Performance of Ex Situ Microalgal–Bacterial Granular Sludge Process in Deeply Removing Nitrogen and Phosphorus in Eutrophication Water

Anthropogenic eutrophication is a worldwide problem, which is easily induced by excessive nutrients of nitrogen (N) and phosphorus (P). In order to treat the simulated eutrophication water (N 10 mg/L, P 0.5 mg/L), the ex situ processes of microalgal–bacterial granular sludge (MBGS) technology and normal aerobic granular sludge (AGS) were introduced and compared in the present study, using four parallel operated sequencing batch reactors (two for MBGS with illumination and two for AGS without illumination). Results showed that during 200 days of cultivation, the removal of total inorganic nitrogen (TIN) and total phosphorus (TP) could both reach >80% using MBGS, while AGS ended up removing only 18.5–23.3% of TIN and 47.4–52.5% of TP. The good removal of N and P with MBGS is probably due to the large expansion of filamentous algae in the phylum Cyanobacteria. Filamentous algae growth is able to largely enrich the lipid content in the MBGS by a factor of 3.4–4.1 compared with AGS. Besides, suspended algae removal tests were also conducted with both the AGS and MBGS, which all reached a relatively good removal efficiency of >69%. As a result, MBGS technology proved to have great potential for remediation of the eutrophicated water, achieving excellent N and P removal and water purification, with promising prospects for restoring contaminated water bodies as an ex situ process.