The concentration of organic compounds was analyzed at each step of BAC process though BDOCtotal/rapid/slow. Further, bacteria communities and biomass concentrations measured FISH and ATP methods were analyzed. The bed volume (BV) of steady state is different from that of based on assessment of organic compounds removal. Bed volumes in DOC, BDOCrapid and BDOCtotal/slow removal at steady state were around 27,500 (185.8 day), 15,000 (101.4 day) and 32,000 (216.2 day), respectively. A biomass didn't change after the bed volume reached 22,500 (152.0 day) according to analyzing ATP concentration of bacteria. The concentration of ATP was 2.14 μg/g in BV 22,500 (152.0 day). The total bacterial number was 4.01±0.4×107 cells/g at the bed volume 1,150 (7.8 day) (the initial operation) and the number of bacteria was 9.27±0.2×109 at the bed volume 58,560 395.7 day) that increased more than 200 times. Bacterial uptrend was reduced and bacterial communities were stabilized since BV 18,720 (126.5 day). When BV were 1,150 (7.8 day), 8,916 (60.2 day), 18,720 (126.5 day), 31,005 (209.5 day), 49,632 (335.3 day), 58,560 (395.7 day), a proportion of total bacteria for the Eubacteria were 60.1%, 66.0%, 78.4%, 82.0%, 81.3% respectively. γ-Proteobacteria group was the most population throughout the entire range. The correlation coefficient (r2) between Eubacteria biomass and ATP concentration was 0.9448.