| A novel liquid-solid circulating fluidized bed (LSCFB) bioreactor was developed for wastewater reclamation emphasizing biological nutrient removal. The LSCFB bioreactor configured with anoxic and aerobic columns utilized attached microbial films for biodegradation of both organics and nutrients within a single circulating fluidized bed unit. Both lab-scale and pilot-scale studies were conducted using degritted municipal wastewater, collected from the Adelaide Pollution Control Plant, London, Ontario, Canada.The UV transmittance of 74% of the LSCFB effluent can easily meet the standard of tertiary treated effluent streams, with typical values in North America ranging form 55-75% UVT. It is potentially pertinent for reuse following filtration and disinfections as the filtered effluent contained &le2 fecal coliform/100 mL at a UV dose of 100 mJ/cm2.A significant reduction (approximately 75%) in biomass yield to 0.12-0.16 g VSS/g COD was observed, mostly due to long biological solids retention time of 20-39 d and anoxic-aerobic COD consumption. Nutrient balances show that approximately 40% of the influent COD was consumed in the anoxic column mostly by denitrification. Again, the reduced yields in the fluidized bed respirometers and the estimated maintenance coefficient of 1.16 d-1 in the LSCFB clearly emphasize that a substantial amount of substrate was utilized for cell maintenance at ambient reactor food to microorganisms ratio.Biofilm kinetics study showed significantly different maximum specific growth rates (mumax) of 3.69+0.44 d-1 and yields (YH) of 0.36+/-0.03 g COD/g COD in the fluidized bed respirometers than the mumax of 5.57-5.72 d-1 and YH of 0.54-0.59 g COD/g COD observed in the conventional respirometric tests. Comparatively higher Monod half saturation coefficients (KS) of 186-219 mg COD/L, observed in the fluidized bed respirometry versus 49 and 58 mg COD/L for activated sludge and the detached biomass using conventional respirometry reveal the presence of mass transfer resistance in the LSCFB despite fluidization. The LSCFB model developed using AQUIFAS and biofilm kinetics successfully predicts effluent characteristics at different nutrients loadings and hydraulic loadings.The LSCFB efficiently removed nutrients from degritted municipal wastewater and generated effluent characterized by <1.0 mg NH4-N/L, <5.0 mg NO3-N/L, <1.0 mg PO4-P/L, <10 mg TN/L, <10 mg SBOD/L, and 10-15 mg VSS/L, which can easily meet the regulations for non-potable applications of treated wastewater without using any chemicals for phosphorus removal and secondary clarifier for suspended solids removal.Key words. liquid-solid circulating fluidized bed, biofilm, nitrification-denitrification, biological phosphorus removal, UV disinfection, biomass yield, biofilm kinetics, modeling... |
