Anaerobic ammonium oxidation (anammox) is an efficient and cost-effective biotechnology for nitrogen removal that directly converts ammonium (NH₄⁺) and nitrite (NO₂^-) to nitrogen gas (N₂) under anoxic conditions. As an essential anammox substrate, nitrite is generally supplied by partial nitrification (NH₄⁺→ NO₂^-). Nitrite is also an intermediate in sulfur-based denitrification, and transient nitrite accumulation is frequently observed, which could potentially supply nitrite for anammox. Thus, it is possible to combine sulfur-based denitrification and anammox (SMOX) and to extend the application of anammox-based biotechnology to sulfur-containing wastewater treatment. This study developed a new sulfur-cycle bioprocess of SMOX (i.e., S₂O₃^2- and S^2-), investigated the process performance...[ Read more ]

Anaerobic ammonium oxidation (anammox) is an efficient and cost-effective biotechnology for nitrogen removal that directly converts ammonium (NH₄⁺) and nitrite (NO₂^-) to nitrogen gas (N₂) under anoxic conditions. As an essential anammox substrate, nitrite is generally supplied by partial nitrification (NH₄⁺→ NO₂^-). Nitrite is also an intermediate in sulfur-based denitrification, and transient nitrite accumulation is frequently observed, which could potentially supply nitrite for anammox. Thus, it is possible to combine sulfur-based denitrification and anammox (SMOX) and to extend the application of anammox-based biotechnology to sulfur-containing wastewater treatment. This study developed a new sulfur-cycle bioprocess of SMOX (i.e., S₂O₃^2- and S^2-), investigated the process performance and microbial community structure, and examined the nitrogen and sulfur conversion mechanisms in this new biosystem.

The feasibility of developing a thiosulfate-driven denitrification and anammox (TDDA) process was first investigated. The thiosulfate-driven denitrification was initially established (1–52 days) in an upflow anaerobic sludge bed (UASB) reactor, and then enriched anammox biomass was inoculated to develop the TDDA process (53–212 days). The results showed that nitrate and ammonium could be efficiently removed from synthetic wastewater in the TDDA system with a total nitrogen removal efficiency of 82.5%. Anammox contributed to 90% of nitrogen removal in the TDDA system. High-throughput sequencing analysis further verified the coexistence of sulfur-oxidizing bacteria (SOB) (e.g., Thiobacillus and Sulfurimonas) and anammox bacteria (e.g., Ca. Kuenenia and Ca. Anammoxoglobus) in this syntrophic biocenosis. A new kinetic model was then developed to evaluate the TDDA process. The model parameters were separately calibrated by fitting the simulated data to the experimental results. The model was further validated under different experimental conditions, and the outcomes demonstrated that the developed model could describe the dynamic behaviors of nitrogen and sulfur conversion in the TDDA system. The newly developed branched thiosulfate oxidation model was also confirmed by metagenomics analysis. Using the developed model, we (i) examined the interactions between SOB and anammox bacteria under steady-state conditions with varying substrates to demonstrate the robustness of TDDA process and (ii) evaluated the feasibility and operation of the TDDA process in practical applications.

Sulfide-driven partial denitrification and anammox (SPDA) process was established in a UASB reactor. The continuous reactor was fed with synthetic wastewater containing 100 mg N/L nitrate, 80 mg N/L ammonium, and 20–80 mg S/L sulfide. After 160 days of operation, the reactor reached stable performance and the nitrogen removal efficiency and rate were maintained at 80% and 0.29 kg N/(m3·d), respectively. Additional batch experiments were conducted to explore the effect of sulfide on anammox and the mechanism of nitrogen removal in the SPDA system. The results showed that (i) sulfide had an inhibitory effect on the specific anammox activity with a 50% inhibition concentration (IC₅₀) of 9.7 mg S-H₂S/L; (ii) the rapid oxidation of sulfide by SOB could relieve the toxic effect of sulfide on anammox in the SPDA system; and (iii) Sulfide bio-oxidation was a two-step reaction with biologically produced elemental sulfur (BPS⁰) as the intermediate and BPS⁰ used as the electron donor in the second step, which could efficiently produce nitrite via partial denitrification as a supply for anammox. The microbial community analysis of the SPDA system verified the dominant SOB were Thiobacillus and Sulfurimonas, and the dominant anammox bacteria were Ca. Kuenenia. This study illustrates the feasibility of the SMOX process for nitrogen removal from wastewater and provides the foundation for the practical application of this innovative biotechnology in the future.