days, while a significant removal of NO3- (41%) was observed in two days, indicating that the removal of organic acids as electron donors might have been linked to the concomitant denitrification. Likewise, the maximum organic acid production occurred after four days when a maximal consumption of NO3- also occurred, but the degree of denitrification was much less (16%) in the control group. This indicates that rapid denitrification can occur in a higher concentration of organic acids and that the activity of the denitrifying microorganisms might be more substantially obvious in the treatment of KBM-1, which might carry denitrifiers.