Achievement of partial nitrification under different carbon-to-nitrogen ratio and ammonia loading rate for the co-treatment of landfill leachate with municipal wastewater

Partial nitrification (PN) is a technically and economically effective solution for the treatment of wastewater featuring low C/N ratio, allowing to achieve approximately 25% energy saving and 40% carbon source for denitrification. This study investigated the effect of different carbon to nitrogen ratio (C/N) and ammonia loading rate (ALR) on PN performances in a sequencing batch reactor (SBR) treating landfill leachate with municipal wastewater. The aim was to find an optimum range for C/N and ALR to maximize PN performances. Results demonstrated that a proper balancing between ALR and C/N is crucial to achieve high PN efficiency. The results highlighted the existence of an optimum range for ALR and C/N of approximately 0.30-0.50 kg NH4-N m-3d-1 and 2-4. Although complete suppression of NOB was not achieved at these values, a predominance of nitrite (125 mg L-1) to nitrate (50 mg L-1) was observed. The results demonstrated the achievement of PN even at high C/N (4) but, on the other hand, C/N higher than 6 were not favorable to autotrophic growth. C/N significantly lower than 4 caused a stress condition for the biomass, leading to an excess in SMP production. Therefore, the operational parameters as well as the co-treatment ratio should be adjusted in order to operate the system under specific ALR (0.30-0.50 kg NH4-N m-3 d-1) and C/N (2-4).