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

## TL;DR

A sunlight-powered system combining bacteria-algae and Anammox reactors efficiently removes nitrogen and color from water.

## Contribution

A novel coupled system using sunlight-enhanced SBABR and Anammox reactors for low-energy nitrogen removal is developed and analyzed.

## Key findings

- The SBABR reactor maintained high nitrite accumulation rates (94.98–98.13%) under varying light intensities.
- The coupled system achieved 81.78% total nitrogen removal and 87.71% ammonia nitrogen removal.
- The Anammox reactor effectively reduced color and chlorophyll-a from the SBABR effluent.

## Abstract

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 Nitrosomonas abundance was 0.69%, while Nitrospira abundance was only 0.01% in the SBABR reactor. In the Anammox reactor, Planctomycetota abundance reached 13.30%, and Candidatus Jettenia 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.