Extended photoperiods enhance the production and water treatment performance of algal-bacterial bioflocs from aquaculture wastewater

Reducing pollution and converting wastewater nutrients into useful biomass are major challenges of intensive aquaculture. We investigated the nitrogen and phosphorus metabolism, nutrient composition, and microbial community of algal-bacterial bioflocs (ABBs) produced under glucose addition and different photoperiods. This biomass was used for aquaculture wastewater treatment for 18 days. ABBs produced under longer photoperiods were smaller and more numerous, which facilitated nitrogen recovery and reduced nitrogen loss. Additionally, nitrogen and phosphorus-metabolizing enzyme activities, as well as the activity of overall microorganisms were positively correlated with the light duration. The removal rates of COD (96.89 %), DTN (93.57 %), and DTP (93.67 %) from wastewater by ABBs were highest when the photoperiod was 16L:8D during the production period. Moreover, the crude protein content (41.77 +/- 0.11 %) was highest under a photoperiod of 12L:12D, and the rich amino acid and fatty acid profile of the ABB under this photoperiod enhanced its utility as a feed additive for aquaculture species. The high-throughput sequencing analysis revealed a high abundance of Hydrogenophaga at the genus level, highlighting its denitrification capacity of ABBs under the 16L:8D photoperiod. Redundancy analysis (RDA) demonstrated that photoperiod, as a key driver in the formation of microbial communities in ABBs, exerted a direct influence on water treatment efficiency and nutrient accumulation. This study provides new insights into the effects of photoperiod on the properties of ABBs, which has implications for the treatment and subsequent application of aquaculture wastewater.