Comparative study on nitrogen removal through partial denitrification coupled with Anammox by using biofilter and continuous stirred tank reactor

The partial denitrification coupled with Anammox (PDN/A) process enables energy-efficient nitrogen removal by overcoming nitrite and nitrate imbalance. This study compared the performance of PDN/A in a biofilter (BF) and a continuous stirred tank reactor (CSTR), focusing on nitrogen removal rates, microbial activity, and system stability. PDN/A-BF achieved a higher nitrogen removal rate (NRR) of 1.36 ± 0.12 kg-N m-3 d-1 compared to 0.67 ± 0.05 kg-N m-3 d-1 for PDN/A-CSTR. The PDN/A-BF system demonstrated superior Anammox nitrogen removal activity, with contributions of 91.09 ± 10.66 %, while PDN/A-CSTR achieved 72.42 ± 10.09 %. PDN/A-CSTR exhibited better stability under ultra-low substrate conditions, with a TN removal efficiency (TNRE) of 64.8 ± 3.41 % and COD removal efficiency (CODRE) of 58.88 ± 5.51 %. Dominant AnAOB genera included Ca. Brocadia in PDN/A-BF and Ca. Kuenenia in PDN/A-CSTR, with Pseudomonas and Thauera contributing to NO2--N accumulation. PDN/A-BF outperformed PDN/A-CSTR in nitrogen removal efficiency but faced challenges like clogging and biofilm sloughing, and limiting long-term operation. PDN/A-CSTR, while less efficient, showed stable performance under low substrate conditions, making it suitable for low-strength wastewater treatment. Future research should focus on optimizing BF reactor design and exploring moving bio-carriers for CSTR to enhance AnAOB activity and system stability. These findings provide valuable insights for the engineering application of PDN/A in wastewater treatment.