Quantifying the chronic effect of low DO on the nitrification process.

Our previous study indicated that a low dissolved oxygen (DO) could enrich and shift nitrifier community, making complete nitrification feasible under long-term low DO conditions. This research determined nitrifier kinetic constants, and quantified the chronic effect of low DO on the overall nitrification process. For ammonia oxidizing bacteria (AOB), the half-velocity constants of DO on the growth (KDO-g) and decay (KDO-d) were 0.29 and 0.48mgL(-1), respectively. For nitrite oxidizing bacteria (NOB), those values were 0.08 and 0.69mgL(-1), respectively. The low KDO-g values for both AOB and NOB suggest that a DO of greater than 1mgL(-1) does not provide further benefit to nitrification, and the lower KDO-g value for NOB suggests that nitrite oxidation is less impacted by a low DO. The KDO-d values of 0.48 and 0.69mgL(-1) for AOB and NOB, respectively, suggest that a low DO of less than 1mgL(-1) significantly inhibits the decay of both AOB and NOB, resulting in their enrichment. The relationship between the operational DO and required SRT for complete nitrification was developed to provide a theoretical foundation for operating an advanced wastewater treatment plant under low DO, to significantly improve aeration energy efficiency.