Microbial community structure and nitrogen conversion rate of size-fractionated granules in partial denitrification and anammox reactor

Abstract

Granule-based partial denitrification and anammox (PDA) process is affected by microbial community. To reveal how the nitrogen conversion rate varies with microbial composition caused by the granule size, PDA granules were divided into five sizes (<0.2, 0.2–0.5, 0.5–0.9, 0.9–1.6, and 1.6–2.0 mm). The abundance of anammox bacteria (dominated by Candidatus Brocadia) increased with particle size and peaked at 14.6% for 0.9–1.6 mm. In contrast, the abundance of denitrifiers (dominated by Thauera) decreased from 83.3% to 23.5% when granule size increased from <0.2 mm to 0.5–0.9 mm, but increased to 48.1% with further increases in particle size to 1.6–2.0 mm. The nitrogen conversion rate was affected by the microbial composition in granules. Nitrogen was autonomously removed in the granules of 0.9–2.0 mm. However, nitrite was accumulated in granules of <0.9 mm. Nitrite cross-feeding occurred inside and between granules. The findings provide a reference for the regulation of granule-based PDA systems.