Improved microbial compatibility and granular stability in the partial nitrification/Anammox process for food waste...

The proliferation of nitrite-oxidizing bacteria (NOB) can lead to microbial imbalance and process collapse, which obstructs the engineering application of the single-stage partial nitrification/Anammox (PN/A) process. This study utilized a gas-lift reactor to investigate the treatment efficacy and process stabilization strategies of the single-stage PN/A process for treating food waste digestate (FWD) under continuous influent and continuous aeration operating conditions. In single-stage PN/A process treatment of FWD, the low free ammonia (FA) concentrations in the FWD influent failed to inhibit. NOB was fast proliferated within 12 days, decreasing nitrogen removal efficiency (NRE) to 53.49%. Meanwhile, the organic matter in FWD promoted the proliferation of denitrifying bacteria (DNB), further weakening the dominance of anammox bacteria (AnAOB). This study developed a strategy for suppressing NOB by progressively adjusting the nitrogen loading rate (NLR) in accordance with the concentrations of effluent NH₄⁺-N and FA. Without external chemical oxygen demand (COD) addition, NOB was effectively suppressed by progressively increasing the influent NH₄⁺-N to maintain effluent NH₄⁺-N and FA at 150 mg/L and 20 mg/L, respectively, raising NRE to 73.56%. Scanning electron microscopy (SEM) revealed the complete replacement of filamentous bacteria by a high-density, uniform granular sludge layer, indicating the recovery of AnAOB activity. The NOB genus Nitrospira declined from 3.44% to 0.24%, while the dominant AnAOB shifted from Ca.Brocadia (9.35% - 1.64%) to the more tolerant Ca.Kuenenia (4.25% - 9.47%). This study serves as a reference for the feasibility of achieving stable nitrogen removal from food waste digestion using the Anammox process.