From Activated Sludge to Microalgae-Bacteria Consortia: A Settleability Improving Strategy Using Filamentous Algae in Seawater Condition

Settleability is vital important for the stability of effluent quality from the widely used activated sludge (AS) process in wastewater treatment plants. In this study, filamentous algae and seawater condition were used to build a microalgae-bacteria (MB) consortia system with the objective of improving the settleability of AS. Filamentous algae were found to flourish more in aeration seawater reactor (R2) than non-aeration (R1). During 90 days, large contents of N, P were firstly released from the biomass, but were absorbed by the algae to relatively low concentrations (N 1.1 mg/L, P 1.4–2.3 mg/L). Meanwhile, the settleability of the two types of MB consortia both significantly increased, but was superiorly enhanced in aeration condition to a low 5-min sludge volume (SV 5 ) (11.5%, 55 d). Filamentous algae Leptolyngbya , as the most dominant part (9.8%) of microbial community in R2, could tightly bind the bacteria cells and extracellular polymeric substances (EPS) to form larger particles, which greatly accelerated the sedimentation. This study is of interest for the potential use of sludge settleability promotion in wastewater treatment plants, which has promising prospects for preventing the sludge bulking or biomass loss in AS systems. Graphical Abstract Highlights A modified MB consortia was studied to enhance the settleability of AS. Filamentous algae flourished in seawater MB consortia with aeration. Settleability was remarkably enhanced by the algae in seawater condition. N and P were released from AS but was mostly absorbed by algae. Filamentous Leptolyngbya was dominant algae in the MB consortia.