The anammox process is considered as a great alternative for treating nitrogen-rich wastewater. However, it limits the total nitrogen removal efficiency under 90 % due to its metabolism. The simultaneous anammox and denitrification (SAD) process, which combines both conventional denitrification and anammox process is a good solution for this problem and thus an improvement of the anammox process. In the present study, the SAD process was proved with the anammox granular sludge by using molecular evidences and lab-scale experiments.
PCR, DGGE and DNA-sequencing were used to detect the anammox bacteria (AnAOB) and heterotrophic denitrifying bacteria (HDB). The co-existence of the AnAOB and HDB was successfully proved. The diversity of the nitrogen-converting bacteria was demonstrated.
Besides, short-term batch experiments and long-term operation of an anaerobic upflow reactor were performed to observe the SAD activity. The maximum N-removal efficiency was close to 100 % in batch experiment and 97 % in the long-term experiment. During the stable operation of the anaerobic up-flow reactor, the average N-removal rate was about 0.80 kg N/(m3∙d). Simultaneous nitrogen and COD-removal was confirmed. In addition, the mechanism of the SAD process was revealed and the influences of several environmental parameters, including temperature, pH, dissolved oxygen (DO) concentration, and organic carbon, were determined on the SAD process.
Moreover, a new mathematic model was built based on the structure of the anammox granules, the distribution of the AnAOB and HDB, as well as their interaction in the SAD process.