Long-term stable simultaneous partial nitrification, anammox and denitrification (SNAD) process treating real domestic sewage using suspended activated sludge

Bottleneck issues such as difficult biofilm culturing, time-consuming granular formation and excessive nitrate production, always limited the application of anammox processes. By using the common but meaningful suspended activated sludge instead of biofilm or granule activated sludge, a combined anammox process, simultaneous partial nitrification, anammox and denitrification (SNAD), was established in a sequencing batch reactor (SBR) in this study to treat real domestic sewage and was operated for 300 days. Results indicated that a high ammonia removal rate and nitrogen removal rate (1.1 and 1.03 (kgN/(m(3)center dot d)), respectively) were achieved during the baseline phase treating high ammonia wastewater (350-550 mg/L). During the experimental phase treating domestic sewage with a C/N of 3-3.5, 86.1% of total nitrogen removal efficiency was achieved and only 1.02 mg/L of nitrate concentration was detected in the effluent with an averagely 64.6 mg/L of ammonium in the influent. Nitrogen mass balance analysis demonstrated that about 89% of total nitrogen (TN) was removed by anammox and the remaining 11% of TN was removed by denitrification. Bacterial abundance of Candidatus Brocadia and Thauera increased from 0.02% to 0.5% and 0.39% to 2.24% (from baseline phase to experimental phase), respectively, which made an essential contribution to the nitrogen removal. The advanced nitrogen removal performance reached in the SNAD process showed the possibility of using suspended sludge as a substitute of biofilm and granule sludge concerning anammox, and the process could treat real domestic sewage with a C/N of 3-3.5 without pretreatment of chemical oxygen demand (COD).