Enrichment of Anammox Bacteria Using Anammox Sludge as a Primer Combined with Ordinary Activated Sludge

Anaerobic ammonia oxidation bacteria (AnAOB) are difficult to cultivate due to their long start-up time and sensitivity to environmental conditions. In this study, anammox granular sludge was cultured with ordinary activated sludge under influent dissolved oxygen concentrations of 6-8 mg/L, successfully enriching AnAOB. The presence of multiple microorganisms in the activated sludge enabled the anammox system to resist the unfavorable influent environment and sustain system stability. The total nitrogen removal rate reached a maximum of 81%, and the TN effective load increased from 0.1 to 1.5 kg N/m(3)/d. The results showed that the dissolved oxygen present in the influent did not lead to a breakdown in the anammox system. The protein in the sludge extracellular polymeric substances played an important role in the enrichment of AnAOB, and the sludge settling performance at the bottom of the reactor was better than that at the top of the reactor, with protein/polysaccharide in the range of 5-6.3. Candidatus brocadia and Candidatus kuenenia were the main anammox functional bacteria in the system. On 153 d of reactor operation, their relative abundances were 8.51 and 5.68%, respectively. This study shows that microorganisms in activated sludge contribute to the stability of the anammox system when the influent conditions are appropriate. This provides a new idea for the rapid start-up of the anammox system and enrichment of AnAOB.