In the KBM-1 treatment, 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 was produced by the control in the same period. However, the total acid production of the control reached a maximum level (268 mg L−1, 4.0 mM, 0.04 kg m-3 d-1) after four days. The production was significantly higher in acetic acid, butyric acid, and propionic acid, in that order, after KBM-1 treatment. The removal of organic acids in the KBM-1 treatment was notable after four days, while a significant removal rate of NO3–N (41%, 0.005 kg N m-3d-1) was observed after two days, indicating that the removal of organic acids as electron donors might have been linked to concomitant denitrification. However,the control removal rate of NO3–N was 14% (0.001 kg N m-3d-1). It has been reported that acetate, butyrate and valerate can speed up denitrification rates twice as much as propionate (Elefsiniotis and Li, 2006; Elefsiniotis and Wareham, 2007). Therefore, the dominant acetic acid and butyric acid appeared to contribute significantly to the denitrification in our study.Rainbow trout solid waste (feces) from an RAS was used to produce soluble organic carbon substances through fermentation (Letelier- Gordo et al., 2017). Here, the protein-to-energy ratios of the feeding diets (P:E) seemed to affect the composition of the readily available carbon (butyric acid and ethanol for lower P:E; acetic and valeric acid for higher P:E). The feasibility of using fish manure waste as a nutrient source for lactic acid fermentation together with cellulosic carbohydrates was tested (Shi et al., 2018). Here, the highest lactic acid yield was 87% and 91%, in which the corresponding lactic acid concentrations for cellulose and paper sludge were 96 and 56 g L−1, respectively. Conroy and Couturier (2010) characterized the production of volatile fatty acids (VFAs) from the hydrolysis/fermentation of fecal wastes. Here, the rate of production of VFAs appeared to be limited by the conversion rate of fecal solids from a salmon smolt hatchery into soluble organic matter. The only recent study on the application of bioaugmentation for VFA production from food waste (Reddy et al., 2018) showed that bioaugmented cultures gave higher butyric acid (8.9 g L-1) and caproic acid (8.1 g L−1) production compared with those of non-augmented anaerobic conditions (6.5 g L−1 butyric acid and 2.68 L−1 caproic acid). From the above reports, it can be assumed that higher protein-to-energy ratios, the addition of carbohydrates, the increase of the rate of conversion of the fecal solid into soluble materials and bioaugmentation technology need to be taken into account to facilitate the production of VFAs for denitrification in our study.