Hydraulic characteristics analysis of an anaerobic rotatory biological contactor (AnRBC) using tracer experiments and response surface methodology (RSM)

The hydraulic characteristic of an anaerobic rotating biological contactor (AnRBC) were studied by changing two important hydraulic factors effective in the treatment performance: the hydraulic retention time (tau) and rotational disk velocity (omega). The reactor hydraulic performance was analyzed by studying hydraulic residence time distributions (RTD) obtained from tracer (Rhodamine B) experiments. The experiments were conducted based on a central composite face-centered design (CCFD) and analyzed using response surface methodology (RSM). The region of exploration for the process was taken as the area enclosed by tau (60, 90 and 120 min) and omega (0.8 and 16 rpm) boundaries. Four dependent parameters, deviation from ideal retention time (Delta tau), dead volume percentage and dispersion indexes (Morrill dispersion index (MDI) and dispersion number (d)), were computed as response. The maximum modeled Delta tau and dead volume percentage was 43.03 min and 37.51% at tau and omega 120 min and 0 rpm, respectively. While, the minimum predicted responses (2.57 min and 8.08%) were obtained at tau and omega 60min and 16 rpm, respectively. The interaction showed that disk rotational velocity and hydraulic retention time played an important role in MDI in the reactor. The AnRBC hydraulic regime was classified as moderate and high dispersion (d=0.09 to 0.253). As a result, in addition to the factors studied, the reactor geometry showed significant effect on the hydraulic regime.