Combined Partial Denitrification (PD)-Anammox: A method for high nitrate wastewater treatment

Elimination of nitrogen pollution from wastewater containing high-strength nitrate (NO₃^--N) is a significant issue to prevent deterioration of water quality and eutrophication of receiving water body. Traditional denitrification process faces several challenges including the huge organic carbon demand, intermediate products accumulation, and long acclimatization period. In this study, an efficient solution was given by a novel two-stage Partial Denitrification (PD)-Anammox process. High NO₃^--N (1000 mg N/L) wastewater and municipal sewage (COD: 182.5 mg/L, ammonia (NH₄⁺-N): 58.3 mg/L) were simultaneously introduced to the PD reactor for NO₃^--N converting to NO₂^--N. The NH₄⁺-N and NO₂^--N in effluent of PD were removed in subsequent anammox reactor. Results showed that a satisfactory nitrogen removal was achieved by optimizing the volume ratios of influent NO₃^--N and municipal sewage, as well as the external organic matter dosage. The NO₃^--N removal efficiency reached up to 95.8% without accommodation period, along with the NH₄⁺-N removal achieving 92.8%. Anammox contributed to 78.9% of TN removal despite the high COD (76.5-98.6 mg/L) in PD effluent was introduced, indicating the significant stability of the integrated process. The microbial analysis suggested that the Candidatus Brocadia, identified as anammox bacteria, cooperated stable with denitrifying bacteria in 215-day operation. The PD-Anammox process offers an economically and technically attractive approach in the high NO₃^--N wastewater treatment since it has great advantages of much low carbon demand, minimal sludge production, enabling simultaneous treatment of municipal sewage, and avoiding the common issues in traditional denitrification process.