Chengcheng Lin, Yanxiao Wei, Sha Wu, Jiao Jin, Yangkai Liu, Hong Chen, Hanbo Yu, Mohd Fadhil Md Din, Eli Hendrik Sanjaya, Binquan Wang
Single-stage partial nitritation–anammox (PN/A) is inherently constrained by nitrate formation, which can keep total nitrogen removal efficiency (TNRE) below regulatory targets without external carbon, while bulk carbon dosing increases operating cost. In this study, a targeted micro-dosing strategy was implemented in a dissolved-oxygen (DO) partitioned airlift inner-circulation partition bioreactor to couple PN/A with partial denitrification (PD) in the sludge-rich low-DO zone where anammox granules accumulate. Over 206 days at 250 mg NH₄⁺–N L⁻¹ and hydraulic retention time = 12 h, sodium acetate was injected into the sludge-rich anaerobic zone as an electron donor in 12 pulses d⁻¹ (0.86–3.00 g d⁻¹). The system achieved TNRE of 95.11 ± 2.39%, with a peak of 98.68% sustained for 26 days. A dosing-efficiency metric (external donor per nitrogen removed, EDNR) quantified a practical dosing–performance relationship, ranging from 0.43 g NaAc g⁻¹ N at TNRE ≈ 88.68% to 1.35–1.40 g NaAc g⁻¹ N when TNRE increased to 95.11–98.68%. On a COD input basis, EDNR corresponded to a COD/N-equivalent of 0.34–1.09 g COD g⁻¹ N, indicating a 52.21–56.43% reduction in external electron-donor (COD) demand compared with conventional bulk dosing. Microbial community analysis showed co-dominance of Nitrosomonas (∼8.9%), Ca. Brocadia (∼4.2%), and Thauera (∼3%). Metagenomic analysis indicated stable hzs and hdh, and a (nirK + nirS)/(napA + narG) ratio of 0.60–0.77, consistent with enhanced nitrate reduction relative to downstream nitrite reduction and supporting PD potential while limiting progression to complete denitrification. These results quantify the electron-donor demand required to close the anammox nitrate loop and provide an operationally feasible dosing strategy for mainstream nitrogen removal. © 2026 Institution of Chemical Engineers. Published by Elsevier Ltd. All rights are reserved, including those for text and data mining, AI training, and similar technologies.
School of Hydraulic and Ocean Engineering, Changsha University of Science & Technology, Changsha, 410114, China; RIKEN Center for Sustainable Resource Science, 1-7-22 Suehiro-cho, Tsurumi-ku, Kanagawa, Yokohama, 230-0045, Japan; School of Transportation, Changsha University of Science & Technology, Changsha, 410114, China; Centre for Environmental Sustainability and Water Security (IPASA), Department of Water and Environmental Engineering, Faculty of Civil Engineering, Universiti Teknologi Malaysia, Skudai Johor, 81310, Malaysia; Chemistry Department Universitas Negeri Malang, 65145, Indonesia
