High organic volumetric loading rates triggered heterotrophic nitrification in wastewater biological nutrient removal systems

This study confirmed the importance of a higher chemical oxygen demand (COD) volumetric loading rate (CODLR) for triggering heterotrophic nitrification in a lab-scale anoxic/microaerobic biological nutrient removal system for sewage treatment by analyzing the ammonia-oxidizing activities, nitrogen mass balance, and ammonia-oxidizing bacterial communities at four CODLR levels: 0.50 (Phase A), 0.75, 1.10, and 1.50 (Phase D) kg COD m- 3 d- 1. A higher CODLR led to a significant increase in the potential heterotrophic nitrification activity by 0.4, 0.9, 1.1, and 1.6 mg NH4 +/--N/g mixed liquor suspended solids h- 1, respectively, contributing 7 %, 14 %, 17 %, and 21 % of the ammonia oxidization in the anoxic/microaerobic system. Furthermore, nitrogen balance analysis revealed that heterotrophic nitrifying bacteria contributed 4 % and 12 % of the ammonia oxidization in the anoxic/microaerobic system during Phases A and D, respectively, and that a more plentiful organic carbon supply in the microaerobic zone stimulated heterotrophic nitrification during Phase D.