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 (V-s). 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/M-bed(3 .) d almost complete denitrification was achieved with a removal efficiency of 99.8% and an effluent concentration of 2 mg N/L at V-s values of 45, 55 and 65 m/h. The maximum efficient loading rate (R-max) 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 V-s. The R-max was found to be 12 kg-N/m(bed)(3 .) d at a V-s value of 45 m/h. As V-s was increased to 55 and 65 m/h, the optimum R-max dropped to 9.5 and 8 kg-N/m(bed)(3 .) 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. (C) 2004 Elsevier Ltd. All rights reserved.