Aerobic granulation and bioresource production under intermittent saline stress

Abstract

Aerobic Granular Sludge (AGS) systems have gained prominence for liquid waste treatment and bioresource recovery. In this regard, various strategies are employed to accelerate granulation processes in sequencing batch reactors (SBRs) and maximize stability and bioresource production. Intermittent stress supplementation can facilitate granule development, promoting slow-growth microorganisms. At the same time, osmotic stress may enhance bioresource production. In this study, an AGS reactor control with no saline stress (R1) was compared to two AGS systems operated under constant (R2) and intermittent (R3) saline stress in terms of efficiency, stability and bioresource productions (alginate-like exopolysaccharides-ALE and tryptophan). Granulation occurred around day 59 and 21 in R2 and R3, respectively, while complete granulation was not achieved in R1 within the 80-day operational period. However, SBRs performed well after 45 days, with 70% of the biomass being granular. The production of the biopolymer ALE remained more stable in reactors with osmotic stress compared to R1. The microbiological analysis revealed specific responses and adaptations to environmental factors, with genera such as Thauera and Pseudofulvimonas showing higher abundance in reactors with complete granulation, indicating a positive correlation with saline conditions (5 g/L). These insights are crucial for optimizing the performance of AGS systems in future applications, emphasizing the benefits of intermittent saline stress in promoting rapid granulation, stability in bioresource production, contaminant removal, and robust granule formation.