Nitrate removal characteristics of high performance fluidized-bed biofilm reactors

Two laboratory-scale high performance fluidized bed biofilm reactors (FBBR) with sand as the biofilm carrier were used to investigate the denitrification of high-strength nitrate wastewater with specific emphasis on the effect the nitrogen loading rate and the superficial velocity (Vs). The results demonstrated that the FBBR system is capable of efficiently handling an exceptionally high nitrate nitrogen concentration of 1000 mg N/L. At a loading rate of 6.3 kg-N/m3bed•d almost complete denitrification was achieved with a removal efficiency of 99.8% and an effluent concentration of 2 mg N/L at Vs values of 45, 55 and 65 m/h. The maximum efficient loading rate (Rmax) at which the US drinking water nitrate-nitrogen standard concentration of 10 mg N/L would be exceeded was found to be a function of the applied Vs. The Rmax was found to be 12 kg-N/m3bed•d at a Vs value of 45 m/h. As Vs was increased to 55 and 65 m/h, the optimum Rmax dropped to 9.5 and 8 kg-N/m3bed•d, respectively. Higher denitrification rates were achieved at relatively lower Vs. However, there is a minimum practical velocity below which agglomeration of biomass would occur. The suspended solids concentration in the effluent was below 30 mg/L throughout the study.