Load maximization of a liquid-solid circulating fluidized bed bioreactor for nitrogen removal from synthetic municipal wastewater

A novel liquid-solid circulating fluidized bed bioreactor (LSCFB) configured with anoxic and aerobic columns and lava rock as the biofilm carrier was used to treat synthetic municipal wastewater. Four different empty bed contact times (EBCTs) of 0.82, 0.65, 0.55, and 0.44 h were examined to optimize nutrient removal capability of the system. The LSCFB demonstrated tertiary effluent quality organic and nitrogen removal efficiencies. Effluent characteristics of the LSCFB were soluble biological oxygen demand (SBOD) ≤ 10 mg l^-1 and total nitrogen (TN) < 10 mg l^-1 at organic loading rate (OLR) of 5.3 kg m^-3 d^-1 and nitrogen loading rate of 0.54 kg N m^-3 d^-1. Remarkably low yields of 0.14, 0.17, 0.19, and 0.21 g VSS g^-1 COD were observed at OLR of 2.6, 3.2, 4.1 and 5.3 kg COD m^-3 d^-1, where increment of biomass growth and detachment rate were also experienced with increasing OLR. However the system demonstrated only 30% phosphorus removal, and mass balances along the anoxic and aerobic columns showed biological phosphorus removal in the system. Organic mass balance showed that approximately 40% of the influent COD was utilized in the anoxic column and the remaining COD was oxidized in the aerobic column. The system is very efficient in nitrification-denitrification, with more than 90% nitrification of ammonium and overall nitrogen removal in the LSCFB was 70 ± 11% even at an EBCT of 0.44 h.