Elemental sulfur-driven autotrophic denitrification for advanced nitrogen removal from mature landfill leachate after PN/A pretreatment

Elemental sulfur-driven autotrophic denitrification (S0dAD) was applied in a packed-bed reactor to remove residual nitrogen from raw mature landfill leachate after partial nitritation and anaerobic ammonium oxidation (anammox) (PN/A) pretreatment. The performance and stability of S0dAD were evaluated with different NOx− (nitrate and nitrite) loadings and hydraulic retention time (HRT) at 15–28 °C over an operational period of 240 days.

Stable and high NOx− removal efficiency (NRE) of 96.6 ± 1.9% was determined under a stepwise decrease in HRT (from 9 h to 2 h), resulting in low total nitrogen concentrations of 24.0 ± 3.9 mg-N/L in the effluent. The circumneutral pH, associated with efficient elemental sulfur supply, facilitated to maintain the high NRE of S0dAD, which contributed to over 86.3% of the total NOx− removal in packed-bed reactor.

Biomass in S0dAD packed-bed reactor was highly enriched with sulfur-oxidizing bacteria (SOB) (58.4%), including a predominant genus of Thiobacillus (47.7%) and two less-abundant genera of Sulfurimonas (4.5%) and Sulfurovum (5.5%). This study highlights the potential implementation of S0dAD coupled with PN/A process for advanced nitrogen removal from carbon-deficient ammonium-laden wastewater, particularly mature landfill leachate.