Effects of light intensity on oxygen distribution, lipid production and biological community of algal-bacterial granules in photo-sequencing batch reactors

The effects of light intensity (0-225 µmol m-2 s-1) on oxygen distribution, lipid production and biological community structure of algal-bacterial granules were investigated in six identical photo-sequencing batch reactors (with a dark/light cycle of 12 h/12 h). Typically green algal-bacterial granules could be developed at a light intensity of ≥135 µmol m-2 s-1. The lipid content was significantly increased under higher light intensity, while the percentage of saturated fatty acid methyl esters was remarkably decreased. Results showed that light intensity ≥90 µmol m-2 s-1 yielded enough O2 production from algae, creating aerobic/anoxic zone (0.3-0.6 mg-O2/L) in the core of granules and thus efficient algal-bacterial symbiosis system. Enhanced nitrogen and phosphorus removals were achieved in the reactors with stronger light illumination, probably attributable to the enrichment of ammonia oxidizing bacteria (Comamonadaceae and Nitrosomonadaceae) and algae (Navicula and Stigeoclonium). Illuminance ≥180 µmol m-2 s-1 was found to be unfavorable for Nitrospiraceae.