Assessing the effectiveness of treating coking effluents using anaerobic and aerobic biofilms

In the present work, a biofilm system was developed by combining one anaerobic biofilm reactor with two aerobic ones, all of which were filled with special carriers. Laboratory scale experiments lasting about a year were conducted to investigate the treatment of coking effluent by the biofilm system. Particular attention was paid to the performance of the biofilm system for different hydraulic retention times (HRT) and recirculation ratios (R). Maximal removal efficiencies of chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) of 91.0% and 96.8%, respectively were obtained without effluent recirculation at HRT = 60 h. Moreover, 77.5% of total nitrogen (TN) removal was achieved for R = 3 and HRT = 45 h. Simultaneous nitrification and denitrification (SND) occurred. Analysis of the organic compounds revealed that phenolic compounds in the influent were biodegraded effectively within 20 h of aerobic treatment. However, there were still some refractory organic compounds remaining in the biological effluent, which were similar to humic substances (HS). After advanced treatment by coagulation, a significant removal efficiency of 48.3% for COD was achieved and organic compounds in molecular weight ranges of 10,000-30,000 Da and 0-2000 Da were mostly removed. After treatment by the integrated biofilm system, the final effluent met the National Discharge Standard of China with regard to COD and NH3-N content. (c) 2007 Elsevier Ltd. All rights reserved.