Impact of carbon/nitrogen ratio on the performance and microbial community of sequencing batch biofilm reactor treating synthetic mariculture wastewater

The differences of cultured organism species, aquaculture model and supervisor mode lead to different carbon/ nitrogen ratios in mariculture wastewater. Therefore, the performance, microbial community and enzymatic activity of sequencing batch biofilm reactor were compared in treating synthetic mariculture wastewater at different chemical oxygen demand/nitrogen (COD/N) ratios. Compared with COD/N ratio of 6, the ammonia oxidizing rate and nitrite-oxidizing rate at COD/N ratio of 5, 4 and 3 increased by 3.66 % and 3.08 %, 11.19 % and 14.95 %, and 24.50 % and 32.54 %, respectively. Similarly, the ammonia monooxygenase and nitrite oxidoreductase activities increased by 3.50 % and 6.76 %, 11.09 % and 16.22 %, and 25.43 % and 39.19 % at COD/N ratio at 5, 4 and 3, respectively. However, the denitrifying rate and denitrification enzymatic activity declined with the decrease of C/N ratio from 6 to 3. The production, protein content and polysaccharide content of loosely bound extracellular polymeric substances (LB-EPS) and tightly bound EPS (TB-EPS) reduced with the decrease of COD/N ratio from 6 to 3. The abundance of nitrifying genera increased with the decrease of COD/N ratio from 6 to 3, whereas most of denitrification genera displayed a decreasing trend. The microbial co occurrence pattern, keystone taxa and significant difference were altered with the decrease of COD/N ratio. Among the keystone taxa, Thauera, Denitromonas, Nitrosomonas and Denitratisoma had a close link with nitrogen transformation. The present results can provide some theoretical basis for evaluating the effect of carbon/nitrogen ratio on the nitrogen removal of biological wastewater treatment systems.