Advanced Nitrogen and Pathogenic Indicator Removal from Digested Livestock Wastewater Using a Partial Nitritation-Anammox Coupled with Partial Denitrification (PN-APD) Process without an External Carbon Source

Digested livestock wastewater contains high concentrations of NH₄⁺-N and residual pathogens, and the Anammox process is a cost-effective process for treating wastewater with high NH₄⁺-N concentrations. However, advanced nitrogen and pathogen removal from high-strength wastewater by Anammox-based processes, without the addition of an external carbon source, is still a challenge. In this study, a partial nitritation-Anammox coupled with partial denitrification (PN-APD) process was constructed using a step-feed mode to treat digested livestock wastewater. The PN effluent served as the first feeding. Digested livestock wastewater served as the second feeding, providing a carbon source for the APD process. The PN-APD process achieved a nitrogen removal efficiency (NRE) of 97.0 ± 1.3%, with total inorganic nitrogen concentrations of 14.8 ± 4.2 mg N/L in the effluent. The suitable biodegradable COD/NO_x^--N ratio of the APD process after the second feeding is key to achieving advanced nitrogen removal, and the suitable ratio ranges between 0.6 and 1.2. The second feeding had no significant influence on Anammox bacteria abundance, with Candidatus Kuenenia being the dominant species. The PN-APD process also removed total coliforms and enterococci by 3.3 ± 0.3 and 3.0 ± 0.3 log, respectively, meeting wastewater discharge standards without further disinfection. This study provides a novel approach for the cost-effective simultaneous advanced removal of nitrogen and pathogens from high-strength digested livestock wastewater.