Effect of C/N Ratio on Nitrogen Removal in a Novel Sequencing Batch Biofilm Reactor

A novel laboratory-scale sequencing batch biofilm reactor (SBBR) based on an intelligent controlling system (ICS) was subjected to synthetic wastewater with different C/N (COD/TN) ratios (3.8, 6.8, 12.5, 22.0) respectively to investigate the effect of C/N ratio on nitrogen removal and furthermore the simultaneous nitrification and denitrification (SND) in the reactor. A special kind of biological sponge with porosity of 98% was used as biofilm carrier in the reactor. The experimental results indicated that the C/N ratio of 12.5 was optimal to the simultaneous removal of nitrogen and COD in SBBR, and the removal efficiencies of ammonia nitrogen (NH₃-N), total nitrogen (TN) and COD were 90.1%, 87.4% and 94.8%, respectively. It was also deduced that the initial decrease of NH₃-N was ascribed from the adsorption of the biofilm formed on the carriers. In addition, the microorganisms grown in the biofilm also had a large capacity of storing carbon source, resulted in the sharp decrease in COD at the beginning of the operation, so the carbon source could be subsequently provided for denitrification. When the C/N ratio was 12.5, no accumulation of NO₃^--N or NO₂^--N was detected, and removal efficiency of TN was 87.4%, while 80.3%, 79.1% and 37.5% at C/N ratio of 3.8, 6.8 and 22.0, respectively, demonstrating the reactor had an efficient SND and the efficiency of SND reached 97.9%.