Effect of hydraulic retention time on solid-phase denitrification reactor in recirculating aquaculture system

Hydraulic retention time (HRT) is one of the most critical operational parameters for solid-phase denitrification. The effect of HRT on solid-phase denitrification reactors (DR) packed with corrugated paperboard was investigated in recirculating aquaculture systems (RAS). Denitrification efficiencies of DR were 81.21–85.05% at HRTs of 0.5–2.0 h. The optimal HRT for denitrification was 2.0 h with a rate of 14.81 mg/(L substrate day). HRT significantly affected the bacterial community structure in DR by changing the population dynamics of the dominant bacteria and denitrifying functional bacteria such as Rhizobiaceae, Desulfovibrionaceae, and Arcobacteraceae. Moreover, the HRT of the DR showed a significant effect on the bacterial community in the nitrification reactor and culture water. Reducing HRT can promote the growth of total bacteria in the DR. However, it revealed a limiting effect on the abundance of key genes of the nitrogen cycle, including the amoA, nirK and nosZ. Under the condition of short HRT, the DR can also achieve a good denitrification effect, which provides feasible management measures for nitrogen removal in RAS.