Nitrogen Removal of the Sunlight-Irradiated SBABR and Anammox Combined System: Performance and Mechanism

To develop a low-energy nitrogen removal system, a coupled system consisting of a sunlight-enhanced bacteria-algae biological rotor (SBABR) and an anaerobic ammonia oxidation (Anammox) reactor was constructed. This study investigated partial nitrification stability in the SBABR reactor, color and chlorophyll-a removal efficiency in the Anammox reactor, and the coupled system's nitrogen and carbon removal performance and microbial community structure using high-throughput sequencing. Under significant light intensity fluctuations (300-2400 μmol/(m²·s)), the SBABR reactor maintained nitrite accumulation rates (NAR) of 94.98-98.13% with effluent NO₂^--N/NH₄⁺-N ratios between 1.01 and 1.18. The coupled system achieved average total nitrogen (TN) removal efficiency of 81.78% and ammonia nitrogen (NH₄⁺-N) removal efficiency of 87.71%. SBABR effluent color decreased from 42 to 17 Hazen units after the Anammox reactor, and chlorophyll-a concentration dropped from 296.40 μg/L to below detection limits. Microbial community analysis revealed that <i>Nitrosomonas</i> abundance was 0.69%, while <i>Nitrospira</i> abundance was only 0.01% in the SBABR reactor. In the Anammox reactor, Planctomycetota abundance reached 13.30%, and <i>Candidatus Jettenia</i> reached 11.57%. Results indicate that the activity of both AOB and NOB is inhibited by sunlight, but the inhibition of NOB is more significant, enabling stable nitrite accumulation. The Anammox reactor demonstrated favorable nitrogen removal performance and effectively removed color and chlorophyll-a.