Purification of rotating biological contactor (RBC) treated domestic wastewater for reuse in irrigation by biofilm channel

Total nitrogen (TN-N) below 10 mg l(-1) was suggested for short-term irrigation application in Taiwan. TN-N in the treated effluent of a Rotating Biological Contactor (RBC) system was about 18 mg l(-1) and further reclamation was required for reuse purpose. A channel with nine sections, 6 m long, 30 cm in width and 20 cm in height, with plastic sheets as a biofilm carrier inserted inside, was set up at a wastewater treatment plant site to test the purification efficiency. Six different flow velocities were tested in this research. The nitrogen conversion rate increased with velocity until an optimal velocity of 1 cm s(-1) was reached. The kinetic constants of Total Kjeldahl nitrogen (TKN) and TN-N were found to be 4.57 and 7.51 (mg l(-1) h(-1)). The unit area biofilm carrier removal rates for TKN and TN-N were found to be 1.34 and 2.20 (g m(-2) d(-1)) and the unit volume removal rates for TKN and TN-N were 140.72 and 231.18 (g m(-3) d(-1)), respectively, at this optimal velocity. The TKN and TN-N concentrations kinetic rates fit a zero-order approach. The TN-N concentration criterion of 10 mg l(-1) was found to be possible with this biofilm channel. (C) 2000 Elsevier Science B.V. All rights reserved.