Dynamic testing of the twin circulating fluidized bed bioreactor (TCFBBR) for nutrient removal from municipal wastewater

The performance of a lab-scale twin circulating fluidized bed bioreactor (TCFBBR) for biological nutrient removal from synthetic and real municipal wastewater was studied with lava rock, 850–1125 μm in diameter, used as a biofilm carrier media. The work showed >90% COD, >85% nitrogen, and 20–55% phosphorus removal efficiencies at an synthetic influent (phase I) and real (phase II) municipal wastewater (MWW) flow rate of 260 L/d, with corresponding organic loading rates (OLR) of 2.7and 4.3 kg COD/(m3 d) and nitrogen loading rates (NLRs) of 0.3 and 0.51 kg N/(m3 d). The overall hydraulic retention time (HRT) was 2.3 h with empty bed contact times (EBCTs) of 0.22 and 0.71 h in the anoxic and aerobic columns, respectively. The TCFBBR effluent was characterized by <1.0 mg NH4-N/L, <5.1 mg NO3-N/L, <8 mg TN/L, and <11 mg SBOD/L throughout the experiment. Due to a long sludge retention time (SRT) of 40 days, 31–32 days in the anoxic column and 6.8–7.6 days in the aerobic column, very low sludge yields of 0.093 and 0.101 g VSS/g COD were observed. The sustainability of the system, in terms of nitrification–denitrification, tested at a hydraulic peaking factor of 4 for 3 h, demonstrated the high efficiency of the TCFBBR during wet weather conditions. Nitrification was found to be very sensitive to the SCOD concentration, with effluent ammonia concentration increasing from 1.8 to 14 mg/L in 10 h concomitant with a rise in effluent SCOD from 18 to 350 mg/L due to a carbon shock test.