Acinetobacter sp. decreased significantly, while Citrobacter tended to increase two-fold after eight days of KBM-1 treatment. Acinetobacter sp. was reported to produce inhibitory substances against Vibrio anguillarum that infected freshwater eels (Spanggaard et al., 2001). Comamonas sp. was one of the dominant genera in all treatments after eight days. In fact, the levels of nitrate-N in the treatments with KBM-1 and BM-S-1 both decreased by 50% after eight days, indicating potential denitrification activity of Comamonas sp. as shown in previous reports (Srinandan et al., 2011; Chu et al., 2013). In the KBM-1 treatment, Bacteroides graminisolvens had approximately half the density of that of the other treatments after four days, but its density increased by 47% after eight days (Fig. 6). B. graminisolvens is a strictly anaerobic bacterium and an important degrader of hemicellulose (Nishiyama et al., 2009). Bacteroides is a common genus of intestinal microbes of various host organisms including fish, and they utilize polysaccharides and generates anti-inflammatory substances to balance the immune system (Van der Meulen et al., 2006; Nayak, 2010; Kabiri et al., 2013). B. graminisolvens could have played a role in the degradation of carbohydrates (e.g., celluloses and hemicelluloses and starch, etc.) from solid wastes. The population of Citrobacter freundii in the control and BM-S-1 treatments decreased by 53% and 71%, respectively, after eight days; however, the population increased by 102% after eight days in the KBM-1 treatment compared to that of a four-day treatment. Citrobacter freundii is important for nitrogen recycling and is a facultative anaerobe capable of reducing nitrate to nitrite (Puchenkova, 1996) and causing hemorrhagic diseases (Sun et al., 2018). It appeared that Citrobacter freundii could play a role in denitrification in the KBM-1 and BM-S-1 treatments, but its population density in the treatments did not seem to be as influential in denitrification (Table 4 and Fig. 7). In all treatments, Bacteroides graminisolvens, Comamonas jiangduensis, and Acrobacter defluvii had 2–3 times higher density after eight days compared to that of the four-day treatments. Comamonas jiangduensis can act as a lignocellulose degrader (Brossi et al., 2016), which could have degraded cellulosic substrates in the solid wastes from the RAS. Arcobacter defluvii was found to be a potential pathogen for edible bivalve molluscs (Collado et al., 2014). However, the facultative anaerobes (Sporolactobacillus inulinus, Lactobacillus mali, and Lactobacillus casei comprising 32% of the total communities) and the obligate anaerobe (Clostridium tyrobutyricums, 9%) present in the inoculated culture of KBM-1 were hardly detected in the solid waste treated with KBM-1.This indicates that the bioaugmentation of KBM-1 may not necessarily contribute to a significant increase in the population density of its composing species, but the bioaugmentation can still facilitate the system functionally. Similar phenomena were observed in a tannery wastewater treatment system undergoing bioaugmentation, as shown in previous reports (Kim et al., 2013, 2014). On the other hand, the dominant VFAs from excess sludge fermented in the expanded granular sludge blanket reactor were acetic acid (84%) and propionic acid (11%), and the dominant bacterial genera were Clostridium, Bacillus, Amphibacillus and Peptostreptococcaceae (Li et al., 2018). However, these anaerobic genera were not found in the bioreactors of our study, which were operated under aerobic and anaerobic conditions. Lactic acid bacteria and yeast strains (LAB-1 and yeast-1; not yet identified) isolated from the active culture of KBM-1 were inoculated into the RAS solid waste (20% slurry), and their growth was observed.These cultures maintained a density of 106–107 c.f.u. L−1 over a period of two to seven days (Supplementary Fig. S5), indicating that these strains should be involved in the decomposition of organic matter within the solid waste and the production of organic acids during decomposition.