The influence of water flow disturbance form on the granulation of algae sludge: Granulation property, treatment effect and algae biological structure

Algal-bacterial granular sludge (ABGS) is a research hotspot in sewage treatment. Water flow disturbance is crucial for sludge granulation in the algae-bacteria system, yet the effects of different disturbance modes on ABGS formation remain unclear. Horizontal stirring and supernatant reflux were used to start the ABGS system, the results showed the mode of horizontal disturbance combined with aeration is more conducive to the enrichment of algae and the formation of granular faster(80 day granulation was essentially completed), and the granular size is larger(more than 1.5 mm), high biomass (mixed liquid suspended solids for 8180 ± 183.61 mg/L) and good settleability (sludge volume index for 25.97 ± 3.00 mL/g), the extracellular polymeric substances secretion is more(147.32 ± 2.30 mg/g VSS), and the removal of nitrogen (N) and phosphorus (P) by horizontal stirring mode is higher, reaching 95.64 % and 99.58 %. High-throughput analyses revealed that horizontal agitation is more conducive to the proliferation of Nitrospira, Flavobacterium and Halochlorella, Scenedesmus taxa associated with nitrogen and phosphorus removal. Kyoto Encyclopedia of Genes and Genomes analysis demonstrated that in the quorum sensing system of the horizontal stirring method, the (suppressor of cell division inhibitor) gene regulated Tricarboxylic Acid cycle and N, P metabolism-related genes (ammonia monooxygenase, nitrite reductase 6-pyrrolidine tetrahydrobiopterin synthase), thereby enhancing metabolic gene expression. Supernatant reflux increased the expression of Uridine Diphosphate genes associated with polysaccharide production.