High-load influent driven to critical free ammonia inhibition on NOB under periodical acidic domestication for...

Partial nitrification is a promising technology for achieving low-cost and energy-efficient denitrification in wastewater treatment. However, it is still difficult to achieve efficient and stable partial nitritation of domestic wastewater with low NH₄⁺-N concentration in the sequencing batch reactor (SBR) process, because stable high-level free nitrous acid (FNA) or/and free ammonia (FA) inhibition of nitrite-oxidizing bacteria (NOB) activity cannot be formed in domestic wastewater. This study aims to establish a novel technical roadmap for robust partial nitritation in the SBR process. By implementing a periodic high-load influent strategy to create alternating cycles of FA and acidic pH conditions, followed by the continuous feeding of domestic wastewater within each cycle, nearly all supernatant is drained at the end of each cycle. The approach targets more effective accumulation of initial in-situ FA concentrations. This precision control strategy leverages the high sensitivity of NOB grown under acidic conditions to FA inhibition, while the high-load influent strategy maximizes FA concentration levels under conventional influent intensities. By ingeniously designing the SBR influent-effluent pattern, a slight increase in initial in-situ FA concentration is sufficient to reach the threshold required for suppressing NOB growth in acidic environments. The results showed that this strategy could achieve stable partial nitritation of domestic wastewater for >200 days. In conclusion, the periodic high-load influent strategy substantially reduced the required influent NH₄⁺-N concentration to achieve stable partial nitritation in SBR systems, thereby providing a novel approach for enabling robust partial nitritation in domestic wastewater treatment.