Optimal Phosphate Concentration for Growth and Normal Functioning of Marine Anammox Bacteria, Candidatus Scalindua sp

The anammox process using marine anammox bacteria is a promising nitrogen removal process for recirculating aquaculture system wastewater. Marine anammox bacteria are typically found in oxygen-deficient zones and coastal areas under low phosphate concentrations. The optimal phosphate concentration for marine anammox bacteria remains unknown because most laboratory studies on these bacteria have been conducted under high phosphate concentrations. Therefore, the present study investigated the long-term effects of varying phosphate concentrations on the marine anammox bacteria, Candidatus Scalindua sp., to identify the optimal range of phosphate. Anammox activity and average growth rates were evaluated under seven phosphate concentrations (0, 0.23, 0.46, 0.68, 1.14, 6.15 [control], and 15.48‍ ‍mg P L^-1) over a period of 70 days. After 50 days of reactor operation, reactor performance under phosphate concentrations ranging from 0.23 to 6.15‍ ‍mg P L^-1 stabilized at 70% of total nitrogen removal efficiency, indicating the successful establishment of the anammox process. Conversely, anammox reactor performance under conditions without phosphate addition (0‍ ‍mg P L^-1) and the highest phosphate concentration (15.48‍ ‍mg P L^-1) did not reach 70% of total nitrogen removal efficiency, indicating a suboptimal phosphate concentration for normal anammox activity. Average growth rates calculated from total biomass samples varied from 0.0006 to 0.0012 h^-1. These results indicate that Ca. Scalindua need to be kept at phosphate concentrations between 0.23 and 6.15‍ ‍mg P L^-1 for optimal functioning in wastewater treatment ecosystems.