Rapid cultivation of anammox bacteria by forming free cells in a membrane bioreactor

The low growth rate of anammox bacteria is one of the main obstacles to its broad use in removing biological nitrogen in sewage treatment. Free cells show the characteristics of relatively rapid growth. To increase the growth rate, this study cultivated free-living anammox bacteria using a membrane bioreactor. The particle size distributions showed that more than 95.48% of biomass was less than 50 μm in size, and the growth rate of free-living anammox bacteria was shortened to 5.68 days after cultivation. Candidatus Brocadia was the most important anammox genus, with a relative abundance of 8.83%. The key functional genes, including hzs, hdh, and hao, were identified and expressed using metagenomic and metaproteomic analyses. After the rapid cultivation of the free-living anammox bacteria, a potential method shortening the start-up time was proposed to rapidly form anammox biofilm by attaching to carriers. PRACTITIONER POINTS: The free-living anammox bacteria are cultivated in a membrane bioreactor. More than 95.48% of biomass size is less than 50 μm. The doubling time of these free anammox bacteria was 5.68 days. The key functional genes of anammox bacteria were identified and expressed. A novel method is proposed to rapidly form anammox biofilm.