Unraveling the nitrogen removal properties and microbial characterization of "Candidatus Scalindua"-dominated consortia treating seawater-based wastewater

Highlights: • Marine anammox bacteria performed well in SWW treatment under low temperature. • Marine anammox bacteria was fast enriched by marine sediments within 106 d. • Nitrogen removal was hardly affected at an influent NO₂⁻ ≤ 224.4 mg/L. • Candidatus Scalindua and Marinicella symbiotically existed and removed nitrogen. "Candidatus Scalindua", as known as marine anammox bacteria (MAB), was engineered to remove nitrogen from seawater-based wastewater (SWW). In this study, "Candidatus Scalindua" was successfully enriched within 106 days with marine sediments as inoculated sludge. The operating temperature was 20 ± 2 °C, and influent pH was 7.5 ± 0.1. Ammonia (NH₄⁺-N) removal rate (ARR) was 0.53 kg/(m³·d) with the NH₄⁺-N loading rate of 0.68 kg/(m³·d), and nitrite (NO₂⁻-N) removal rate (NRR) was 0.57 kg/(m³·d) at 0.89 kg/(m³·d) NO₂⁻-N loading rate. Nitrogen removal was negatively affected at an influent NO₂⁻ above 224 mg/L, which decreased the ARR and NRR to 0.36 and 0.31 kg/(m³·d), respectively. The genus "Ca. Scalindua" dominated the reactor, and it synergistically coexisted with Marinicella to achieve efficient nitrogen removal. This work would help to better understand the nitrogen removal properties and microbial characterization of MAB in SWW wastewater treatment under low temperature.