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<p>The outstanding tolerance of the heterotrophic nitrification-aerobic denitrification (HN-AD) process to elevated salinity and ammonia concentrations makes it a promising option for nitrogen bioremediation in extreme conditions over conventional methods. Previous studies have mainly focused on isolating pure strains and their application for synthetic wastewater treatment; however, their effectiveness in treating complex wastewater such as landfill leachate needs further investigation. Unlike a single strain, using an inoculum containing HN-AD bacteria alongside other denitrifiers could promote symbiotic microbial interactions and reduce organic matter supplementation in organic-deficient environments. This study investigated three continuous-flow reactors, each inoculated with different HN-AD bacteria-containing sludges, for treating landfill leachate with varying biochemical oxygen demand to nitrogen (C/N) ratios. The results revealed that higher C/N ratios enhanced ammonia oxidation and nitrogen removal. The anoxic/oxic reactor inoculated with leachate sludge exhibited the best performance, recording maximum ammonia and nitrogen removal efficiencies of 92.5% and 87%, respectively, at a C/N ratio of 2.30. This sludge showed excellent organic biodegradability and high resistance to organic fluctuations, particularly in environments with low organic content. The coexistence of heterotrophic denitrifiers (<i>Ottowia</i> and <i>Truepera</i>), autotrophic denitrifiers (<i>Moheibacter</i>), and endogenous denitrifiers (<i>Rhodobacteraceae</i> and <i>Rhizobiaceae</i>) together with HN-AD bacteria (<i>Paracoccus</i>, <i>Flavobacterium,</i> and <i>Pseudomonas</i>) significantly improved nitrogen removal. Higher C/N favored the abundance of HN-AD bacteria and denitrifiers but immensely suppressed ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). This study provides a thorough understanding of the role of the C/N ratio and inoculated sludge in improving the efficiency of the HN-AD system for landfill leachate treatment.</p> Graphical Abstract <p></p>

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Effect of the C/N Ratio on Heterotrophic Nitrification-Aerobic Denitrification (HN-AD) Systems Inoculated with Different Seed Sludges for Nitrogen Removal from Landfill Leachate

  • 期刊论文

  • 发表日期：

    2025年10月3日

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  • Hassan Ramadan,
  • Bixiao Ji,
  • Zhaoji Zhang

摘要

The outstanding tolerance of the heterotrophic nitrification-aerobic denitrification (HN-AD) process to elevated salinity and ammonia concentrations makes it a promising option for nitrogen bioremediation in extreme conditions over conventional methods. Previous studies have mainly focused on isolating pure strains and their application for synthetic wastewater treatment; however, their effectiveness in treating complex wastewater such as landfill leachate needs further investigation. Unlike a single strain, using an inoculum containing HN-AD bacteria alongside other denitrifiers could promote symbiotic microbial interactions and reduce organic matter supplementation in organic-deficient environments. This study investigated three continuous-flow reactors, each inoculated with different HN-AD bacteria-containing sludges, for treating landfill leachate with varying biochemical oxygen demand to nitrogen (C/N) ratios. The results revealed that higher C/N ratios enhanced ammonia oxidation and nitrogen removal. The anoxic/oxic reactor inoculated with leachate sludge exhibited the best performance, recording maximum ammonia and nitrogen removal efficiencies of 92.5% and 87%, respectively, at a C/N ratio of 2.30. This sludge showed excellent organic biodegradability and high resistance to organic fluctuations, particularly in environments with low organic content. The coexistence of heterotrophic denitrifiers (Ottowia and Truepera), autotrophic denitrifiers (Moheibacter), and endogenous denitrifiers (Rhodobacteraceae and Rhizobiaceae) together with HN-AD bacteria (Paracoccus, Flavobacterium, and Pseudomonas) significantly improved nitrogen removal. Higher C/N favored the abundance of HN-AD bacteria and denitrifiers but immensely suppressed ammonia-oxidizing bacteria (AOB) and nitrite-oxidizing bacteria (NOB). This study provides a thorough understanding of the role of the C/N ratio and inoculated sludge in improving the efficiency of the HN-AD system for landfill leachate treatment.

Graphical Abstract